GMC 4000 Series, 6500 Series Service Manual

GMC 4000 SERIES is a powerful and versatile truck series that offers a wide range of features and capabilities. With its rugged construction and reliable performance, the GMC 4000 SERIES is ideal for a variety of applications, from construction and landscaping to transportation and delivery. Whether you're looking for a tough workhorse or a comfortable and efficient daily driver, the GMC 4000 SERIES has the features and capabilities you need to get the job done right.

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SERVICE

MANUAL

SERIES

4000 THRU 6500

This m a n u a l in clu d es p r o c e d u re s for

m a in te n a n ce a n d a d ju stm e n ts, m in o r se rv ic e

o p e ra tio n s a n d re p la c e m e n t o f com p o n en ts

GMC TRUCK & COACH DIVISION

GENERAL MOTORS CORPORATION

PONTIAC

MICHIGAN

General Motors Corporation, 1968

GM C Truck & Coach Division

10M 9-68

Printed in U.S.A.

X-6933

SECTION INDEX

LUBRICATION

CABS, HEATING AND

AIR CONDITIONING

<■

FRAME

FRONT SUSPENSION

REAR SUSPENSION

BRAKES

GASOLINE ENGINES

cm cm

trm

TORO-FLOW

DIESEL ENGINES

ENGINE MOUNTINGS

ENGINE COOLING SYSTEM

ENGINE FUEL SYSTEM

AIR COMPRESSOR

AND GOVERNOR

ENGINE ELECTRICAL

CM

£Z|

TRANSM ISSIO NS

AND CLUTCHES

FUEL TANK & EXHAUST

STEERING SYSTEM

WHEELS & TIRES

SHEET METAL

CHASSIS ELECTRICAL

AND INSTRUMENTS

RADIATOR AND

SURGE TANK

SPECIAL TOOLS

INTRODUCTION

This manual contains on-the-vehicle maintenance, light repair information, and unit replacement on all truck series listed on page v. Overhaul proce dures for major units w ill be published in separate “Unit Overhaul” manuals.

Important information on the arrangement and use of this manual w ill be found on page iv. Operation of the vehicles from the standpoint of the driver is contained in a separate Owner’s and D river’s manual which is furnished with every new GMC Truck.

Every effort has been made to include tim ely and adequate information on the various units and system s used on GMC Trucks. The general maintenance and light repair procedures in the various manual sections are the result of extensive service experience. This information should serve not only as a ref erence for the experienced mechanical force, but also as a com prehensive text for training purposes.

In some cases, considerable space is devoted to describing the operation of a unit or system. The use of this space is justified by the presumption that in order for a mechanic to maintain a unit or system in a serviceable condition, he must first understand how the unit or system should function.

A ll information contained in this manual is based on the latest product information available at the time of publication approval. GMC Truck and

Coach Division reserves the right to make changes in design or add improve ments at any time without incurring any obligation to install same on vehicles previously purchased.

TRUCK MODEL DESIGNATION

(“L” SERIES 4000)

(L ) Tilt Cab (V ) Hydraulic Brakes (A ) Air Brakes

CHASSIS TYPE

SYMBOL

(E) Conv. Cab (92" BBC)

(P ) Forward Control

(T) Tilt Cab

(S ) Schoolbus Cowl

ENGINE TYPE

SYMBOL

(G ) V6 Toro-Flow (D iesel)

(M ) V6 Gasoline

(S ) In-Line Gasoline

(ALL OTHER SERIES)

GVW RANGE NUMBER

See “Load Capacity Chart” in Owner’s and Driver’s

Manual.

MODEL YEAR

SERIAL NUMBER

E M 40 V - D 020001

BODY AN D BRAKE TYPE

P —Chassis Only (Hyd. Brakes)

V —Cab & Chassis (Hyd. Brakes)

A —Cab & Chassis (Air Brakes)

M—Cowl & Chassis (Hyd. Brakes)

Y —Cowl & Chassis (Air Brakes) iii

GENERAL INFORMATION

IM PO R TA N T-R EA D THIS PAGE

TRUCK MODELS COVERED

This manual contains “on-the-vehicle” mainte nance and light repair information on GMC Truck

Models listed on page v. Since many truck models with various combinations of equipment are cov ered in this manual, the reader must necessarily refer to truck model applications and methods of distinguishing design differences in each manual section.

A ll standard equipm ent and the most commonly used regular production options are included in this manual. Many special equipment and acces sory item s are available on these GMC Trucks, however, these item s are too numerous to permit their coverage in this manual.

MANUAL ARRANGEMENT

This manual is divided into major sections in the sequence shown on the margin of the title page.

A black tab bearing the major section number is placed on the first page of each major section which indexes with the tab on the title page. Many of the major sections are divided into sub-sections, each sub-section containing important and specific in formation on related units or components. A section index is also included on the first page of each major section, w hen the major section is divided into sub-sections.

PAGE AND ILLUSTRATION NUMBERS

The manual pages are numbered consecutively throughout the manual. Illustrations are numbered consecutively within each section, or within each sub-section w hen the major section is so divided.

also be made to these “Specifications.” for model application and methods of distinguishing the various design and construction differences.

Manufacturers model or part numbers are used in many instances in the “Specifications” tabula tions. These numbers are provided primarily for unit identification or truck model application refer ence, and should be referred to when ordering parts. A ll detail service part numbers must be obtained from the applicable Parts Book.

SPECIAL TOOLS

Special tools and equipment are mentioned, and in many instances illustrated, throughout the text.

These tools are specially designed to accomplish certain operations efficiently and readily. Such tools are mentioned in the text by tool vendor’s numbers. These tools are not offered for sale by

GMC Truck and Coach Division. Information re garding availability of these tools can be obtained from your Zone Office or directly from the Tech nical Publication Department at the Factory.

SERVICE BULLETINS

Service bulletins are issued, when required, sup plementing or in some cases superseding infor mation in this manual. Information in these bul letins should be noted in the text of the applicable manual section and the bulletin filed for ready reference.

OPERATION

Operating instructions from the standpoint of the driver are included in a booklet entitled “Own er’s and D river’s Manual” which is placed in the cab of every new GMC Truck.

SPECIFICATIONS

Service data, fits, and tolerances are listed at end of each section or sub-section under the head ing “Specifications.” In some cases reference must

ALPHABETICAL INDEX

Important subjects, with manual page number references, are alphabetically listed in the index in the back of this manual.

MODEL DATA

TRU CK

S E R IE S

LA, LV-4000

GMC

ENGINE

STD.

OPT

305C 351C

DLA, DLV-4000 DH478

EM -4500

ES-4500

PS-4500

EG-5500V

EG-5500A

EM-5500

EM-5500 A & Y

ES-5500 V & M

SG-5500M

SG-5500Y

SM-5500M

SM-5500Y

SS-5500

305E

250

DH478

292

DH478

305C

351C

305C

351C

292

DH478

305C

292

EG-6500

DH478

EM-6500 305C

SM-6500 M & Y 351M

351C

—

CLU TCH

STD.

OPT.

12 13

FRONT AXLE

STD.

F070

OPT.

—

F070

F055

F050

F055

F070

F055

F070

F055

F070

F055

F070

F055

F070

—

F07C

F070

—

STD.

H150

H110

H150

G161

H150

G161

H150

REAR A XLE

OPT.

G161,16121,

T150, G361,

16221

G161,16121,

T150, G361,

16221

H135, H150,

T150

H135, H150,

T150

H135

G161,16121,

T150, G361,

16221

16121, G361,

16221

G161, 16121,

T150, G361,

16221

16121, G361,

16221

G161,16121,

T150, G361,

16221

G161,16121,

T150, G361,

16221

G161

H150

G161

H150

16121, G361,

16221

G161,16121,

T150, G361,

16221

16121, G361,

16221

G161,16121,

T150, G361,

16221

16121

TRA NSMISSION

STD.

435GL

SM465

435GL

17121, 16221,

17221

435GL

17121, 16221,

17221

17121, 16221,

17221

435GL

OPT.

435GD,

540GD, 540GL

435GD,

540GD, 540GL

«5G D

435GD

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD,

540GD, 540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD,

540GD, 540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

435GD, 540GD,

540GL

VEHICLE MODEL IDENTIFICATION

AND WEIGHT RATING PLATE

The vehicle identification and weight rating plate is located on th e cab le ft door p illa r of a ll models except “P ” and cowl mod els. Plate location on “P ” and cowl models is determined by the body manufacturer.

ENGINE SERIAL NUMBERS

The engine serial number on “V ” engines is stamped on top of the cylinder block ahead of the right-bank cylinder head as shown below. Engine serial numbers are not used on in-line engines; numbers appearing on crankcase boss at rear of distributor are manufacturing location and building date codes.

SERVICE PARTS IDENTIFICATION

The “Service Parts Identification” label is located on inside of glove compart ment door of steel tilt and conventional cab models. Location of label on “P ” and cowl models is determined by the body manufacturer. This label lists all special equipment installed on the vehicle. This information is imprinted on the label at the factory and represents only the special equipment on the vehicle when it was shipped from the factory. A lways refer to this information when ordering parts.

G M C S E R V I C E M A N U A L

SECTION O

Sec. 0

Page 1

INDEX

Subject

Lubrication Charts

Page No.

Except Steel Tilt Cab Models .....................

Steel Tilt Cab Models ....................................

6 Engine and A ccessories ................................

Capacities

Crankcase .........................................................

T r a n s m is s io n .....................................................

Rear A x l e ............................................................

Engine Oil - Symbol "E" ...................................

Engine Oil Recommendations .....................

V iscosities .........................................................

Checking Engine Oil L e v e l ............................

8 Engine Oil F i l t e r ..............................................

Air Cleaners

Oil Bath Type ..............................................

Paper Element T y p e ...................................

Brake Power and Axle C y lin d e r ..............

Air Compressor Air Strainer ..................

Other Engine Oil U ses ...................................

Crankcase Ventilation (G a so lin e )..................

Crankcase Ventilation ( D i e s e l ) .....................

Subject Page No.

Multi-Purpose Gear Lubricant Symbol "MP"

V iscosities ......................................................... 12

Rear A x l e ............................................................ 12

T r a n s m is s io n ..................................................... 13

Chassis Lubricant - Symbol " C " ..................... 13

Steering Gear Lubricant - Symbol "SG" . . . 14

High Temperature Grease - Symbol "S2" . . 14

Wheel B e a r i n g s .................................................. 14

Other High Temperature U s e s ..................... 14

Petroleum Jelly - Symbol "S3" ...................... 14

Distributor ......................................................... 14

Battery Terminals ........................................... 14

Waterproof Grease - Symbol "S4" .............. 15

Hydraulic Brake Fluid - Symbol "S12" . . . 15

Clutch and Brake Master C y lin d e r .............. 15

Soft, Smooth Cup Grease - Symbol "S16" . . . 15

Special Grease - Symbol "S17" ..................... 15

Automatic Transmission Fluid - Symbol "S19" . 16

Power Steering S y s t e m ................................... 16

High Temperature Grease - Symbol "S28" . . 16

Stop master Brake U n i t ................................... 16

GENERAL INFORMATION

Lubrication charts on following pages will lo cate each lubrication point on the ser ie s shown under each chart. Each point is numbered on the charts, and each number is keyed to explanatory text on same or opposite page.

Each item shown on charts requiring lubrica tion is covered with a lubricant symbol. Explan ations of symbols start on page following charts.

Explanations include type of lubricant recommend ed, and detailed instructions regarding its applica tion. The charts show recommended intervals when various item s should be lubricated. The intervals are recommended for normal use; however, oper ating conditions may require more frequent inter vals. Recommended intervals should be followed until operating experience indicates other periods.

No particular brand of lubricant is recom mended as many reputable oil dealers can furnish the right lubricants when advised of the correct specifications or descriptions. The lubricant man ufacturer must be responsible for the quality and satisfactory performance of his product. His rep utation is your best indication of quality.

LUBRICANT SYMBOLS

Symbol Explanation

"E"

"MP"

"C"

"SG"

Engine Oil

Page No.

...........................................

Multi-Purpose Gear Lubricant . .

Chassis L u b r ic a n t............................

Steering Gear L u b r ic a n t..................

"S-2"

"S-3"

"S-4"

High Temperature G r e a s e ..............

Petroleum Jelly ................................

Waterproof Grease .........................

"S-12" Hydraulic Brake F l u i d ..................... 15

"S-16" Soft, Smooth Cup Grease .............. 15

"S-17" Special G r e a s e ................................... 15

"S-19" Automatic Transmission Fluid . . 16

"S-28" High Temperature Grease (Special) 16

Sec. 0

Page 2

LUBRICATION

G M C S E R V I C E M A N U A L

Figure 1 — Lubrication Chart (Except Steel Tilt C ab M odels)

G M C S E R V I C E M A N U A L

Sec. 0

Page 3

LUBRICATION

LUBRICATION DATA

(CHART O N OPPOSITE PAGE)

Item

No.

Item

Spring Shackles and Brackets (1)

2 Spring Slip Pads (1) .......................

3 Steering Knuckles .......................

4 Steering Tie Rod Ends .................

5 Steering Drag L i n k .......................

6 Power Steering Cylinder Ends (1)

7 Prop. Shaft U -J o in ts.......................

8 Prop. Shaft Slip Joint ....................

10 Speedometer A d a p ter....................

Brake Camshaft (2) .......................

12 Brake Master Cylinder ( 3 ) ...........

Steering Gear Housing ..............

Battery T e r m in a ls..........................

Electric Shift Unit (2-Spd.) . . . .

T ra n sm issio n ..................................

Rear Axle ........................................

Front Wheel Bearings .................

Rear Wheel B e a r in g s ....................

20 Brake Cam Roller Pins (2) ..........................

21 Brake and Axle Cyl. Air Cleaner (1) . . . .

22 Steering Column U-Joints ..........................

23 Steering Column Slip Joints .......................

Remarks Sym.

2 fittings each s h a c k le ................. .. C

1 fitting each b r a c k e t.................... ... C

Apply each e n d ............................... ... C

2 fittings each side .......................... C

1 fitting each end ............................. C

2 fittings ......................................... ....C

1 fitting each j o i n t ............................ GO

1 fitting each j o i n t ............................ C

1 f i t t i n g ............................................. .. C

1 fitting ea. (apply sparingly) . . C

Fill - 1/2" below o p e n in g ...............S12

To level of filler plug ................. ...SG

Keep coated ..................................... .. S3

To level of filler plug ................. ...S7

To level of filler plug ................. ..MP

Drain and refill ................................MP

To level of filler plug ................. ...MP

Drain and refill ................................MP

Hand pack or use lubricator . . . S2

Hand pack or use lubricator

Series 4500 & 5500

H110, H135, T150, H150,

G161, G361 ................................S16

All O t h e r s ...........................................S2

Apply ................................................ ...E

Clean and reinstall ..........................-

1 fitting each joint ....................... ..C

1 fitting .............................................C

20,000*

20,000

6,000

* Or once a year, whichever occurs first.

# Or every 6 months, whichever occurs first.

t When "C" Chassis Lubricant is specified, lubricate every 6,000 m iles or 60 days, whichever occurs first.

(1) Some Models.

(2) Air Brake only.

(3) Hydraulic Brakes only.

Miles i

6,000

12,000

6,000

12,000

6,000

24,000#

20,000*

Sec. 0

Page 4

LUBRICATION

G M C S E R V I C E M A N U A L

Figure 2 — Lubrication Chart (Steel Tilt C a b M odels)

G M C S E R V I C E M A N U A L

Sec. 0

Page 5

LUBRICATION

LUBRICATION DATA

(CHART O N OPPOSITE PAGE)

Item

No.

Item

Remarks Sym.

Spring Shackles and Brackets ....................

fittings each s h a c k le ............

. . c

1 fitting each bracket ............

. . c

Spring Slip Pads - R e a r ..................................

Apply each end ..........................

. . c

Steering K n u ck les...........................................

fittings each s i d e .................

. . c

Steering Tie Rod E n d s ..................................

1 fitting each e n d .......................

. . c

Steering Drag L in k s........................................

1 fitting each end ....................

. . c

Power Steering Cylinder Ends ( 1 ) ..............

f i t t in g s .....................................

.. c

Cab H in ges.........................................................

1 fitting each s i d e ....................

.. c

Cab Hold-Down Latch ..................................

1 fitting .....................................

. . c

Brake Camshafts

( 2 ) ............................

1 fitting e a c h .............................

. . c

Clutch and Brake P e d a ls ...............................

2 f i t t i n g s

..........................

. . c

Air-Hydraulic Cylinder ( 3 ) ..........................

To level of plug .....................

. . S6

Prop. Shaft U-Joints .....................................

1 fitting each joint .................

. GO

Prop. Shaft Slip Joints ..................................

1 fitting each joint .................

Steering Column U -J o in ts .............................

1 fitting each joint .................

Steering Column Slip J o i n t ..........................

1 fitting .....................................

.. c

. .

.. c

16 Speedometer A d a p te r .....................................

1 fitting .....................................

. . c

Transmission Shift L e v e r s ..........................

2 fittings ..................................

.. c

Transm ission Shift Linkage (NP 540) . . . .

1 fitting .....................................

.. c

19 Steering Gear Housing ..................................

To level of filler plug ............ . . SG

20 Brake Master Cylinder ( 3 ) .............................

Fill - 1/2" below opening . . . . . S12

21 Battery T e r m in a ls ...........................................

Keep coated ............................. . . S3

22 Electric Shift Unit (2-Spd.) ..........................

To level of filler plug ............

. S7

T r a n s m is s io n ...................................................

To level of filler plug ............

Drain and refill .......................

Rear Axle .........................................................

To level of filler plug ............

Drain and refill .......................

Front Wheel B e a r in g s.....................................

Hand pack or use lubricator

. .

. . S2

Hand pack or use lubricator

H110, H135, T150, H150,

G161, G361 ....................... . . S16

All Others .............................

Brake Cam Roller Pins (2) ..........................

Apply ........................................... . .

Brake Power and Axle Cylinder

Air Cleaner (1) ...........................................

Clean and reinstall .................

* Or once a year, whichever occurs first.

# Or every 6 months, whichever occurs first.

+ When "C" Chassis Lubricant is specified, lubricate every 6,000 m iles or 60 days, whichever occurs first.

(1) Some Models.

(2) Air Brakes only.

(3) Air-Hydraulic Brakes only.

Miles $

6,000

12,000

6,000

12,000

6,000

12,000

6,000

24,000#

20,000*

20,000

6,000

Sec. 0

Page 6

LUBRICATION

G M C S E R V I C E M A N U A L

Item

No. Item

1 Engine .............................................................

2 Engine Oil Filter .......................................

3 Engine Air Cleaner ....................................

4 Crankcase Breather ( 1 ) ................................

5 Air Compressor Air Strainer (1) . . . .

6 Governor Air Filter (2) .............................

7 Distributor (2) ..............................................

8 Generator ..................................................

9 Starter ......................................................

10 Power Steering Reservoir ( 1 ) ..................

Remarks Sym.

Keep to "FULL" mark . . . . . .

See in s t r u c tio n s .................. . . .

Clean and r e f i l l ..................

See in s t r u c t io n s .................. . . .

Clean and i n s t a l l .................. . . .

Clean and i n s t a ll .................. . . .

1/2 turn of cam lubricator . . . .

Breaker pivot - 1 drop . . . . . . E

Rotor felt - 4 drops . . . . . . .

No lubrication required . .

See in s t r u c tio n s .................. . . .

To "OIL LEVEL" mark . . . . . S19

(1) Some Models.

(2) Gas Engine Only.

# Replace lubricator at 24,000 mile intervals.

Figure 3 — E n g in e Lubrication Charts

—

Miles

Daily

3,000

- -

6,000

12,000#

6,000

- -

—

6,000

G M C S E R V I C E M A N U A L

Sec. 0

Page 7

LUBRICATION

CAPACITIES

CRANKCASE CAPACITIES

ENGINE

MODEL

LESS FILTER WITH FILTER

QTS.* QTS.*

U.S.. IMP.

U.S.

IMP.

250 .................... . . 4 3 -1 /4 5 4 -1 /4

292* - 305E . . .

5 4 -1 /4 .6

305C* - 351C*. .

8 6 -3 /4

351M ..................

6 -3 /4

D H 4 7 8 * * ............ . . 11 9 -1 /4

9 7 -1 /2

10 8 -1 /2

13 10%

* Add one quart when 2-■qt. filter is used.

** Add one quart when oil cooler is drained.

Crankcase capacities are for normal refill.

Add oil as indicated when oil filter is drained and element changed. Capacities given may be approx im ate - keep level as close as possib le to "FULL" mark without over-fillin g. Do not operate with lev el below "ADD" mark.

TRANSMISSION CAPACITIES

U.S.

PINTS

IMPERIAL

SM465 ............................. 8 .............. 6 -3 /4

NP435 ............................. 7 ............... 5 -3 /4

NP540 ............................. 10 .............. 8 -1 /4

REAR AXLE CAPACITIES

BEVEL U.S.

PINTS

IMPERIAL

H110 ............................. 14 ............... 11-3/4

H135 ............................. 20 ............... 16-3/4

H150 ............................. 20 ............... 16-3/4

G161 ............................. 21 ............... 17-1/2

E16121 ......................... 24 ............... 20

E17121 ......................... 29 ............... 24-1 /4

TWO-SPEED

T150 .................................18 ............... ... 15

G361 .................................21 ............... ... 17-1/2

E16221 ......................... ....24 ............... ... 20

E17221 ......................... ....29 ............... ... 24 -1/4

ENGINE OIL

(SYMBOL “E” O N CHARTS)

R EC O M M EN D A TIO N S

The oil industry markets various types of en gine oil under certain service designations and specification numbers.

The selection of a reliable supplier, with close attention to his oil and filter element change rec ommendations can provide satisfactory lubrication and longer life for engine.

The use of proper engine oils and oil change intervals are your best assurance of continued re liability and performance of engine.

IMPORTANT: Non-detergent and other lower quality engine o ils are specifically not recommend ed in diesel engines.

GASOLINE ENGINE

DIESEL ENGINE

Use Only High Quality Oils Which Are:

(1) MIL-L-2104B engine o ils (see Note).

- or -

(2) Oils which pass the vehicle manufacturers te sts (including General Motors Standard

GM 6042M).

Use Only High Quality Oils Which Are:

(1) Intended for Service Designations "MS" and "DM" (see Note).

- or -

(2) Products passing vehicle manufacturers tests (including General Motors Standard

GM 6042M).

NOTE: Supplement 1 engine oils (based upon now obsoleted MIL-L-2104A) have been superseded by MIL-L-2104B engine o ils, so these Supplement

1 o ils are therefore becoming unavailable. How ever, where a history of satisfactory performance with Supplement 1 o ils has been established, they can still be used.

NOTE: Supplement 1 engine oils based upon now obsoleted MIL-L-2104A) have been superseded by MIL-L-2104B engine oils. However, Supplement

1 engine oils (MS - DM) with a history of sa tis factory performance are available and may be used.

The use of proper engine o ils and oil change intervals are your best assurance of continued re liability and performance of engine.

Sec. 0

Page 8

LUBRICATION

G M C S E R V I C E M A N U A L

IMPORTANT: Non-detergent and other lower quality engine o ils are specifically not recom mended.

BREAK-IN OILS AND ADDITIVES

The use of proprietary blends of supplement ary additives or concentrates such as engine oil supplements, break-in o ils, tune-up compounds, friction reducing compounds, etc., is not recom mended in lubricating oils of the diesel engines in GMC Truck and Coach vehicles. For gasoline engines, if greater stability or detergency is de sired to reduce varnish and sludge formations, and minimize wear, a thoroughly tested and approved concentrate is available from GMC D ealers.

VISCOSITIES

Atmospheric temperatures and severity of service determine the viscosity grade of engine oil to use. V iscosity numbers constitute a cla ssifica tion of lubricants in term s of viscosity or fluidity, but with no reference to any other characteristics or properties.

GASOLINE ENGINES

As a guide to the selection of the proper grade or viscosity of oil to be used in gasoline engines at various atmospheric temperatures, refer to "Vis cosity Chart" (fig. 4).

VISCOSITY CHART

For cold w eather, select visc o sity b a s e d o n low e st a n ticip a te d tem perature.

For hot w eather, select visco sity b a s e d o n h ig h e s t te m p erature e xpected d u r in g the d a y . T _4 5 5 ,

Figure 4 — G a so lin e E n g in e O il Viscosity Chart

DIESEL ENGINES

S.A.E. 30 engine oil is recommended for year around use. Where cold weather starting isa p r o b lem, it is suggested that other starting aids, oil and coolant system heaters, as well as proper fuel selection will be helpful. For further assistance, consult your authorized GMC Dealer.

Lower S.A.E. engine oil grades (S.A.E. 20,

S.A.E. 10, etc.), and the m ulti-viscosity oils(10W -

30, etc.), are not recommended, except as a last resort. If used, they should be replaced withS.A.E.

30 as soon as possible.

MULTI-VISCOSITY TYPE ENGINE OILS

M ulti-Viscosity lubricating oils, as a group, are not normally recommended. However, some may be effectively used to facilitate starting when prolonged exposure of the engine to temperatures below freezing is unavoidable. Consult your sup plier regarding the performance characteristics of this type of oil and obtain his assurance of ade quate lubrication before subjecting the engine to heavy-duty service.

OIL CHANG E INTERVALS

It is recommended that new engines should have the first oil change at 3,000 m iles.

The drain interval may then be increased or decreased, depending upon experience with specific oils or the recommendations and used oil analyses as furnished by the supplier. Such a procedure would be helpful in establishing the most practical oil change period for the particular service.

CHECKING ENGINE OIL LEVEL

Daily, or oftener if necessary, check oil level.

Make the check perferably after a day’s run and after engine has been stopped for a few minutes.

Remove dipstick, wipe clean with cloth, reinsert and remove again. The upper mark on dipstick is

"FULL," the lower "ADD." Keep level as close as possible to "FULL" mark without overfilling. Do not operate with level below "ADD" mark.

On gasoline and diesel engines dipstick is on right side and engine can be filled at right filler on valve rocker cover after removing filler cap (fig.

5).

On steel cab models, accessibility is through door behind passenger seat. On other models, dip stick and oil filler are accessib le when hood is raised.

ENGINE OIL FILTER

Oil filter element changing periods are closely related to crankcase oil changing periods, the qual ity of oil used, or the severity of the trucks service.

G M C S E R V I C E M A N U A L

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Page 9

LUBRICATION

It is recommended that element be changed initially at first oil change and thereafter at intervals in dicated under "Engine Oil Recommendations."

Location of oil filter is at left rear on gasoline and diesel models (fig. 6).

ELEMENT TYPE

1. Remove plug in filter shell to drain oil from filter.

2. Back out center stud and withdraw shell, element, and stud as an assem bly.

3. Remove and discard element.

4. Clean filter shell of old oil or other deposits.

5. Replace old filter shell gasket in groove of filter base.

6. Position new filter element in shell, THEN

FILL SHELL WITH OIL.

7. Install shell and element assem bly on filter base, then tighten center stud being careful that gaskets are not damaged. Torque to 40 to 50 foot pounds.

8. Start engine and operate at idle speed for a few minutes until oil p ressure builds up to normal.

9. Check filter for leaks, then check dipstick level. Add oil to bring level up to (not above) dipstick mark.

DISPOSABLE TYPE

1. Turn filter from mounting on engine, then discard assembly.

2. Thoroughly clean mounting at gasket area.

3. Apply lubricant to filter gasket. Fill ele ment shell with engine oil, then thread filter onto mounting stud until gasket touches mounting, then tighten filter two-thirds more, which should pro vide the required torque of 10 to 15 foot-pounds.

4. Whenever new element is installed, the engine should be run and the filter inspected for signs of an oil leak. The engine should then be stopped, and the oil level brought up to the "FULL" mark on the oil level dipstick.

AIR CLEANERS

Air cleaners must be serviced a minimum of every 3,000 m iles, or whenever dirt becom es v is ible in the element or oil. Under extreme dirty conditions inspection may be required daily. Air cleaners on vehicles operating in dust storm areas should be cleaned immediately after such storm s occur.

Several types of air cleaners are used. De pending upon the vehicle model, each type cleaner is serviced and mounted in a different manner.

Figure 5 — O il Filler and Dipstick IGasoline and Toro-Flow)

W A R N IN G — DIESEL ENGINE

USE E X T R E M E CAUTION TO BE

SURE THAT A LL V O L A T IL E C L E A N IN G

F LU ID (GASOLINE, KEROSEN E, ETC.)

IS R E M O V E D FR O M AIR C L E A N E R AT

T IM E OF CLEA N IN G , U N CO NTRO LLED

FU EL E N T E R IN G THE COMBUSTION

C H A M B E R IN THIS M A N NER CAN CAUSE

THE ENGINE TO "R U N -A W A Y " AND

POSSIBLY DESTROY ITSELF AN DCAU SE

INJURY TO PERSONNEL.

OIL BATH TYPE (Figs. 7 and 9)

Oil bath type air cleaners are mounted direct ly to the engine or on cab dash. Loosen thumb screw on top, then separate cover and element from reservoir.

T H R O W - A W A Y TYPE R E P L A C E A B L E E L E M E N T TYPE

T-3456

Figure 6 — E n g in e O il Filters

Sec. 0

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LUBRICATION

G M C S E R V I C E M A N U A L

Figure 7— Air Cleaner— Oil Bath ITypical)

Remove reservoir and drain oil. Immerse all parts in cleaning solution until all dirt or other foreign matter is removed. Do NOT use com pressed air on element. Be sure all volatile fluid is removed.

Fill reservoir to "OIL LEVEL" mark, using same grade oil used in engine. Assem ble and re install reservoir and element in reverse order of removal and disassem bly.

PAPER ELEMENT TYPE

- DRY OR PAPER WETTED (Fig. 8)

Remove wing nut from stud at top of air clean er, then lift cover and element from base.

To determine if an air filter element requires cleaning or replacement, use air filter viewer,

A.C. Part Number 6484631, which has a special lens for this purpose. A dirt-clogged element pre vents the light from being visible from outside.

The paper-wetted type has been impregnated with oil and cannot be cleaned. When dirt clogged, or when light as described above is not visible, the element must be replaced.

Some dry elem ents are washable; refer to decal for instructions.

Clean element by shaking out accumulated dirt, or clean by washing with water and detergent only. Rinse until water runs clean. Shake off ex c e ss water and dry. DO NOT OIL ELEMENT.

NOTE: Install a new element after five (5) cleaning. Some elements also have a band of syn thetic material (polyurethane) which is cleanable in kerosene or mineral spirits.

Install assembly in reverse order of "Re moval" and ’’Disassembly" procedure.

BRAKE POWER AND AXLE

CYLINDER AIR CLEANER

Several types of cleaners are used for this purpose. Two types - one disposable and the other

Figure 8 — Air Cleaner— Paper Element with Polyurethane (Typical)

BASE

T-5773

Figure 9 — Air C leaner (Toro-Flow Engine)

G M C S E R V I C E M A N U A L _________________________ page

LUBRICATION

Figure 10— Air Compressor Air Strainer

cleanable - is located on inside of cab at left rear corner. Another type is made of polyurethane and is installed in brake booster cylinder.

Cleanable Type

Lift element assem bly from tube. Wash e le ment thoroughly in cleaning solvent until all a c cumulated dirt is removed. Dry thoroughly, then reinstall. Do not oil element.

Disposable Type

Remove retaining bolt, then lift assembly from tube. When inspection indicates the assembly is dirty it should be discarded and a new assembly installed.

Polyurethane Type

This cleaning element is removable for in spection and cleaning as instructed in BRAKES

(SEC. 5). Element is cleaned by immersing and squeezing in kerosene or mineral spirits.

IM PORTAN T

Regardless of where an air cleaner

is used, it is extremely important that

element be cleaned as directed to assure

extended life of applicable unit.

AIR COMPRESSOR AIR STRAINER

(Refer to Fig. 10)

The air com pressor air strainer should be replaced regularly.

Figure 1 1 — Crankcase Breather (V6 Gasoline Engine)

Paper element type air com pressor cleaner is used on all models and should be replaced when element shows visible evidence of damage or a dirt clogged condition or is oil saturated.

OTHER ENGINE OIL USES

DISTRIBUTOR

Breaker Pivot. Remove distributor cap and apply one drop of S.A.E. 10 engine oil to breaker arm pivot. Do not apply excessive lubricant.

Rotor F elt. A felt is used under rotor of some distributors. Apply 3 or 4 drops of S.A.E. 20 engine oil.

SE P A R A T O R

FILTER

Figure 12— Crankcase Ventilation System (Diesel)

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LUBRICATION

G M C S E R V I C E M A N U A L

STARTER

Some starters are equipped with oiler or plug at drive end, plug at commutator end, and plug at middle bearing. At the time of installation, apply

S.A.E. 20 at plugs or oilers.

LINKAGE

Engine oil is used also to lubricate clevis pins, linkage, clev ise s, etc. Application should be made by brush or spray.

AXLE SHIFT UNIT

Remove plug in cover and fill to level of open ing with S.A.E. 10 engine oil.

CRANKCASE VENTILATION

GASOLINE ENGINES

The closed positive crankcase ventilation sy s tem makes an important contribution to the reduc tion of air pollution by recycling fuel fumes, which enter the crankcase, back to the combustion cham ber to be burned, and achieves nearly one-hundred percent elimination of crankcase em issions - onethird of total hydrocarbon em issions from vehicle.

Ventilation valves on "V" engines are threaded into cylinder heads, while valve on In-line engines is installed in rocker arm cover. At first engine oil change ventilation valve(s) should be checked for proper operation as described in GASOLINE

ENGINES (SEC. 6A) under "Crankcase Ventilation

System." Every 12 months or 12,000 m iles, which ever occurs first, the valve(s) MUST be replaced.

Also, all hoses and fittings (including flame a rrest er on In-line engine) should be inspected, cleaned, and replaced if necessary.

On V6 engines, a crankcase breather (fig. 11) is installed at valve rocker arm cover and should be removed and cleaned at each oil change interval.

DIESEL ENGINE

Oil separator, breather tube and filter assem bly (fig. 12) are installed at opening in rear of crankcase on diesel engines. A mesh filter element is contained in a retainer which should be removed every 30,000 miles and cleaned of accumulations by immersing repeatedly in fuel oil or cleaning solvent, until all deposits are removed.

MULTI-PURPOSE GEAR LUBRICANT

(SYMBOL “M P” O N CHARTS)

REAR AXLE

Multi-Purpose Gear Lubricant, meeting U.S.

Army Ord. Specification MIL-L-2105B and indi cated by the symbol "MP” on charts, must sa tis factorily lubricate heavy duty truck hypoid or bevel axles, and transm issions, under maximum torque and speed conditions. It must provide necessary and suitable load-carrying characteristics to p re vent scoring and wear, good stability in storage and service, and give good resistance to corrosion.

Suppliers should assure these characteristics, and be responsible for the quality and satisfactory per formance of their products.

CHECKING LEVEL

Remove filler plug and if necessary, add suf ficient lubricant to bring the level up to filler plug lev el. Install and tighten plug. On the forward rear axle with torque divider, be sure that vehicle has stood for at least 5 minutes before checking level; then check level AT REAR FILLER HOLE.

VISCOSITIES

ROCKWELL AXLES

In Rockwell axles, S.A.E. 140 should be used the year around except in cases of extremely low temperatures. If trucks are parked in temperaatures below +20°F., or operated in temperatures consistently below 0 °F ., it is advisable to use S.A.E.

90.

OTHER UNITS

S.A.E. 90 may be used the year around. If truck is operated in temperatures consistently below 0°F ., use S.A.E. 80. If the truck is operated in consistently high temperatures (over 100°F.),

S.A.E. 140 may be used.

DRAINING AND FILLING

When axle is new, or after overhaul, it is recommended that lubricant be drained after the first 3,000 m iles of operation, and thereafter at recommended intervals. Draining at an early m ile age removes fine particles of metal or other for eign material.

At specified intervals remove plug at bottom of axle housing, also at bottom of torque divider or inter-axle differential housing on tandem bevel axles. Drain when unit is hot, preferably immed iately after operation. Reinstall drain plugs.

Fill axle to level of filler plug opening. On tandem axles with torque divider, add specified quantity through filler plug on side of case or add two pints of lubricant at top of inter-axle differ ential housing.

SPECIAL AXLE LUBRICATION

Special lubrication is required on all axles as

G M C S E R V I C E M A N U A L

Sec. 0

Page 13

LUBRICATION

follows: (1) when axle has not been operated for a long period (2) has been out of normal position or

(3) after overhaul.

Add one pint of lubricant through plug opening in top of pinion cage or differential carrier. Re check lubricant.level at filler plug.

TRANSMISSION

CHECKING LEVEL (Fig. 13)

At specified intervals remove filler plug at side of case and, if necessary, add sufficient rec ommended lubricant to bring lubricant level up to level of opening. Install and tighten filler plug.

DRAINING AND FILLING (Fig. 13)

When transm ission is new, or after overhaul, it is recommended that lubricant be drained after the first 3,000 m iles of operation, and thereafter at recommended intervals. Draining at early m ile age removes fine metal or other foreign material.

At specified intervals, preferably immediately after operation while unit is hot, remove plug to drain lubricant. Clean drain plug, then reinstall

Filler P lu g

D ra in P lu g

TP M -8839

Figure 13— Transmission Drain and Level Plug (Typical)

and tighten securely. Refill to level of filler plug opening as directed above. Use S.A.E. 90 the year around in transm issions.

CHASSIS LUBRICANT

(SYMBOL “C” O N CHARTS)

The lubricant indicated by symbol "C" on charts should be a high grade p ressu re gun lubricant.

Good quality lithium soap multi-purpose grease is recommended, especially for extreme operating conditions - water, heat, etc.

UNIVERSAL JOINTS

At specified intervals, use p ressure gun to apply lubricant through fitting in universal joint trunnion. Apply until lubricant is forced out around all four trunnion seals (fig. 14). Good quality Lith ium soap multi-purpose grease is recommended.

APPLYING CHASSIS LUBRICANT

All lubrication fittings must be clean before applying lubricant. Always be sure equipment used in applying lubricant is clean. Every precaution should be taken to prevent entry of dirt, grit, lint, or other foreign matter into lubricant containers.

Fittings that have become broken or damaged should be replaced with new part, and can be re moved with a wrench or suitable extracting tool.

COLD WEATHER PREPARATION

When hard steering is encountered as a result of cold weather, the steering system should be lu bricated as follows:

Use steering gear lubricant (Symbol "SG") or

Multi-Purpose Grease (N.L.G.I. #0) to lubricate all steering linkage such as steering knuckles, tie rod ends, and (if used) power steering booster cyl inder ends. In warmer weather, relubricatelinkage with chassis grease previously recommended.

U - J O IN T F IT T IN G

T-2451

Figure 14 — U niversal a n d Slip Joint Lubrication

Sec. 0

Page 14

LUBRICATION

G M C S E R V I C E M A N U A L

STEERING GEAR LUBRICANT

(SYMBOL “SG ” O N CHARTS)

The lubricant indicated by the symbol "SG" is a special steering gear lubricant. No. 0 grade with low cold test characteristics and extreme pressure properties. This type of lubricant is marketed by many oil companies.

Multi-Purpose gear lubricant "MP" previously described, may be used to replenish steering gear housing when additional lubricant is required; how ever, lubricant as described previously must be used as initial fill after overhaul, or in a new gear.

At specified intervals, remove filler plug in housing and add lubricant to bring level up to filler plug opening. Do not. overfill housing.

HIGH TEMPERATURE GREASE

(SYMBOL “S2” O N CHARTS)

The type of lubricant indicated by the symbol

"S2" on charts should be a short fiber, non-fluid, sodium soap grease having a high melting point

(350 F., min.). Good quality lithium soap grease is also highly recommended, especially where corrosion is evident due to moisture. Use No. 2 grade in each case.

WHEEL BEARINGS

CLEANING

With a stiff b ristle brush and cleaning solvent, thoroughly clean bearings and hubs, making sure that all old lubricant and dirt is removed. Check bearings and cups and replace damaged parts.

PACKING

Some wheel bearings are lubricated from axle differential after the initial lubrication. However, whenever wheel hub is removed, bearings should be cleaned, inspected, and re-lubricated. Some rear wheel bearings require cleaning, inspection, and lubrication at regular intervals as specified on lubrication charts.

When packing by hand, be sure that lubricant is kneaded between rollers and races. A mechan ical lubricator can be used; however, bearings must be thoroughly lubricated.

DO NOT FILL HUB. Coat inside hub and axle spindle with thin coat (1/8" thick) of grease to re tard rusting. Allow some excess grease at inner side of bearings and around adjusting nut. DO NOT

PACK HUB WITH GREASE. The lubricant applied to bearings is sufficient to provide lubrication until next service period. Readjust bearings as des cribed in "FRONT HUBS AND BEARINGS" (SEC.

3D) or "REAR HUBS AND BEARINGS" (SEC. 4D) of this manual.

OTHER HIGH TEMPERATURE

GREASE USES

The following points require use of high temperature grease at assem bly. Methods of applying grease to these points are covered in applicable sections of this manual.

Clutch Pilot Bearing

Clutch Release Bearing Collar

Clutch Shift Fork Ball Stud

Steering Column Upper Bearing

PETROLEUM JELLY

(SYMBOL “S3” O N CHARTS)

The type lubricant indicated by the symbol

"S3" is petroleum jelly or petrolatum.

BATTERY TERMINALS

To prevent corrosion, remove cables, clean term inals on cable and battery, and reinstall cables to battery term inals. Tighten cables securely, then apply petroleum jelly.

DISTRIBUTOR BREAKER CAM

At recommended intervals, apply a sm all amount of petroleum jelly on distributor breaker cam. Do not use an excessive amount.

G M C S E R V I C E M A N U A L

Sec. 0

Page 15

LUBRICATION

WATERPROOF GREASE

(SYMBOL “S4” O N CHARTS)

This type of lubricant should be waterproof grease containing 20% to 35% calcium soap. On models equipped with propeller shaft center bear ings, both sides of the shield should be packed with this lubricant at the time of assem bly. This lubricant excludes water and dirt from bearing.

Refer to "PROPELLER SHAFTS" (SEC. 4D) of this manual for procedure.

HYDRAULIC BRAKE FLUID

(SYMBOL “SI 2 ” O N CHARTS)

The fluid indicated by the symbol ”S12” must be genuine heavy duty brake fluid meeting the heavy duty standards of S.A.E. 70R3.

CLUTCH AND BRAKE

MASTER CYLINDER

Check master cylinder fluid level at intervals indicated on charts. Remove dirt from around the plug or cover, then remove.

Fill with fluid until level is within 1 /2 ” of open ing. Inspect to be sure vent hole is clean, then in stall and tighten filler plug or cover (refer to figure 15).

Figure I S — Clutch an d Brake Master Cylinder (Typical)

SOFT, SMOOTH CUP GREASE

(SYMBOL “SI 6 ” O N CHARTS)

Lubricant indicated by the symbol "S16" on charts should be No. 2VZ soft, smooth cup grease.

Fibrous types of lubricant are not recommended for spherangular (barrel) type roller bearings.

High quality lithium soap grease is also highly recommended, especially where corrosion is evi dent due to moisture.

REAR WHEEL BEARINGS

At regular intervals as specified on Lubrica tion Charts, or whenever wheel hub is removed, bearings should be cleaned, inspected, and re lubricated as previously described under "Symbol

S2.”

SPECIAL GREASE

(SYMBOL “SI 7 ” O N CHARTS)

A sem i-fluid grease having extreme pressure properties and containing zinc oxide.

At regular lubrication intervals, or whenever accessib le during repairs or overhaul, apply lub ricant sparingly to the following item s and areas:

Door Striker Plates

Door Checks and Trunnions

Door Hinge Pins

Door Lock Remote Control Link

Cowl Ventilator Linkage

Seat Adjuster Slides

Door Lock Mechanism

Door Dove Tails

Window Regulator Channels

Window Regulators

Hood Hinges

Tilt Cab Guide Pin

In addition to item s just mentioned, which are lubricated periodically, many other units use this lubricant at time of assembly after overhaul, as indicated in various sections of this manual.

Sec. 0

Page 16

LUBRICATION

G M C S E R V I C E M A N U A L

AUTOMATIC TRANSMISSION FLUID

(SYMBOL “S I 9 ’

O N CHARTS)

The fluid indicated by the symbol "S19" must be an "Automatic Transm ission Fluid,” which has been tested and approved and qualified to bear GM trademark ”DEXRON.” DO NOT USE ANY OTHER

FLUID.

POWER STEERING SYSTEM

Power steering system reservoir is located on power steering hydraulic pump (fig. 16). R eservoir is marked with an "OIL LEVEL" mark. Use only

"Automatic Transm ission Fluid GM DEXRON."DO

NOT USE HYDRAULIC BRAKE FLUID, SHOCK

ABSORBER FLUID, OR SIMILAR OIL.

Fluid level should be kept at "OIL LEVEL" mark on reservoir. After cleaning reservoir and cover, loosen cover bolt and remove. Using a clean receptacle, pour fluid through a 200-m esh screen

- NOT A CLOTH STRAINER. Keep fluid clean and free from water.

For cold weather preparation on steering link age refer to information under "Chassis Lubricant"

(Symbol "C") in this section.

Figure 16— Power Steering Fluid System Reservoir (Typical)

BLEEDING SYSTEM

Whenever a line is disconnected or a pump is replaced, the air that has entered the hydraulic system must be bled out, otherwise noisy and un satisfactory operation will result.

ALLISON AUTOM ATIC TRANSM ISSION

Allison Automatic Transm ission is filled with

GM DEXRON Automatic Transmission Fluid at the factory. DO NOT MIX TYPES OF FLUID.

CHECKING FLUID LEVEL

Dipstick and filler tube are located at right side.

1. Apply PARKING BRAKE FIRMLY AND

BLOCK WHEELS. Start engine and warm fluid to operating temperature.

IMPORTANT: Do not operate retarder while warming fluid. Move selector lever through all speed ranges.

2. Run engine at "IDLE" speed with lever in

"N" (Neutral).

3. Clean dipstick and adjacent area, then re move dipstick, clean, re-in sert, again remove and note fluid level.

4. Add one quart of fluid when level reaches

"ADD" mark.

DRAINING AND FILLING

When new, or after overhaul, drain fluid and change filter element after 3,000 m iles, thereafter at recommended intervals. Drain while fluid is at operating temperature.

1. Loosen acorn nut which secures filter cover to oil pan.

2. When drainage is complete, remove acorn nut, washer, cover, gasket, retainer, and filter element.

3. Install new element in reverse order of removal. Tighten nut to 8 to 10 foot-pounds torque.

4. Pour eight quarts of fluid into transm ission using clean container and spout, or funnel.

5. Start engine and check fluid level. Add fluid as necessary to bring level up to markon dipstick.

DO NOT OVERFILL.

HIGH TEMPERATURE

(SYMBOL “S28’

GREASE (SPECIAL)

ON CHARTS)

The lubricant indicated by the symbol "S28” must be a water-proof, non-soap, smooth fibre grease having a #1 N.L.G.I. stable consistency, and must withstand extended high temperatures.

STOPMASTER BRAKE UNIT

At time of assem bly after overhaul apply above lubricant to areas indicated in "AIR BRAKES"

(SEC. 5B) of this manual.

G M C S E R V I C E M A N U A L

Sec. 1

Page 17

SECTION 1 Gahi and Ai/i GonSitianin^

Maintenance information on subjects common to all cabs, such as painting, checking for water and dust leaks, cab alignment, windshield wipers, and replacement of windshield glass is covered in the "GEN

ERAL MAINTENANCE" section following. For all other information, refer to respective cab section as listed in Index below:

Subject

General M a in te n a n c e ...........................................................................

Page No.

Conventional Model Cabs (Includes H e a tin g )................................

T ilt Model Cabs (Includes H e a tin g )..................................................

Body Mountings ..................................................................................

Air Conditioning (Conventional Cab Models) ............................. 69

***QeM£A<*l flo-dtf, M ain ten an ce.***

This section includes general maintenance information on subjects common to all cabs. Subjects are listed in Index below:

Subject Page No.

G e n e r a l ................................................................................................... ........... 17

Key In form ation ................................................................................................ 17

Exterior M aintenance.......................................................................... ........... 18

Interior M a in ten a n ce .......................................................................... ........... 18

Dust and Water Leaks .................................................................................. 18

Cab Alignment ................................................................................................ 19

Straightening ........................................................................................ ........... 19

Dinging and Finishing .................................................................................. 19

P a in t in g ................................................................................................... ........... 19

Windshield Glass R e p la c e m e n t.................................................................... 19

Rear Window R e p la c e m e n t........................................................................... 21

Windshield Wipers ......................................................................................... 21

GENERAL

All cab assem blies for models covered by this manual are of welded steel construction. Heavy box-type cab framing is used to form a str e s sresistant foundation to fortify cab against twisting and flexing.

Principle steel panels are lap-jointed and welded for maximum sealing and structural strength

Further rigidity is achieved by strategically lo cated reinforcement braces and brackets. Sturdy steel door frames serve as upright structural members for rigid cab side support to assure prop er door fit. Heavy-duty hinges assure sa g -r e s ist ant doors while doors are of double-panel con struction for extra strength. Primary sheet metal panels have stamped depressions to minimize cab drumming and vibration. Sheet metal components receive several protective finishes to provide ample resistance to rust and corrosion.

Flexible mounts cushion cab assem bly against shock and protect cab panels from str e ss and strain. Periodic inspections are recommended to ensure that all cab mounting bolts and sheet metal screw s are properly tightened.

Refer to LUBRICATION (SEC. 0) for inform ation regarding lubrication of cab components such as door hinges and seat adjuster slid es. In formation on sheet metal components used with conventional cab is described in SHEET METAL

(SEC. 11) of this manual.

KEY INFORMATION

All models have lock cylinders incorporating coded keyways and keys. The code letter is located

Sec. 1

Page 18

GENERAL MAINTENANCE

G M C S E R V I C E M A N U A L on key shank and the code number is stamped on the knock-out portion of the key head. These numbers identify the locks in which the keys are used and are required when ordering or making new keys.

Notch depth information on current production keys will be provided upon request through the manufacturer of your key cutting equipment or his locksmith association. Also, he w ill be able to furnish a conversion package for your cutter, if required, for grinding new keys.

EXTERIOR MAINTENANCE

Entire vehicle should be regularly inspected for condition of paint and for corrosion damage, with particular attention given to chrome. Inspec tion should be made more frequently in freezing weather due to the corrosive effect of road deicing m aterials (salt, calcium chloride, etc.) on metal.

If inspection d iscloses any evidences of corrosion, paint failure, or bare metal, corrective measures as outlined under "Painting” (later in this section) should be immediately employed.

Body painted surfaces and chrome plating should be protected by a coating of wax, applied at regular intervals. Periods between applications should be sufficiently short to assure continuous protection of the finish; 30 days after delivery, and at least once a year thereafter. Any good body wax can be used for both painted and chrome surfaces.

Wax should be applied immediately after vehicle has been cleaned.

NOTE: Calcium chloride and other salts, road tar, excretion from insects ("tree sap"), chem icals from factory chimneys and other foreign matter may permanently damage paint and chrome. F re quent, regular washing and a thorough cleaning after exposure is recommended to prevent damage by these substances.

INTERIOR M AINTENANCE

Care of the upholstery is a relatively simple but important matter. Accumulation of dirt on the surface eventually turns into a hard, gritty, sub stance which cuts into the surface of the upholstery.

VINYL COATED CLOTH

To clean the seats, use lukewarm, not hot or cold water, and any mild soap or liquid household detergent. Work up thin suds on a piece of cheese cloth and rub upholstery briskly. Remove suds with a damp cheesecloth, using no soap, and finish by wiping lightly with a dry soft cloth. Do not use furniture polishes, o ils, varnishes, or ammonia.

As required, stubborn stains may be removed with common foaming-type upholstery cleaner prepared for use on vinyl cloth.

WOVEN NYLON FABRIC

Soap and toater, regardless of the basic type of soap, is not recommended for cleaning flat cloths, particularly broadcloths.

1. Carefully brush all loose particles of dirt and soil.

2. Immerse sm all cloth in volatile type clean ing solution, wring out thoroughly, open cloth and allow medium evaporation.

IMPORTANT: Use only volatile cleaning solu tions prepared specifically for use on nylon fabrics.

DO NOT USE bleaches, reducing agents, acetone, lacquer thinners, enamel reducers, nail polish re mover, gasoline, or cleaning solvents which con tain dyes or caustic agents. Use of these solvents tends to weaken and change color of fabric.

3. Place cloth on soiled spot and blot area gently - DO NOT RUB. This will pick up particles which are too embedded to be removed in the brush ing operation. This operation should be repeated several tim es - in each instance using a clean area of cloth.

IMPORTANT: DO NOT use too much cleaning fluid; some interior trim assem blies are padded with rubber and volatile cleaners are generally solvents for rubber. The application of too much cleaner may destroy these rubber pads or cause the rubber itself to penetrate the upholstery fabric and spoil appearance.

4. Immerse second cloth, wring out, and allow evaporation until barely damp, then apply to both the soiled and the area surrounding same, using a light swabbing motion.

5. Repeat brushing operation.

6. If a cleaning ring should form, the entire area of the assembly which is being cleaned should be thoroughly brushed and gone over lightly with the solvent.

FLOOR AND SIDE PANELS

Floor should be cleared of debris by sweeping or vacuuming. Using mild soap and water sparing ly, sponge clean side panels and floor. Repeat clean ing operation with clean damp sponge or towel to remove soap film and allow to dry thoroughly.

P ressure spray cleaning and use of strong solvents are not recommended since damage to interior finishes and upholstery could result.

DUST A N D WATER LEAKS

Test windshield, windows, and cab underfloor ing for leaks by spraying water under pressure against cab while assistant inside cab marks points of leakage, if any exist.

If location of leak has been determined to be around glass, dry surface and apply rubber cement.

Apply cement to outside, both between glass and weatherstrip and between weatherstrip and body.

To determine the exact location of leak at flooring or cowl, remove floor mat and dash panel pad. Water which shows up at a certain place in side cab may actually be entering at a point other than where water is found. Back-track path of water to point of entry. Apply body sealing com pound over all leak points.

If leakage occurs at door opening, check wea therstrip. Seal with rubber cement or replace if necessary. If door does not firm ly contact weather strip, align door as described in applicable cab section.

CAB ALIGNMENT

Since cab is an integrally welded structure, repair should be attempted only by competent craftsman using proper tools and equipment. For best results, only genuine factory parts should be used for replacement. As work p rogresses, c r o ss checking with an adjustable tram bar is recom mended for obtaining proper alignment.

STRAIGHTENING

Before attempting repair of a damaged cab, the ch assis frame must be checked and aligned as described in FRAME (SEC. 2). To straighten frame, it may be necessary to remove cab.

Never attempt to straighten cab unless cab is firm ly attached to ch assis. The inner paneling of cab should be straightened first. Use of a pushpull hydraulic jack, together with extension and adapters is recommended for this type of repair.

After straightening, it is important that strains set up in cab framing be relieved or "normalized."

Normalizing consists of heating areas of greatest s tr e ss with a torch. Holding torch nozzle about

2 inches from metal, move torch over an area of

3 to 4 inches until the metal barely begins to turn red. Cooling must be slow to avoid changing char acteristics of the metal. Apply slight heat with torch, if necessary, to retard cooling.

DIN G IN G A N D FINISHING

Paint is quickly scuffed off sharp dents leaving metal exposed to rusting and corrosion; therefore, damaged panels should be repaired as soon as possible. Proper metal finishing is required to assure a smooth surface. Application of hammer directly to panel tends to stretch the metal and cause a great deal of unnecessary work. Whenever possible, a spoon should be used under the hammer when bumping a panel. Repair damaged panels by forcing outward in direction opposite to force which caused damage. In this way metal strains, set up when damage occurred, are relieved.

G M C S E R V I C E M A N U A L

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Page 19

GENERAL MAINTENANCE

PAINTING

REPAINTING

1. Thorough cleaning is essential. All corro sion products, grease, and other foreign matter must be removed. Use of phosphoric base metal conditioners, such as "Metalprep" (Neilson Chem ical Co.) or "Dioxidine" (American Chemical Paint

Co.) or equivalent is recommended in preparing steel for painting. These materials vary in method of application and use, and should be employed only as directed by the manufacturer. Solvent cleaning, pressure steam cleaning, wire brushing, and hand sanding methods are recommended.

2. Completely remove old paint by use of organic or alkaline solvents. However, if alkaline rem overs are used, all traces of alkali must be washed off before primer is applied. If old primer is very difficult to remove, and if there is no evi dence of metal corrosion, old primer may be left on, but all loose paint must be removed.

3. Apply prim er, preferably by spraying, and allow to dry. Use a good oxide primer obtained from a reputable manufacturer.

4. Apply finish coats: a. For understructure or other parts not re quiring color, apply two coats of a good air-drying black or other automotive lacquer.

b. To exposed body parts, apply surfacer and paint in accordance with standard practice.

PAINTING NEW PARTS

New replacement parts should be thoroughly cleaned and painted, as outlined previously under

"Repainting," after installation in vehicle. In addi tion, hidden surfaces of panels should be cleaned and coated with one heavy coat of sheet metal deadener.

WINDSHIELD GLASS REPLACEMENT

Windshield glass is retained in cab opening by a molded rubber weatherstrip with an inserttype rubber seal as illustrated in figure 1. A single windshield glass is used in the conventional cab models whereas two glass sections are used on steel tilt and "P" models.

When replacing a cracked windshield glass, it is very important that the cause of the glass break age be determined and the condition corrected be fore a new glass is installed. Otherwise, it is high ly possible that a sm all obstruction or high spot somewhere around the windshield opening will con tinue to crack or break the newly installed wind shield; especially when the strain on the glass caused by the obstruction is increased by such conditions as wind pressu res, extrem es of temp erature, motion of the vehicle, etc.

Sec. 1

Page 20

GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

C le a ra n c e Blocks;

(J -9 3 1 6 )

Figure 2 — Checking Class Clearances (Tilt Cab)

a. Chipped edges on glass.

b. Irregularities in body opening.

strip.

c. Irregularities in rubber channel weather

2. Remove all sealer from flange and body around windshield opening.

3. Check flange area for solder, weld high spots, or hardened spot-weld sealer. Remove all high spots.

IN S T A L L IN G IN SER T IN SE A L

Figure 1 — Installing Insert-Retained Class

REMOVAL (Fig. 1)

If cracks in glass extend to outer edge of glass, mark cab or cowl with chalk at these points so that weatherstrip flange in cab opening can be examined later for possible distortion.

Protect the interior paint finish by placing a protective covering over steering wheel and dash panel. Mask around the windshield opening and lay a suitable cover over hood and fenders.

GLASS-TO-OPENING CLEARANCE

CHECK (TILT CAB)

Before installing new glass, check glass open ing for proper clearance, using five special spacer blocks (J-9316) as shown in figure 2. With the aid of an assistant, place blocks around perim eter of new glass, two at bottom and top and one at outer side of opening. A 5/16to 3/8 inch clearance should exist between glass and opening flange. Insert blocks into gap, then rotate blocks perpendicular to flange surfaces. If all blocks cannot be installed, rework metal flange or grind off edge of glass at the side where block or blocks could not be in stalled.

CAUTION

C A U T I O N :

DO NOT strike glass

against body metal. Chipped edges on the

glass can lead to future breaks.

ALWAYS W EA R HEAVY G LO V ES TO

P R E V E N T P OSSIBLE

INJURY WHEN

HANDLING GLASS.

If glass clearance is too sm all and glass is to be ground off, place a strip of tape on a line where glass is to be removed. Grind up to edge of tape.

1. Pry end of insert out of rubber seal with a pointed tool; pull insert completely out of seal.

2. With aid of an assistant to hold glass out side cab, push glass forward from inside cab.

If glass clearance is found too large, braze a continuous piece of 1/8 inch diameter wire to edge of cab windshield glass opening flange. This will provide a closer glass and seal fit.

INSPECTION

Due to the expanse and contour of the wind shield, it is imperative in the event of a strain break that the windshield opening be thoroughly

NOTE: Add build-up to flange where n eces sary. Usually the building up to only one side and one-half way around one corner will provide proper glass and seal fit. Taper off ends of build-up to conform to edge of glass, otherwise glass break checked before installing a replacement windshield.

1. Check for the following conditions at the previous marked point of fracture: age may occur, originating at a point adjacent to the end of flange build-up.

G M C S E R V I C E M A N U A L

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GENERAL MAINTENANCE

INSTALLATION (Fig. 1)

NOTE: If desired, sealing cement can be ap plied between lip of seal and glass and seal lip at cab opening flange.

1. Reposition rubber seal on cab opening flange. Raise new glass to outside of seal; then with hook end of installer tool (J-2189) in glass groove of seal as shown in figure 1, move tool around glass to force outer lip of seal over edge of glass.

2. Thread end of rubber insert through handle and loop of installer tool (fig. 1). Push tool loop and end of insert into groove of seal. Feed in rub ber insert, while proceeding around window. Use a hitching movement of tool to avoid elongating insert. If new insert is being used, cut off insert allowing sufficient overlap for a tight joint; then butt into groove.

3. Install insert in center vertical seal (2p iece windshield) in sam e manner previously des cribed in Step 2.

REAR W IN D O W GLASS REPLACEMENT

(ALL CABS)

Rear window glass is retained by means of rubber seal and seal insert (fig. 1). No sealing compound or cement is used.

If body prevents access to rear window, glass can be installed from inside cab by reversing seal so that insert is located inside cab.

1. Pry end of seal insert out of seal with a pointed tool; then remove rubber insert completely.

Push glass from inside cab. Pull seal from opening.

2. If necessary, straighten any irregularities of seal flange in cab opening which may have caus ed breakage of glass.

3. Install new rubber seal over panel flange, pushing it completely into corners. Avoid stretch ing seal during installation. Cut seal to allow suf ficient overlap for a tight joint, then butt ends.

4. Position glass to seal and insert hook end of installer tool (fig. 1) into seal groove. Move tool around glass to force outer lip of seal over glass.

5. Thread end of rubber insert through handle and loop of installer (fig. 1). Push tool loop and end of insert into groove at bottom center of window.

Feed in the rubber insert while proceeding around window. Use a hitching movement to avoid elong ation of insert.

6. Cut off end of insert, allowing sufficient overlap for a tight joint; then butt into groove.

WINDSHIELD WIPERS

GENERAL DESCRIPTION

Conventional cab and steel tilt models have tw o-speed electric E-type windshield wipers with washers as standard equipment. The wiper a ssem bly used on cowl, "P," and school bus models is determined by the body manufacturer.

A single wiper motor, mounted on engine side of cowl, powers both wiper blades on conventional cab models. Two separate motors are used with tilt cab models where each wiper motor is bracketmounted to rear side of cowl under dash.

Tilt cab models employ separate wiper motor control switches; the left switch incorporates a push-type control for operation of windshield w ashers.

WIPER A RM ADJUSTMENT

To adjust sweep of blades to provide maximum visibility, turn on wipers, then note sweep of arms.

CAUTION: DO NOT A T T E M P T TO

M A N U A L L Y MOVE W IP E R ARMS AS

DAM AG E TO LINKAGE OR MOTOR MAY

OCCUR.

If necessary, remove arms as follows:

CONVENTIONAL CAB MODELS

1. Pull outer end of arm away from glass which will trip lock spring at base of arm and re lease spring from undercut of pivot shaft.

2. While holding arm in this position, pull out ward on cap section at base of arm to remove the arm.

Figure 3 — W iper Arm Installed (Tilt Cab)

Sec. 1

Page 22

GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

WIPER A R M TRANSMISSION A N D

LINKAGE REPLACEMENT

(CONV. CAB MODELS)

Figure 4 — Blade A n g le Adjustment (Tilt C a b )

3. Arm can be reinstalled in any one of sev eral positions due to serrations on pivot shaft and in arm cap.

TILT CAB MODELS

Wiper Arm Adjustment (Fig. 3)

Wiper arm can be repositioned on pivot shaft to provide proper sweep as follows:

1. Remove hex crown nut and washer which at tach wiper arm to knurled driver and pivot shaft.

2. Relocate arm on driver to desiredposition.

3. Install washer and hex crown nut.

REMOVAL (Fig. 5)

NOTE: Both right and left wiper transmission units with connecting link rod and motor link rod are replaced as an assem bly.

1. Remove both right and left wiper arms from transm issions. Pull arms outward to disen gage arm retaining clip.

2. Remove special retaining nut, steel washer, and seal washer from each transm ission at front of windshield.

3. Underneath the dash, remove defroster air outlet tubing if necessary, and any other item s to allow access to transm ission linkage.

4. At motor crank arm under dash, remove the two nut assem blies which secure link rod to arm. Disengage end of rod from arm.

NOTE: Alternate methods of obtaining a ccess to these two nuts are to move the wiper motor forward from the cowl opening or to remove the ash tray panel.

5. Using a short c r o ss-r e c e ss type screw driver, remove two screw s and washer assem blies which attach each transm ission unit to underside of cowl. Remove the transm issions with linkage as an assem bly.

Blade Angle Adjustment (Fig. 4) cap screw which attaches blade to arm. Rotate blade to new position against adjustment washer on arm, then tighten cap screw firm ly. When wiper motor is in "PARK" position, blade should be ap proximately parallel to the horizontal windshield seal.

To change angle of wiper blade on arm, loosen

INSTALLATION (Figs. 5 and 7)

Perform the installation procedures in the reverse of the "Removal" procedures. Make sure the seal washers located below the transm ission units at front of windshield are new or in good condition before installing; otherwise leakage may occur later at these two points.

IMPORTANT: Before locating the wiper arms on transm ission shafts, make sure wiper motor was stopped in the "PARK” position (fig. 7). Oper ate motor, then turn switch off and allow it to stop in "PARK” position. If motor is not in "PARK” position and arms are installed, the arm travel

Figure 5 — W ip er M otor a n d Lin k ag e (C onventional Cab)

G M C S E R V I C E M A N U A L

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GENERAL MAINTENANCE

Figure 6 — W iper Motor Installed (Conventional Cab)

may be restricted when motor is started, resulting in a blown fuse. In any case when motor is first started, be prepared to turn wiper switch off in the event wiper arms were installed out of proper sweep position. Reposition arm s if necessary.

WIPER MOTOR REPLACEMENT

(CONV. CAB MODELS)

REMOVAL (Fig. 6)

1. Disconnect wiring harness at motor.

2. If windshield washers are used, disconnect washer lines at pump.

3. Remove three screw assem blies which at tach motor assem bly to front of cab cowl.

4. Pull motor forward from opening, then through the opening, remove two nuts from armto-link rod ball clamp to separate motor from link rod. Remove motor assem bly.

INSTALLATION (Figs. 6 and 7)

Before installing motor, scrape any of the old sealing compound from around cowl opening, then apply a bead of new compound around the opening.

Perform the installation procedures in the re verse of "Removal'' procedures.

IMPORTANT: Make sure motor ground strap is free of paint before installing motor mounting screw s; otherwise motor will not operate. Also, be sure that wiper motor crank arm is in "PARK" position before attaching linkage and wiring harness.

pivot shaft. Remove arm and driver.

2. Remove rubber rainshield, hex nut, flat steel washer, and leather washer from pivot shaft housing.

3. Inside of cab, disconnect electrical wiring at connector on motor drive unit. If equipped with washers, disconnect hoses.

4. Remove four cap screw s which attach motor and drive unit to cab panel.

INSTALLATION (Figs. 3 and 8)

1. Position styrofoam pad on pivot shaft hous ing, then locate motor and drive unit to cab panel.

Attach unit mounting bracket to panel with four cap screw s and washers.

IMPORTANT: Be sure a good m etal-to-m etal contact is made between panel and mounting bracket so as to provide an electrical ground for motor.

2. Connect electrical wiring to terminals on drive unit. If equipped with washers, connect hoses.

3. Install leather washer, flat steel washer, hex nut, and rubber shield on pivot shaft housing.

Position arm driver on pivot shaft.

4. Before installing wiper arms, operate wiper motor momentarily, then turn it off which should rotate pivot shaft to "PARK" position (fig. 7).

5. Install arm on driver of shaft so that it is located in the "PARK" position. Wet windshield, then again operate wiper and check arm sweep.

Reposition arm on shaft driver if necessary. Se cure arm on shaft with crown nut.

WIPER MOTOR REPLACEMENT

(TILT CAB MODELS)

WIPER TRANSMISSION LINKAGE A N D

M O UNTING BRACKET REPLACEMENT

(TILT CAB MODELS)

REMOVAL (Figs. 3 and 8)

1. Remove hex crown nut and lock washer which attaches wiper arm to knurled driver and

REMOVAL (Fig. 8)

1. Remove sm all retaining ring near end of

Sec. 1

Page 24

GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

G ro u n d Stra p

M o u n t in g Bracket

Sh aft H o u s in g

A s s e m b ly

Thrust

W a s h e r

T ra n sm issio n

Sh aft A s s e m b ly | Sh aft H o u s in g

A s s e m b ly

M o u n t in g

Bracket

C ra n k A rm

C ra n k A rm N u t

R e ta in in g

R in g

T ra n sm issio n

Sh aft A s s e m b ly

D R IV E L IN K A G E D IS A S S E M B L E D

R e ta in in g R in g

M o t o r A s s e m b ly

D R IV E U N IT A N D M O T O R A S S E M B L E D

T-031

Figure 8 — W iper Motor and Bracket Com ponents (Tilt Cab)

transm ission shaft, then slide the flat washer and thrust washer from end of shaft.

2. Remove the three sm all screw s which at tach motor mounting bracket to motor. Move motor with attached linkage from mounting bracket suf ficiently to allow a cc ess to connecting link retain ing rings.

3. Remove connecting link retaining rings, then remove link. Separate motor from mounting bracket.

4. The transm ission shaft can be removed only after the shaft housing is separated from mounting bracket. Housing is attached with two screw s, nuts, and w ashers.

INSTALLATION (Fig. 8)

1. If transm ission shaft was separated from housing, locate sm all tension washer on shaft be fore inserting shaft into housing.

2. Locate shaft and housing assembly to mount ing bracket and attach housing to bracket with two screw s, nuts, and washers.

3. Locate motor into mounting bracket, then install connecting link.

IMPORTANT: Make sure end of link marked

"Crank End" is connected to motor crank arm.

Install link retaining rings.

4. Attach motor to mounting bracket with three screw s. Make sure motor ground strap is sandwiched between motor and bracket.

5. At outer end of wiper transm ission shaft, install bronze thrust washer, flat steel washer, and the shaft retaining ring.

WIPER OPERATION

DESCRIPTION

The type "E" two-speed electric windshield wiper assembly incorporates a non-depressedtype

(blades park approximately 2 inches above wind shield molding) motor and gear train. The rec tangular, 12 volt, compound wound motor is coupled to a train consisting of a helical drive gear at the end of the motor armature shaft, an intermediate gear and pinion assembly, and an output gear and shaft assem bly. The crank arm is attached to the output gear shaft.

Two switches, a control switch on dash and a parking switch within wiper unit, control the start ing and stopping of wiper. Parking switch contacts, located on a terminal board at bottom of drive unit are actually connected across the dash switch and act as a set of holding contacts when the dash switch is turned off. This keeps the wiper circuit closed so wiper can keep operating until the blades reach their predetermined "PARK" position.

When the wipers are turned on, current flows from battery through the circuit breaker or fuse through the motor field and armature to the dash switch and on to ground, starting the wiper.

NOTE: Refer to "Windshield Washer" later in this section for operation of washers.

TWO-SPEED OPERATION (Figs. 9 and 10)

Low Speed Operation

When the dash switch is placed in "LOW" speed position, current from the battery flows

G M C S E R V I C E M A N U A L

Sec. 1

Page 25

GENERAL MAINTENANCE

SHUNT W IN D IN G

SERIES W IN D IN G

WIPER TERMINAL BOARD

# 3 TERMINAL

# 1 TERMINAL

# 2 TERMINAL

D A S H SW IT C H

BATTERY

W A S H E R U N IT

M O T O R U N IT

PARKING SW ITCH

C O N TAC TS

T-5827

Figure 9 — W iper Motor and W asher W iring D iagram

through the ser ie s field coil and divides; part passing through the shunt field coil to ground at the dash switch, the remaining part passing through the armature to ground at the dash switch.

High Speed Operation

Moving the dash switch to "HIGH” speed p o si tion opens the shunt field circuit to ground at dash switch and keeps the armature circuit closed to ground. The shunt field current must then pass through a resistor located on the wiper terminal board, and then through the same lead that connects the armature circuit to ground through the dash switch.

Parking Circuit

When wiper is turned off, circuit is broken at the dash switch. However, current from battery continues to flow through motor, through the park ing switch contacts to ground. When wiper blades reach "PARK" position at the inboard end of wiper pattern, the parking switch contacts open, stopping the motor.

TROUBLESHOOTING WIPER MOTOR

Refer to figures 9, 10, and 11 when trouble shooting two-speed wiper.

TYPICAL TROUBLE CONDITIONS

1. Wiper will not shut off.

2. Wiper inoperative.

3. Wiper has one speed (HIGH).

4. Wiper has one speed (LOW) and shuts off with dash switch in "HIGH" position.

5. Blades do not return to "PARK" position when wiper is turned "OFF."

6. Wiper speed normal in "LOW" speed p osi tion but too fast in "HIGH" speed position.

7. Wiper operates intermittently.

CHECKING INSTALLED WIPER

Wiper Will Not Shut Off

1. Determine if wiper operates in both "HIGH" and "LOW” speeds, "LOW" speed only, or "HIGH" speed only.

IMPORTANT: Wiper must operate in "LOW" speed during parking cycle.

2. Disconnect the wiring harness from wiper motor and try operating wiper independently of the dash switch as shown in figure 11. If wiper oper ates correctly independently of the dash switch

(shuts off correctly with crank arm in "PARK" position) refer to possible causes below: a. If wiper operates in both speeds, lead be tween wiper terminal No. 1 and dash switch is grounded, or the dash switch is defective.

b. If wiper operates in "LOW" speed only, the lead between wiper terminal No. 3 and dash switch is grounded, or the dash switch is defective.

c. If wiper operates in "HIGH" speed only, the lead between wiper terminal and dash switch is open, or the dash switch is defective.

3. If wiper still fails to operate correctly, remove it from cab, then remove covering from over drive gears and check parking switch contacts which may be broken or stuck in closed position; check for a grounded lead at No. 1 or 3 terminals

(fig. 11), or for a grounded shunt field.

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Page 26

GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

Series W in d in g Shunt W in d in g

lGr

r - f < 7 |— t i— ' r f

2 4 O H M

IRT— I

Resistor

Battery

L O W SPEED C IR C U IT S

Battery

Series W in d in g S h u n t^ W in d in g

( G ra y

-W

2 4 O H M

Resistor

L ^ p

A rm a tu re

H IG H SPEED C IR C U IT S

| i \ _v

Park Sw itch

D a s h Sw itch

Figure 10— H igh-Low Speed Circuits

Wiper Inoperative

1. Check wiring harness connections at motor and at dash switch.

2. Check fuse (if used) or circuit breaker.

3. See if wiper motor ground strap is secure.

4. Check for loosely mounted dash switch.

5. If wiper still fails to operate, disconnect wiring from motor, and check for 12 volts at motor

No. 2 terminal (fig. 11). No voltage indicates de fective wiring.

6. With harness disconnected from motor, try operating motor as shown in figure 11. If wiper fails to operate, remove wiper transm ission linkage and recheck wiper operation. If wiper operates, linkage is at fault. If wiper does not operate, remove unit from vehicle for disassem bly.

Wiper Has One Speed - Fast

Check for a defective dash switch or open lead between motor No. 3 terminal and dash switch.

Wiper Has One Speed (LOW) and Shuts Off

With Dash Switch in ’’HIGH” Speed Position

R everse harness leads that connect to motor term inals Nos. 1 and 3.

Blades Do Not Return to "PARK" Position

When Wiper is Turned Off

1. Check wiper motor ground connection to the cab.

2. Remove wiper motor from cab and check for dirty, bent or broken "PARK" switch contacts.

Wiper Speed Normal in "LOW"

But Too Fast in "HIGH"

Remove wiper motor from cab and check for an open motor resisto r.

NOTE: Terminals Are Numbered

For Purposes of Explanation

LO SPEED—As Shown

HI SPEED—Disconnect Jumper Wire

From Terminal No. 3

O FF—Leave Jumper Connected to

Terminals 1 and 3 But Disconnect

it From Ground

Jum pe r W ire

For Bench Testing

Connect to

W ip e r H o u sin g

A m m eter

T-030

Figure 1 1 — Troubleshooting W iper Motor Circuit

Intermittent Operation

Check for loose wiper ground connection and/ or loose dash switch mounting.

WIPER M O TO R A N D GEAR B O X

DISASSEMBLY A N D ASSEMBLY

DISASSEMBLY (Fig. 12)

Gear Box

1. Remove washer pump mounting screw s and lift pump from motor.

2. Remove washer pump drive cam (fig. 16).

Cam is pressed on shaft but may be removed by carefully wedging two screw drivers between cam and plate.

3. Lightly clamp crank arm in a vise and re move crank arm retaining nut. Separate arm from shaft.

NOTE: Failure to clamp crank arm may re sult in stripping of drive gears when retaining nut is removed.

4. Remove seal cap, retaining ring, and endplay washers.

5. Drill out gear box cover attaching rivets and remove cover from motor assem bly.

NOTE: N ecessary parts for reassem bly of gear box cover to motor is contained in service repair package.

6. Remove output gear and shaft assem bly, then slide intermediate gear and pinion assembly off shaft. Note position of wave washers.

7. If necessary, remove terminal board and

"PARK" switch by marking w ires and unsoldering at terminal lugs. Drill out terminal board attaching rivets and remove board.

G M C S E R V I C E M A N U A L

Sec. 1

Page 27

GENERAL MAINTENANCE

1 Nut

2 Crank Arm

3 Seal Cap

4 Retaining Ring

5 Washer

6 Gear Box Cover

7 Output Gear and

Shaft Assy.

8 Intermediate Gear

9 Wave Washer

10 Gear Box Housing

11 Brush Plate Assy, and

Mounting Brackets

12 Brushes

13 Wave Washers

14 Flat Washers

15 Armature

16 Thrust Plug

17 Frame and Field

18 End Plate

19 Tie Bolts

(Two Required)

T-3642

Motor

8. Remove motor through bolts, tap motor frame lightly, and separate motor assem bly from gear box housing.

9. Remove brush tension by placing brush spring in holder groove as shown in figure 13.

10. Slide armature and end plate from motor frame and field. Note arrangement of wave wash ers (fig. 14) on gear end of armature shaft before removing to assure proper installation upon motor assem bly.

Figure 12— Wiper Motor and Gear Box Assem bly (Typical)

11. Pull end plate from armature. Note thrust plug between tip of armature shaft and end plate.

INSPECTION

Check armature shaft, gears, and supporting bushings for wear. Inspect commutator for evi dence of arcing or loose solder joints to armature windings. Check "PARK" contacts for dirt or oxi dation. Inspect for worn brushes, weak springs, and binding in holders.

In general, inspect all parts for serviceability and replace as required. All parts can be replaced individually except motor frame and field which is serviced as an assembly. Service kits provide all necessary attaching parts for installation of gear cover and terminal board.

ASSEMBLY (Fig. 12)

Motor

Reassem ble motor using reverse order of

"Disassembly" procedures.

NOTE: Be sure wave washers on armature shaft are installed properly as shown in figure 14.

Lightly lubricate armature shaft bushings with light machine oil. Be sure brushes are properly positioned in holders before armature commutator protrudes between brushes.

Gear Box

1. Assem ble gear box in reverse order of

"Disassembly" procedures.

NOTE: Lubricate gear teeth with Delco Cam and Ball Bearing Lubricant or equivalent. Be sure cover is properly located over dowel pins and that

BRUSH H OLDER

REMOVE BRUSH SPRING FROM SLOT

A N D PLACE IT IN G ROOVE A S SH O W N

Figure 13 — R e leasing Brush Sp rin g Tension

Sec. 1

Page 28

GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

Figure 14— End Play W ave W asher Installation

ground strap is properly positioned before securing cover.

Seal cap (fig. 12) should be cleaned and r e packed with water-proof grease before reassem bly.

2. Install crank arm on output shaft so that alignment marks line up with those on cover when wiper motor is in "PARK'.’ position (fig. 7). Re place and tighten retaining nut after placing crank arm in vise.

3. Check operation by connecting assem bled motor to battery as shown in figure 11.

WINDSHIELD WASHER PUMP

GENERAL INFORMATION

The "E" type washer pump used on the "E" type rectangular non-depressed park wiper motors re sem bles previous models somewhat in physical appearance but it has been changed considerably internally. Refer to figure 15 for view of pump mounted on wiper motor assembly. Past model pumps used a bellows system for the pumping mechanism whereas the new design incorporates a piston enclosed in a plastic cylinder housing.

The piston type pump provides higher p ressures and increased volume (fig. 18).

The basic principle of operation is very sim ilar to past model pumps of this type. The pumping mechanism is powered by a four-lobe cam which is p ressed on wiper motor output shaft. This cam

Figure 15— W asher Pum p Attaching

Screws

rotates whenever the wiper motor is running. P ro gramming is accomplished electrically and mech anically through use of a pump solenoid circuit and ratchet wheel arrangement.

OPERATION

Conventional Cab Models (Single Wiper Motor)

Pushing in on the wiper switch knob causes the washer to activate and also causes wipers to ac tivate in "LOW" speed. If operator wishes high speed wiper action he must manually switch to

"HIGH" speed. At the end of washer cycle, washer will automatically shut off; wiper must be shut off manually, regardless of high or low speed.

Tilt Cab Models (Two Wiper Motors)

Pushing in switch knob of left-hand wiper switch causes washer to activate, and also causes left-hand wiper to activate in "LOW" speed. If operator wishes "HIGH" speed and/or right-hand wiper action also, he must manually control both.

At the end of washer cycle, washer will automatic ally shut off; wiper(s) must be shut off manually regardless of speed (both left- and right-hand).

PUMP REMOVAL (Figs. 15 and 16)

1. Disconnect water hoses to washer pump making certain they are properly marked to a s sure correct installation.

2. Disconnect electric wiring from washer term inals.

G M C S E R V I C E M A N U A L

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GENERAL MAINTENANCE

Figure 16— Separating Pum p from Motor

3. Remove washer pump attaching screw s, then lift pump off wiper motor.

3. If all item s in Step 2 check out, start wiper motor only, then push washer button and listen for

"click" as washer solenoid pulls in. If no "click" is heard, check for 12 volts at terminal No. 2 (fig.

17). No voltage indicates defective wiring. If "click" is heard, proceed to Step 5.

PUMP INSTALLATION (Figs. 15 and 16)

1. Place washer pump in position on wiper motor making sure lever arm pin properly engages four-lobe cam.

2. Secure pump to motor with two mounting screw s.

3. Reconnect electric wiring.

4. Reconnect water hoses.

4. If correct voltage was found in Step No. 3, connect a jumper wire from washer terminal No.

1 to ground (fig. 17) and operate wiper. If washer relay "click" is heard and pump functions correctly, a defective dash switch or an open circuit between washer pump and dash switch is indicated - "No

Click" indicates an open pump solenoid.

TROUBLESHOOTING WASHER PUMP

(Refer to Fig. 17)

On-Vehicle Check

1. If washer pumps continuously when wiper is on, disconnect wiring from washer pump.

a. If pump shuts off, trouble is located in w ir ing harness or dash switch.

b. If pump fails to shut off in Step a, remove pump assem bly from vehicle for further checking.

5. If relay "click" is heard in Step 3, listen for the soft clicking as the pump ratchet wheel is rotated.

a. If soft clicking is not heard, the pump mech anism is faulty and should be removed from the wiper motor and checked.

b. If soft clicking is heard but no pumping ac tion occurs, replace the valve assembly and r e check pump.

INTAKE V A L V E

PISTON

2. Check the following item s if pump is in operative: a. R eservoir contains water solution.

b. Hoses are not damaged and hose connec tions are tight.

c . Screen at end of jar cover hose is not plugged.

d. Electrical connections to washer pump and dash switch are secure.

e. Nozzles are not plugged.

EXHAUST VALVE

SP R IN G

ACTUATOR

PLATE T A N G

AC TU ATO R PLATE

T-5881

Figure 1 8 — W a sh e r Pum p Piston a n d V a lv e A ssem bly

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GENERAL M AINTENANCE

G M C S E R V I C E M A N U A L

NOTE: Ratchet pawl spring removed in above view

1 Coil Term inals

2 Solenoid Plunger

3 Actuator P late Tang

4 Cam Follower Upper Pin

5 Ratchet Pawl

6 Cam Follower Lower Pin

7 Ratchet Wheel

8 Valve A ssy. Mtg. Screws

9 Valve Assem bly

10 Ratchet Dog

11 Dog Retaining Screw

12 Solenoid Coil A ssem bly

13 Pivot Pin

14 Piston Actuator P late

15 Ratchet Wheel Spring

16 Ratchet Pawl Spring

Figure 19— W asher Hump M echanism

Bench Check

1. Manually actuate the solenoid plunger and check for binding condition.

2. Check relay coil as follows: Connect 12 volt supply to washer terminals (fig. 17). Observe if solenoid plunger pulls in. Failure of solenoid plunger to pull in indicates an open solenoid coil or poor solder connections.

3. If solenoid plunger pulls in correctly, man ually actuate the cam follower lower pin and ob serve if pump piston and actuator plate operate freely. Locate and correct cause if binding occurs.

4. Attach a hose to the large or intake pipe.

You should be able to blow, but not draw, through intake pipe (fig. 18).

5. Attach a hose individually to each of the sm all exhaust pipes. You should be able to draw, but not blow, through them. If any of the valves allow air to pass in both directions, the valve a s sembly is defective and must be replaced.

PUMP DISASSEMBLY AND ASSEMBLY

(Refer to Fig. 19)

1. Remove washer pump cover.

2. Remove ratchet dog retaining screw . Hold spring loaded solenoid plunger in position and carefully lift the solenoid assem bly and ratchet dog off the frame of the pump.

3. Disconnect ratchet pawl spring. Remove ratchet pawl retaining ring and slide ratchet pawl off cam follower shaft.

4. Move ratchet wheel spring out of shaft groove and slide ratchet wheel off shaft.

5. Pull pump housing away from frame until housing grooves clear frame. Remove actuator plate from ratchet wheel and cam follower shafts.

6. Remove screw s that attach valve assembly to pump housing. Separate valve assem bly from pump housing.

NOTE: Observe direction of pipes before re moving pipe assem bly from pump housing.

7. To assem ble, reverse "Removal"procedure

NOTE: During reassem bly, be sure gasket be tween housing and valve plate is properly positioned in the housing and valve plate grooves. Also, be sure triple O-ring is properly installed between valve body and pipe assem bly. Hose connections on pipe assembly should be pointed in same direc tion as original position.

G M C S E R V I C E M A N U A L

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Go-twesitiosial Gab

Contents of this section are listed in Index below:

Subject

Cab Description ............................................................

Page No.

Cab M o u n tin g s................................................................

S e a t s .................................................................................

Doors ..............................................................................

Cab Replacement .........................................................

Heating and Ventilation ..............................................

NOTE: Maintenance information on painting, windshield glass, and windshield wipers which is common to all types of cabs is explained at beginning of this group in "GENERAL

MAINTENANCE" section.

Information on sheet metal components is covered in

SHEET METAL (SEC. 11) of this manual.

CAB DESCRIPTION

The basic conventional cab is of all steel welded construction (fig. 1). Cab side construction consists of a one-piece body door opening frame which assures more positive sealing around the door when closed.

The one-piece roof panel has longitudinal ribbing to stiffen and reinforce the roof. The floor panel, also of one-piece construction eliminates joints, pockets and seam s which normally act as moisture traps. In most cases, all paneling pieces are lap-jointed and welded for maximum in sealing and structural strength.

Front outside air intake is located at top cen ter of cowl. Opening and closing of intake is con trolled by push-pull lever at top of dash panel.

Outside air for the heating system enters through a separate louvered opening at right side of cowl.

Doors are of double-wall construction. Lower inner panel of door has a cut-out allowing access to door control mechanism for adjustment and parts replacement. Horizontal slots in door hinge assem bly provides for adjustment of door in cab opening. Door vent window is of friction-type with positive theft-resistant latch.

The windshield used on all conventional cab models covered in this manual is of the one-piece type.

CAB MOUNTINGS

removing one mounting bolt.

At regular intervals, all cab mountings should be checked for loose attaching parts and for de teriorated or collapsed rubber cushions.

Any one cab mounting can be readily replaced after removing the weight of cab at that particular mounting.

IMPORTANT: Raise cab only to height n eces sary to replace mounting components. If cab is raised too high, damage to vehicle operating con trols, wiring and lines may occur. Before lowering cab, be sure cushion is properly centered between frame and cab.

Four point type cab mountings are used on these vehicles. The front mount consists of an upper and lower cushion assembly as shown in figure 2. Cab rear mounts are of the compression type (fig. 3), utilizing rubber biscuit cushions. This compression-type mounting is readily replaced by

Figure 1 — C a b W e ld e d Construction

Sec. 1

Page 32

CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

FO RE A N D AFT

A D JU S T IN G LEVER

SE A T B A C K

A D JU S T IN G STUD

A N D N U TS

Figure 2 — Cab Front M o un ting

SEATS

SEAT ADJUSTMENT

If right- and left-hand seat adjusters do not release simultaneously, lengthen or shorten ad juster lock rod underneath the seat assembly.

A stud adjustment nut and wing nut at ends of seat-back frame (fig. 4) provide a means of chang ing tilt of seat-back. To change tilt of seat-back, loosen each wing nut and turn adjustment nuts

o

CRO SSM EM BER

FLAT W ASH ER

UPPER C U SH IO N

ASSEM BLY

LOW ER C U SH IO N

ASSEM BLY

CROSSM EM BER

BRACE

NUT (TORQUE

20-25 FT. LBS.)

T-5707

Figure 3 — C a b Rear M o u n tin g

Figure 4 — Full Width Seat Back Adjustment

above seat-back fram? brackets an equal amount to raise or lower seat-back. Tighten wing nuts to secure desired position.

SEAT TRACK REPLACEMENT

NOTE: The seat track assem blies are more readily replaced after seat assem bly is removed from cab.

1. Remove four screw s which attach each track assembly to seat cushion. Lift seat assembly from cab.

2. If only one track assem bly is to be remov ed, disconnect lock rod between tracks, then re move four bolts which attach each track to cab floor panel. Remove track assem bly.

3. Reverse the above procedure to install track assembly.

DOORS

Component sub-assem blies of cab doors, such as window regulator, door lock, remote control, and vent window can be replaced without necessity of removing door from cab. Doors can be replaced without prior removal of above components.

Replacement of door glass is explained later in this section.

Instructions for replacing door assembly are as follows:

REMOVAL (Fig. 5)

1. Using sm all punch, drive spring pin up from door check strap at cab bracket.

2. With aid of an assistant to support weight of door, remove three cap screws which attach each hinge strap to door. Remove door and hinge shim s (if used).

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CONVENTIONAL CAB

Figure

5 — C a b

Door Hinges and Check Link

INSTALLATION (Fig. 5)

1. Position door to hinge straps and install attaching cap screw s loosely. Insert shim s (if used) between hinge and door. Note direction of slots in upper and lower hinge shim s as illustra ted in figure 5.

2. Adjust door-to-cab opening as explained later under "Door Adjustments."

3. Connect door check strap to cab pillar bracket by driving spring pin down from the top.

NOTE: It is not recommended that the a ccess panel be removed from door inner panel for pur pose of storing heavy tools in door compartment.

DOOR ADJUSTMENTS

Doors can be adjusted for alignment or clear ance in the cab door opening (fig. 6), and for proper latching. The door, when properly located in door opening, will have equal clearance around its perim eter.

Door alignment adjustments are made at the striker bolt and door hinges. Rubber seal around door should be lubricated with silicone lubricant and door vent window should be open before open ing and closing door while making door adjustment.

Before adjusting hinges, remove the striker bolt from the cab pillar.

DOOR "FORE" AND "AFT" POSITIONING

The fore and aft adjustment of door is pro vided by the removal or installation of shim s in serted between door and hinge strap (fig. 5). At only one hinge at a time, loosen three cap screw s

Figure 6 — Door Clearances

which attach hinge strap to door. Add shim to in crease clearance at door leading edge or remove shim (if used) to decrease clearance. Repeat ad justment at other hinge, as required.

Door should have equal clearances at both front and rear (fig. 6). After making adjustment, tighten hinge screw s firm ly.

DOOR "IN” OR "OUT” POSITIONING

Horizontal slotted cap screw holes in door half of hinge provide the ”in” and "out” adjustment of door (fig. 5). Loosen three cap screws which attach each hinge strap to door. Reposition door on hinge straps so that door outer surface is flush with cowl surface.

Perform clearance adjustment at rear of door as directed later under "Door Striker."

DOOR STRIKER PLATE

The door striker consists of a special bolt and washer assem bly which is threaded into a tapped, floating cage plate located behind the cab lock pillar as shown in figure 7. The door is s e cured in closed position when the lock cam in door engages and snaps-over the striker bolt. Striker bolt can be replaced or adjusted as directed under applicable headings.

STRIKER BOLT REPLACEMENT

Removal (Fig. 7)

1. Mark position of striker bolt spacer or

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

Figure 7— Door Striker Bolt and W ashers

washer on door pillar using pencil or crayon.

2. Insert a 5/16-inch hex wrench into head of striker bolt, then turn bolt counterclockwise from plate in cab pillar.

Figure 8 — Sight Checking Striker Bolt A lignm ent

shoe which is located just in back of the lock cam.

To obtain this dimension, remove the striker

Installation (Fig. 7)

1. To install, reverse "Removal" procedure.

NOTE: Make sure the thin plastic washer is positioned against the painted door opening pillar bolt and install or remove shim spacers. Spacers are available in two thicknesses: 5/64-inch and

5/32-inch. Make sure the thin plastic washer is and center the bolt washer within marks on pillar.

2. If door has been removed and then installed located next to cab pillar.

After obtaining proper fore and aft adjustment, tighten bolt snug only at this time and then proceed with the "Striker Bolt Height Adjustment." or aligned in opening, the door should not be closed completely until a visual check is made to deter mine if lock cam in door will engage the striker bolt correctly. Center of striker bolt should be in direct alignment with "V” slot in door. See figure

8. If necessary, reposition striker bolt as direc ted below under "Striker Bolt Adjustment."

Striker Bolt Height Adjustment

This adjustment is important to assure that the right proportion of door's weight will rest on striker bolt when door is closed. If bolt is p osi tioned too high on pillar, rapid wear will occur to the lock cam; if too low, an extra load will be placed on door hinges as well as pull door down ward and out of alignment.

STRIKER BOLT ADJUSTMENT

IMPORTANT: This adjustment should be check ed and if necessary adjusted after door is aligned properly in cab opening.

Striker bolt on cab pillar is adjustable vertic ally and transversely after loosening the bolt with a 5/16-inch hex wrench. The bolt fore and aft ad

Generally the striker bolt height adjustment can be checked quite accurately by just sighting the center of "V" slot on door with the center of striker bolt as illustrated in figyre 8. However, justment is obtained by use of shim spacers lo cated between the bolt washer and the cab pillar.

Figure 7 illustrates location of bolt, w ashers, and spacer.

to make a more positive check, perform the fol lowing:

1. Mark a horizontal line through center of

"V" slot and on door lock cam as shown in figure 9.

2. Smear some grease or paint on contact

Striker Bolt "Fore" and "Aft" Adjustment

1. To check striker bolt for proper fore and aft adjustment, sm ear grease or paint to contact side of bolt as shown in figure 9.

2. Slowly close door until lock cam of door just contacts the side of striker bolt and makes an im pression in the grease or paint.

3. Measure distance between head of bolt and the cam im pression in grease. Distance should m easure 1/8-inch as shown in right view of figure

9. This dimension is necessary to assure that the head of striker bolt will ride at center of nylon edge of lock cam as shown in figure 9.

3. Slowly close door until cam barely contacts the striker bolt to leave an im pression in grease.

Open door and check contact mark on edge of cam.

Mark should be located approximately 1/16-inch below the horizontal mark if properly aligned.

4. If necessary, raise or lower the loosened striker bolt up or down by tapping on the washer or spacer at base of striker bolt. DO NOT TAP

ON HEAD OF BOLT.

NOTE: If striker bolt reaches end of adjust ment travel it will then be necessary to add or remove shim s at the door hinges.

G M C S E R V I C E M A N U A L

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CONVENTIONAL CAB

APPLY PAINT O R G R EA SE

TO EDGE OF LOCK C A M

STRIKER BOLT

1 / 1 6 " BELO W LINE

SCRIBE H O R IZ O N T A L

LINE THROUGH

CENTER OF LOCK ‘‘V ’’

STRIKER BOLT M A RK

IN PAINT OR G R EA SE

DAB OF PAINT

OR G R EA SE

D O O R STRIKER

C A M M A RK

Figure 9 — Striker Bolt A lign m en t Points

After obtaining proper height adjustment, pro ceed to make "Door Rear Edge "In" or "Out" Ad justment."

Door Rear Edge "In" or "Out" Adjustment

This adjustment is for purpose of aligning the rear surface of door flush with adjustment surfaces of cab. If surfaces are not flush, proceed as follows:

1. Mark a horizontal line on cab pillar at top of striker bolt base washer or spacer.

2. Loosen striker bolt slightly, then tap against bolt base washer, to move bolt "in" or "out" as necessary to locate door surface flush with cab surface when door is closed. Before tightening the striker bolt make sure top of bolt base washer is contacting the horizontal mark on cab pillar. Final tighten striker bolt.

Two rubber bumper blocks are inserted into door rear edge panel to absorb closing shock and to lim it the "in" adjustment. If bumper blocks are deteriorated or damaged otherwise, they should be replaced. Pull blocks from door to remove. A flat bladed tool, such as a putty knife, can be used for installing blocks in manner shown in figure 10.

DOOR CHECK REPLACEMENT

Remove check assem bly.

3. Attach check assem bly to door, then con nect check strap to cab bracket with spring pin, which must be installed from top side.

DOOR WEATHERSTRIP

REPLACEMENT

Door weatherstrip is retained to cab opening with adhesive cement. Weatherstrip at bottom of door opening is retained by the sill plate shown in figure 12.

1. Remove weatherstrip, then scrape all old cement from cab flange.

RUBBER BUMPER

IMPORTANT: Do not allow door to swing be yond the normal full-open position when the check strap is disconnected.

1. Using a sm all punch, drive spring pin up from bottom of strap bracket (fig. 11).

2. Remove the two screw and washer assem blies which attach the check strap catch to door.

Figure 10— Installin g Rubber Bum per in Door

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

Figure 11

— D oor

Check Installed

2. Apply cement to cab flange surfaces, then position seal to cab. Referring to figure 12, note the installed position of seal ends of the door weatherstrip. Also note the position of the cut ends of weatherstrip in cab opening.

3. After installing weatherstrip in cab opening, install sill plate.

NOTE: An application of silicone lubricant or equivalent to weatherstrip and adjacent contact

Figure 12— D o o r W eatherstrip Installed

Figure 13— Installing Access Panel Insert

areas will prevent weatherstrip from sticking or freezing between cab and door.

DOOR ACCESS PANEL

REPLACEMENT

REMOVAL (Fig. 13)

1. Pry end of sm all rubber insert out of re tainer seal groove with a pointed tool, then pull insert completely out of seal.

2. Engage hook end of tool (J-2189) under edge of access panel, then run hook along panel to force panel out of rubber seal.

3. Pull seal from door.

IMPORTANT: Inside edge of opening may be sharp. Do not attempt to perform operations through opening unless sharp edge is removed or covered with tape.

INSTALLATION (Fig. 13)

1. Position rubber seal around opening in door.

2. Place access panel to seal, then with hook end of tool in panel groove of seal, move tool around panel to force outer lip of seal over edge of panel.

3. Thread end of sm all rubber insert through handle and loop of installer tool (fig. 13). Push tool loop and end of insert into groove of seal. Feed in rubber insert, while proceeding around panel. Use a hitching movement of tool to avoid elongation of insert. If new insert strip is being used, cut off insert allowing sufficient overlap for a tight joint, then butt into seal groove.

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CONVENTIONAL CAB

Figure 14— Door H andle Installation

DOOR OUTSIDE HANDLE

REPLACEMENT

REPLACEMENT (Fig. 14)

1. Remove the access panel from lower por tion of door as directed previously under "Door

A ccess Panel Replacement."

2. Roll window to top of door, then using a

7/16-inch wrench, reach up through access open ing and remove two lock-type screw and washer assem blies which attach handle to door. Remove handle and handle gaskets.

3. Install door handle, using procedures in reverse of handle removal. Make sure the handle reinforcement plate is in position, inside of door at handle mounting.

DOOR HANDLE PUSH BUTTON A N D

SHAFT REPLACEMENT

DISASSEMBLY (Fig. 15)

1. Remove handle from door as directed pre viously under "Door Outside Handle Replacement."

2. Remove the button shaft retainer by first depressing, then rotating retainer as shown in figure 16. Remove shaft spring and button assem bly with O-ring seal from handle.

ASSEMBLY

1. Place button assem bly with installed O-ring seal in handle.

2. Locate spring over button shaft, then install spring retainer (fig. 16).

Figure 15— Door Handle Disassembly

DOOR LOCK CYLINDER

REPLACEMENT

REMOVAL (Fig. 17)

1. Using flat blade screwdriver, pry retainer from edge of door.

CAUTION: HOLD ON TO R E T A IN E R

WHEN R EM O V ING AS R E T A IN E R MAY

F L Y FR O M POSITION.

2. Remove the lock cylinder from door. Cyl inder must be rotated and tilted slightly to permit cylinder lug to disengage from lock mechanism stud. Remove lock cylinder gasket.

INSTALLATION (Fig. 17)

1. With gasket in position on lock cylinder, insert cylinder into door to engage cylinder lug over lock mechanism stud within door.

2. While holding cylinder in door, force the

Figure 16 — D is e n g a g in g H an d le Sp rin g Retainer

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

RETAINER

SCREWDRIVER

IN S T A L L IN G C Y L IN D E R

R E M O V IN G R E T A IN E R

Figure 17— Door Lock Assem bly Replacement

cylinder retainer through slot at edge of door to engage grooves at side of cylinder body. It may be necessary to drive the retainer into final engage ment with a light hammer. Make sure both legs of retainer are engaged in grooves of lock cylinder.

If one of the retainer legs is not engaged, the re tainer flange will not be vertical in door slot.

DOOR INSIDE HANDLES

REPLACEMENT

If removing door inside handle, the handle position should be marked in relation to door panel to assure that handle is installed later at the same operating angle. See figure 18 which shows proper handle position.

REMOVAL

1. Insert tool (J-9886) between handle flange and escutcheon plate as shown in figure 18.

2. Force lock spring from grooves in base of door handle. DO NOT LOSE SPRING. Remove handle and escutcheon plate.

NOTE: The lower view in figure 18 shows how the tool engages the clip at underside of handle when removing.

INSTALLATION

1. Insert lock spring in handle grooves from direction shown in figure 18.

2. Place the escutcheon plate on handle spindle.

3. If installing door lock release handle, make sure handle is in position previously marked on door inner panel. To install either handle, force handle with installed lock spring over spindle until lock spring becomes fully engaged.

DOOR LOCK AN D REMOTE CONTROL

MECH ANISM REPLACEMENT

REMOVAL (Fig. 19)

1. Remove the door inside lock knob which is threaded on lock rod.

2. Remove the a ccess panel from door inner panel as directed previously under "Door A ccess

Panel Replacement."

3. Remove the door lock inside handle as directed previously under "Door Inside Handles

Replacement.”

4. Remove three screw s which attach the re mote control to door inner panel. Lower the con trol to door access opening, then disengage fasten er at pull-rod. Separate rod from control.

5. Remove the lock cylinder assembly from outer side of door as directed previously under

"Door Lock Cylinder Replacement."

6. At rear edge of door, remove three special locking-type screw s which attach lock mechanism to door frame. Lower the lock and attached two rods out through access opening in door.

INSTALLATION

Install lock mechanism with rods and remote control in reverse of the "Removal" procedures.

IMPORTANT: Be sure to use the three special locking-type screw s which attach lock mechanism to door frame. Check for proper operation of in stalled lock assembly before attaching a ccess panel to door.

G M C S E R V I C E M A N U A L

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CONVENTIONAL CAB

THREADED

LO C K IN G K N O B

HANDLE P O SIT IO N M A RK

ESC U T C H E O N PLATE

LO C KIN G ROD

REMOTE CONTROL

ATTACHING SCREW S

CLIP REM O VER

(TOOL J-9886)

R E M O V I N G H A N D L E CLIP

CLIP REM O VER

T O O L

PR O P ER T O O L -T O -C L IP E N G A G E M E N T

T-2548

Figure 18— Door Inside H andle Replacement

DOOR VENT GLASS REPLACEMENT

1. Squirt gasoline on rubber filler all around glass frame to soften old filler. When seal softens sufficiently, pull glass and old filler from glass channel.

2. Thoroughly clean the inside of the glass channel with sandpaper to remove all rust and foreign matter.

NOTE: Ventilator glass rubber filler is sup plied in two thicknesses - 0.067" and 0.080" for select fit between glass and channel.

3. Cut new piece of glass channel rubber filler two inches longer than required. Position filler

(soapstoned side away from glass) over that part

PULL ROD

LOCK M E C H A N ISM

ATTACHING SCREW S

L. LO C K IN G TYPE).

Figure 19— Door Lock

M e c h a n ism

and Rods

of glass which will be inserted in frame. Punch to gether projecting length of filler at each end to retain filler in place during installation.

4. Brush inner channel of glass frame with soap solution. P ress glass and filler into frame until firmly seated. Purpose of soap solution is to facilitate assem bly. DO NOT USE GREASE OR

OIL.

5. Trim off excess filler material around frame and at end of frame.

DOOR VENT W IN D O W TENSION

REPLACEMENT

Vent windows are of friction type having a theft-resistant latch. Friction mechanism consists primarily of a coil spring mounted on vent window lower pivot, which exerts frictional force against mounting lower support.

If friction mechanism is adjusted too tight, it will be difficult to open or close vent. Too loose an adjustment will result in a fluttering vent or one having a tendency to close with wind pressure.

If necessary to change vent friction, perform procedures as follows:

1. Remove access panel from door inner panel as directed previously under "Door A ccess Panel

Replacement." Panel is retained to door with rub ber insert-type retainer.

2. Reaching up through access opening in door,

PageUp__________________________ G M C S E R V I C E M A N U A L

CONVENTIONAL C A B ^

Figure 2 0 — Adjusting Vent W in do w Tension

Figure 2 1 — Vent W in d o w Attachm ent

Figure 2 2 — Replacing Vent W in d o w

as shown in figure 20, turn adjustment nut with a

^-inch speed wrench to obtain five to seven pounds torque, while moving vent window from a tendegree open position to a full-open position. Use either a push or pull type spring scale, positioned at rear edge of vent glass. Turning adjustment nut clockwise increases operating tension.

3. Install door a ccess panel.

DOOR VENT W IN D O W ASSEMBLY

REPLACEMENT

REMOVAL

The channel between the door window glass and the door vent is part of, and is removed with, the vent window assem bly.

1. Regulate the window to the full down position.

2. Remove the a ccess panel from door inner panel as directed previously under "Door A ccess

Panel Replacement."

3. Remove lower two channel retaining screws from door inner panel bracket (fig. 21).

4. Remove three screw s which attach vent framing to door (fig. 21).

5. Rotate the vent window assembly and care fully lift it up and out of door (fig. 22).

INSTALLATION

1. With window glass down, lower the glass channel portion of vent assem bly down into the

G M C S E R V I C E M A N U A L

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CONVENTIONAL CAB

Figure 2 3 — Replacing Door W in d o w Class Assem bly

door and rotate it to locate in position (fig. 22).

2. Make sure that the rubber lip around for ward portion of vent is properly mated over door vent opening contours.

3. Install two screw s attaching lower channel portion of vent assem bly to door inner panel brac ket (fig. 21).

4. Referring to figure 21, install three screws to attach vent frame to door structure.

5. Adjust the vent opening and closing tension as directed previously under "Door Vent Window

Tension Adjustment."

6. Install door a ccess panel.

DOOR W IN D O W GLASS

REPLACEMENT

REMOVAL

1. Remove the vent window assem bly as di rected previously under "Door Vent Window A s sembly Replacement."

2. Regulate window to two-thirds closed p osi tion.

3. Disengage the glass from the regulator guide by positioning the roller at the guide openings and then lifting out the window (fig. 23).

4. If desired, the horizontal seal strips can be replaced using a flat-bladed tool to pry strips from door as shown in figure 27.

5. Also if desired, the door glass run channel assem bly can be removed at this tim e. Pull run channel from door.

6. To replace the glass in glass channel per form the following: a. Squirt gasoline along glass filler on both sides of glass to soften seal. Remove glass from channel when filler is sufficiently soft. Pull rubber filler from channel.

b. Thoroughly clean inside of glass channel, removing all rust and foreign matter.

c. Window glass rubber filler is supplied in three thicknesses - 0.037", 0.047", and 0.057" for select fit between glass and channel.

d. Cut new piece of channel filler slightly longer than channel. Position filler (soapstone side away from glass) around glass.

e. Brush inside of channel with a light appli cation of liquid soap solution to facilitate install ation. DO NOT USE GREASE OR OIL.

f. P re ss channel on filler and glass until firm ly seated.

IMPORTANT: Make sure channel ends are equal distance from edge of glass (fig. 24) and that regulator arm slot in channel, is facing the right direction in respect to rounded and squared corn ers at upper edge of g la ss. Trim off excess filler material along channel and at ends.

channel into place around door frame.

2. If the glass horizontal seal strips were removed from door, p ress new seal strips into position making sure all strip attaching clips are fully engaged.

3. Lower the door window assem bly into door

(fig. 23).

4. Engage glass channel on the roller of reg ulator arm. NOTE: Regulator arm should be in

INSTALLATION

1. If glass run channel was removed from door framing, install channel by pressing run

Sec. 1

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

Figure 25 — Replacing Door W in d o w Glass Regulator

the window two-thirds closed position.

5. Install vent assembly as directed under

"Door Vent Window Assembly Replacement."

6. Check operation of vent assembly and win dow raising and lowering action for possible binding.

DOOR W IN D O W REGULATOR

REPLACEMENT

To replace regulator, it is first necessary to

Figure 2 6 — Installin g W in d o w G lass C h an nel Run

Figure 2 7 — Rem oving Glass Horizontal Seals

remove the door window assembly and the vent window assembly as directed previously under

"Door Window Glass Replacement.”

1. Remove regulator handle.

2. Remove four screw s which attach regulator to door inner panel.

3. Referring to figure 25, remove regulator.

4. To install regulator, perform the "Re moval” procedures in reverse sequence.

DOOR GLASS RUN CHANNEL

REPLACEMENT

REMOVAL (Fig. 26)

1. Roll window to bottom of door.

2. At upper end of channel, next to vent win dow frame, pry end of channel from door using a sm all flat-bladed instrument.

3. Continue to pull channel downward from top of door, then upward to remove from side frame of door.

INSTALLATION (Fig. 26)

1. Apply thin coat of silicone type lubricant to back and sides of run channel.

2. Start end of run channel into door side frame, then force it downward in manner shown in figure 26. By engaging length of channel required to butt against vent window frame, the amount of channel to be inserted downward can be determined.

Use thumbs to p ress channel into position.

NOTE: The run channel can be inserted down ward more readily if the window is rolled up and down during the p rocess. If run channel cannot be installed as instructed, it will then be necessary to remove the door window glass.

Referring to inset of figure 26, be sure to properly position run channel so that channel lips lock behind grooves of window frame.

G M C S E R V I C E M A N U A L

DOOR W IN D O W GLASS HORIZONTAL

SEAL REPLACEMENT

1. Remove the vent window and door window as directed previously under applicable headings.

2. Using a thin flat-bladed instrument, pry

Sec. 1

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CONVENTIONAL CAB

seals from door panel in manner shown in figure

27. Pry a small amount at each fastener to prevent seal channel distortion.

3. To install, p ress seal assembly evenly into door panel.

4. Install door glass.

CAB REPLACEMENT

REMOVAL

NOTE: N ecessary equipment for efficient and safe replacement of cab consists of a chain hoist

(3/4-ton minimum capacity), a sling having padded hangers, and two or more support blocks to rest cab on once the cab is removed from ch assis.

1. Disconnect the battery.

2. Remove the hood panels.

3. Drain cooling system if equipped with heater and disconnect heater hoses at cab cowl.

4. If equipped with air brakes, exhaust the p ressure from air system .

5. Disconnect all necessary wiring harnesses and cables from cab or ch assis.

6. If air conditioned, refer to "AIR CONDI

TIONING" section and open system and cap lines observing precautions found in above references.

7. Detach and/or disconnect all lines between cab and ch assis.

NOTE: Do not attempt to salvage clutch or brake hydraulic fluid.

8. Disconnect accelerator linkage at cab cowl.

9. Disconnect mechanical parking brake.

10. Remove closure panel from cab floor at transm ission shift lever.

11. Disconnect speedometer cable at trans m ission or at the dash unit.

12. Mark for alignment purposes later, the steering shaft joint flange-to-steering gear shaft, then remove the flange clamp bolt. When cab is raised later, this connection will separate.

13. Remove the cab mounting bolts.

14. With a hoist sling device having padded hangers, open doors and engage hangers to cab door openings. DO NOT ATTACH HANGERS TO

DOORS.

NOTE: If sling device of type described above is not available, a solid hardwood 4 x 4, 1%. feet long, positioned through the cab with' hoist chain attached securely to each end, can be used. Place padding at points where beam contacts cab.

15. Raise cab and remove from ch assis.

INSTALLATION

1. Place cab mounting components in position on chassis frame brackets. If desired, masking tape can be applied to retain loose parts tempor arily in position.

2. Carefully lower the cab to chassis and at same time engage the steering shaft to gear shaft using marks made prior to removal for alignment.

Tighten shaft clamp bolt (when used) to 35 to 40 foot-pounds torque or clamp bolt nut (when used) to 40 to 50 foot-pounds torque.

3. Install balance of cab mounting components.

4. Connect speedometer cable.

5. Connect hand brake if mechanical.

6. Connect accelerator linkage.

7. Connect all control and gauge lines.

8. Connect fuel line if previously disconnected.

9. Connect heater hoses (if used), then fill cooling system .

10. Service the hydraulic brake system , if used.

11. Service the clutch hydraulic system . Use new fluid.

12. Connect all electrical wiring.

13. Refer to "AIR CONDITIONING” later in this section, for service of the air conditioning system , if used.

14. Connect battery cables.

15. Install hood panels and align, if necessary.

Refer to SHEET METAL (SEC. 11) of this manual.

16. Recheck all connections of wiring, lines, and control linkage.

17. With wheels blocked as a safety measure, start engine, then final check all connections and linkage.

HEATERS

CAB HEATING A N D VENTILATION

Two types of heaters may be used in these conventional cabs, the standard duty air-flow type

(fig. 28), and the heavy duty air-flow type (fig. 29).

All the heater components are located within cab, under the dash.

Description, operation, and maintenance information for each type heater is explained under applicable headings. Service diagnosis information,

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

DEFROST

CONTROL

SPEED CONTROL

RESISTOR UNIT

AIR FLOW!

CORE UNIT

AIR FLOW

[CONTROL

DISTRIBUTOR DUCT

BLOWER SCROLL

M O TO R W IRIN G

CO N N ECTO R

Figure 2 8 — Standard Duty Air-FI

o w

Heater

covering both types of heaters, is explained later at end of the "Heaters" section in this group.

STANDARD AIR-FLOW HEATER

The standard air-flow heater provides heated outside air for heating and defrosting requirements.

Outside air is drawn through the air inlet grille at right side of cab cowl and through the heater by the blower motor. The degree of heated air to be expelled by heater is determined by the position of

"OFF-AIR-ON" lever at side of the air distributor.

IMPORTANT: Avoid operating blower motor with this control lever in "OFF" position.

The control marked "ON-DEFROST-OFF" regulates the flow of heated air to either the wind shield defroster outlets or onto floor, or to both.

The blower motor speed is regulated by the dash switch and a resistor unit. R esistor unit is attached to top of blower shroud with two screw s.

If resistor should become defective the result will be high speed blower motor operation in both the

"MEDIUM" and "LOW" speed switch positions.

HEATER CORE, BLOWER AN D

DISTRIBUTOR DUCT REPLACEMENT

(STANDARD AIR-FLOW HEATER)

Both the distributor duct and the blower a s sembly can be readily replaced separately without having to remove the heater core unit from cab.

The replacement procedure following describes the method for replacing the heater air distributor, the blower and motor assembly, and the heater core unit which are all shown in figure 28.

REMOVAL (Fig. 28)

1. Drain the cooling system to just below level of heater core fittings.

2. Mark the heater hoses and piping at front of cowl for identification purposes later at install ation, then disconnect hoses.

3. Separate the defroster air duct tubes from air distributor.

4. Disconnect electrical wiring from heater speed control resistor and from blower motor.

R esistor is located at top of blower scroll.

5. Remove screw s which attach the air d is tributor to cowl and to blower scro ll. Remove air distributor.

6. To remove the heater core and blower unit as an assem bly, remove the screw s which attach the heater core housing to the outside air inlet duct. Carefully lower heater unit and remove from compartment.

7. To remove the outside air inlet duct, re move screw s which attach duct to fire wall and in strument panel, then remove duct and seal gasket.

8. Remove screw s which attach heater core in housing. Remove core.

9. Remove screws which attach blower motor to scro ll. Remove motor and blower fan assem bly.

NOTE: The heater core can be repaired by a competent radiator core repairman.

INSTALLATION (Fig. 28)

Assem ble and install the heater components in reverse of "Removal" procedures using new gaskets and seals where necessary.

IMPORTANT: When connecting heater hoses to core piping make sure the 5/8 inch I.D. hose is connected to sm all core pipe and that 3/4 inch I.D.

hose is connected to larger pipe.

If hoses are not installed as directed, poor heat output and/or a ruptured heater core may re sult. The core, internally, is designed to accept the higher p ressure at the inlet (5/8 inchl.D. pipe) side of core only.

HEAVY DUTY AIR-FLOW HEATER

The heavy duty air-flow heater operates on full outside air and has a three lever control panel and a blower motor control switch on dash (fig. 29).

Temperature control is by means of the airmix method; mixing heated outside air which has passed through the heater core and outside air which has by-passed the core in proportions nec essary to provide the desired temperature. The control on dash for this purpose is marked "TEMP."

With lever to the left, all the incoming air by p asses the heater core. With lever to the far right, all outside air must pass through the core, thus providing maximum heat. When lever is positioned

G M C S E R V I C E M A N U A L

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CONVENTIONAL CAB

ADAPTER ASSEM BLY

BLOWER A N D HEATER

CORE ASSEMBLY

H EATER U N IT M O U N T IN G

M O T O R

G R O U N D WIRE

AIR DISTRIBUTOR

ASSEM BLY

“ A IR ”

HEATER C O N T R O LS

Figure 2 9 — H e a v y D u ly A ir-Flo w Heater

T-2428

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CONVENTIONAL CAB

G M C S E R V I C E M A N U A L

ROTATE TO C H A N G E

CABLE LENGTH

Figure 3 0 — Heater Control Cable Adjustment Sleeve

part way, part tempered and part untempered air p a sses through the heater.

The control on dash marked "AIR" regulates the flow of outside air which p asses through heater and into cab. This control must be positioned all the way towards the right in order to obtain heat.

IMPORTANT: DO NOT operate the blower motor when "AIR" control lever is in the full left position. The heater fan speed is controlled by moving blower switch lever from left to right p osi tions "OFF-LOW-SPEED," "MEDIUM SPEED,” and "HIGH SPEED."

The "DEFROST" lever controls flow of air to the windshield defroster ducts. With knob all the way to the right, entire heater output is divert ed to the defroster ducts for defrosting.

For warm weather ventilation, place "DE

FROST" and "TEMP." control knobs in extreme left positions, move "AIR" knob to extreme right, then place fan switch lever to desired fan speed position. The fan speed control resistor unit is attached to the blower shroud with two screw s. If resistor should become defective, the result will be high speed blower motor operation with blower switch lever in both the "LOW" and "MEDIUM" speed positions.

HEATER UNIT REPLACEMENT

(HEAVY DUTY AIR-FLOW TYPE)

REMOVAL (Fig. 29)

1. Drain cooling system to just below level of heater core.

2. Mark hoses for identification, then discon nect hoses at heater core fittings.

3. At front side of cowl, remove single bolt which attaches the heater blower bracket to cowl.

4. At front side of heater core housing, re move protective shield and the small spring-type retaining washer from "TEMP" control lever, then remove the control wire clamp screw. Pull wire from lever.

5. At top of blower motor, disconnect the

"AIR" control wire in same manner.

6. Disconnect the blower adapter-to-air d is tributor hose.

7. At top *of blower housing, near the cowl, separate the wiring connection at the blower speed control resistor.

8. Separate wiring connector at rear of blower motor. Pull outward on connection.

9. Underneath the dash, at right side of core, remove four bolts which attach heater unit to cowl extension.

10. Remove single bolt which attaches heater support bracket to bottom of dash panel. This same bolt attaches the blower motor ground wire.

11. Using care not to damage heater unit, work the unit rearward and down from compartment.

12. If desired, the unit can be readily d is assem bled for inspection or replacement of the blower, motor, core, etc.

INSTALLATION

1. Make sure the cellular dust pad is located over heater core water inlet and outlet pipes.

2. Place the heater core and blower assembly into position, then install all attaching bolts.

IMPORTANT: Make sure blower motor ground wire is sandwiched under head of heater support bracket attaching bolt at dash panel.

3. Connect wiring at blower speed control re sistor unit and also at the blower motor. Make sure connections are secure.

4. Connect the blower air outlet tube.

5. Connect the "AIR" and "TEMP." controls to heater assem bly. Lower view in figure 29 shows connections.

6. Referring to identification marks made on heater hoses prior to disconnecting, connect the hoses to respective heater core piping.

IMPORTANT: Make sure the 5/8-inch I.D.

hose is connected to sm all core pipe and that the

3 /4 inch I.D. hose is attached to the larger pipe. If hoses are not installed as directed, poor heat out put and/or a ruptured heater core will result. The core internally is designed to accept the higher pressure at the inlet (5/8 inch I.D. pipe) side of core only.

7. Replenish cooant in system then start and operate engine until normal operating temperature is obtained.

8. Check for possible leakage and check the operation of heater and controls.

G M C S E R V I C E M A N U A L

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CONVENTIONAL CAB

AIR DISTRIBUTOR REPLACEMENT

(HEAVY DUTY AIR-FLOW HEATER)

The air distributor can be readily replaced after disconnecting the attaching air hoses and the

"DEFROST" control wire, then removing the three screw s which attach distributor to dash and cowl

(fig. 29).

HEATER CONTROL CABLE

ADJUSTMENT

Each control wire conduit is equipped with a threaded-sleeve (fig. 30) which can be turned to obtain full opening and closing of air doors and to even up the heater knobs on control panel. Make adjustment to control wire conduit if desired.

SERVICE D IAG N O SIS

The following applies to both the Standard and

Heavy Duty Air-Flow Heater system s:

POOR OR NO HEATING

1. Heater hoses are kinked, deteriorated, or switched around at the core piping.

2. Heater core plugged.

3. Poor blower motor ground connection.

4. Blower malfunctioning.

5. Low coolant temperature.

BLOWER INOPERATIVE

1. Check dash switch and blower motor con nections.

2. If blower operates at high speed with switch in either "MED." or "SLOW" position, the speed control resistor at top of blower shroud is defec tive and should be replaced.

NOTE: R esistor is attached to the blower motor scro ll by two screw s. Only one-half of resistor winding may be defective; if so, replace the r e s is tor assem bly.

3. Check the blower motor.

VENTILATION

A single vent intake at front center of cab cowl

(fig. 31) perm its outside air to enter cab under dash panel. The vent is controlled by "VENT" con trol handle located at top center of dash panel.

Pulling "VENT" handle rearward opens the vent.

Vent clo ses when handle is pushed forward.

Sponge rubber seal under vent cover should be replaced if deteriorated or damaged. Before installing new seal, remove all the old seal and adhesive from seal channel.

Figure 31 illustrates the vent control mech anism shown in closed position. If vent cover fails to close firmly against seal, the link rod under dash can be bent slightly as required to increase the closing p ressure.

NOTE: Do not bend rod excessively as the control handle will fail to remain in closed detent position.

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____________G M C S E R V I C E M A N U A L

CONVENTIONAL CAB

NOTE

For all "Air Conditioning" information, refer to separate "AIR CONDITIONING" sub-section at end of this section.

G M C S E R V I C E M A N U A L

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l i l t Gab

Maintenance information on windshield wipers, windshield and rear window glass replacement, and cab painting is explained in "GENERAL

MAINTENANCE" section at beginning of this group. Refer to LUBRICA

TION (SEC. 0) for cab lubrication information. Contents of this section are listed in Index below:

Subject

D e s c r ip t io n ...................................

Cab Tilting Instructions . . . .

Cab Mountings .............................

I n s u la t io n .......................................

Seats ..............................................

D o o r s ..............................................

Cab Ventilation and Heating . .

Cab R e p la c e m e n t.........................

Torsion Bar Replacement . . .

Torsion Bar Tension Adjustment

Page No.

CAB DESCRIPTION

The "L" Model is a tilt cab type of a ll-stee l welded construction (fig. 1). Cab fully surrounds engine and can be tilted 55 degrees to expose en gine for servicing. The cab tilting mechanism is integral with cab front mountings and tilting is accomplished by means of a torsion bar extending across cab front hinge mountings. One end of tor sion bar is anchored to cab, whereas opposite end is anchored to ch assis. Cab is retained in lowered

(operating) position by positive locking mechanism located at rear of cab.

A ccess for minor engine servicing, such as oil and engine coolant, is accomplished without tilting cab through access doors in panel at rear of passenger seat and at top of seat back riser. A concealed step is constructed in floor of each door opening. Also, a central island shifting area that is not disturbed with the cab tilted, is located be tween the seats. Island contains transmission shift lever, hand brake lever and ignition or control switch.

Two-piece windshield is retained in cab open ings with a one-piece rubber seal expanded into position by a small rubber insert. No sealing com pound or cement is used. Rear window glass and rear side glass is retained in same manner as windshield glass.

Doors are on swing-out type hinges with the upper hinge incorporating a spring-loaded door check for holding door open. Door is retained at the rear by a striker bolt on cab pillar. Outside handles are stationary-type screw retained to door and have a push button-type latch control.

Vent window in forward portion of door is of friction-type having a positive theft-resistant latch.

Friction mechanism consists of a nylon bushing on lower pivot of vent which exerts frictional force against tension clamp mounted to door paneling.

Outside air enters cab through a vent directly in front of driver and through the outside air heat ing system . Air entry from outside of cab is made through a louvered, removable panel, located in front center of cab just above radiator grille open ing. Air flows through plenum chamber between

Figure 1— Tilt Cab Interior Construction

PageUp___________

TILT CAB

G M C S E R V I C E M A N U A L

Figure 2 — Releasing Cab H old -D ow n M echanism

outer and inner cab paneling and is dispersed to heater and vent outlet.

Cab is three-point mounted to ch assis. Weight of cab at front is supported on cab right and left tilt hinges and a support bracket having rubber cushions, supports cab at rear center. Cab tilt holddown mechanism locks cab firmly on cushions.

The underside of cab is completely insulated to deaden sound and prevent corrosion. A rubber weatherstrip around perim eter of door is used for sealing door to cab opening.

CAB TILTING INSTRUCTIONS

TO RAISE CAB (Fig. 2)

IMPORTANT: Before tilting cab forward, re move loose articles in cab; also place transm is sion shift lever in neutral and apply hand brake.

1. Close both doors of cab.

Sill Brackets

2. At right rear of cab remove safety chain hook.

3. While holding safety catch release rod to the right, pull hold-down release lever out and up ward until hold-down catch becomes disengaged and rear of cab raises from mount (fig. 2). Tilt the cab completely forward until check link at right front mounting locks cab safely in full-tiltposition.

IMPORTANT: Make sure check link is proper ly engaged with frame anchor pin.

TO LOWER CAB (Fig. 2)

IMPORTANT: Before lowering the cab to oper ating position, make sure transm ission shift lever is in neutral position and that hand brake lever is in the applied position.

1. Release check link at right front mounting

(see inset, fig. 2) by pulling rearward on link r e lease rod, then pull cab back to operating position.

2. Safety catch at rear of cab will automatic ally become engaged. Pull downward on hold-down release lever and engage lower end of lever in lever spring catch, bracket-mounted to rear of cab.

3. Engage safety hook through matching holes in clip bracket and lug on lever by inserting the chain hook from underside.

NOTE: The raising and lowering effort of cab can be adjusted as desired by means of relocating torsion bar anchor lever at left frame bracket. If required, make adjustment as directed later under

"Torsion Bar Tension Adjustment."

CAB MOUNTINGS

Cab is three-point mounted with two pivot-type mountings at front and twin cushion-type mountings at rear. Refer to figure 3 for typical views of mountings.

Cab Rear Support

Lubrication Fitting

Cab Hold-Down Catch

Return Spring

Cab Rear Mounting

Cushions

Hold-Down Catch

Release Rod 1

Safety Catch

Release Rod

Release Rod Lever

Check Link and

Release Rod

Cab Right

Frame Bracket

CAB FRONT MOUNTING

Cab Left

Frame Bracket

Figure 3 — C a b M o u n tin g s

Check Link

Release Rod

CAB REAR MOUNTING

G M C S E R V I C E M A N U A L

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TILT CAB

Figure 4 — A p p ly in g Insulation

Interconnected with the cab front mountings is a torsion bar (fig. 3) which is under load when cab is in either the operating or full-tilted position.

Right end of bar is anchored to cab bracket and left end is anchored by lever to frame bracket as shown in figure 3. Bar is unloaded when cab is tilted approximately 45 degrees, therefore, torsion bar a ssists operator in both the raising and lower ing of cab.

CAUTION: UNDER NO C I R C U M 

STANCES SHOULD THE BOLTS WHICH

ATTACH TORSION BAR RIGHT ANCHOR

B R A C K E T TO C A B AND THE TORSION

BAR L E F T ANCHOR L E V E R TO F R A M E

BE LOOSENED OR R E M O V E D WHEN CA B

IS IN O PE R A T IN G OR F U L L T IL T POSI

TIONS WHICH IS WHEN BAR IS LOADED.

AN INJURY COULD

RESU LT WHEN

ANCHOR B R A C K E T AND TORSION BAR

IS A LLO W ED TO R E L E A S E .

Attaching bolts can be removed safely when bar is unloaded, cab tilted part way (approx. 45 degrees). Normally it should never be necessary to remove bolts. Whenever torsion bar is inoper ative, cab must be supported safely.

Attaching bolts at front pivot mountings should be checked at regular intervals for tightness. Loose mountings will allow shifting of cab and eventual failure of other item s connecting cab to ch assis.

Front pivot mountings have fittings for lubrication purposes. Lubricate as directed under LUBRICA

TION (SEC. 0) of this manual.

Rear mounting has positive locking mechan ism to retain cab in normal operating position in relation to ch assis frame. The rear mounting also includes an additional safety catch. Tightness of cab hold-down lock can be adjusted by shortening or lengthening catch release rod. After adjusting

.j Four A tta c h in g Studs

/ (Stud N u ts A cce ssib le from U n d e r C ab)

Figure 5 — Driver’s Seat M o un ting and Adjustment

rod, tighten end yoke lock nut. Cab hold-down catch shaft is equipped with a lubrication fitting.

A check link is provided near the right front mounting (see inset, fig. 2) which lim its the dis tance cab can be tilted forward and automatically locks the cab in the fu ll-tilt position. Check link must be released before cab can be returned to normal operating position.

INSULATION

Insulation, applied to cab understructure di rectly over engine, is highly resistant to abrasion and corrosion and is designed to give maximum sound deadening and insulation.

In the event a repair such as welding is re quired to that part of cab covered with insulation, it is first necessary to remove the insulation from that area. After completing repair, insulation s e c tions can be cut to size and cemented over the re paired area (fig. 4). Be sure to clean area thor oughly before installing new section of insulation.

SEATS

SEAT ADJUSTMENT (Fig. 5)

Driver’s seat is provided with "fore"and "aft" adjustment only. Pull out on lever at left side of seat to disengage seat position lock.

SEAT TRACK REPLACEMENT (Fig. 5)

1. Tilt cab forward, then remove four nuts and washers from studs which attach seat tracks to seat riser of cab.

2. Lower cab to operating position, then lift seat assembly from cab.

3. Remove four nuts which attach each track assem bly to seat assem bly and remove track.

4. R everse the above procedure to install track assembly.

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TILT CAB

G M C S E R V I C E M A N U A L

DOORS

Component sub-assem blies of cab doors, such as window regulator, door lock, remote control, vent window, and door window can be replaced without necessity of removing door from cab. Doors can be removed, however, without prior removal of above components. Removal and installation of door window glass is described later in this section.

DOOR REPLACEMENT

REMOVAL

1. With the aid of an assistant to support weight of door, remove the screw s which attach hinge straps to door. A ccess to one cap screw at door upper hinge is gained by removing plug from door inner panel.

2. Carefully remove door assembly from cab.

INSTALLATION

Attach door to hinge straps with six cap screw s.

Adjust door in cab opening as instructed later under

"Door Adjustments."

DOOR ADJUSTMENTS

Doors can be adjusted for alignment or clear ance in the cab door opening (fig. 6), and for proper latching. Door alignment adjustments are made at the striker bolt, and at door hinges. The door, when properly located in door opening, will have equal clearance around its perimeter.

Figure 7 — Door Hinges

If door has been replaced, adjustments should be made in sequence described in the following paragraphs:

REPOSITION DOOR "UP" OR "DOWN" (Fig. 7)

Door "up” and "down" adjustment in cab open ing is provided by means of floating hinge cap screw tapping plates within door framing. Hori zontal slotted cap screw holes in cab half of hinge assem bly provide the "in” or "out” adjustment of door.

1. Remove striker bolt from cab pillar.

2. Loosen hinge-to-door cap screw s slightly.

Reposition door on hinges to provide equal clear ance around perimeter of door in cab opening.

NOTE: A ccess to one cap screw at door upper hinge is gained after removing plug from door inner panel.

3. After satisfactory adjustment has been ob tained, tighten hinge cap screw s firm ly. Open and close door to check operation. If necessary, repeat adjustment. Install hinge cap screw access plug in door inner paneling after making final adjustment.

4. Install striker bolt and adjust as directed later under "Striker Bolt Adjustment.”

REPOSITION DOOR ”FORE” OR ”AFT” (Fig. 7)

Only the upper portion of door can be adjusted

”fore” or "aft.” This adjustment is made at the upper hinge. No means for this adjustment exists at the lower hinge.

1. Remove striker bolt from cab pillar.

2. Loosen upper hinge-to-door cap screw s slightly. A ccess to one cap screw at door upper hinge is gained after removing plug from door inner panel.

G M C S E R V I C E M A N U A L

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TILT CAB

SPACER

PLASTIC W ASH ER

STRIKER BOLT

A N D W ASH ER

TAPPED FLOATING

PLATE

Figure 8 — Door Striker Bolt and W ashers

3. Lift upward or pull downward at rear of door to tilt upper portion of door "fore" or "aft" as desired.

4. Tighten hinge cap screw s firmly after mak ing adjustment. Open and close door to check oper ation. Repeat adjustment if necessary. Install cap screw access plug in door inner paneling.

5. Install striker bolt and adjust as directed later under "Striker Bolt Adjustment."

REPOSITION DOOR "IN" OR "OUT" (Fig. 7)

Horizontal cap screw slots exist in cab half of hinge assem bly to permit this adjustment.

The outer surface of door, when properly in stalled, should be flush with adjacent surfaces of cab. If necessary, reposition door as follows:

1. Loosen slightly all cap screw s which attach hinge half to cab pillar.

2. If door is to be brought outward from cab opening, apply pressure at door hinge area from inside cab. If door is to be moved inward, apply p ressu re on door outer panel at hinge area. Be careful not to damage door paneling by applying excessive pressure.

3. After adjustment has been made, tighten hinge cap screw s firm ly. Open and close door to check operation. Readjust if necessary.

Figure 9 — Sight Checking Striker Bolt Alignment

2. Insert a 5/16-inch hex wrench into head of striker bolt, then turn bolt counterclockwise from plate in cab pillar.

3. R everse above procedure to install striker bolt. Make sure the thin plastic washer is position ed against the painted door opening pillar and cen ter the bolt washer within marks on pillar.

4. If door has been removed and then installed or aligned in opening, the door should not be closed completely until a visual check is made to deter mine if lock cam in door will engage the striker bolt correctly. Center of striker bolt should be in direct alignment with "V" slot in door. See figure

9. If necessary, reposition striker bolt as directed below under "Striker Bolt Adjustment."

STRIKER BOLT ADJUSTMENT (Fig. 10)

Striker bolt on cab pillar is adjustable vert ically and transversely after loosening the bolt with a 5/16-inch hex wrench. The bolt fore and aft adjustment is obtained by use of shim spacers lo cated between the bolt washer and the cab pillar.

Figure 8 illustrates location of bolt, washers, and spacer.

NOTE: It may be necessary to reposition striker on pillar after making above adjustment.

See "Striker Bolt Adjustment."

DOOR STRIKER

The door striker consists of a special bolt and washer assembly which is threaded into a tapped, floating cage plate located behind the cab lock pillar as shown in figure 8. The door is s e cured in closed position when the lock cam in door engages and snaps-over the striker bolt. Striker bolt can be replaced or adjusted as directed under applicable headings.

Striker Bolt Fore and Aft Adjustment

1. To check striker bolt for proper fore and aft adjustment, sm ear grease or paint to contact side of bolt as shown in figure 10.

2. Slowly close door until lock cam of door just contacts the side of striker bolt and makes an im pression in the grease or paint.

3. Measure distance between head of bolt and the cam impression in grease. Distance should measure 1/8-inch as shown in right view of figure

10. This dimension is necessary to assure that the head of striker bolt will ride at center of nylon

STRIKER BOLT REPLACEMENT (Fig. 8)

1. Mark position of striker bolt spacer or washer on door pillar using pencil or crayon.

shoe which is located just in back of the lock cam.

To obtain this dimension, remove the striker bolt and install or remove shim spacers. Spacers

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TILT CAB

G M C S E R V I C E M A N U A L

DEPRESS RETAINER

THEN ROTATE

Figure 10— Striker Bolt A lign m en t

are available in two thicknesses: 5/64-inch and

5/32-inch. Make sure the thin plastic washer is located next to cab pillar.

After obtaining proper fore and aft adjustment, tighten bolt snug only at this time and then proceed with the "Striker Bolt Height Adjustment."

Striker Bolt Height Adjustment

This adjustment is important to assure that the right proportion of door's weight will rest on striker bolt when door is closed. If bolt is p osi tioned too high on pillar, rapid wear will occur to the lock cam: if too low, an extra load will be placed on door hinges as well as pull door down ward and out of alignment.

Generally the striker bolt height adjustment can be checked quite accurately by just sighting the center of "V” slot on door with the center of striker bolt as illustrated in figure 9. However,

REAR GASKET

REINFORCEMENT

PLATE

A T TAC H IN G BOLTS

Figure 11 — D oor H a n d le Installation

HANDLE

FRONT GASKET

Figure 12— D ise n ga gin g Handle Spring Retainer

to make a more positive check, perform the fol lowing:

1. Mark a horizontal line through center of

"V" slot and on door lock cam as shown in left view of figure 10.

2. Smear some grease or paint on contact edge of lock cam as shown in same view.

3. Slowly close door until cam barely contacts the striker bolt to leave an impression in grease.

Open door and check contact mark on edge of cam.

Mark should be located approximately 1/16-inch below the horizontal mark if properly aligned.

4. If necessary, raise or lower the loosened striker bolt up or down by tapping on the washer or spacer at base of striker bolt. DO NOT TAP

ON HEAD OF BOLT.

Door Rear Edge "In" or "Out" Adjustment

This adjustment is for purpose of aligning the rear surface of door flush with adjacent surfaces of cab. If surfaces are not flush, proceed as follows:

1. Mark a horizontal line on cab pillar at top of striker bolt base washer or spacer.

2. Loosen striker bolt slightly, then tap against bolt base washer, to move bolt "in" or "out" as necessary to locate door surface flush with cab surface when door is closed. Before tightening the striker bolt make sure top bolt base washer is contacting the horizontal mark on cab pillar. Final tighten striker bolt.

DOOR OUTSIDE HANDLE

REPLACEMENT

REMOVAL

1. Remove eight screw s which attach access panel to lower portion of door. Remove access panel.

G M C S E R V I C E M A N U A L

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TILT CAB

Figure 13— Door Handle Components

2. Roll door glass to top, then through access opening, using a 7/16" wrench, remove two bolts which attach door handle to door outer panel. Re move handle and handle gaskets (fig. 11).

NOTE: Reinforcement plate is spot-welded to inside of door outer panel.

3. Remove the button shaft retainer by first depressing, then rotating retainer as shown in figure 12. Remove shaft spring and button assem bly with O-ring seal from handle (fig. 13).

INSTALLATION

1. Place button assem bly with installed O-ring seal in handle.

2. Locate spring over button shaft, then in stall spring retainer (fig. 12).

3. Position door handle with gaskets to door outer panel, then through a ccess opening at bottom of door, install two attaching bolts.

4. Install access panel to bottom of door.

DOOR LOCK CYLINDER

REPLACEMENT

REMOVAL (Fig. 14)

1. Remove access panel at bottom of door.

2. Through access panel opening, pull lock cylinder retainer from beneath the lock cylinder grooves by grasping retainer lip with p liers.

3. Tilt lock assembly to permit cylinder lug to disengage from lock mechanism lever. Remove lock cylinder and gasket from door.

INSTALLATION (Fig. 14)

1. With gasket in position on lock cylinder, insert cylinder in door and engage lug over lock mechanism lever.

2. While holding cylinder, insert legs of re-

Figure 14— Door Lock Cylinder Replacement

tainer into grooves of lock cylinder body. Be cer tain legs of retainer are fully engaged. It may be necessary to drive retainer into final engagement with a light hammer.

3. Insert key and check operation of lock. If lock operates freely, install lower access panel to door.

DOOR INSIDE HANDLE

REPLACEMENT

Window regulator crank handle and door lock handle are retained on shafts by lock springs. If

Figure 15 — D is e n g a g in g Door In sid e H a n d le

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TILT CAB

G M C S E R V I C E M A N U A L

1 Vent Window Glass

2 Division Channel

3 A ccess Panel

4 Remote Control Handle

5 Inside Lock Knob

6 Weatherstrip Seal Clip and Screw

7 Weatherstrip Seal

8 A ccess Panel

IN T E R IO R O F D O O R

9 Division Channel Lower

Attaching Screws

10 Escutcheon Plates

11 Regulator Handle

12 Division Channel Upper

Attaching Screws

13 Door Window

14 Sash Channel

D O O R C O N S T R U C T I O N

15 Door Lock Remote Control

Assembly

16 Door Lock Mechanism

17 Run Channel Retainer Screw

18 Run Channel Retainer

19 Door Window Stop Bumper

20 Window Regulator A ssy.

21 Division Channel Center

Attaching Screw t

-5/89

Figure 16— Door Construction

removing door lock inside handle, the handle p osi tion should be marked in relation to door panel to assure that handle is installed later at the same operating angle.

REMOVAL (Fig. 15)

1. Insert tool (J-9886) between handle flange and escutcheon plate.

2. Force lock spring from grooves in base of handle. DO NOT LOSE SPRING. Remove handle and escutcheon plate.

NOTE: The lower view in figure 15 shows how the tool engages the clip at underside of handle when removing. Clip may be installed in opposite direction than shown.

INSTALLATION

1. Insert lock spring in handle grooves.

2. Place the escutcheon plate on handle spindle.

3. If installing door lock handle, make sure handle is in position previously marked on door inner panel. To install either handle, force handle with installed lock spring over spindle until lock spring becomes fully engaged.

G M C S E R V I C E M A N U A L

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R E G U L A T O R A R M

T-5805

Figure 17— Door Lock Attaching

Screw s

DOOR LOCK A N D REMOTE CONTROL

M ECH AN ISM REPLACEMENT

NOTE: Figure 16 illustrates the position of the lock and remote control mechanism components.

REMOVAL (Fig. 17)

1. Remove the door inside lock knob which is threaded on lock rod.

2. Remove the lower access panel from door inner panel as directed previously.

3. Raise window and then remove the door in side handle as directed previously.

4. Remove three screw s which attach remote control to door inner panel. Lower control to door acc ess opening, then disengage fastener at pullrod. Separate rod and remove control from door.

5. Remove the lock cylinder assembly from outer side of door as directed previously.

6. At rear edge of door, remove two run chan nel retainer screws to provide clearance for re moval of lock mechanism.

7. At rear edge of door, remove three special locking-type screw s which attach lock mechanism to door frame. Lower the lock and attached two rods out through access opening in door.

8. Separate rods from lock mechanism by disengaging fasteners.

INSTALLATION (Figs. 16 and 17)

Install lock mechanism with rods and remote control in reverse of the "Removal" procedures.

IMPORTANT: Make sure to use the three

Figure 18— Rem oving Regulator Arm from Track

special locking-type screw s which attach lock mechanism to door frame. Check operation of door lock and remote control mechanism after install ation. As required, remote control unit may be shifted slightly on door inner panel to obtain sat isfactory lock operation.

DOOR W IN D O W REGULATOR

REPLACEMENT

REMOVAL

1. Remove access panel from lower portion of door.

2. Lower window and remove window regula tor handle and escutcheon plate.

R E G U L A T O R

A S S E M B L Y

Figure 1 9 — Low ering Regulator from D oor

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G M C S E R V I C E M A N U A L

A S S E M B L Y

Figure 2 0 — Rem oving Door W in d o w Class

3. While holding regulator assembly through opening in door, remove four screw s (figs. 16 and

17) which attach regulator assembly to door inner panel.

4. Guide regulator arm to remove roller from window channel track (fig. 18). Carefully lower regulator assem bly from door (fig. 19).

INSTALLATION

Install door window regulator in reverse order of "Removal" procedures. Before installing access door, operate window regulator to be sure roller is not binding in window channel track. If binding occurs, bend window regulator arm slightly until roller turns freely in channel. Also, check division and run channels for alignment.

DOOR W IN D O W GLASS

REPLACEMENT

REMOVAL

1. Remove access panel from door inner panel below vent window.

2. Unlatch vent window and swing outward.

3. Remove five screw s which attach access trim panel to door just below vent window.

4. Remove frame to door screw and frame to divisional channel screw (fig. 16).

5. Remove three division channel lower at taching screw s (fig. 16).

6. Remove division channel screw s at top of door (fig. 16).

7. Remove two screw s at edge of door which attach run channel to door (figs. 16 and 17).

8. Lower window and remove window regu lator assem bly as described previously (figs. 18 and 19).

9. Tilt and lower glass assem bly through low er access opening (fig. 20).

INSTALLATION

1. Squirt gasoline along glass filler on both sides of glass to soften seal. Remove glass from channel when filler is sufficiently soft.

2. Thoroughly clean inside of glass channel by removing all rust and old glazing rubber filler.

3. Cut new piece of glazing rubber filler to length of glass regulator channel.

4. Position glazing rubber filler (soapstone side away from glass) on bottom edge of glass

1.24-inch from lower corner as shown infigure 21.

5. Carefully position edge of glass regulator channel 1.24-inch from lower right corner (fig.

21) and then p ress channel over glass and glazing

G M C S E R V I C E M A N U A L

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TILT CAB

P ivot Sc re w

V e n t W in d o w G la ss

V e n t W i n d o w Top

R e ta in in g S c re w s

D iv is io n

C h a n n e l

Sc re w

A C C E S S H O L E T O P IV O T S C R E W

V e n t W in d o w O uter

Fram e a n d R u bber Seal

D ivisio n C h a n n e l

Fram e To D o o r Screw

Fram e To D ivisio n a l

C h a n n e l Screw

N y lo n Friction

Friction

C la m p

JffTTHf.J_

Figure 2 3 — Door Vent W in d o w Installed

rubber filler. Lightly tap channel with rubber ham mer to firm ly seat channel over glass and filler.

6. Install assem bled window into door in re verse order of "Removal" procedures.

NOTE: When inserting glass assembly into door run channels, be careful not scratch or place undue str e ss on glass. After installation, raise and lower window to check for binding. If binding occurs, adjust appropriate run channels by loosen ing applicable channel attaching screw s.

DOOR W IN D O W GLASS HORIZONTAL

SEALS REPLACEMENT

Figure 2 4 — Rem oving Vent W in d ow

4. Install and adjust window glass as explained previously under "Door Window Glass Replace ment."

DOOR VENT W IN D O W TENSION

ADJUSTMENT

1. Remove a ccess panel from bottom of door.

This will remove window stop attached to access panel and allow top of window to be lowered to a point below horizontal weatherstrips.

2. Using a flat-blade screwdriver, pry wea therstrips from door (fig. 22).

3. Install weatherstrips to door, making sure retaining clips are fully engaged.

4. Raise window, then install a ccess panel to bottom of door.

DOOR W IN D O W RUN

CHANNEL REPLACEMENT

1. Remove door window as explained previ ously under "Door Window Glass Replacement."

2. Remove applicable screw s which attach either division channel or run channel to door framing (fig. 16) and lower channel(s) through a ccess opening at bottom of door.

3. Install channel(s) in reverse order of re moval procedures.

Cab vent windows are of friction type having a positive theft-resistant latch. Friction mechan ism consists of a bushing attached at lower end of vent shaft which rotates in a stationary friction clamp.

If friction mechanism is adjusted too tight, it w ill be difficult to open or close vent. Too loose an adjustment will result in a fluttering vent or one having a tendency to close with wind pressure.

If necessary to change vent friction, perform procedures as follows:

1. Remove a ccess trim panel attached to door just below vent window with five screw s. Figure 23 shows access opening to friction components.

2. Using screwdriver, turn clamp screw (fig.

23) to obtain two to four pounds torque while mov ing vent window from a ten-degree open position to a full-open position. Use either a push or pull-type spring scale positioned at rear edge of glass.

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TILT CAB

G M C S E R V I C E M A N U A L channel.

Figure 2 5 — Vent W in d o w Disassembled

3. After obtaining proper tension, install ac cess trim panel.

DOOR VENT GLASS REPLACEMENT

REMOVAL

1. Remove sm all access panel from inner side of door below vent window.

2. At bottom of vent glass (fig. 23), place hand to catch vent friction components, then remove screw from friction clamp. Slide clamp, friction bushing, and flat steel washer from vent shaft.

3. At top of door through sm all access open ing (see inset, fig. 23), turn vent upper pivot screw from vent frame.

NOTE: Screw need not be removed completely, just enough to become disengaged from vent glass

4. Remove three screw s which attach division channel to vent channel just below vent latch. Using a screwdriver, pry down on vent channel as shown in figure 24, which w ill cause upper part of channel to become disengaged from pivot screw . Rotate g lass channel lower pivot shaft up out of vent channel.

5. Remove two screw s which attach glass up per channel to glass lower channel (fig. 25).

6. Apply gasoline on vent glazing rubber to soften old rubber. When rubber softens sufficiently, separate upper and lower glass channels, then re move old glass.

INSTALLATION

1. Thoroughly clean inside of glass channels to remove old glazing rubber, rust, or other for eign matter.

2. Position new glazing rubber (soapstone side away from glass) around edge of glass. P ress glass with glazing rubber into lower channel, then p ress upper channel over top of glass. Make sure channels are firmly seated, then install two small screw s which attach channels together (fig. 25).

3. If necessary, trim glazing rubber at ends of channels and along sides of channel each side of g lass. As required, seal cracks at latch bracket.

4. Insert pivot stud of vent lower channel into hole of vent frame as shown in figure 24. Through sm all a cc ess hole at top of door, install vent upper pivot screw . Install three screw s which attach bracket of vent channel to glass division channel just below vent latch.

5. Install special flat washer, nylon friction bushing, and friction clamp on vent lower channel pivot shaft, positioned as shown in figure 23.

NOTE: Make sure that tab on special flat washer is positioned properly to act as a stop of vent when it is in full open position. Attach friction clamp to vent lower frame with screw. Tighten screw to obtain two to four pounds torque while moving vent window from a ten-degree to a fullopen position. Use either a push or pull type spring scale positioned at rear edge of glass.

6. Install a ccess panel to inner side of door.

DOOR WEATHERSTRIP

REPLACEMENT

1. Remove screw -retained clips from weather strip around perim eter of door. Figure 26 shows view of weatherstrip installed at retainer.

2. Pull weatherstrip from door, then scrape any rubber or adhesive material which may have become bonded to door surface.

G M C S E R V I C E M A N U A L

3. Apply coat of weatherstrip adhesive to seal and seal surfaces of door as directed by manu facturer of adhesive. Directions for application are usually found on adhesive container.

4. Position seal around perim eter of door,

Sec. 1

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TILT CAB

making sure corners of seal engage respective corners of door.

5. Install screw -retained clips (fig. 26) to door and weatherstrip. Tighten clip screws firmly but be careful not to tear weatherstrip.

CAB VENTILATION A N D HEATING

VENTILATION

A single grilled intake at front center of cab

(fig. 26) perm its outside air to enter plenum cham ber located between the cab outer and inner panels.

From the plenum chamber, outside air can be di rected into cab interior through opening at front of driver and through opening at front of passenger.

When heater is used, the outside air enters heat ing system through the right side opening.

The outlet located ahead of driver is opened and closed manually by control knob on dash. The control knob pushed inward clo ses outlet door and pulling out on knob opens outlet door. A springloaded door prop retains door snug in either the fully opened or closed positions. A rubber seal around perim eter of outlet door provides positive sealing of outlet. Seal, which is glued to door, can be readily replaced if necessary.

CONTROL ADJUSTMENT (DRIVER"S SIDE)

NOTE: Refer to inset of figure 27.

When control knob on dash is pushed complete ly in, the air outlet door should close snug to out let opening.

If door is not seated completely with control knob in this position, loosen screw at control con duit clamp above door which will allow com pres sion spring within door telescopic prop to force door tight to opening. Retighten clamp screw after making adjustment.

HEATING

The heater is of the water valve temperature control type (fig. 28) and is serviced in same man ner as M under "Conventional Model Cabs."

Figure 27 — Outside Air Intake

CAB REPLACEMENT

N ecessary equipment for efficient and safe replacement of cab consists of a chain hoist (1-ton minimum capacity), a sling having padded hangers, and two or more support blocks to rest cab on when it is removed from ch assis.

NOTE: A wood 4 x 4 , 7 ^ feet long positioned through cab door openings with a hoist chain at tached securely to each end can be used. However, means of protecting top of cab from chain must be provided. Also, be sure to provide padding at points where beam contacts cab openings and carefully position beam to assure proper cab support.

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TILT CAB

G M C S E R V I C E M A N U A L

Figure

2 9

— Lifting Sling Attached to Cab

CAB REMOVAL

1. Disconnect battery ground strap.

2. On vehicles with air brakes, exhaust air supply from air tank at drain fitting. Remove bump er (with attached air tank, if used).

3. Open heater temperature control on dash to full open position, and drain radiator. Disconnect heater hoses at cab connections.

4. Disconnect accelerator linkage and ste e r ing flexible coupling, marking for later alignment.

Disconnect brake lines and clutch line.

5. Disconnect speedometer cable and a lle le c -

Figure 3 0 — M o u n t in g at C a b Rear Support

Figure 3 1 — Rear H o ld -D o w n Catch on W oo d Block

trie connectors that junction cab with the ch assis.

Remove cab -to-ch assis ground straps.

NOTE: REMOVE OR SECURE ALL LOOSE

ITEMS IN CAB BEFORE TILTING. PLACE SHIFT

LEVER IN NEUTRAL AND THE HAND BRAKE IN

FULL-APPLIED POSITION.

6. Attach a suitable padded lifting sling (fig.

29) to cab with doors partly open (lifting cab with doors closed will disturb door alignment later).

7. Using aid of assistant and hoist, tilt cab approximately 45° to the unloaded position of cab mounting torsion bar (refer to preceding caution) and suspend safely there. While cab is in this p osi tion, insert a pry bar in between cab right support and cab s ill. Remove three forward bolts, lock washers and nuts from cab right support to sill brackets (B, fig. 30). Use pry bar to a ssist in r e moving bolts. Disconnect check link at right side of cab.

8. Place a short piece of wood 2" x 4" over catch hole in cab rear support (fig. 31), then with aid of assistant, lower cab until catch at bottom of cab rests on block. This w ill prevent engagement of cab hold-down catch. Remove two retaining bolts from torsion bar at cab left support and remove support cap. Raise cab slightly, and remove rear mounting bolt (C, fig. 30) attaching right support to sill brackets.

9. Raise cab slightly to clear cab lift mech anism, then forward and up to clear shift control panel. Figure 32 shows cab and ch assis disconnect points.

10. Lower cab onto suitable blocks, then r e move chainfall and lifting sling.

NOTE: Left support can be removed from cab, if desired.

CAB INSTALLATION

1. Install lifting sling and chainfall to cab with doors slightly open (fig. 29).

G M C S E R V I C E M A N U A L

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TILT CAB

C a b Right

Sill Brackets.. H e a te r Line

------- —

\ v

Connec t i ons —

' " T

A cc e le ra tor Control.

C on n ec tions

Stee ring

Connection1 C ab Left

Sill Bracket!

.eft Support]

A n d C a p :

Stop Bracket

B ra ke Control H o s e '

Clutch Control H ose

W ir in g Junction

Lever

R igh t Support!

Torsion Bar

B ra k e Control

H ose C on n e c tio ns

Clutch Control

H ose C onnections

Stop Bracket

T orsion Bar

R igh t Fram e

Bracket

Stee ring

Connection

Torsion Bar

Left Fram e

Bracket

CHASSIS DISCONNECT POINTS

Figure 3 2 — Cab and Chassis Disconnect Points (Typical)

2. Raise cab and install support (if previously removed) loosely to cab left s ill brackets.

NOTE: Cab tilt torsion bar, check link, and right cab to sill support should be in position on ch assis as shown in lower view of figure 32.

3. Raise cab over ch assis and lower into p o si tion, forward slightly to clear shift control panel, then back and down until steering gear coupling can be engaged using marks made previously for proper alignment.

4. Finish lowering cab until left support rests on torsion bar. Install support cap with two bolts, torque bolts to 50-60 foot-pounds.

5. Install check link retaining clevis pin with cotter pin (A, fig. 30). Install bolt (C, fig. 30) into rear hole of cab right s ill brackets and support.

6. Insert a pry bar in between cab right sup port and cab sill.

7. With two assistants, one holding pry bar and the other helping to tilt cab forward (approx imately 45 degrees), install the three remaining bolts, lock washers, and nuts (B, fig. 30) in the right cab support and sill brackets. Use pry bar to align bolt holes. Torque bolt nuts to 40-50 foot pounds.

8. Tighten steering coupling clamp bolt to 40-

50 foot-pounds torque. Connect speedometer cable

Figure 3 3 — Torsion Bar Tension Adjustment Lever Installed

and all electric connectors that junction with the cab -to -ch assis.

9. Connect accelerator linkage and adjust as outlined under ENGINE FUEL SYSTEM (SEC. 6M).

Connect all ground straps.

10. Connect brake lines and hoses. Bleed the brakes as outlined under "HYDRAULIC BRAKES"

(SEC. 5A) if equipped with hydraulic brakes.

11. Connect clutch flexible line and bleed as outlined under "CLUTCH CONTROLS" (SEC. 7D).

12. Connect heater hoses and fill radiator.

13. Install bumper to front of frame. If vehicle is equipped with air brakes, connect air lines.

14. Check cab tilting and lock action.

TILT CAB TORSION BAR

REPLACEMENT

A chain hoist and a lifting sling are required to properly replace cab torsion bar as the weight of cab must be removed from bar. Also, the aid of one or more assistan ts is recommended.

REMOVAL

Instructions below pertain to cab replacement procedures when cab is tilted (approximately 45 degrees) and suspended safely with weight of cab removed from ch assis. A chain from hoist hook, down over rear center of cab and attached to cab rear hold-down catch will a ssist in maintaining cab safely at a 45-degree angle.

IMPORTANT: Protect top of cab from damage by hoist equipment.

1. Secure hoist sling at rear of door openings.

2. Remove weight of cab from chassis.

3. Remove two retaining bolts from mounting cap at torsion bar right frame bracket and from support cap left support.

4. Remove bolt, nut, and washers which at tach torsion bar anchor lever to cab mounting left

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TILT CAB

G M C S E R V I C E M A N U A L

C a b Su p p o rt

Bracket

Stop Bracket

T orsio n B a r

C la m p B olt—

T o rq u e To

6 5 To 7 5 Ft.-Lbs.

R IG H T M O U N T I N G

Fram e Bracket

T-3420

Figure 3 4 — C ab Torsion Bar Stop Brackets Installed

frame bracket. Remove arm from bar and bracket.

5. Loosen cap screw which clamps cab right mounting -bracket to right end of torsion bar.

6. Slide torsion bar from cab right frame bracket, then slide bar in opposite direction from cab left support.

CAUTION: DO NOT hammer on end of bar.

INSTALLATION

1. Before replacement of torsion bar, inspect frame brackets (castings) and cab supports (cast ings) for cracks. DO NOT WELD OR BRAZE

BRACKETS. If cracked, replace.

2. Prelubricate left frame bracket opening and right frame bracket. Slide hex end of torsion bar into left frame bracket, then insert opposite end into cab right support.

3. Install torsion bar anchor lever over end of bar and into frame bracket.

NOTE: Lever should be located on bar so that opposite end of anchor lever is located near center of serrations on cab bracket (fig. 33).

4. Install cab stop brackets (if previously re moved) to torsion bar cab and frame brackets as shown in figure 34. Torque attaching bolts to 35 to

50 foot-pounds. Make sure stop brackets are in stalled as shown.

5. Install torsion bar right frame bracket cap and cab left support cap with two bolts and wash ers. Torque bolts to 50-60 foot-pounds.

6. Tighten bolt which clamps cab right mount ing bracket to end of torsion bar (fig. 34) to 65-75 foot-pounds.

7. Lubricate all cab tilt lubrication fittings with lubricant specified in LUBRICATION (SEC. 0).

8. Raise and lower cab to check operation. If cab r ise s too fast from operating position or if considerable effort is required to raise cab, make torsion bar tension adjustment as directed under

"Torsion Bar Tension Adjustment."

TORSION BAR TENSION

ADJUSTMENT

1. Tilt cab forward to an angle whereby the torsional load is removed from torsion bar. Usually the bar will become unloaded when cab is tilted

45 to 50 degrees. This unloaded angle position may vary slightly on different vehicles.

IMPORTANT: Before continuing, check tight ness of screw which clamps cab right mounting bracket to torsion bar. Tighten screw firmly ONLY when torsion bar is unloaded - cab tilted part way.

If screw is loose, cab bracket may fracture when torsion bar is loaded.

2. SAFELY support cab at angle at which tor sion bar becom es unloaded. An overhead hoist is recommended for supporting cab in this position as it will allow cab to tilt slightly fore or aft to facilitate alignment of torsion bar anchor lever to cab frame bracket.

3. Loosen nut on bolt which attaches the anchor lever and serrated spacer block to the cab frame bracket (fig. 33). Loosen nut only enough for spacer to clear serrations.

4. By tilting cab slightly fore and aft, the sm all serrated spacer block can be relocated to new related serrations on cab frame bracket as desired.

5. Tighten anchor bolt nut to 80-90 foot-pounds.

6. Check cab tilting action. If necessary, r e position anchor point of torsion bar anchor lever as directed above.

NOTE: If adjustment is such that cab rises rapidly to fu ll-tilt position, damage to cab check link could occur and also upon lowering of the cab to operating position, considerable effort may be required.

IMPORTANT: Final check tightness of anchor lever bolt nut.

G M C S E R V I C E M A N U A L

Sec. 1

Page 65

(lady MountitKfi

PLATFORM BODY M O UNTING S

Before any body mounting is attempted, this section should be studied carefully and the re c ommendations followed as closely as possible.

When mounting bodies, certain important pro cedures should be followed. Unless such practices are followed, strains of load and ch assis weave may not be distributed correctly, causing damage to body or frame.

IMPORTANT: Avoid drilling additional holes in frame for mounting bolts. Use existing holes if possible; if additional holes are necessary, close unused holes by welding.

LONGITUDINAL SILL M O U NTING

If body is equipped with longitudinal sills, observe following standard practices.

1. Wooden longitudinal sill should rest direct ly on top flange of ch assis frame side rail. If pro jecting rivet heads prevent a solid bearing, coun tersink longitudinal s ills just enough to clear rivet heads.

IMPORTANT: Do not use spacers to raise s ills above rivet heads. If body longitudinal sill is of metal, it will be necessary to use a one-piece full length hardwood strip, with holes to clear rivet heads between body s ill and frame rail. Wood strip should be firm ly fastened to body sill.

2. Sill should extend as close as possible to back of cab without interfering with mounting or movement of cab.

3. Make sure height of sill is sufficient to prevent body from striking tires, or other parts of ch assis, with maximum spring deflection. Take into consideration full load operation over ex trem ely rough terrain.

4. Sill must rest squarely on frame flange and not overhang outside of frame. If sill width does not cover entire width of frame, install a spacer block as shown in figures 1 and 2. Blocks should

TO P V IEW

1 Frame Side Rail

2 Longitudinal Sill

3 Spacer Block

SID E V IEW

4 W ood Filler Block

5 Clip Plate

6 Metal Channel

7 Mounting Bolt

Figure 1— Typical B o d y M o u n tin g s

EN D V IEW

8 Lock Nut

9 Nut

10 Cross Sill

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Page 66

BODY M OUNTINGS

G M C S E R V I C E M A N U A L

STUD TYPE M O U N T IN G

1 Lock Nut

2 Nut

3 Clip Plate (not tapped)

4 Metal Channel

5 Longitudinal Sill

T A P P E D PLATE TYPE M O U N T IN G

6 Spacer Block

7 Frame Side Rail

8 Wood Filler Block

9 Mounting Stud

10 Clip Plate (Tapped)

U-BOLT TYPE M O U N T IN G

11 Mounting Bolt

12 Lock Washer

13 U-Bolt Clip

14 U-Bolt

TP-9732- 1

Figure 2 — Recom m ended Methods of M oun ting Body

extend beyond width of frame flanges to permit grooving blocks to maintain position of mounting bolts. If desired, block can be attached to sill with screw s as shown in figure 2.

Wood grain of block should be perpendicular

(up and down) to grain of sill.

5. Wood s ills must be chamfered 1/2" at the front end, tapering to meet the frame 12 to 18 inches from end of sill (fig. 1). Tapered front of sill is required for all Van or torsionally rigid bodies. Notch or spot drill sill to clear the rivet heads.

6. To prevent mounting clip plate becoming embedded in longitudinal sill, install a sheet metal channel on top of sill at each mounting point (figs.

1, 2, and 3). Rabbet grooves along each side of top edges of longitudinal sills to permit flush mounting of sill channels.

M O UNTING BOLTS

1. Install one mounting near front end of sill, one near rear end of sill, and space others as nearly equal as possible between front and rear mountings. It may be necessary to vary distances to clear chassis brackets, etc., but approximately equal spacing should be maintained.

2. Use two bolts or studs of proper length with a diameter of at least 7/16" and preferably 1/2" for each mounting. Use a clip plate, of same thick n ess as diarneter of bolts, at upper ^nd lower end of bolts. Use at least three, and preferably four mountings on each side.

3. Hex head bolts are preferred for body mountings; however, carriage bolts, U-bolts, and threaded rods (studs) can also be successfully employed. If design of body does not permit use

G M C S E R V I C E M A N U A L

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BODY M O U NTING S

of nuts at top of sill, tapped plate, as shown in figure 2 can be used.

4. Insert a block of hard, dry wood (with grain running up and down) in channel of frame at each mounting. Block must be of sufficient length to ex tend well under clip plates. Thickness of block should extend beyond width of frame flanges to permit grooving the blocks. Inner mounting bolt will fit into groove and hold block firmly in place

(fig. 1 or 2).

5. If shoulder on bolt head is square, as on carriage bolts, the holes in upper clip plates should also be square. Shoulder of bolts should be driven into holes to prevent bolts turning. If U-bolts are used, bolt must be of "flatted" type as shown in figure 2. A clip or spreader must be used on each

U-bolt, and bolt must not be used in reverse of position shown in figure 2.

6. Use two nuts on threaded end of each bolt.

Tighten inner nut firm ly, then tighten outer (lock) nut firmly against inner nut. DO NOT USE SINGLE

NUT AND LOCK WASHER. However, lock washer should be used with tapped plate type of mounting.

CROSS SILL M O U NTING

If body is not equipped with longitudinal sills , attach s ills , if possible, as shown in figure 3, since mounting on cross s ills (bolsters) is not recommended. Longitudinal s ills can be easily made of dry hardwood and attached to either wood or metal cross s ills by means of angle irons and bolts. General practice of body mounting is on longitudinal sills; however, where the conditions n ecessitate mounting directly on cross s ills , the following practices should be observed:

1. Sills must rest squarely on frame top flange. Countersink sill, if necessary, to clear rivet heads - - d o not use spacer.

2. Use same type of mounting bolts and clip plates as described in ’’Mounting Bolts." The num ber of clips to use is of course dependent upon

Figure 3 — M ethod of Attaching Longitudinal Sills to Body

load, body style, etc. Carriage or step bolts are useful in this type mounting, since bolt heads pro ject above floor.

3. Use wood blocks in frame channel when ever mountings are used on frame. Mount clip plates diagonally across frame rail - - with one bolt forward of cross s ill and inside frame rail and other bolt to rear of cross sill and outside frame rail.

4. U-bolts cannot be used with this type of mounting since mounting bolts, of necessity, pro ject through floor or platform of body. Make sure that heads of bolts are well supported at body floor with plates or washers.

Sec. 1

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________________________G M C S E R V I C E M A N U A L

BODY M OUNTINGS

IMPORTANT

DO NOT drill additional holes in frame.

Refer to F R A M E (SEC. 2) for additional cautions.

G M C S E R V I C E M A N U A L

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A il G&n&itiosiincj,

(CONVENTIONAL CAB MODELS)

This sub-section contains service information on the following:

Subject

General Information ..........................................................................

Page No.

Operating Instructions .......................................................................

System Operation ..............................................................................

On-Vehicle Service ...........................................................................

Insufficient Cooling Diagnosis Chart ...........................................

GENERAL INFORMATION

The optional air conditioning system used on conventional cab models operates in conjunction with the heating system to cool and dehumidify the incoming air, the recirculated inside air, or a com prised of the following basic system s: mixture of both as required for optimum driver comfort. Briefly, the air conditioning system is pressure relief valve to reduce excessive refrig erant pressure.

The complete com pressor-clutch assem bly is serviceable. The com pressor, which may be r e moved for repairs, is mounted towards front of engine parallel to the engine crankshaft.

2. Tne condenser is a fin and tube-type core designed to change entering refrigerant vapor to a liquid by the removal of heat. The condenser is mounted in front of engine cooling radiator where

CONDENSING SYSTEM

This system is composed of three major units which are located behind the radiator shell sheet metal assem bly. Units are described as follows:

1. The six-cylinder double-action piston-type com pressor, which is belt-driven by the engine crankshaft through an electromagnetic clutchpulley assem bly. The com pressor pumps refriger ant through the system as required and operates when the com pressor clutch coil is energized. The com pressor is equipped with an automatic high it receives a high volume of air from movement of the vehicle and the engine fan.

3. The receiver and dehydrator unit, usually mounted to right side of radiator shell, is designed to store liquid refrigerant and to remove sm all traces of moisture that may be in system after purging and evacuating. A sight glass at the top of this component is used to observe flow of liquid refrigerant in system .

A ir O u tle t

Deflector

W INDSH IELD

OUTLETS

EVAPORATOR

CORE

RECIRCULATED

AIR

OUTSIDE

AIR

DASH OUTLETS

DISTRIBUTOR

M A N IFO LD

OUTLET D O O R

BLOWER

Figure 1 — System A ir-Flo w

TEMPERATURE

SELECTOR D O O R

HEATER CORE

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

COOLING SYSTEM

This system con sists of three major compon ents located at the cowl and dash assem bly. These components are described as follows:

1. The evaporator, located under right side of dash in an enclosed housing assem bly, is de signed to cool, dry, and clean the air that enters the cab. Refrigerant enters the evaporator as a low -pressure mixture of liquid and vapor. The liquid vaporizes at this low pressure, absorbing large quantities of heat from air that is forced through the evaporator core fins. Thus, air direc ted into the cab from the evaporator w ill be cooled

(fig. 1). Also, moisture in air that p a sses through the evaporator condenses on fins and is drained off carrying away dust and pollen.

2. The refrigerant expansion valve, located below evaporator core in enclosed dash housing assem bly, regulates the flow of liquid refrigerant into the evaporator automatically in accordance with requirements of evaporator.

3. The suction throttling valve (S.T.V.) is de signed to maintain the evaporator p ressure suf ficiently high to avoid freezing of moisture on evaporator core and at the same time, provide maximum cooling efficiency.

The suction throttling valve is mounted at top of enclosed dash housing assem bly and is a c c e ss ible after opening the dash compartment door.

AIR CIRCULATION SYSTEM

The air flow forced through the evaporator core and heater core results from the use of a m ulti-speed blower and motor assem bly mounted at side of dash unit (fig. 1). Motor speed is con trolled by a fan switch located on instrument panel

(fig. 2).

NOTE: A thorough technical description of all air conditioning components is given later in this section.

OPERATING

INSTRUCTIONS

DESCRIPTION OF CONTROLS (Figs. 1 and 2)

1. The "AIR CONDITION” lever, when moved to the extreme right "ON" position, energizes the com pressor circuit for refrigerant flow in system .

This results in cooling of air directed through evaporator core.

2. The "DEFROST” lever controls air flow to the windshield defroster ducts. When the lever is moved to the extrem e right "ON" position, max imum air flow is diverted to the windshield de froster ducts.

3. The "TEMP" lever directs air flowthrough either the heater core, the evaporator core, or through both. Lever may be set at any position

Figure 2 — A ir C o n d itio n in g Control Sw itches

between "COOL” and "HOT” to control temper ature of air circulated through cab.

4. The "AIR" lever controls amount of re cir culated and outside air through system . With lever in extreme left position, system operates entirely on recirculated air. Intermediate positions of lever will result in proportional amounts of outside and recirculated air flow through system .

5. The "FAN SWITCH" controls the threespeed blower motor. Switch has four positions:

Off, Low Speed, Medium Speed, and High Speed.

6. Direction of air flow from dash outlets

(fig. 1) can be controlled by positioning of outlet inner deflector. The inner deflector can also be oscillated to completely close the outlet if desired.

To close off any one of the outlets will increase the flow from remaining open outlets. The small outlet door at base of distributor duct can be open ed if desired by pulling downward on door tab.

OPERATING AIR CONDITIONING SYSTEM

IMPORTANT: Be sure "AIR CONDITION" lever is in the "OFF" position to reduce electrical load on battery when starting engine.

1. With engine running, move "AIR CONDI

TION" control lever to "ON" position. Blower motor will automatically operate at low speed.

2. Move "TEMP" and "DEFROST" levers to extreme left position.

3. Move "AIR" control lever to "A/C" and then select desired blower speed.

For increased cooling, place blower control switch to high speed position and open windows for a few minutes to expel warm air from cab.

G M C S E R V I C E M A N U A L

When cab begins to cool, close windows tightly and move ”AIR" lever to "NORMAL" position to pro vide desired mixture of both recirculated air and outside air. As required, "TEMP” lever can be moved towards "HOT" position to allow mixing of hot and cool conditioned air as required for com fortable system outlet temperatures.

OPERATING HEATING SYSTEM ONLY

For heating only, move "AIR CONDITION" lever to "OFF" and "AIR" lever to "OUTSIDE."

Position "TEMP" lever as required for desired

Sec. 1

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AIR CONDITIONING

temperature of incoming air. Should defogging of windshield be required, open door ventilator win dow slightly, place "DEFROST" lever to extreme right "ON" position, and operate blower motor at high speed.

For warm weather ventilation le s s air condi tioning, place "AIR CONDITION," "DEFROST," and "TEMP" levers in extreme left positions, move "AIR" lever to extreme right position, then place fan switch lever to desired speed position.

Air flow will be directed through heater outlets and not "A/C" outlets.

V E N T ILA T IO N

W ARNING - CARBO N MONOXIDE

Keep cowl vent air intakes closed when operating in congested traffic to prevent

deadly exhaust gases from entering cab.

Exhaust gases may have strong odors which normally should give warning of

their presence. However, the exhaust gases from some vehicles may not be so not

iceable under certain conditions and the senses of people react differently. Exhaust

gases contain a percentage of carbon monoxide which is poisonous gas that, by it self, is tasteless, colorless, and odorless.

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

SYSTEM OPERATION

Contents of This Sub-Section are as Follows:

Subject

General Operation ..............................................................................

Page No.

Fundamental Principles of Refrigeration ....................................

R e f r ig e r a n t ............................................................................................

Refrigerant Circulation ...................................................................

Air C ir c u la tio n .....................................................................................

Operation of Individual U n i t s ............................................................

GENERAL OPERATION

Some controls and units used with the air con ditioning system are common to the heating s y s tem. These controls and units are: Control switches, heater core, air intake and distribution ducts.

The heating and cooling system s operate in dependently of each other, except under certain conditions of cooling system operation when there is an overlapping operation of both system s as explained previously under "Operating Instructions."

NOTE

Refer to applicable Wiring Diagram

Manual for schem atics of air conditioning electrical circuits.

REFRIGERAN T-12

PRESSURE-TEMPERATURE R ELAT IO N SH IP

-2 0

-1 0

- 5

The ta b le b elo w in d ic a te s th e p r e s s u r e of

R e fr ig e r a n t -12 at v a r io u s te m p e r a tu re s . F or in s ta n ce , a drum of R efr ig era n t at a te m p e r a tu re o f 8 0 ° F . w ill have a p r e s s u r e o f 84.1

p s i. If it i s heated to 1 2 5 °F . the p r e s s u r e w ill in c r e a s e to 167.5 p s i. It a ls o can be u se d co n v e r s e ly to d e te r m in e the tem p er a tu re at w hich

R e fr ig e r a n t-1 2 b o ils un der v a r io u s p r e s s u r e s .

F o r ex a m p le, at a p r e s s u r e of 30.1 p s i, R e fr ig e r a n t b o ils at 32 F .

PRESSURE (PSIG) TEMP. (°F.)

PRESSURE (PSIG)

TEMP. (°F.)

-2 1 .7

0 (a tm o sp h eric p r e s s u r e )

2.4

4.5

6.8

9.2

11.8

14.7

17.7

21.1

24.6

28.5

30.1

3 2.6

37.0

41.7

4 6 .7

100

105

110

115

120

125

130

140

108.1

116.9

126.2

136.0

146.5

157.1

167.5

179.0

204.5

52.0

57.7

63.7

70.1

76.9

84.1

91.7

9 9.6

Figure 3

—

Pressure-Tem perature Chart

FUNDAMENTAL PRINCIPLES OF

REFRIGERATION

The principle of operation of the refrigeration system is based on a few simple laws of physics which are stated informally as follows:

1. Temperature is a measurement of the in tensity of heat.

2. Heat is a form of energy. When heat is added to a substance, it usually is noticed by an increase in temperature. For example, in order to raise the temperature of water from 35°F. to

100°F., it is necessary to add a certain amount of heat.

3. When an object cools, it does not absorb cold, but rather it lo ses heat to a colder object or substance nearby. When a bottle containing warm liquid is placed on a cake of ice, the ice will melt and the bottle and its contents will become cool.

Heat from the bottle and its contents is lost to the ice.

4. When a liquid boils, turning to vapor, it absorbs a great amount of heat. For instance, water boiling on a stove is absorbing a great amount of heat from the burner as it is changing to the vapor commonly called steam. Boiling is a rapid form of evaporation.

When a liquid boils, it absorbs heat without changing temperature. For example, when heat is added to water at sea level, as when heating on a stove, the temperature of the water will rise until it reaches 212°F. If the water remains on the hot stove, it will boil, but the temperature will remain at 212 F. The heat being absorbed by the water is changing it to steam rather than raising the temp erature.

Refrigerant-12 used in air conditioning s y s tem boils at 21.7 F., below zero. Thus, if it were exposed to the air at normal room temperature, it would absorb heat from surrounding air and boil, immediately changing to a vapor.

5. When heat is removed from water vapor, it will condense back into a liquid. For example, the steam caused by boiling water on a stove will condense into water on the underside of the cover.

This is due to the fact that the cover is not as hot as the steam. The cover, therefore, takes heat from the steam, condensing it back to water.

6. The temperature at which substances will boil or condense is affected by pressu re. Refer to

"Pressure Temperature Chart" (fig. 5). If the p ressure is increased, the liquid will not boil until a higher temperature is reached. Thus, we can prevent refrigerant from boiling if it is kept under high pressure. If this high pressure is suddenly released, refrigerant will immediately boil. This has been demonstrated on modern vehicles with pressure cooling system s.

When the pressure of a vapor is increased, the temperature at which it will condense is also raised. Steam condenses below 212°F., if heat is removed from it, but it can be made to condense at higher temperature by increasing the pressure.

7. Compressing a vapor increases its temp erature. For example, when pumping air into a tire with hand pump, the pump will become warm due to the heating of the air as it is com pressed.

8. When a liquid is heated until it is converted to a gas, then this gas is heated additionally with out changing pressure, the gas is said to be super heated. For instance, in the evaporator,refrigerant absorbs heat and boils at a constant temperature and pressure until it has been completely vapor ized, and it continues to absorb heat from the warm air passing over the evaporator without any in crease in pressure. Since this heat is no longer being used to convert the refrigerant from a liquid to a gas, it will now cause the temperature of the refrigerant to r ise. The refrigerant is then super heated.

REFRIGERANT

The refrigerants used are commonly known by their trade name of Freon-12, Ucon-12, or Genetron-12. Regardless of brand, refrigerant-12 must be used. The chemical name of refrigerant-12 is dichlorodifluoromethane (CCL

REFRIGERANT CHARACTERISTICS

Refrigerant exists as a gas at atmospheric pressure and must be held under pressure to r e main liquid. At ordinary temperatures, it will exist as a liquid under a p ressure of about 75 pounds per square inch.

Refrigerant has very little odor, but in large concentrations a distinct odor may be detected. It is co lo rless in both its liquid and gaseous states.

Refrigerant is nonpoisonous, nonflammable, and nonexplosive. It is noncorrosive to any of the ordinary metals.

Goggles should be worn whenever there is the slightest possibility of refrigerant coming in con tact with the face or eyes, because refrigerant

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

evaporates and cools so rapidly it will cause an injury sim ilar to frostbite.

PROCUREMENT

Refrigerant is generally shipped and stored in 25-lb. drums and 15-oz. cans.

It will be im possible to draw all the refriger ant out of the drum. The use of warm water when charging the system will assure the extraction of a maximum amount of refrigerant from the drum.

Be sure to follow the instructions under "Charging

The System" explained later.

NOTE: Approximately 3 -1 /4 pounds of refrig erant is required in system .

PRECAUTIONS IN HANDLING REFRIGERANT

1. Do not leave container of refrigerant un capped.

2. Do not subject container to high tem per ature.

3. Do not weld or steam clean on or near system .

4. Do not fill drum (when used) completely.

5. Do not discharge vapor into area where flame is exposed.

6. Do not expose eyes to liquid.

All refrigerant drums are shipped with a heavy metal screw cap. The purpose of the cap is to protect the valve and safety plug from damage.

It is good practice to replace the cap after each use of the drum for the same reason. If the drum is exposed to the radiant heat from the sun, the resultant increase in pressure may cause the safety plug to relea se or the drum to burst.

For the same reason, the refrigerant container should never be subjected to excessive temper ature when charging a system . The refrigerant drum (when used) should be heated for charging purposes by placing in 125 F., water. Never heat above 125°F., or use blowtorch, radiator, or stove to heat the drum.

Welding or steam cleaning on or near any of the refrigerant lines or components of the air con ditioning system could build up dangerous and damaging p ressu res in the system .

If a small drum is ever filled from a large one, never fill the drum completely. Space should always be allowed above the liquid for expansion.

Weighing drums before and during the transfer will determine fullness of drums.

Discharging large quantities of refrigerant into a room can usually be done safely as the vapor would produce no ill effects. However, this should not be done if the area contains a flame-producing device such as a gas heater. While refrigerant normally is nonpoisonous, heavy concentrations of it in contact with a live flame will produce a

Sec. 1

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AIR COND ITIO N IN G

G M C S E R V I C E M A N U A L

Figure 4 — Schematic of Refrigerant Cycle

poisonous gas. The same gas will attack all bright metal surfaces.

DO NOT EXPOSE EYES TO REFRIGERANT

One of the most important precautions is pro tection of the eyes when handling refrigerant. Any liquid refrigerant which may accidentally escape is approximately 21.7 F.', below zero. If any re frigerant com es in contact with the eyes, serious injury could result. Always wear goggles to pro tect the eyes when handling refrigerant.

eyes:

If refrigerant should come in contact with the

1. DO NOT rub the eyes. Splash the eyes with cold water to gradually get the temperature above the freezing point.

2. Apply a protective film of an antiseptic oil over the eye-ball to reduce the possibility of infection.

3. Consult a doctor or an eye specialist immed iately.

Should liquid refrigerant come in contact with the skin, the injury should be treated the same as though the skin had been frostbitten or frozen.

REFRIGERANT CIRCULATION

Refrigerant control units and piping is illu s trated in figures 1 and 4. A complete cycle of the refrigerating system is as follows:

1. Refrigerant in its gaseous state is drawn into the com pressor where it is com pressed and discharged into the condenser.

2. As the heated gas circulates through the condenser co ils, it is cooled by air being forced through the condenser by an engine cooling fan. The combined effects of the decreased temperature and increasing pressure cause the gas to condense

(liquify).

3. The liquid refrigerant is then forced from condenser into the liquid receiver.

4. By its own pressure, liquid refrigerant is forced from liquid receiver-dehydrator through the expansion valve and into the evaporator.

5. In the evaporator, where the pressure is reduced, the liquid refrigerant evaporates, or changes into its gaseous state. As the liquid evap orates, heat is absorbed from the air passing through the evaporator coils, thus the air is cooled.

6. Flow of refrigerant into the evaporator is regulated by the expansion valve. The expansion valve is actually a pressure reducing valve which serves two purposes: a. It maintains pressure on the liquid line.

b. It admits only the required amount of liquid refrigerant into the evaporator, this requirement being determined by the temperature of the gaseous refrigerant at the evaporator outlet.

7. The low pressure refrigerant gas passes

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

from the evaporator through the suction throttling valve, then back through the suction line to com pressor thus completing the cycle.

AIR CIRCULATION

Air circulation is common to both the heating and air conditioning system s. For detailed d es cription of air circulation in vehicle, refer to

"Operating Instructions" explained previously.

OPERATION OF INDIVIDUAL UNITS

Figures 1 and 4 illustrate the location of the

Air Conditioning (and Heating) System units. Each of the units in the air conditioning system is d es cribed following:

AIR OUTLETS

Refrigerated air enters the interior of the cab through four outlets below the instrument panel

(fig. 1).

Air outlets can be individually controlled to provide a comfortable air flow in any direction de sired by the occupants.

EXPANSION VALVE

The expansion valve (fig. 5) consists of a cap illary bulb and tube which is connected to an oper ating diaphragm (which is sealed within the valve itself) and an equalizer line which connects the valve and the low pressure return line.

The purpose of the expansion valve is to reg ulate the flow of liquid refrigerant into the evap orator automatically in accordance to the require ments of the evaporator.

The valve is the dividing point in the system between high pressure liquid refrigerant supplied from the receiver-dehydrator and relatively low p ressure liquid and gaseous refrigerant in the evaporator. It is so designed that the temperature of the refrigerant at the evaporator outlet must have 10.6 F., of super heat before more refriger ant is allowed to enter the evaporator. Superheat is an increase in temperature of the gaseous r e frigerant above the temperature at which the re frigerant vaporizes.

A capillary tube filled with carbon dioxide and the equalizer line provide the temperature regu lation of the expansion valve. This capillary tube is fastened to the low pressure refrigerant pipe coming out of the evaporator so that it communi cates the temperature of the refrigerant at this point to the expansion valve. If the superheat at the outlet d ecreases below 10.6°F ., the expansion valve w ill automatically reduce the amount of refrigerant entering the evaporator, thus reducing the amount of cooling. If the superheat increases, the expan sion valve will automatically allow more refriger-

F ig u r e S — Expansion Valve

ant to enter the evaporator, thus increasing the cooling.

The equalizer line joining the suction throttling valve with the area behind the operating diaphragm acts with the capillary to measure superheat.

It is the temperature of the air passing over the evaporator core that determines the amount of refrigerant that will enter and pass through the evaporator. When the air is very warm, the heat transfer from the air to the refrigerant is great and a greater quantity of refrigerant is required to cool the air and to achieve the proper superheat on the refrigerant gas leaving the evaporator. When the air passing over the evaporator is cool, the heat transfer is sm all and a le sse r quantity of refrig erant is required to cool the air and to achieve the proper superheat on the refrigerant gas leaving the evaporator.

Since the evaporator outlet pressure is propor tionate to the amount of heat (superheat) picked up by the refrigerant gas in passing through the evap orator, it can be seen that adjusting spring tension which works against capillary pressure and equal izer line p ressure controls the volume of refrig erant entering the evaporator as signaled by the temperature and pressure in the evaporator outlet pipe.

When the air conditioning system has not been operating, all p ressu res within the expansion valve assembly will have equalized at the ambient (sur rounding air) temperature, thus the pressure above and below the operating diaphragm and at the inlet and outlet side of the valve will be equal (fig. 5).

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

(Pressure under the diaphragm is evaporator p res sure. It reaches this area by means of clearance around the operating pins in the valve body which connects the area under the diaphragm with the evaporator pressure area.) While p ressu res in the expansion valve are almost equal, the addition of the valve adjusting spring pressure behind the valve will hold the valve over to clo se the valve orifice.

When the air conditioning system first begins to operate, the com pressor will immediately begin to draw refrigerant from the evaporator, lowering the pressure in the evaporator and in the area under the operating diaphragm. As the pressure in this area d ecreases, the pressure above the dia phragm exerted by the carbon dioxide in the capil lary tube will overcome spring pressure and push the diaphragm against the operating pins, which in turn will force the needle valve off its seat.

Refrigerant will then pass through the expan sion valve into the evaporator where it will boil at a temperature corresponding to the pressure in the evaporator. This will begin cooling the air passing over the evaporator, and, also it will begin to cool the evaporator outlet pipe.

As the evaporator outlet pipe cools, the p r e s sure of the carbon dioxide in the capillary tube

(contacting this outlet pipe) decreases, exerting le s s force on the operating diaphragm.

The valve adjusting spring is calibrated so that the pressure of the refrigerant in the evaporator, plus the spring force, will equal the force above the operating diaphragm when the temperature of the refrigerant in the evaporator outlet is 10.6°F., above the temperature of the refrigerant entering the evaporator. In other words, the refrigerant should remain in the evaporator long enough to

LEVER HELPER

SPRIN G S

ADJU STIN G

PIN NUT ADJUSTIN G

SCREW

PISTON

FROM

EVAPORATOR

ADJUSTING

CON TRO L

LEVER

ASSEM BLY OUTER

INNER

SPRIN G DIAPH RAG M

SPRING

TO CO M PRESSO R

T-3310

Figure 6 — Suction Throttling V a lv e

completely vaporize and then warm (superheat)

10.6°F.

If the temperature differential begins to go below 10.6 F. (outlet pipe becom es too cold), ca r bon dioxide pressure in the capillary tube and area above the diaphragm d ecreases, allowing the valve adjusting spring to move the needle valve toward its seat, closing off the flow of refrigerant past the needle valve.

If the temperature differential begins to go above 10.6°F. (outlet pipe too warm), the pressure in the capillary tube and area above the operating diaphragm will increase, pushing this diaphragm against the operating pins to open the needle valve further, admitting more refrigerant to the evap orator.

EVAPORATOR

The evaporator is actually the device which cools and dehumidifies the air before it enters the cab. High pressure liquid refrigerant flows through the valve orifice in the expansion valve into the low pressure area of the evaporator. This regu lated flow of refrigerant boils immediately. Heat from the core surface is lost to the boiling and vaporizing refrigerant, which is cooler than the core, thereby cooling the core. The heat in the air passing over the evaporator lo ses its heat to the cooler surface of the core, thereby cooling the air.

As the process of heat lo ss from the air to the evaporator core surface is taking place, any m ois ture (humidity) in the air condenses on the outside surface of the evaporator core and is drained off as water.

Since Refrigerant-12 will boil at 21.7°F., b e low zero at atmospheric pressure and water freezes at 32°F., it becomes obvious that the temperature in the evaporator must be controlled so that the water collecting on the core surface will not freeze in the fins of the core and block off the air p a ss ages. In order to control the temperature, it is necessary to control pressure inside the evapor ator and this is done by the suction throttling valve.

To obtain maximum cooling the refrigerant must remain in the core long enough to completely vaporize and then superheat a minimum of 10.6°F.

If too much or too little refrigerant is present in the core, then maximum cooling efficiency is lost.

An expansion valve in conjunction with the suction throttling valve is used to provide this necessary refrigerant and pressure control.

SUCTION THROTTLING VALVE

The main function of the Suction Throttling

Valve (fig. 6) is to maintain the evaporator p res sure at a pressure sufficiently high to avoid fr eez ing of moisture on the evaporator core and at the same time provide maximum cooling efficiency.

' Qpp 1

G M C S E R V I C E M A N U A L __________________ Page 77

AIlT CONDITIONING

O -R IN G SEAL

PISTON

M A INSH AFT

THRUST

DRIVE BALL S U C T IO N ^ O N T ^

SHAFT

SEAL

PULLEY

BEARING

OIL PUMP

REAR HEAD

DISCHARGE SUCTION

VALVE PLATE REED

Q IL M AINSHAFT

PICK-UP

TUBE

REAR

BEARING

SW A S H

PLATE

M AINSHAFT

FRONT

BEARING

\ \ \

ARMATURE

PLATE

FRONT CLUTCH

HEAD COIL

PULLEY

A N D HUB

ASSEMBLY

T-31 1 9

The opposing forces, spring pressure and at mospheric pressure on the one side of the valve diaphragm and evaporator pressure on the opposite side of the diaphragm constitute a balanced valve and control its operation.

When the evaporator pressure rise s above the manual spring setting, this increase in evaporator pressure is exerted against the valve piston and through the bleed holes in the piston to the under side of the diaphragm. The p ressu res under the diaphragm overcome the spring pressure causing the valve piston to move in an opening direction.

As the piston opens, it reaches a balanced position and the evaporator p ressure returns to its original setting (23-24 p .s.i.g .).

When the evaporator p ressure drops below the predetermined setting, the spring pressure over com es the opposing evaporator pressure and forces the piston in a closing direction until the predeter mined pressure setting is maintained (23-24 p .s.i.g.)

The minimum operating pressure of the suction throttling valve is p re-set by an adjustment screw.

Maximum operating p ressure may be obtained by

Figure 7— Refrigerant Compressor

means of a cable operated from the instrument panel to the lever arm on the valve. When reduced load conditions require elevated control pressu res, the lever arm actuates the inner spring assembly causing the piston to throttle in a closing direction.

This results in a higher evaporation pressure and the desired increase in discharge air temperature.

COMPRESSOR

The com pressor is of basic double-action piston design. Three horizontal double acting pistons make up a six-cylinder com pressor, and are mounted axially around the com pressor shaft to operate in a front and rear cylinder assem bly.

These pistons operate in a 1-1/2" bore, have a

1-3/16" stroke and are actuated by a swash plate pressed on the com pressor crankshaft (see fig. 7).

Reed-type suction and discharge valves are mounted in valve plates between the cylinder a s sembly and the head at each end of the com pressor.

The heads are connected with each other by gastight passage ways which direct refrigerant gas to a common output.

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

LIGHT

M IRRO R

SIG H T G L A S S

Figure 8

—

Receiver-Dehydrator

The com pressor mainshaft is driven by the pulley when the clutch coil is energized. It extends through the com pressor front head, to the com p ressor rear head and drives the oil pump in the rear head pump cavities.

The com pressor is fitted with a high pressure relief valve. If the discharge pressure ever ex ceeds approximately 440 psi, the relief valve opens automatically to relieve the pressure and closes again when the p ressure recedes.

The pulley assem bly contains an electrically controlled magnetic clutch, permitting the com pressor to operate only when air conditioning is desired.

The clutch actuating coil is molded into the coil housing with a potted epoxy resin; therefore, the coil and housing are replaceable only as a com plete assem bly. The coil has 3.85 ohms resistance at 80 F. (surrounding temperature) and should not demand more than 3.2 amperes of 12 V.D.C.

Compressor Operation

When the "AIR COND." lever is placed in "ON," the electrical circuit to the com pressor clutch c lo se s.

Current flowing through the coil creates a magnetic force which flows through the pulley to draw the armature plate (forward of the pulley a s sembly) rearward toward the pulley. As the arm ature plate moves toward the pulley, it contacts the pulley shaft face (which rotates freely about the com pressor shaft).

When the "AIR COND." knob is placed to "OFF," the electrical circuit to the com pressor clutch is opened and the magnetic pull on the clutch no long er ex ists. The armature plate to driven ring ac tuating springs will then pull the armature plate away from the pulley and the plate lo ses contact with the pulley.

A gauge fitting containing a Schrader valve is located in both the discharge and suction passage to permit pressure gauge readings.

CONDENSER

The condenser is sim ilar to the ordinary rad iator but is designed to withstand much higher p ressu res. It is made up of tubes which carry the refrigerant and cooling fins which provide rapid transfer of heat.

The condenser is located in front of the engine cooling system radiator so that it receives a high volume of air from the movement of the vehicle and from the engine fan. Air passing over the con denser cools the hot high pressure refrigerant gas, causing it to condense into high pressure liquid refrigerant.

RECEIVER-DEHYDRATOR

ASSEMBLY

The receiver-dehydrator assembly is mounted vertically along the right rear side of the radiator support.

The purpose of the receiver part of this s y s tem is to insure a solid column of liquid refrig erant to the expansion valve at all tim es, provided the system is properly charged.

The liquid indicator (many tim es referred to as a sight glass) is in the refrigeration system as an aid to diagnosis (see fig. 8). The appearance of bubbles or foam beneath the sight glass (liquid in dicator) above 70°F., ambient indicates air or a partial discharge of refrigerant in the system . A solid liquid column as seen in the sight glass is difficult to tell from one that has no refrigerant in the system at all. Two ways to establish whether the system is properly charged or empty are to feel the suction pipe in the suction throttling valve or to disconnect the com pressor clutch while ob serving the sight glass. If the system has the proper refrigerant charge, the suction line at the suction throttling valve will be cool. Also, the refrigerant column in the sight glass will be seen to collapse soon after the clutch has been disconnected. Foam may be noted in the sight g la ss below 70°F., even when the system is free of air and properly charg ed. Details of these conditions are in the "Insuf ficient Cooling Diagnosis Chart,"

Liquid refrigerant from the condenser enters the receiver to flow into the upper portion of the receiver which contains desiccant confined in a

G M C S E R V I C E M A N U A L white felt bag that is not attached to anything but m erely rests on the baffle in the lower portion of the receiver. As the refrigerant flows through an opening in the lower portion of the receiver, it is also filtered through a 100 mesh screen attached to a baffle at the bottom of the receiver.

The desiccant in this assembly is to absorb

Sec. 1

Page 79

AIR CONDITIONING

any moisture that might be present in the system after assem bly. The screens trap any foreign ma terial which may enter the system during assembly.

These features of the assem bly prevent obstruc tion to the valves or damage to the com pressor.

NOTE: Markings on top of the receiver show the proper inlet and outlet fitting connections.

ON-VEHICLE SERVICE

Contents of this Sub-Section are as follows:

Subject

Periodic Service ............................................................................................

Page No.

Precautionary Service M e a s u r e s ................................................................

Performance Testing .....................................................................................

Depressurizing the S y s t e m ...........................................................................

Evacuating the System ..................................................................................

Charging the System .....................................................................................

Adding Refrigerant (Small Amount) .........................................................

Checking Compressor Oil Level and Adding O i l ....................................

Checking for L e a k s .........................................................................................

Replacing Compressor ..................................................................................

Servicing Seals and Hoses ...........................................................................

Condenser Assembly R e p la c e m e n t............................................................

Receiver-Dehydrator Assembly Replacement .......................................

Expansion Valve Replacement ....................................................................

Suction Throttling Valve Replacement .....................................................

Evaporator and Heater Core Assembly R e p la c e m e n t.........................

Collision Service ............................................................................................

Blower Motor R e p la c e m e n t...........................................................................

PERIODIC SERVICE

(60 Days or 6000 M iles whichever occurs first)

1. Check front of condenser for an accumula tion of dirt, such as leaves, bugs, dirt, etc. Also check to see that the space between the condenser and radiador is also free of this material.

2. Inspect com pressor drive belt. Check and adjust tension to 100 to 105 lbs. on belt tension gauge. Adjust new belt tension to 120 to 130 lbs.

3. Operate system and check for correct oper ation in all control positions.

4. Check for refrigerant leaks and observe refi-igerant passing through the sight glass with system operating to see if there is any evidence of bubbles (above 70°F. ambient).

PRECAUTIONARY SERVICE

MEASURES

Before any service is attempted which requires the opening of refrigeration pipes or units, the person doing the work should be thoroughly familiar with "General Information" on refrigeration ser v ice.

The major reasons behind these m easures are for safety and to prevent dirt and moisture from getting into the system . Dirt contaminant is apt to cause leaky valves or wear in the com pressor, and moisture will freeze into ice at the expansion valve and freeze the valve stem.

PRE -ASSEMBLY

1. All sub-assem blies are shipped, sealed and dehydrated. They are to remain sealed until just prior to making connections.

2. All su b-assem blies should be at room temperature before uncapping. (This prevents con densation of moisture from the air that enters into the system .)

3. If, for any reason the caps are removed, but the connections are not made, then the tubes and other parts should not remain unsealed for more than 15 minutes. Reseal connections if period is to be longer. This applies particularly to par tially built-up system s that will be left overnight.

4. Compressors are shipped with 10 - 11 oz.

of Frigidaire-525 Viscosity Oil and charged with a mixture of Refrigerant-12 and dry nitrogen to

Sec. 1

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

TEST READINGS

Ambient Air in Degrees F. (In Auxiliary

Fan Air Blast

Ahead of Condenser).

70 80 90 100 110

Air Quality

Average Compressor Head

Pressure— PSI

Average Suction Throttling Valve

Pressure— PSI

Center Outlet Tem perature Degree F.

Arid

125/155 150/180 160/190 180/210 197/227 213/243 225/255 250/280 270/300 290/320

20/23

41/44

Humid Arid Humid Arid

21/24

48/52

20/23

44/48

22/25

53/57

21/24

48/52

Humid Arid Humid Arid Humid

25/28

58/62

24/27

52/57

29/32

62/68

28/31

58/65

36/39

68/75

Shown in the above table are the average readings expected in arid or dry air, and in humid or moist air with maximum allowable tolerance shown.

Humid air is considered 20—90% R.H. Nozzle

A rid a ir is co nsidered 5—20% R.H. Nozzle

Figure

— Operational Test Data Chart

provide an internal pressure at slightly above atm ospheric.pressure.

been connected. This is necessary to insure opti mum dehydration and maximum moisture protec tion of the refrigeration system .

ASSEMBLY

1. All precautions should be taken to prevent damage to fittings or connections. Even minute damage to a connection could cause it to leak.

2. Any fittings getting grease or dirt on them should be wiped clean with a cloth dampened with alcohol. Do not use chlorinated solvents such as trichloroethylene for a cleaning agent, as they are contaminants. If dirt, grease or moisture gets in side the hoses and cannot be removed, the hose should be replaced.

3. Sealing caps should be removed from subassem b lies just prior to making connections for final assem bly.

4. Use a small amount of clean refrigeration oil (525 or 1000 viscosity) on all tube and hose joints, and dip the O-ring gasket (when used) in this oil before assembling the joint, as this oil will help in making a leak-proof joint.

5. Do not connect the receiver-dehydrator a s sembly until all other sealed sub-assem blies have

CAUTION - LIQUID INDICATOR (SIGHT GLASS)

Under normal conditions, the receiver-dehy drator will show clear with about 3 pounds of r e frigerant in the system . However, the air condi tioner will not produce its best performance until

3 -1 /4 pounds of refrigerant are in the system . Do not overcharge with refrigerant, as this will result in extremely high head p ressu res and the com pressor safety valve will "blow."

PERFORMANCE TESTING

In order to determine if an air conditioning system is operating properly and efficiently, it must be performance tested. The first step to diagnosing a system that has been malfunctioning should be a complete performance test (see fig. 9).

Correct pressures indicate that the required charge of refrigerant is in the system and that it is functioning properly.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

Testing to determine if the discharge air temp erature, suction pressure, and discharge pressure meet the specifications at a particular ambient condition is called a "Performance Test."

The suction throttling valve is p re-set at the factory to maintain the minimum and maximum evaporator core pressure and generally should never require resetting. If a malfunction in the r e frigerant system due to above or below normal evaporator core p ressu res is suspected, check the following:

1. Restrictions in evaporator core, hoses, tubes, etc.

2. Refrigerant leaks.

3. Compressor clutch slippage.

4. Improper drive belt tension.

5. Capillary tube broken or not tight to evap orator tube.

6. Expansion valve inoperative.

7. Suction throttling valve stuck.

The purpose of performing an operational test is to prove that the air conditioning electrical s y s tem, air system , and refrigeration system are operating properly and efficiently. Results of the test are as follows: a. Operation of the air conditioner blower at all speeds and engagement of the com pressor clutch would indicate that the electrical circuits are func tioning properly.

b. A clear sight glass would indicate a properly charged refrigeration system .

c. Proper evaporator pressure, as controlled by the Suction Throttling Valve would provide prop er "freeze protection" for the evaporator.

d. Proper nozzle temperatures would indicate a system free from warm air leaks.

Check and correct all air and refrigerant leaks in the air conditioning system as well as operation of cable-operated air doors.

Check for proper com pressor oil level during the repair of refrigerant leaks, before conducting an operational test.

PRELIMINARY CHECKS

1. Check com pressor belt for proper tension; if below 100 lbs. (used belt) adjust to 100-105 lbs.

using belt tension gauge.

2. Check all refrigeration lines for leaks, kinks, or other restrictions.

3. Check outer surfaces of radiator and con denser cores to be sure they are not plugged with dirt, leaves or other foreign material. Be sure to check between the condenser and radiator as well as the outer surfaces.

4. Connect engine tachometer.

5. Start engine and operate at 2000 rpm with

"AIR" lever on "OUTSIDE" and "TEMP" lever set for maximum cooling, and blower on high. After at lea st five minutes of engine operation, observe for

V A L V E F IT T IN G

G A U G E H O S E

Figure JO— G a u g e Hose Connection at Suction Throttling Valve

bubbling at the sight glass (above 70°F. ambient).

If the system is low on refrigerant, add refriger ant until liquid indicator just shows clear and add an additional 1/2-pound of refrigerant.

6. Under the same conditions as in step 5 above, move "AIR COND" lever to "OFF." This should disengage the com pressor clutch. If clutch does not disengage, check the clutch control switch adjustment.

7. Move "AIR COND" lever to "ON" again and observe clutch engagement action which should be without slip. If clutch slips, check clutch for proper adjustment, short in clutch coil, or leaking com pressor shaft seal.

8. Change blower speed to medium, and to low, and observe for d ecreases in air flow.

FUNCTIONAL TEST

NOTE: This test should not be performed in direct rays of sun.

1. Connect gauge set high pressure hose to outer gauge fitting at rear of com pressor and con nect 30-inch vacuum, 60-p si compound test gauge hose to refrigerant fitting at suction throttling valve (fig. 10).

2. Locate auxiliary fan (at least 20" in diam eter) in front of condenser. Leave hood open.

3. Open both cab doors.

4. Place a calibrated thermometer in front of condenser in auxiliary fan air stream.

5. Place a second calibrated thermometer in

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AIR CONDITIONING

G M C S E R V I C E M A N U A L auxiliary fan air stream to measure wet bulb temperature.

6. Connect engine tachometer.

7. Open all air outlets below dash.

8. Locate a calibrated thermometer in center outlet. Sensing bulb must not touch metal.

9. Place transm ission lever in "Neutral,"with parking brake on.

10. Start engine and set "AIR" lever at "OUT

SIDE," "TEMP" lever full left for maximum cooling and blower switch at high blower speed.

11. Set engine speed at 2000 rpm.

C O M P R E SSO R

SU C T IO N THROTTLING VALVE TO C O N D E N S E R

EVA P O RAT O R

C A r M M O i u n

VALVE

G A U G E H IG H

PRESSURE H O SE

■FROM RECEIVER DEHYDRATOR

V A C U U M PUMP

LO W PRESSURE

H IG H PRESSURE

G A U G E L O W

PRESSURE H O SE

TO SYSTEM

SU C T IO N LINE

TO V A C U U M

PUMP, REFRIGERANT,

OR REFRIGERANT OIL

G A U G E SET

TO SYSTEM

D ISC H A R G E LINE

G A U G E H O S E C O N N E C T IO N S A T C O M P R E S S O R

Figure 11 — H o o k -U p of G a u g e s a n d E vacua ting Pum p

12. Allow engine to run for 10 minutes, or until stabilized.

NOTE: If at any time during test.com pressor head pressure exceeds 375 psi, discontinue test and check the following: a. Engine cooling system .

b. Restricted receiver and liquid indicator assem bly.

c. Air in refrigeration system or overcharge of refrigerant.

d. Insufficient auxiliary fan air on radiator and condenser.

13. At the end of this time record the following: a. Ambient air at condenser.

b. Wet bulb temperature in auxiliary fan air stream.

c. Compressor head pressure.

d. Refrigerant test fitting gauge pressure.

e. Center outlet temperature.

Compare above with system pressures and temperature shown on "Operational Test Data

Chart" (fig. 9). If not within the lim its shown, r e fer to the "Insufficient Cooling Diagnosis Chart" for possible cause of sub-standard performance.

Reference should be made in the order listed with head pressure first, if not within "Operational

Test Data Chart" lim its, then check suction throt tling valve inlet pressure and finally center outlet temperature.

NOTE: For altitude lev els at or near sea level, set the suction throttling valve as specified (23 psig). For higher levels, set valve 1/2 lb. per sq.

in. higher for each 1,000 feet of elevation.

14. Remove charging manifold gauge set, test fitting gauge, and install the fitting caps.

DEPRESSURIZING THE SYSTEM

Any time the system is to be opened, it must first be depressurized. Depressurize the system as follows:

NOTE: Install gauge set to com pressor gauge fittings (fig. 11).

1. Remove caps from gauge fittings at com p ressor.

2. With both valves on the manifold gauge set

J-5725-04 closed (clockwise), attach manifold hoses to com pressor fittings, using J-5420 Schrader valve adapter at the suction gauge fitting and J-

9459 Schrader valve adapter at the discharge gauge fitting.

3. Crack open the high p ressure valve on mani fold gauge set to allow slow escape of refrigerant from the system through the manifold gauge set and out the center fitting and hose. (Place end of hose in clean container.) If oil drips from the hose into the container, refrigerant is escaping too rapidly.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

4. When hissing ceases (indicating all refrig erant has escaped) close valves on manifold gauge set by turning valve clockwise.

EVACUATING THE SYSTEM

When the refrigeration system is depressur ized and opened for service, some air will enter the lines regardless of how quickly the openings are capped. In order to remove this air and as much as possible of the moisture it contains, the complete system must be "evacuated." Evacuating is merely the p rocess of removing all air from the system , thereby creating a vacuum in the system .

CAUTION: Under no circum stances should alcohol be used in the system in an attempt to remove moisture, regardless of the successful use of alcohol in other refrigeration system s.

PREPARATION FOR EVACUATING

COMPLETE SYSTEM

1. Check the low pressure gauge for proper calibration, with the gauge disconnected from the refrigeration system . Be sure that the pointer on the gauge indicates to the center of "O." Tap the gauge a few tim es lightly to be sure pointer is not sticking. If necessary, calibrate as follows: a. Remove the cover from the gauge.

b. Holding gauge pointer adjusting screw firm ly with one hand, carefully force pointer in the proper direction in the proper amount to position the pointer through the center of the "O" position.

Tap gauge a few tim es to be sure pointer on gauge is not sticking. Replace gauge cover.

2. If gauge set is not already connected to com pressor fittings, connect as follows (refer to fig. 11): a. Close hand shut-off valves on gauge set by turning clockwise.

b. Remove caps from gauge fittings at com p ressor.

NOTE: To shorten evacuating and charging time, the valve core in each com pressor gauge fitting can be unseated using Tool J-22132-01. The gauge lines are then connected to the tool fittings.

Turn tool knobs counterclockwise to unseat cores.

c. Attach Schrader valve adapter J-5420 to end of hose from suction valve low pressure gauge and connect this adapter fitted hose to the com p ressor suction gauge fitting or to Tool J-22132-01

(if used).

d. Attach Schrader valve adapter J-9459 to end of hose from com pressor gauge and connect this adapter fitted hose to the discharge gauge fit ting or Tool J-22132-01 (if used).

3. Attach a flexible gauge hose to the center fitting of the gauge set and attach the other end of this hose to the vacuum pump J-5428-03 (fig. 11).

S ec. 1

Page 84________________

AIR CONDITIONING

G M C S E R V I C E M A N U A L

C O M PRESSO R

______

/

SUCTION THROTTLING VALVE

‘C O N D EN SER

LO HI

-5725-04

, J-6272 -01

: I V

DRUM ^ J

EVAPORATOR

" 0 7

REFRIGERANT-12

FROM RECEIVER-DEHYDRATOR

T-5939

Figure 12— H o ok-U p of G a uges and C ha rging Equipment

4. The system can now be evacuated.

EVACUATING COMPLETE SYSTEM

1. Turn hand shut-off valve on low pressure gauge of gauge set to the full clockwise (closed) position.

2. Slowly turn valve on high pressure gauge counterclockwise from the full clockwise position, letting any pressure build-up escape completely.

Close high pressure valve.

3. Check oil level in vacuum pump ( J-5428-03) and add Frigidaire-150 viscosity oil or equivalent, if necessary, to bring to proper level. Make sure dust cap on discharge side of vacuum pump has been removed.

4. Start the vacuum pump and slowly open the low and high p ressure sides of the manifold gauge set to avoid forcing oil out of the refrigeration system and the pump. Pressure is now being reduc ed on both sides of the refrigeration system .

NOTE: If oil is blown from the vacuum pump, it should be refilled to the proper level with Frig idaire-150 viscosity oil or equivalent.

5. Observe low pressure gauge and operate vacuum pump until gauge shows 26-28" vacuum.

Continue to run pump for ten additional minutes.

NOTE: In all evacuating procedures the sp eci fication of 26-28 inches of vacuum is used. This evacuation can only be attained at or near sea level.

For each 1000 feet above sea level where this operation is being performed, the specification should be lowered by one inch of mercury vacuum.

For example: at 5000 feet elevation only 21 to 23 inches of vacuum can normally be obtained.

If vacuum cannot be pulled to the minimum specification for the respective altitude, it indi cates a leak in the system , gauge connections or a defective vacuum pump. In this case, it will be necessary to check for leaks as outlined later, after a small amount of Refrigerant-12 has been added to the low side of the system .

a. Turn the hand shut-off valves at the low and high pressure gauge of the gauge set to the full clockwise position with the vacuum pump oper ating, then stop pump.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

b. Connect flexible line from center fitting of the gauge set to refrigerant container (container should be at room temperature).

3. Place refrigerant drum (in pail of water) on sca les (bathroom or com mercial, preferably com mercial) (fig. 12).

4. If line at center gauge fitting has not been purged of air, loosen line at center fitting on gauge

NOTE: It may be necessary to use reducer fitting J-8695-18 if attaching flexible hose to drumtype refrigerant container.

c. Open shut-off valve on container and loosen flexible line fitting at center fitting at gauge set so and high p ressure gauge of the gauge set to the full clockwise position with the vacuum pump operating, then stop pump. Carefully check low pressure gauge to see that vacuum remains constant. If vacuum set and "crack" valve on refrigerant drum to blow air from line. Retighten line at center fitting and record exact weight of refrigerant tank in water on the sca les.

that refrigerant will purge all air from line. Tighten flexible fitting when certain all air has been purged from line.

d. Open suction valve on gauge set. This will allow refrigerant to pass from the container into the system . When pressure stops rising, close su c tion valve on gauge set and valve at refrigerant container (as refrigerant container is at room temperature, only a sm all refrigerant charge will

CAUTION: When purging a line by cracking a fitting, wrap a cloth around connection to prevent injury due to release of pressurized refrigerant. Also, be sure to wear eye protection.

5. Open valve on refrigerant drum and both valves on gauge set to allow refrigerant to flow into the system . Continue charging until the scales enter the system ).

e. Using leak detector J-6084, check all fit tings in the system , com pressor shaft seal and on show that 3 -1 /4 pounds of refrigerant have been transferred from refrigerant drum to the system .

the gauge set for evidence of leakage. When general area of leak has been found with the test torch, a

NOTE: If full charge cannot be attained, close both valves on gauge set, start engine, place "AIR

COND" lever to "ON,” the ”AIR” lever to "OUTliquid leak detector may be helpful in locating the exact point of leakage. After leak has been co r

SIDE," and then place ”TEMP" lever to full cold rected, evacuate the system again for 15 to 20 minutes.

6. Turn the hand shut-off valves at the low position. Open low p ressure valve on gauge set slowly and leave open until full charge of 3-1 /4 pounds of R efrigerant-12 is taken in.

CAUTION: Observe high pressure gauge while charging with com pressor running. Shut off engine if pressure ex reduces, it indicates a leak in the system or gauge connections. See "NOTE" in step 5 previously for method of locating leak.

ceeds 375 p si. A large fan placed in front of the vehicle will help reduce excessively high head pressure.______

CHARGING THE SYSTEM

6. Close both valves on gauge set (high p res sure valve will already be closed if charging was completed by running com pressor) and close valve on refrigerant drum.

The system should be charged only after being evacuated as outlined in "Evacuating The System .”

REFRIGERANT DRUM METHOD

1. Connect center flexible line of gauge set to refrigerant drum.

NOTE: It may be necessary to use adapter

J-8695-18 to attach flexible line to refrigerant drum.

2. Place refrigerant drum in a pail of water which has been heated to a maximum of 125°F.

CAUTION: Do not allow tem per ature of water to exceed 125°F. High temperature will cause excessive p res sure and possible softening of the fu s ible safety plugs in the refrigerant drum. It may not be necessary to use hot water if a large drum is used (over approximately 100 pounds).

NOTE: If the engine was used to complete the

Refrigerant-12 charge into the system , close valve on refrigerant drum to perm it com pressor to draw any refrigerant left in the line from the drum to the center fitting of the gauge set, then close the low pressure valve on the gauge set.

7. Operate engine at 2000 rpm with "TEMP" control knob at full cold position and blower con trol for high speed with "AIR" lever to "OUTSIDE."

After ten minutes of operation observe appearance of refrigerant in receiver-dehydrator. If bubbles are observed, open low pressure gauge valve and valve on refrigerant drum to allow more refriger ant to enter system . Close valve when receiverdehydrator clears up.

NOTE: If air inlet temperature is below 70°F., when this check is made, bubbles may appear even

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G M C S E R V I C E M A N U A L though the proper amount of refrigerant is in the system . Air inlet temperature must be 70°F., or above to make an accurate check. In no case should the system be charged with more than 3 -1 /4 lbs.

of refrigerant.

8. When refrigerant has been injected, con tinue to operate system and test for proper oper ation as outlined under "Performance Testing."

9. When satisfied that air conditioning system is operating properly, stop engine, remove gauge set and replace protective caps on com pressor fittings.

gauge set and "crack" valve at can opener (for a second or two) to force air from th eline. Retighten line at center fitting.

4. Open valve on No. 4 Multi-opener (or on single can) and also low pressure and high p res sure valves on manifold gauge set. Leave can valve open until all refrigerant has entered the refrig eration system . Close valve on can.

a. If the system is charged using single cans and the J-6271 valve, disconnect valve from can, leaving valve closed to flexible line to the center fitting of the manifold gauge set. Install valve on a new and full disposable can of Refrigerant-12, and

CAUTION: A considerable amount of refrigerant will collect in the high p ressure line, since some of this r e frigerant will have condensed into liquid refrigerant. Wrap the high pressure gauge fitting at the com pressor with a shop cloth before disconnecting the

Schrader valve from the gauge fitting, to prevent injury to personnel.

10. Using leak detector J-6084, check com plete system for leaks, as explained later under

"Checking For Leaks."

REFRIGERANT-12 DISPOSABLE CAN METHOD

After having depressurized, repaired (if n eces sary), and evacuating the refrigerant system , the system may be charged as follows when using Re frigerant-12 disposable cans:

1. Obtain five "one"pound cans of Refrigerant-

1 2

2. Mount four cans in J-6272-01 No. 4 Multi opener or attach J-6271 F its-A ll valve (single can repeat until three and one quarter "one-pound" cans of refrigerant have been used to charge the system . The system requires 3 -1 /4 pounds of re frigerant to have a proper charge. (Actually the net weight of refrigerant is 15 ozs. per can, there fore it will be necessary to use 3 -1 /2 to 4 cans. In no case should the system be charged with more than 3 -1 /4 pounds of refrigerant.)

If the J-6271 F its-A ll valve for single cans is available, complete charging as explained in 4a previously.

5. Close valves on manifold gauge set.

6. Operate engine at 2000 rpm with "TEMP" control knob at full cold position and blower con trol for high speed with "AIR" knob in "OUTSIDE" position.

NOTE: If air inlet temperature at the con denser is below 70°F., when this check is made, bubbles may appear even though the proper amount of refrigerant is in the system . Air inlet tem per ature must be 70°F., or above to make an accurate check. In no case should the system be charged with more than 3 -1 /4 pounds of refrigerant.

opener valve) on one can.

CAUTION: Make sure outlet valve on opener is closed (clockwise) before installing opener.

a. If the J-6272-01 No. 4 Multi-opener is used, raise locking lever, position four cans of refrig erant and force the locking lever down to secure

7. When refrigerant has been installed, con tinue to operate system and test for proper oper ation as outlined previously under "Performance

Testing."

8. When satisfied that air conditioning system is operating properly, stop engine, remove gauge set and replace protective caps on suction and d is charge fittings.

cans and at the same time puncture the top of the can to make it ready for charging.

b. If the J-6271 Fits-A ll valve is used, back off the valve from the can top retainer, slip the valve on to the can and turn the valve into the re tainer until tight. DO NOT open outlet valve during this operation as turning the valve into the retainer

CAUTION: A considerable amount of refrigerant will collect in the high pressure line, since some of this re frigerant will have condensed into liquid refrigerant. Wrap the high pressure fitting at the com pressor with a shop cloth before disconnecting the Schrader punctures the top of the can to make it ready for charging.

valve from the gauge fitting to prevent damage or injury to personnel.

3. Connect center flexible line of gauge set to the fitting on a can opener valve.

NOTE: If line at center gauge fitting has not been purged of air, loosen line at center fitting on

9. Using leak detector J-6084, check complete system for leaks as explained later under "Check ing For Leaks."

SERVICE STATION METHOD

The J-8393 Deluxe Portable Air Conditioner

Service Station supplies all evacuating and charg ing equipment assembled into a compact portable unit.

1. Be certain com pressor hand shut-off valves are closed to gauge fittings (counterclockwise).

2. Be certain all valves on charging station are closed.

3. Connect high pressure gauge line (with J-

9459 attached) to com pressor high pressure gauge fitting or to core remover Tool J-22132-01 (if used).

4. Turn high p ressure hand shut-off valve one turn clockwise, and high pressure control (2) one turn counterclockwise (open). Crack open low p res sure control (1) and allow refrigerant gas to h iss from low pressure gauge line for three seconds, then connect low p ressure gauge line to low p res sure gauge fitting on com pressor. Place J-5420 adapter on hose, then attach adapter to gauge fitting or fitting core remover tool.

Filling Charging Cylinder

1. Open control valve on refrigerant container.

2. Open valve on bottom of charging cylinder allowing refrigerant to enter cylinder.

3. Bleed charging cylinder to valve (behind control panel) only as required to allow refriger ant to enter cylinder. When refrigerant reaches desired charge level (3 -1 /4 lbs.), close valve at bottom of charging cylinder and be certain cylinder bleed valve is closed securely.

NOTE: While filling the cylinder, it will be necessary to close the bleed valve periodically to allow boiling to subside so that refrigerant level in the charging cylinder can be accurately read.

Charging The System

Using Service Station J-839 3

1. With charging station installed as previ ously described, remove low pressure gauge line at com pressor.

2. Crack open high (No. 2) and low (No. 1) pressure control valves on station, and allow r e frigerant gas to purge from system . Purge slowly enough so that oil does not escape from system along with refrigerant.

3. When refrigerant flow nearly stops, connect low p ressu re gauge line to com pressor.

4. Turn on vacuum pump and open vacuum con trol valve (No. 3).

5. With system purged as directed previously, run pump until 26-28 inches of vacuum is obtained.

Continue to run pump for 15 minutes after the s y s tem reaches 26-28 inches vacuum.

NOTE: In all evacuating procedures, the sp eci fication of 26-28 inches of mercury vacuum is used.

These figures are only attainable at or near sea level. For each 1000 feet above sea level where this operation is being performed, the specifica-

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tions should be lowered by 1 inch. Example: At

5000 ft. elevation, only 21 to 23 inches vacuum can normally be obtained.

6. If 26-28 inches vacuum (corrected to sea level) cannot be obtained, clo se vacuum control valve (No. 3) and shut off vacuum pump. Open r e frigerant control valve (No. 4) and allow some r e frigerant to enter system . Locate and repair all leaks.

7. After evacuating for 15 minutes, add 1/2 pound of refrigerant to system as described in step 6 previously. Purge this 1/2 pound and reevacuate for 15 to 30 minutes. This second evac uation is to be certain that as much contamination is removed from the system as possible.

8. Only after evacuating as directed previously system is ready for charging. Note reading on sight glass of charging cylinder. If it does not con tain a sufficient amount for a full charge, fill to the proper level.

9. Close low pressure valve on charging sta tion. Fully open station refrigerant control valve

(No. 4) and allow all liquid refrigerant to enter system . When full charge of refrigerant has enter ed system (3 -1 /4 lbs.), turn off refrigerant control valve (No. 4) and close both hand shut-off valves.

10. If full charge of refrigerant will not enter system , close high pressure control and refrig er ant control valves. Start engine and run at slow idle with com pressor operating. Crack refrigerant control valve (No. 4) and low pressure control on station. Watch low side gauge and keep gauge below

50 psi by regulating refrigerant control valve.

Closing valve will lower pressure. This is to pre vent liquid refrigerant from reaching the com p ressor while the com pressor is operating. When required charge has entered system , close refrig erant control valve and close low pressure control.

11. System is now charged and should be per formance tested before removing gauges.

AD D IN G REFRIGERANT

(SMALL AMOUNT)

The following procedure should be used in add ing sm all amounts of refrigerant that may have been lost by leaks, or while opening system for servicing the com pressor. Before adding refriger ant to replace that lost by leaks, check com pressor oil level and add oil if necessary. See'Adding Oil" later. NOTE: This procedure will only apply if the air inlet temperature is above 70°F., at the con denser.

1. Remove caps from com pressor gauge fit tings. Attach gauge set to gauge fittings, making sure Schrader adapter is between low pressure gauge hose and suction gauge fitting, and between high p ressure gauge hose and discharge gauge fitting.

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2. Start engine, turn air conditioning tem per ature control to full cold position, blower control for high speed, and also move "AIR" lever to "OUT

SIDE." Operate for ten minutes at 2000 rpm to stabilize system .

3. Observe the refrigerant through the sight glass of the receiver-dehydrator with the system operating, to see if there are any bubbles evident.

a. If no bubbles are evident, then bleed system slowly through the discharge valve until bubbles appear in the receiver-dehydrator right glass. Add one pound of refrigerant as explained under "Charg ing The System." b. If bubbles are visible in the receiver-d e hydrator sight glass with the "TEMP" control knob at the full cold position and the blower at high speed, it indicates partial or complete plug in a line, or a shortage of refrigerant, or both. Cor rect condition. Add refrigerant as explained below until the sight glass clears, then add another one pound of refrigerant.

4. Attach flexible hose from center fitting of gauge set loosely to refrigerant drum or on d is posable can valves. Open high and low pressure valves on the gauge set slightly to purge pressure gauge lines of air. Tighten fitting of refrigerant drum or can, when satisfied that all air has been removed from gauge lines. Close (clockwise) both hand shut-off valves of gauge set.

5. Partially charge system .

a. Refrigerant-12 Drum Method.

(1) Place pail containing hot water that does not have a temperature exceeding 125°F., on scales, place refrigerant drum in pan containing water, note weight, and only open low p ressure valve on gauge set.

(2) Start engine, move "Temp" control knob to full cold position, and place blower control for high speed. Operate engine for ten min utes at 2000 rpm to stabilize system .

(3) With com pressor operating, slowly open valve on refrigerant drum and allow re frigerant to flow into system (through man ifold gauge set) until liquid indicator clears up and immediately shut off valve at gauge set or on refrigerant drum. Check weight of refrigerant drum and pail of water. Then slowly open valve on gauge set (or refrig erant drum) and add one more pound of refrigerant. Note total amount of refriger ant added.

b. R efrigerant-12 Disposable Can Method (15 oz. per can).

(1) Make sure the outlet valve on the J-6271

Fits-A ll valve is fully clockwise and at tach the J-6271 to a "one pound" can of r e frigerant as follows: Back off the valve from the top of the retainer, slip the valve onto the can and turn the valve into the r e tainer until tight. DO NOT accidentally open outlet valve during this operation as turning the valve into the retainer punc tures the top of the can to make it ready for charging.

(2) Connect center flexible line of gauge set to the fitting on the valve.

(3) Start engine, place "TEMP" control knob to full cold position and blower control for high speed with "AIR" knob in "OUTSIDE" position. Operate engine for ten minutes at

2000 rpm to stabilize system .

(4) With com pressor operating, slowly open valve on refrigerant can and allow refrig erant to flow into system (through manifold gauge set) until liquid indicator clears up and immediately shut off valve at gauge set and on refrigerant can. Check weight of can and valve assembly and record.

(5) Add an additional one pound of refrigerant by adding refrigerant from the can just weighed until can is empty. Attach another can and add refrigerant until can and valve assembly weigh the same as recorded.

6. Close valves at refrigerant drum or can.

7. Test for leaks and make operational check of system as outlined under "Performance Testing."

CHECKING COMPRESSOR OIL LEVEL

A N D AD D IN G OIL

The refrigeration system with the six-cylinder axial com pressor requires 11 fluid ozs. of 525 viscosity oil. After the system has been operated, oil circulates throughout the system with the r e frigerant. Hence, while the system is running, oil is leaving the com pressor with the high pressure gas and is returning to the com pressor with the suction gas.

NOTE: The oil level in the com pressor should not be checked as a matter of course, such as is done to the truck engine crankcase.

In general, the com pressor oil level should be questioned only in ca ses where there is evidence of a major lo ss of system oil such as:

1. Broken hose or severe hose fitting leak.

2. Oil sprayed in copious amounts under the hood due to a badly leaking com pressor seal(s).

3. Collision damage to refrigeration system components.

REPLACING REFRIGERATION SYSTEM

COMPONENTS OTHER THAN COMPRESSOR

When refrigerant system components other than the com pressor are replaced, the com pressor must also be removed and oil drained from the

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com pressor. The amount of oil to put back into the com pressor is found as follows: DO NOT add any more oil than is necessary or maximum cooling will be reduced.

1. Remove the com pressor and place in a hor izontal position with the com pressor drain plug downward, drain com pressor in an empty grad uated bottle, measure the amount of oil and discard this oil.

2. If the quantity of oil measured is more than

4 fluid ozs., replace into the com pressor the same amount of clean oil as the oil drained, plus the following amount for the refrigeration system com ponent being changed.

a. Evaporator - 3 fluid ozs.

b. Condenser - 1 fluid oz.

c. Receiver-dehydrator assembly - 1 fluid oz.

Neglect any fluid oil coating lo ss in case of line change.

3. If the oil quantity drained from the com p ressor is le s s than 4 ozs., replace into the com p ressor 6 fluid ozs. of clean oil, plus the amount shown previously for the respective component replacements.

4. Replace com pressor and system compon ents.

5. Evacuate, charge and perform operational test.

CHECKING FOR LEAKS

ASSEMBLING AND LIGHTING THE UNIT

1. Remove dust cap from cylinder.

2. Close valve knob on detector unit.

3. Thread detector unit onto top of fuel cylin der. Tighten finger tight.

4. Attach search hose assembly to detector unit (fig. 13).

5. Open control valve until slight hiss of gas is heard, then light gas at opening in chimney.

Figure 13— Checking for Refrigerant Leak

Leak detector J-6084 as used for checking for leaks in system , is a gas-operated torch-type leak detector using a replaceable cylinder.

inspirated or the reaction plate is dirty. Insuffic ient air may be caused by:

1. Obstructed or partially collapsed suction tube.

2. Dirt or foreign substance in burner tube.

3. Dirty or partially clogged orifice.

Blowing air through the suction tube and back through the detector will usually clear dirt or foreign matter. If a yellow flame is caused by dirty reaction plate, allow the flame to burn for several minutes. This will usually burn the plate clean. If an oxide film appears on the reaction plate from continued use, it will reduce the se n si tivity of the detector. This may be remedied by removing the plate and scraping the surface gently with a knife.

CAUTION: Do not use lighted de tector in any place where combustible or explosive gases, dusts or vapors may be present.

6. Adjust the flame until the desired volume is obtained. A pale blue flame approximately 3 /8 ” above the reaction plate is best for detecting leaks.

NOTE: The reaction plate will be heated to a cherry red.

CORRECTION FOR YELLOW FLAME

If the flame is yellow, insufficient air is being

TO CLEAN ORIFICE

1. Never attempt to clean orifice by passing anything through the hole.

2. Unthread burner head assembly from burner tube. This will expose orifice block which is in serted into the end of the tube.

3. Remove orifice block from tube.

4. Reverse orifice block and replace against burner tube; thread burner head onto burner tube

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(hand tight), then open valve quickly, admitting several short blasts.

5. To reassem ble: Unthread burner head, in sert orifice block into burner tube, and thread burner head onto burner tube with a wrench to form a gas-tight joint.

Replacement parts can be obtained from Kent -

Moore Corp., Detroit, Michigan.

CHECKING FOR REFRIGERANT LEAKS

After the leak detector flame is adjusted, check for refrigerant leaks in an area having a minimum amount of air flow in the following man ner (see fig. 13):

Explore for leaks by moving end of sampling tube around all connections and points where a leak may be. Check around bottom of connections, since Refrigerant-12 is heavier than air and will, therefore, be more apparent at bottom of fitting.

The color of the flame will turn to a yellowgreen when a sm all leak is detected. Large leaks will be indicated by a change in color to brilliant blue or purple. When the suction hose is moved away from the leak the flame will clear to an al most co lo rless pale blue again.

a closure plate which can be improvised and in stalled as shown.

If the system has been or can be operated for more than two minutes, circulation of oil from the com pressor to other components of the system will require adjustment of the oil charge in the new com pressor as explained previously, under "Re placing Components Other Than Compressor."

After draining and measuring the oil from the crankcase, the amount that has migrated to other parts of the system, can be determined by subtract ing the amount drained from the original oil charge of 11 fluid ozs. The amount of oil equal to this lo ss shall be drained from the new com pressor a ssem bly before it is installed.

REPLACING AN OPERABLE COMPRESSOR

After idling com pressor (on vehicle) to be r e placed for 10 minutes at 1500-2000 engine rpm, at maximum refrigeration and blower at high speed:

DO NOT add any more oil to the com pressor than is necessary or maximum cooling will be reduced.

CAUTION: Do not breathe the fumes and black smoke that are produced if the leak is a big one. They are poison ous! Any time an open flame is used near a vehicle there is a certain amount of danger. Although the torch flame is sm all and well protected, it is recom mended that fire extinguisher be close at hand for any emergency that might arise.

1. Compressor replaced with service com p ressor assem bly.

a. Remove com pressor and place in a hori zontal position with drain plug downward, drain com pressor, measure quantity of oil drained and then discard it.

b. Drain oil from replacement com pressor and save it.

c. (1) If amount of oil drained in'^ "p reviou s ly is more than 4 o zs., place into the new com pressor the same amount of oil drained from the replaced com pressor.

(2) If amount of oil drained in "a"previous ly is le s s than 4 ozs., place 6 ozs. of oil in the replacement com pressor.

d. Install com pressor.

LIQUID-TYPE LEAK DETECTORS

There are a number of fittings and places throughout the air conditioning unit where a liquid leak detector solution may be used to pinpoint leaks.

By merely applying solution to the area with the swab that is usually attached to the bottle cap, bub bles will form within seconds if there is a leak.

For confined areas, such as sections of the evaporator and condenser, the torch-type detector is the only practical kind which should be used for determining leaks.

2. Compressor replaced with a field repaired

(overhauled) com pressor.

a. add one extra oz. of oil. (More oil is retained in a drained com pressor than one that has been rebuilt.)

Proceed as in step 1 previously, and then

ELECTRONIC LEAK DETECTOR frigerant leaks is also available. Instructions for operation of this type detector are supplied with the unit.

An electronic leak detector for detecting re

REPLACING COMPRESSOR

The com pressor removed must be closed im mediately. See lower View of figure 14 which shows

REPLACING AN INOPERATIVE COMPRESSOR

In the case when it is not possible to idle the com pressor to be replaced to effect oil return to it the following will apply. DO NOT add any more oil than is necessary as maximum cooling will be reduced.

1. Remove com pressor from vehicle, drain and measure the oil.

2. If amount drained in step 1 above is more than 1-1 /2 fluid ozs., subtract this amount drained from the original oil charge of 11 ozs., to obtain

"oil loss." Take the new com pressor assembly and drain from it the amount of "oil loss" above; provided the refrigeration system shows no evi

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dence of a major leak, indicating that little or no oil has been lost from the system . (Minor leak in dicating very slow leakage.)

3. If oil drained in step 1 previously contains any foreign material such as chips, or there is evidence of moisture in the system , replace the receiver-dehydrator assem bly and flush all com ponent parts, or replace if necessary. After flush ing refrigeration system in this manner, the full oil charge should be left in the new service com p ressor or 11 ozs., installed in an overhauled or repaired com pressor.

COMPRESSOR REMOVAL

1. Connect the high and low pressure gauge lines from the gauge set to the respective connec tions on the old com pressor on the vehicle. Be sure valves on gauge set are fully clockwise to close gauge set to center fitting, and that a J-5420 or J-9459 Schrader adapter is between low pressure hose and suction gauge fitting, and also at the d is charge gauge fitting.

2. Remove the flare nut from center connec tion on gauge manifold or the plug in the gauge line attached to the center connection. Wrap the line at the outlet with a cloth to protect persons and v e hicle surfaces from oil or refrigerant.

3. Slowly depressurize refrigeration system as instructed previously under "Depressurizing The

System."

4. While system is depressurizing, remove (if desired) clutch assembly and coil from old com p resso r. If parts are not oil soaked and are in good condition, lay them aside on a clean surface as they may be installed on the new com pressor.

5. After the system is completely depressur ized, very slowly loosen screw which retains com p ressor fittings assembly to com pressor (see fig.

14). As screw is being loosened, work fittings a s sembly back and forth to break seal and carefully bleed off any remaining pressure.

CAUTION: High pressure may still exist at the discharge fitting. If this p ressure is released too rapidly there will be a considerable discharge of re frigerant and oil.

6. When all pressure has been relieved, r e move fittings assembly and O-ring sea ls.

7. Immediately cover com pressor openings.

A simple way is with a plate (sim ilar to the one on new com pressor) which can be attached with fittings seal. See lower portion of figure 14.

8. Disconnect com pressor clutch coil wire and bolts, front and rear.

assem bly screw , using the O-rings to provide a remove com pressor mounting plates to bracket

3 / 1 6 " TO 1 / 4 " STEEL ST O C K

Ve -24

O -R IN G SEALS

3/4,;B F

: / 'L A I j

IM P R O V IS E D C L O S U R E PLATE IN S T A L L E D T

-3 3 1 3

Figure 14— Compressor Fittings Installation

9. If there is any possibility that broken parts from the com pressor got into the discharge line or the condenser, all refrigeration system parts should be cleaned and a new receiver-dehydrator assem bly should be installed.

10. Drain all oil from com pressor just remov ed in a clean dry container and replace com pressor drain plug screw. Measure amount of oil drained.

See "Checking Compressor Oil Level and Adding

Oil" previously.

COMPRESSOR INSTALLATION

NOTE: Before installing a new com pressor, rotate com pressor shaft four or five tim es. This perm its proper lubrication of com pressor seal over all its surface. Before com pressor clutch is mounted to the new com pressor, wipe the front face of the com pressor thoroughly with a clean dry cloth and, if necessary, clean front of com pressor with a solvent to remove any excess oil. Cleaning com pressor in this manner will prevent any oil

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Figure 15— Hose and Clam p Properly Installed

from being thrown onto the clutch surfaces which would cause slippage and eventual clutch failure.

1. Stamp refrigerant charge of the refrigerant system on new com pressor in space on plate pro vided for this information.

NOTE: Follow procedure for replacing oil in new com pressor explained previously under "Re moving Malfunctioning Compressor and Installing

New Compressor."

2. Install new com pressor to engine, leaving com pressor fittings opening cover plate on the com pressor.

3. Remove cover plate over com pressor open ings very slowly to bleed off pressure.

CAUTION: New com pressors are charged with a mixture of nitrogen and

R efrigerant-12 and 11 fluid ozs. of

Frigidaire - 525 viscosity oil. If the cover is removed too rapidly, the oil w ill be blown out violently with the sudden release of pressure.

4. Install coil and clutch parts if not already installed.

5. Evacuate, charge and make a test of s y s tem as explained previously under "Performance

Testing."

SERVICING LEAKING SEALS

A N D HOSES

When refrigeration system components other than the com pressor are replaced, the com pressor must also be removed and oil drained from the com pressor if oil was sprayed in copious amounts due to severe leaks or broken lines. DO NOT add any more oil than is necessary or maximum cooling will be reduced. See "Checking Compressor Oil Level and Adding Oil" previously.

1. Replace leaking seal, hose, or line. See figure 15 for proper positioning of hose and hose clamp.

NOTE: The initial clamp screw torque is 25 to 32 inch-pounds. After short period of time, torque may drop off as low as 10 inch-pounds.

Final torque the clamp screw to 20 - 25 inchpounds.

2. Evacuate, charge and make performance test.

CONDENSER ASSEMBLY

REPLACEMENT

NOTE: When refrigeration system components other than the com pressor are replaced, com pres sor must also be removed and oil drained from com pressor if oil was sprayed in copious amounts.

See "Checking Compressor Oil Level and Adding

Oil" explained previously.

1. D epressurize the refrigeration system .

2. Remove radiator grille.

3. Remove com pressor discharge hose clamp at condenser inlet.

4. Remove hose from condenser inlet. Plug openings.

5. Disconnect hex nut connection at condenser outlet, then plug openings.

6. Remove four condenser assem bly retaining bolts and remove condenser.

7. Replace by reversing the above procedures, using a new rubber O-ring seal well lubricated with clean com pressor oil at line connection.

8. Evacuate and charge system .

9. Make a performance test.

RECEIVER-DEHYDRATOR ASSEMBLY

REPLACEMENT

NOTE: When refrigeration system components other than com pressor are replaced, the com pres sor must also be removed and oil drained from com pressor if oil was sprayed in copious amounts due to leaks or collision damage to receiver-dehydrator. See "Checking Compressor Oil Level and Adding Oil" explained previously.

1. D epressurize the system .

2. Disconnect inlet and outlet connections of receiver at receiver-dehydrator assembly and plug openings.

3. Loosen the receiver-dehydrator assembly clamp screw s and remove assem bly.

4. Replace the receiver-dehydrator assem bly by reversing the previous procedures, using new rubber O-ring seal, well lubricated with clean com pressor oil, at line connection.

5. Evacuate complete system .

6. Charge complete system .

7. Make performance test.

EXPANSION VALVE REPLACEMENT

NOTE: When refrigeration system components other than the com pressor are replaced, the com pressor must also be removed and oil drained from the com pressor if oil was sprayed in copious amounts due to leaks or collision damage to valve.

See "Checking Compressor Oil Level and Adding

Oil" explained previously.

1. D epressurize the system .

2. Drain the cooling system .

3. Remove the evaporator and heater core unit from under dash as directed later under "Evap orator, Heater Core and Blower Replacement."

4. Remove the heater core from unit after r e moving unit lower cover.

5. Disconnect expansion valve capillary tube bulb at evaporator outlet pipe.

6. Disconnect expansion valve equalizer line at suction throttling valve.

7. Disconnect thermostatic expansion valve inlet and outlet connections carefully, as some pressure may still exist, and plug openings.

8. Separate unit upper cover, then lift out the coil assem bly. Remove expansion valve, noting amount of oil that drains from fittings, and plug openings.

9. Replace by reversing the previous pro cedure, using new rubber O-ring seals, well lub ricated with clean com pressor oil, at each fitting connection.

10. Evacuate and charge system .

11. Make a performance test.

SUCTION THROTTLING VALVE

REPLACEMENT

See "Checking Compressor Oil Level and Adding

Oil" explained previously.

1. D epressurize the refrigeration system .

2. Disconnect expansion valve equalizer line at the suction throttling valve plug openings.

3. Disconnect suction valve to com pressor hose elbow.

4. Disconnect suction valve from evaporator outlet. Remove two bracket attaching cap screw s, then remove valve.

5. Replace the suction throttling valve by re versing the above procedures, using new rubber

O-ring sea ls, w ell lubricated with com pressor oil, at each connection.

6. Evacuate complete system .

7. Charge complete system .

8. Make a performance test.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

EVAPORATOR HEATER CORE

ASSEMBLY REPLACEMENT

See "Checking Compressor Oil Level and Adding

Oil" explained previously.

1. D epressurize the system .

2. Drain coolant.

3. Disconnect heater hoses at cowl.

4. Disconnect air distributor tube from blower.

5. Disconnect all heating and cooling control cables. Also, disconnect blower motor ground wire at dash.

6. Disconnect refrigerant hoses from unit.

7. At base of unit, pull the drain tube from floor opening.

8. Remove four screw s which attach unit to right side cowl. There are two at the top and bot tom of unit.

9. At front of cowl remove single attaching bolt. Carefully remove unit from cab.

10. Replace evaporator unit and blower motor duct assembly by reversing previous procedures.

11. Evacuate and charge system .

12. Make a performance test.

COLLISION SERVICE

The severity and circum stances of the collision will determine the extent of repair required. Good judgment must be used in deciding what steps are necessary to put the system back into operation.

Each part of the system must be carefully in spected. No attempt should be made to straighten kinked tubes or repair any bent or broken units.

Check especially for cracks at soldered connections.

REFRIGERATION SYSTEM

OPEN TO ATMOSPHERE

Broken tubes or units will allow air, moisture and dirt to enter. These parts should be sealed as soon as possible until such time as they are r e placed.

If the system is open for more than 15 or 20 minutes (depending on humidity), the receiverdehydrator assembly will absorb an excessive amount of moisture and should be replaced, and each component of the system should be cleaned with dry nitrogen and flushed with liquid refriger ant to remove dirt and moisture.

FLUSHING SYSTEM

Flushing can be accomplished by connecting a refrigerant drum to the unit to be flushed and then turning the drum upside down and opening the drum

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

B L O W E R M O T O R

W IR IN G C O N N E C T IO N

Figure 1

— Blower Motor W iring Connection

shut-off valve to force refrigerant through the unit.

The unit should be supported so that the refriger ant passing through it will be directed into an area where -21.7 F., will do no damage.

CAUTION: Remember that when liquid refrigerant is released from the drum into an area where atmospheric pressure exists, its temperature will immediately drop to -21.7°F ._________

In order to keep the expansion valve open when flushing the evaporator, the expansion valve bulb must be detached from the evaporator outlet tube.

INSPECTING COMPRESSOR

If there is no visible evidence of damage, ro tate com pressor shaft to test for normal reaction.

A quick check for broken reed valves is to turn com pressor shaft (using box end wrench on com pressor shaft nut) and check for resistance when turning the shaft. An irregular resistance force will be felt as each of the pistons goes over top center for each revolution of the crankshaft. If this pattern is not felt, it indicates one or mere broken com pressor reed valves and the com pressor must be repaired.

Inspect oil for foreign material which would indicate internal damage to the com pressor. If no foreign matter is found in oil, com pressor can be used. Flush entire refrigeration system with r e frigerant, drain oil from com pressor and pour in

11 oz. of new Frigidaire 525 viscosity oil.

BLOWER MOTOR REPLACEMENT

1. Disconnect motor ground wire from dash panel flange.

2. Pull motor switch lead at quick-disconnect terminal (fig. 16).

3. For access to blower mounting screw s, pull back the cellular insulating material at motor hose plate. Remove screw s, then pull motor a s sembly from shroud. Rotate hose plate so that cut off is at the top before removing.

4. Install the motor unit by reversing the previous procedures.

NOTE: After installing attaching screw s, seal down the insulating material using a light coat of rubber cement.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

SPECIFICATIONS

Refrigerant Capacity................................................................... 3 lbs. 4 oz.

Refrigerant Oil Capacity (entire syste m )......................................... 11 oz.

Compressor Clutch Coil

Current (maximum dem and)...................................3.2 Am ps.'at 12v.

Resistance............................................................... 3.85 Ohms, at 80°F.

Compressor Belt Tension (Using Tension Gauge)

New................................................................................... 130 to 140 lbs.

Used.................................................................................. 100 to 105 lbs.

Circuit B reaker................................................................................. 30 Amp.

Heater and AC Blower Fuse...........................................................15 Amp.

Evacuation Period (@ 26 to 28 in. of v a c .)......................... 15 to 30 min.

Refer to "Insufficient Cooling Diagnosis Chart" on following two pages.

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

Inspect sy stem for visual defe c ts . Check airt tem perature.

HIGH AIR

TEMPERATURE

Check sight g la s s .

NORMAL AIR

TEMPERATURE

Check for air leaks at cab doors, windows, cowl, or unit drain hose.

Check blower operation.

AIR TEMPERATURE

VARIES

If 7° F. variation at nozzle exist, .

replace suction throttling valve.

See Note "A." i

BLOWER NOT

OPERATING

Check for blown fuse, defective blower switch, broken w ire, loose ground w ire, defective blower motor.

NORMAL BLOWER

OPERATION

Check for loose h oses, restriction or leakage in air ducts, partially closed air outlet valve or clogged evaporator core.

---

BLOCKED

EVAPORATOR

If iced, check for low evaporator p ressu re.

Adjust suction throttling valve. If dirty, rem ove using vacuum cleaner hose.

NO FOAMING

H L _

FOAMING

Check evaporator p ressu re.

System is probably low on refrigerant. Check for leak s, repair and add refrigerant. If foaming still occu rs check for restriction in refrigerant system between condenser and *sight g la s s . See Note "C."

NORMAL

EVAPORATOR PRESSURE

C h e c k - com p ressor d ischarge p r e ssu r e .

COMPRESSOR HIGH

DISCHARGE PRESSURE

Check for air in sy stem , e x ce ss refrigerant, restr ictio n in con denser refrigeran t tubes or air fin s. See Note "B."

LOW

EVAPORATOR PRESSURE

If ice is blocking evaporator, adjust suction throttling valve. If cooling rem ains low, follow diagnosis under

"Normal Evaporator P ressure." If valve does not respond to adjust ment, h oses to and from valve and suction hose may be restricted or valve may be defective.

COMPRESSOR LOW

DISCHARGE PRESSURE

RESPONDS TO

ADJUST MENT

Check for low refrigerant, r e s tr ic tion in liquid lin e, plugged or de fectiv e expansion valve, or defective co m p resso r or suction throttling v alve. See Note "C."

NORMAL

EVAPORATOR PRESSURE

If cooling rem ains low after p ressu re is normal, check the discharge p ressu re.

COMPRESSOR NORMAL

DISCHARGE PRESSURE

Check for proper se a l around evaporator core and tem p er ature door.

EVAPORATOR PRESSURE

REMAINS THE SAME

Valve is stuck open and too much r efrig erant is entering evaporator. Replace expansion valve. See Note "E."

HIGH

EVAPORATOR PRESSURE

Adjust to normal evaporator p ressu re.

If unable to adjust-

NO RESPONSE

TO ADJUSTMENT

Repair or replace su c tion throttling valve.

HIGH

EVAPORATOR PRESSURE

Check installation of capillary bulb. If bui» is secured properly and p r e ssu re is high, rem ove bulb from pipe. See Note "D."

EVAPORATOR PRESSURE

INCREASES

Check for clutch slippage, belt slippage and listen for unusual n o ise s.

G M C S E R V I C E M A N U A L

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AIR CONDITIONING

INSUFFICIENT CO O LIN G D IA G N O SIS CHART NOTES

(Used in Conjunction With Chart on Opposite Page)

NOTE “A ”

Suction throttling valve piston sticking; if stuck closed, no cooling due to lack of flow of refrig er ant through the evaporator core; if stuck open no controlled cooling and cab may get too cold - evap orator may freeze. Replace valve.

as a possibility of a restriction in the high p r e s sure side of the refrigeration system . The system will have high p ressure control more frequently under this condition.

NOTE “B”

System with ex cess discharge p ressu re should be slowly depressurized at the receiver-dehydrator inlet connection, observing the behavior of the high p ressu re gauge indicator.

1. If discharge p ressu re drops rapidly, it in dicates air (with the possibility of moisture) in the system . When p ressu re drop lev els but still indi cates in ex cess of specifications shown in the

OPERATIONAL TEST DATA CHART, slowly bleed system until bubbles appear in the sight g lass and stop. Add refrigerant until bubbles clear, then add one (1) pound of refrigerant. Recheck operational p ressu re s. If discharge p ressu re still rem ains above specifications and the suction pressure is slightly above normal, then a restriction exists in the high pressure side of the system .

Install gauge set and bleed off refrigerant from com pressor suction and discharge side for 20 s e c onds. After 20 seconds clo se valves and recheck operating p ressu res. Repeat until discharge p res sure is normal. Check sight glass; if bubbles ap pear it indicates that air was in system . Charge with refrigerant as follows: 2000 engine rpm,

"OUTSIDE” air, "HI” blower and maximum cooling.

Add refrigerant until sight g la ss clea rs, then add

1 pound additional.

NOTE “C”

Check for presence of bubbles or foam. If bubbles or foam is noted, charge with refrigerant as fo l lows: 2000 engine rpm, "OUTSIDE” air, ”HI” blower and Maximum Cooling. Add refrigerant until sight g lass clea rs, then add an additional 1 pound.

2. If discharge p ressu re drops slowly, it in dicates ex cessive refrigerant. If p ressure drops to specifications and sight gla ss rem ains clear, stop depressurizing and recheck operational p ressu res.

If p ressu res are satisfactory, d epressurize until bubbles appear in the sight g la ss, stop d epressur izing, then add one (1) pound of refrigerant. Re check operational p ressu res.

3. If discharge p ressu re rem ains high after depressurizing the system , continue d ep ressu riz- ing until bubbles appear in the sight g la ss. If su e- tion p ressu res also remain high, then the suction throttling valve may require adjustment, as w ell

NOTE: It is not unusual for bubbling to occur on minimum cooling and "LO” blower in mild weather even with a fully charged system .

NOTE “D ”

Remove insulation and inspect for clearance be tween tube and bulb. If gap exists, move bulb to establish contact, reclamp and reinsulate.

NOTE “ E”

Remove expansion valve and inspect internal screen for foreign objects. If present, there is a p o ssibility seat is being held open. Install new expansion valve; if condition is corrected, discard the valve removed.

Refer to "Refrigerant Line Connections Torque Specifications" chart on following page.

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AIR CONDITIONING

G M C S E R V I C E M A N U A L

REFRIGERANT LINE CONNECTIONS

TORQUE SPECIFICATIONS

OUTSIDE DIAMETER

OF METAL TUBING

(INCHES)

1/4

3/8

1/2

5/8

3/4

TORQUE FT.-LBS.

(STEEL)

10 - 15

30 - 35

TORQUE FT.-LBS.

ALUMINUM OR COPPER

5 - 7

11 - 13

15 - 20

21 - 27

28 - 33

NOTE: Steel torques to be used only when tube is mated ste e l-to -ste e l. If steel connection is made to aluminum or copper tube fittings, use appropriate "ALUM

INUM OR COPPER" torque specifications.

G M C S E R V I C E M A N U A L

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SECTION 2

f y t i a m

GENERAL

This section includes general instructions for checking frame alignment and recommendations for frame repair and reinforcement. It must be pointed out that the information is provided to a s s is t in the repair or reinforcement of fram es, u s ing the most desirable p ractices. This section was prepared to aid competent personnel in the repair or reinforcem ent of fram es.

Channel-type frame (fig. 1) construction with riveted crossm em bers is used on all models.

Frame side rails are usually of S.A.E. 1023 steel.

Figure 1 illustrates typical arrangement of frame mounted suspension and body attaching brackets.

In the event the vehicle is damaged in a col lision, carefully check for proper frame alignment in addition to steering geometry and axle alignment.

FRAME ALIG NM ENT CHECK

The most convenient way tocheckfram e align ment, particularly when the cab or body is on the ch assis, is to select various corresponding points of measurement on the outside of each side rail and then, by use of a plumb bob, transfer these points to a layout on a level floor. (NOTE: Flange width may vary - 3 /1 6 M.) The selection of these points is an arbitrary matter; however, it is an important factor to remember that for each point selected on the left side rail, a corresponding point

must be used on the right rail. The illustration

(fig. 1) is used merely to serve as a guide in the selection of checking points "M."

In order to obtain reliable results, checking must be done thoroughly and accurately. After all corresponding points have been carefully transfer red from the vehicle frame to the floor layout, move the vehicle away from the layout andproceed as directed in the following steps:

NOTE: Key letters in the following text refer to figure 1.

1. Check the fram e width at front and rear ends using the corresponding marks on the floor.

If widths correspond to specifications (refer to

"Specifications"), draw centerline full length of vehicle layout bisecting points indicating front width (WF) and rear width (WR). If frame widths are not correct, layout centerline as directed in

Step 4.

2. With centerline properly laid out, measure the distance perpendicular from the centerline to corresponding points on each side over the entire length of the ch a ssis. If the frame is in proper alignment, measurement should not vary more than an 1/8" at any corresponding point.

3. Where improper alignment is encountered, the point at which the frame is sprung may be lo cated by measuring pairs of corresponding diag onals marked "A" or "B." If the length of each pair of diagonals ("A" or "B") are within 1/8" and the intersection point of the diagonal pairs is within

1/8" of the centerline, the portion of the fram e

W F

T-1844

Figure 1— Typical Fram e A lig n m e n t Points

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FRAME

G M C S E R V I C E M A N U A L included between the points of measurement may be considered to be in proper alignment. Variation of more than a 1/8" indicates misalignment.

4. If the fram e centerline cannot be determ in ed by method indicated in Step 1, the centerline may be established by drawing a line through the intersection points of equal pairs of diagonals or from the intersection of equal diagonals through the midpoint of either correctly established front or rear fram e widths. This method is usually r e quired when front or rear end damage is incurred as the result of a collision .

5. After it has been determined that the fram e is properly aligned, axle alignment with respect to the fram e can be checked as directed below: (See fig. 1.) a. Front axle alignment with respect to the frame is correct if ”FR” equals "FL" and "DR" equals "DL." This can be concluded if both front and rear frame ends have been established as properly aligned (Step 3).

b. Rear axle alignment with respect to the fram e is correct if "ER" equals "EL" and "GR" equals "GL." NOTE: Alignment may appear to be off if rear ends of fram e rails are not cut-off evenly when reducing cab to end of fram e (CE) for specific operations.

Straightening Fram es

The practice of straightening fram es should not be attempted by inexperienced personnel, as more damage can result from improper methods.

Internal s tr e s s e s can be introduced into the m ater ial by improper fram e straightening. For this reason the following restrictions should be ad hered to completely:

1. Fram e straightening should be attempted only by experienced personnel.

2. Heat may be applied to S.A.E. 1023 steel only by competent personnel. The material temp erature should not exceed 1200° (dull red glow).

It must be strongly pointed out that ex cessiv e heat w ill damage the material structure characteristics of the frame rail.

3. Frame members which are bent or buckled sufficiently to show strains or cracks after straight ening should be replaced.

IDENTIFICATION OF MATERIAL

The importance of properly identifying the base rail before attempting to straighten or repair cannot be overemphasized. The results of incor rect welding or straightening methods may cause more damage to the fram e than was originally ex perienced. Frame str e ss concentrations resulting from improper welding methods are a major cause of future frame failu res.

The standard models as quoted in the GMC

Data Book describe the physical dimension of the frame rail and specify the type of material used.

However, due to the number of RPO's and Special

Quotations available on most models, the Data

Book inspection is not always a valid identification.

The material can be identified by the type of cut-out in the frame side rail at the front axle center line.

Any reinforcem ents added must be of the same or better material than the base frame rail. This would permit the use of S.A.E. 950 reinforcem ents on S.A.E. 1023 base rails.

Max. Bending Moment

T-2993

Figure 2 — Fram e B e n d in g M o m e n t (Typical Tractor)

Listed under "Specifications” at the end of this section are selected s iz e s of welding elec trodes for use in repairing frame side ra ils. R ec ommended current ranges for various electrodes are given when performing either flat or overhead welding. When welding SAE-1023 steel, type E-7011 electrodes are recommended with type E-7016 suggested as an alternate. To ensure permanent fram e repairs, correct material identification, proper electrode selection, and professional weld ing techniques are required.

A N A LY Z IN G FAILURE CAUSES

This analysis is not intended to cover the cau ses of all possib le frame problems; however, it should be of valuable assistan ce in preparing com plete, concise reports.

The purpose of this discussion is to emphasize the fact that frame failure don't just happen, there must be a cause or reason. An example of this would be a vehicle involved in a collision. The rea son for failure in this case is apparent; however, other failures can be encountered where the rea sons are not so apparent.

Fram e failu res can be cla ssified by three types:

(1) Collisions

(2) E xcessive bending moment

(3) Localized s tr e ss concentration

Failures caused by collision should be repair ed, using proper methods and reinforcem ents, where necessary.

G M C S E R V I C E M A N U A L

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FRAME

E xcessive bending moment failures are cau s ed by overload, improper weight distribution, or misapplication of the vehicle. E xcessive bending moment failure will occur at different areas on various types of vehicles; therefore, for easier understanding, the effects of excessive bending mo ments will be discussed by type of vehicle.

TRACTORS

The maximum bending moment of vehicles used in tractor service is in the area of the leading edge of fifth wheel (fig. 2). Failures maybe caused by overload, ex cessiv e fifth wheel setting, e x c e s sive fifth wheel heights, poor fifth wheel in stall ations, sev ere operating conditions and severe braking operations (inertia of certain loads), which induce ex cessiv e bending moments in the fram e.

These failures will start at edge of lower flanges and p rogress across the fram e flange and up the web section of the fram e rail. Instances may occur where upper or lower fram e flanges buckle.

STRAIGHT TRUCKS

The maximum bending moment occurs in the area near the rear of the cab on vehicles having van or platform bodies (fig. 3). Failures may be caused by overload or can occur when loads are dispersed in diminishing quantities allowing the balance of a load to remain in the extreme front of the body.

In both tractor and straight truck operation the highest tensile s tr e s s is applied to the bottom side of the lower frame flange. However, it must

Figure 3 — Fram e B e n d in g M o m e n t (Typical Straight Truck)

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FRAME

G M C S E R V I C E M A N U A L be pointed out that dump trucks, as an example, when operated with the box in a raised position causes the center of gravity of the load to move behind the rear axle centerline resulting in a change of maximum tensile str ess location from the bottom of the lower flanges to the top of the upper flanges (fig. 4). This information can be very useful when examining cracks on vehicles used in dump service, as it would appear that the vehicle has been operated at excessive speed over rough terrain while spreading with the dump box in the raised position or with too long a dump box for wheelbase selected.

Localized str e ss concentration failures may be the result of bending moment str esses; how ever, it must be pointed out that the str ess lev els would not be high enough to cause any difficulty without localized str e ss concentration points. These localized str e ss concentrationpoints may be caused by poor body or fifth wheel mountings, special equipment or accessory installation, improper welding or welding methods, improper reinforce ments, loose bolts or rivets and defective material.

They may also occur as a result of high bending loads, coupled with severe torsional loads as may be found in off-road service.

The proper installation of fifth wheels or bodies is covered in the "Body Builder's Book"; however, it should be re-em phasized that the use of U-bolts for attachment of fifth wheels or bodies is not an approved installation as high str e ss con centration may develop. The desired fifth wheel or body mounting is attached to the frame rail web section, not through flanges. Heat-treated rails must not have attachments welded to the fram e. Wood s ills should be used between main rails and sub-frame on body installations to insure good load distribution.

Special equipment or accessory installation can cause high str ess concentrations due to the method of attachment or the weight of the equip ment. Holes should never be drilled through the flanges and rapid changes of section modulus should be avoided. These section modulus changes usually occur when large mounting plates are added for supporting special equipment. Heavy equipment mounted across the flanges 6r on the web of a side rail may cause enough str ess concentration to cause failu resat the nearest crossm em ber, bracket, or other frame stiffener or through a nearby hole in the frame flange.

IMPORTANT

Improper welding or welding methods are a major cause of str e ss concentration points, which may ultimately result in frame failure. (Refer to "General WeJding

Instructions.")

Figure 4 — Fram e B e n d in g M o m e n t (Typical D u m p Truck)

CAUTION

G M C S E R V I C E M A N U A L

Improper reinforcement or attachment of r e inforcement may cause more difficulty than the original problem as the creation of localized stress concentrations may reduce the frame load carry ing capacity below the original frame before add ing reinforcem ents. The use of rivets for attaching reinforcement duringfield modification is generally not recommended due to the lack of proper rivet ing equipment in most service locations. For this reason it is recommended that most reinforce ments be attached with 300-M bolts and that hard ened washers be placed on both ends of the bolt to provide a good torquing surface and to maintain tight bolts.

GENERAL WELDING INSTRUCTIONS

Good welding is a very favorable method of attachment or repair; however, improper welding or welding procedure may result in further frame damage. Additives of reinforcem ents may be nec essary in the repair area to prevent reoccurrence.

WARNING: Before welding, disconnect one or both battery cables.

WELDING EQUIPMENT

NEVER USE OXYACETYLENE

FOR WELDING FRAME RAILS!!

There are several types of welding machines that are used for welding on frame rails. Listed below are the three most commonly used machines and their advantages:

1. DC (Rectifier Type) - This machine re quires very little service as there are no moving parts, also reduces chance of arc blows.

2. DC (Motor-Generator Type) - Theprinciple advantage is the power supply may be self-co n tained; thereby, this machine is readily portable and has very good voltage variation control and versatility with all types of electrodes.

3. AC - This is the least expensive and re duces possibility of arc blows; however, some difficulty may be encountered in striking an arc when using sm all diameter electrodes.

It is recommended that for all-purpose weld ing, the minimum capacity of any machine should be 350 amperes. There are four basic types of welding used in the repair or reinforcing of frame rails. All of these can be used with any type of material except heat-treated material which re quires electrodes E12016 or E11018. Following are the descriptions of the types of welds; a. Continuous Fillet Weld - This is used to weld a continuous bead along a reinforcement plac ed on the web section of the frame rail or for add ing gussets or plates to crossm em bers. Continuous fillet welds should never be made across frame flanges or along inside edges of frame flanges.

When welding in the flat position use high range of electrode current and voltage chart. When welding overhead or in difficult areas, use low range of the electrode chart.

b. Groove Welding - This is a basic repair weld which is applied after the surface has been vee ground for good penetration. Particular care should be taken when welding cracks which cross either the upper or lower flanges. Weld completely then grind off the ex cess weld to eliminate the p os sibility of notches or weld build-ups on the flange edge. Use medium range of electrode chart.

c. Plug Welding - This is a good method of at taching reinforcements as it eliminates the p o ssi bility of loose fitting bolts; however, care must be exercised in locating plug welds in different types of reinforcem ents. E-6011 electrode is highly re c ommended for plug welding because of its good penetration and light coating. Use high range of electrode chart for flat or vertical plug welds.

Overhead plug welding is very difficult and should not be used unless other approaches are not prac tical, then use high range for first pass and com plete plug at medium range. Refer to plug weld table for size of hole to use for variations of ma terial thickness.

d. Stitch (Intermittant Fillet) Welding - This type is not generally used on fram es as continuous fillet welding provides better attachment; however, where warpage and heat control is critical, use stitch welding at medium range of electrode chart.

Other recommendations for all types of weld ing include:

1. Connect welding machine ground cables as clo se to working area as possible.

2. Where possible, use sm aller diameter e le c trode and make several p asses rather than large diameter electrode and single pass.

FRAME RAIL REPAIR

Sec. 2

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FRAME

It is very important that repairs be correctly applied, as inadequate repairs will create addi tional localized str ess concentration which may result in repeat failures. There are two basic types of cracks which may be encountered in frame difficulties (fig. 5). The straight crack or the mul tiple sunburst cracks which will radiate from a hole in the web section.

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FRAME

G M C S E R V I C E M A N U A L

The straight crack will normally start from the edge of a flange and p rogress across the flange and then travel through the web section toward the opposite flange of the same rail. This may be caus ed either by localized str e ss concentration, ex c e ssiv e bending moment, or torsional loading. The sunburst type cracks are caused by high loads ap plied locally at the mounting bracket or crossm em ber whose attachment is not sufficiently adequate or is not securely fastened to the side rail.

In either case both types of cracks may be repaired using sim ilar methods. The procedure for repairing frame rail cracks is as follows:

1. Remove any equipment that will interfere with workable a cc ess to the failure.

2. Locate the extreme end of the crack and drill a quarter inch hole. (NOTE: It may be n eces-

Figu re 6 — Scarfed (Tapered) Ends of Reinforcem ent

sary to align the frame and level the rails before repairing the frame.)

3. Vee grind the entire length of the crack from the starting point to the quarter inch hole at the extreme end. Using a hack-saw blade, the crack should be opened (1 /1 6 ”) to allow complete penetration of the weld.

4. Weld with proper electrode corresponding to the material of the basic rail.

5. Grind the weld smooth on both inside and outside of rail or reinforcement, being extrem ely careful to eliminate weld build-up or notches on the flange edges. (NOTE: Care should be taken when grinding not to reduce thickness of base rail.)

6. Quality and neatness of workmanship can not be overemphasized. After the repair is com pleted, the repaired area should be painted and should not be readily discernible from the unre paired area of side rail. Use a copper spacer b e tween the flanges of cracked base rail flanges and reinforcement flanges and repair each flange sep arately as the flanges must react independently to prevent localized str e ss concentration.

Buckled frame flanges should be straightened using proper alignment procedures, then an ade quate reinforcement should be used (see frame reinforcement) or offending equipment remounted to obtain an improved transition of loaded to non loaded areas. DO NOT USE OXYACETYLENE FOR

WELDING FRAME RAILS.

Crossm ember and Brackets

The repair of crossm em bers may be accom plished if the damage is not extensive. C rossm em ber mounting flange cracks may be repaired in the same manner as side rail cracks; however, the weld bead should be built up to provide a good smooth radius. If extensive damage is incurred to a crossm em ber, the crossm em ber should be r e placed, using bolts rather than rivets. All cast mounting brackets that are damaged should be r e placed as it is not practical to weld a cast bracket.

In the event that a frame crack appears in the area of cast bracket, the bracket must be removed while repair is made. Under no circum stances should a cast bracket be welded to the frame side rail.

REINFORCEMENTS

Review the discussion on analyzing causes of failures before applying reinforcement. A common misconception in the past was to patch a cracked fram e. This is incorrect; reinforce the failed area.

A reinforcement must be large enough (approx. 30 inches) to provide adequate str ess relief from rapid changes in section modulus. For this reason it is extremely important that all reinforcement ends be scarfed to change section modulus as grad

G M C S E R V I C E M A N U A L

Sec. 2

Page 105

FRAME

ually as possible with the longest section installed

(fig. 6) in the area of highest loads.

There are five basic types of reinforcem ents that may be used on truck fram es. However, it must be pointed out that the material used for the reinforcem ent must be sim ilar to that of the base rail. B ase rails of S.A.E. 1023 material could use reinforcem ents of S.A.E. 950 material. S.A.E. 1023 rails may be reinforced with S.A.E. 1023 steel,b u t under no circum stances should strength of rein forcem ent be le s s than base rail. Figures 7 and 8 illustrate the five basic reinforcem ents.

1. Upright ”L” Reinforcement - Maybe placed on either the inside or outside of the fram e side rail. It should be used where maximum str e ss o c curs at the bottom of the lower flange and buckling of the upper flange is not a problem. This rein forcem ent is quite versatile as it may be used in full length or in a short localized reinforcement.

The configuration of the fram e or spring hanger brackets may lim it the use of the upright "L" r e inforcement.

2. Inverted "L" Reinforcement - This may be used on the inside or outside of the frame rail. It is recommended where the maximum str e ss area is transferred to the upper flange; for example, dump trucks with the box in the raised position.

This is also readily adapted where fram e and hang er bracket design restricts using an upright "L" reinforcem ent or where fram e upper flange buckl ing has been noted.

3. Channel Reinforcement - This may also be installed on the inside or outside of the fram e side rail and can be full length o ra lo ca lized reinforce ment. The principle disadvantage of the channel is additional weight and hours of labor required to make an installation. Additional difficulty may arise when attempting to place the channel inside or over the existing rail due to manufacturing tol erances, cro ss members or mounting brackets.

4. Strap Reinforcements - This type of rein forcem ent may also be used to increase the section modulus of a frame if previous damage and repair has resulted in a lo ss of fram e strength which would require additional modulus to return the fram e strength to original design. These reinforce ments are plug welded at 6 to 8 inch intervals. Do not weld across the end or along the flange edges.

Ends should be cut at an angle and edges of plug welds must not be closer than 3 /4 ” to the edge of a frame flange.

5. Inverted "J" Reinforcement - This is a rather new type of fram e reinforcement that is de signed to increase the flange strength to prevent flange buckling due to high torsional inputs or shock loading during tractor hook-up operations.

The inverted "J" reinforcem ent is attached to the web section only with a spaced bolt pattern. This

Figure 7 — Frame Reinforcements

reinforcement has been released in six-foot lengths through the Factory Warehouse under GMC Part

Number 2446489.

The attachment of reinforcement to the basic rail may vary somewhat with m aterials. The fo l lowing general rules apply:

1. Do not use rivets. Proper riveting equip ment is not generally available in most field serv ice outlets; therefore, the use of 300M bolts and hardened flat washers are recommended.

2. Reinforcements, with the exception of strap

Sec. 2

Page 106

FRAME

G M C S E R V I C E M A N U A L

Figure 8 — P lug Patterns of Strap Reinforcements

type, should not be attached to the flanges except in the case where a mounting bracket or crossm em ber holes are already through the frame flange.

3. Plug welds may be used in a staggered 8 to

10 inch pattern when attaching reinforcem ents to the web section (fig. 8).

4. Strap reinforcem ents may be plug welded at 6 to 8 inch intervals to the flanges in som e cases; however, as pointed out, this is for section modulus increase and should only be attempted by highly qualified sp ecia lists.

The termination of reinforcem ents is very important. Reinforcement ends must be scarfed or str e ss relieved to prevent localized str e ss con centration. This scarfing should not be greater than 45 (fig. 6). It should also be strongly empha sized that in c a se s where several reinforcem ents are used, the ends of the reinforcem ents must overlap and be staggered so that the reinforcement ends overlap by eight to ten inches.

— CAUTION —

GENERAL RULES

Listed below are general rules which apply to frame repair and reinforcem ents. Most of these rules are discussed earlier in this section; how ever, the importance of adhering to them cannot be overemphasized.

1. Always identify the material of base rail.

2. Frame straightening or repair must be at tempted only by highly qualified sp ecialists.

3. Always attempt to identify the cause of failure.

4. Fifth wheel, body, and accessory mountings should not be made through frame flanges. (See

"Body Builder’s Book".)

5. Do not drill holes in the lower flanges.

6. Use only proper electrodes as specified for base rail material when welding is necessary.

7. Do not use oxyacetylene welding equipment on fram es.

8. Do not weld reinforcem ents across the fram e flanges.

9. Do not weld within 3/4 inch of the edge of a frame flange.

10. Remove all notches or weld build-ups from flange edge when repairing a broken frame.

11. Do not weld cast brackets to frame.

12. Do not weld the flanges of cracked rein forcem ents and base rails together.

13. Do not patch cracks. Reinforce the area.

14. Reinforcement should be of the same or better material than base rail.

15. Always scarf reinforcement ends to pro vide adequate str e ss relief.

16. Always stagger ends of reinforcements by a minimum of eight inches apart.

17. Before welding, disconnect negative bat tery cable to prevent p ossible electrical damage to generating system .

G M C S E R V I C E M A N U A L

Sec. 2

Page 107

FRAME

ELECTRODE CHARTS

E-7011

Available

Sizes

Current

Flat Welding

Arc

Range Voltage

3 2

" X 1 2".................................................... 4 5 - 80

Vs"

X 1 4 ".................................................... 8 0 -1 1 5

5/32" X 1 4".................................................... 1 25 -1 6 5

3/ie" X 1 4".................................................... 1 60 -2 0 0

3 2

" X 1 8".................................................... 2 0 0 -2 5 0

V i" X 1 8".................................................... 2 5 0 -3 2 0

5/ i

6" X 1 8 " .................................................... 3 2 5 -4 0 0

2 1 - 2 3

2 2 - 2 4

2 3 - 2 5

2 4 - 2 8

Overhead Welding

3 2

" X 1 2".................................................... 4 5 - 75

Vs"

X 1 4".................................................... 8 0 -1 1 0

3 2

" X 14".................................................... 1 25 -1 5 0

3/ i

6" X 1 4".................................................... 1 50 -1 7 5

2 0 - 2 2

2 1 - 2 3

E-7160 Flat Welding

5/64" X 9 " .................................................... 3 0 - 60

3 2

" X 1 2".................................................... 5 0 - 80

Vs"

X 1 4".................................................... 9 0 -1 2 5

3 2

" X 1 4".................................................... 1 20 -1 9 0

3/16"

X 1 4".................................................... 1 75 -2 4 0

2 0 - 2 2

2 2 - 2 4

FRAME SPECIFICATIONS

PLUG WELD CHART

Thickness of

Material

Diameter of Plug

Depth

Plug

V \

...........

................................. 3/4 ..........................

..........

V a

3/s

.......... .................................

......................

..........

V i

.......... .................................P /8........................... ..........

7/l6

5/s

........... .................................

P A

...........................

..........

3/4 ........... .................................l 3/s ........................... ..........

9/l6

.................................

1V2

........................... .......... 9/l6

FRAME WIDTHS

Model Front Width*

Rear Width*

Cowl and Cab

(E4500/5500)..........

Cowl and Cab (all o th e rs).................

T ilt C a b ........

..............................

*0utside Dimension of Base Rails

34"

341/s"

533/8"

34"

341/8"

341/ie"

ELECTRODE USAGE W ITH FRAME MATERIAL

M aterial....................................................................................... S A E -1023

Type of Electrode............................................................................ E-7011

Alternate Electrode......................................................................... E-7016

S id e Rail M a te ria l Id e n tifica tio n

(L o c a tio n -C e n te r lin e of Fro n t A x le )

0

S A E 1023

Sec. 2

Page 108

______________________ G M C S E R V I C E M A N U A L

FRAME

Frame repairs should be undertaken only by competent mechanics, and only the recommended materials should be used.

G M C S E R V I C E M A N U A L

SECTION 3

Sec. 3A

Page 109

This group is divided into four sub-sections as shown in index below:

Section

Front End Alignment ..................................................

Front Axle ....................................................................

Front Springs and Shock A b s o r b e r s ......................

Front Hubs and Bearings ...........................................

Page No.

109

113

117

122

SECTION 3A

Proper alignment of front wheels must be maintained to insure efficient steering and sa tis- factory tire life. The most important factors of front end alignment are wheel toe-in, wheel cam - ber, and axle caster. Front end alignment should be checked at regular intervals, and particularly after front axle has been subjected to heavy im pacts such as a collision or a hard curb bump.

Before checking alignment, wheel bearings must

, x ° wheel toe-m , wheel camber, and axle caster.

When checking alignment, instructions outlined in this section should be followed carefully, as well as instructions covering related units such as brakes, springs, steering gear, hubs and bear-

° , A1 . , ’ , - . _, , other sections of this manual. Front End Alignment

Chart (fig. 1) indicates points at which alignment x dimensions are taken.

The caster, camber, and toe-in dimensions are for vehicle at design load (with frame level).

If frame is not level on alignment equipment, the frame angle must be considered. This is especially important when making caster check for the frame angle must be added to the caster angle to obtain a true setting. All alignment checking should be done with precision equipment and instruments. Refer to "Alignment Specifications" at end of this section,

DEFINITION OF TERMS

. . , .

WHEEL TOE IN

, , ,, ,

. , ,, , . , , OT,j

WHEEL CAMBER

Amount wheels are inclined from vertical plane (see "C," fig. 1).

FRONT AXLE CASTER

t i •

.. ,,,

• *

KING PIN INCLINATION

The slant of the king pin toward the center of the vehicle at the top and outward at the bottom

(see ”D," fig. 1).

CONDITION

Noisy Front End

SERVICE DIAG NO SIS CHART

POSSIBLE CAUSE

CORRECTION

1. Loose tie rod ends.

2. Lack of proper lubrication.

3. Broken spring leaf.

4. Loose U-bolts or spring clips.

1. Replace ends.

2. Refer to LUBRICATION (SEC. 0).

3. Replace spring leaf.

4. Tighten

Wheel Bounce 1. Unbalanced wheels or tires.

2. Unequal tire pressure.

3. Weak or broken front spring.

4. E xcessive wheel or tire runout.

1. Refer to "Balancing" (SEC. 10).

2. See "Load and Inflation Table" (SEC. 10).

3. Replace.

4. Refer to WHEELS AND TIRES (SEC. 10).

E xcessive Tire Wear 1. Incorrect wheel alignment.

2. Failure to rotate tires.

1. Align wheels (SEC. 3A).

2. Refer to WHEELS AND TIRES (SEC. 10).

3. Improper tire inflation.

3. Refer to "Load and Inflation Table"(SEC.10)

4. Overloaded or improperly loaded.

4. Avoid overloading vehicle.

Sec. 3A

Page 110

FRONT END ALIGNMENT

G M C S E R V I C E M A N U A L

Vertical

G Caster A n gle

K ing Pin $

FR O N T A X L E C A ST ER

C A M B E R A N D K IN G P IN IN C L IN A T IO N T O E -IN

K IN G PIN IN C L IN A T IO N

B MINUS A ................................................... Camber (Inches)

C ................................................ Camber (Degrees Positive)

D ........................................... King Pin Inclination (Degrees)

E MINUS F ...................................................... Toe-in (Inches)

G ................................................... Caster (Degrees Positive)

K MINUS L ................................King Pin Inclination (Inches)

Refer to "Specifications" for correct dimensions.

T-3073

Figure 1 — Front End Alignm ent Chart

FRONT END INSPECTION

Before checking front end alignment, the fol lowing front end inspection should always be made:

1. Check tires for proper inflation. NOTE:

Rim -to-floor dimension should be the same at each wheel.

2. Check wheel installation and run-out.

3. Check wheel bearing adjustment.

4. Check steering tie rod and drag link ends for looseness.

5. Check king pins for looseness.

suspension must be neutralized; that is, all com ponent parts must be in the same relative position when making the adjustment as they will be when in operation. To neutralize the suspension, the ve hicle must be rolled forward 12 to 15 feet. By roll ing the vehicle forward, all tolerances in the front suspension are taken up and the suspension is then in normal operating position. Neutralizing the front suspension is extremely important, especially if the vehicle has been jacked up in order to scribe the tires, otherwise the front wheels will not re turn to the normal operating position due to the tires gripping the floor surface when the vehicle is lowered on the jack.

CHECKING A N D CORRECTING

FRONT WHEEL TOE-IN

Incorrect toe-in results in excessive tire wear caused by side slippage and also unstable steering with a tendency to wander. Toe-in may be measured from center of tire treads or from inside of tires.

Measurements at both front and rear of axle (see

"E" and "F," fig. 1).

When setting "toe-in" adjustment, the front

IMPORTANT

"TOE-IN" MEASUREMENTS MUST BE MADE

AT THE HORIZONTAL AXIS OF THE WHEEL.

"Toe-in" is corrected by loosening clamp bolt at tie rod ends, then turning tie rod with pipe wrench until wheels have proper toe-in. On some vehicles with power steering, loosen the power

G M C S E R V I C E M A N U A L

Sec. 3A

Page 111

FRONT END ALIGNMENT

cylinder to tie rod ”U" bolt nuts. With both tie rod ends in same plane, tighten clamp bolts securely.

Refer to "Specifications" for correct toe-in.

On some vehicles with power steering, tighten power cylinder to tie rod bracket "U" bolt nuts.

Adjust power cylinder as directed in "POWER

STEERING” (SEC. 9B) of this manual.

NOTE: Tie rod clamps must be lined up with slots in tie rod tube or difficulty in tightening clamps securely will be experienced.

FRONT WHEEL CAMBER

Camber is the amount in inches or degrees that front wheels are tilted outward at top from vertical position (see "C," fig. 1). Camber offsets wheel deflection, due to wear of front axle parts, and prevents a reverse or negative camber con dition. A reverse or negative camber is an inward inclination of wheels at the top.

If camber is extrem e or unequal between wheels, improper steering and excessive tire wear w ill result. Camber variations may be caused by wear at wheel bearings and steering knuckle bush ings, or by a bent steering knuckle or axle center.

Specifications are listed at end of this section.

CHECKING AND CORRECTING CAMBER

Before checking camber, check wear at king pins as follows:

Jack up front of vehicle, pull bottom of wheel outward and take a camber reading; then pull top of wheel outward and take a camber reading. If readings vary more than 1/4 , make following adjustments:

1. Adjust wheel bearings as directed in

"FRONT HUBS AND BEARINGS” (SEC. 3D), then take camber readings as shown on Front End Align ment Chart (fig. 1). If readings still vary over 1/4°, replace steering knuckle bushings and king pins as instructed in "FRONT AXLE” (SEC. 3B).

2. Check the wheel run-out as instructed in

WHEELS AND TIRES (SEC. 10). If run-out is ex ce ssiv e , straighten or replace wheel.

3. Place vehicle on level surface, with normal weight of vehicle on wheels, then take final camber reading. If camber gauge is not available, readings can be taken as shown on Front End Alignment

Chart in figure 1. Place square as shown and mea sure distances "A" and ”B.” ”B” SHOULD EXCEED

”A” by amount specified. Camber dimensions of right wheel should not vary over 3 /3 2 ” from cam ber dimensions of left wheel. If final camber read ing is incorrect, either steering knuckle or axle center is bent.

4. To determine which part is bent, check king pin inclination ("D," fig. 1). Camber plus king pin inclination is the "included angle" of steering knuckle. If "included angle" of knuckle varies more than 1 /2° from value specified in "Specifications," knuckle is bent and should be replaced. Excessive positive camber results in irregular wear of tires at outer shoulder. Negative or reverse camber causes wear at inner shoulder. Ease of steering is affected by any deviation from specified camber.

AXLE CASTER

Positive caster is the rearward tilt from the vertical of the king pin. Negative or reverse caster is the forward tilt from the vertical of the king pin.

Incorrect caster may result from sagging springs, bent axle, twisted axle, or uneven tight ening of spring U-bolt nuts. Tighten all U-boltnuts equally. Refer to "FRONT SPRINGS" (SEC 3C) for

U-bolt torque specifications. Generally, if the axle is twisted, the caster will be unequal for right and left side.

CHECKING AND CORRECTING CASTER

IMPORTANT: Caster, camber, and toe-in di mensions are for vehicle carrying its design load whereby the frame in most instances would be level.

If alignment check is to be made with frame NOT

LEVEL the frame angle (fig. 2) must be determin ed and added to the caster angle to obtain a true caster reading.

1. Position vehicle on a smooth level surface.

2. Using a bubble protractor, measure the frame angle (FA). See figure 2. Frame angle is the degree of tilt in the frame from the level p o si tion. Negative frame angle is when the frame is high (above level) in the rear. Positive frame angle is when the frame is low (below level) in the rear.

3. Determine the caster angle for the left wheel using the alignment equipment.

4. Add the frame angle (FA) found in step 2 to the left wheel caster reading found in step 3 to determine the "corrected caster" for left wheel.

To determine "corrected caster" with various frame and caster readings the following rules apply:

(a) - Negative frame angle must be added to positive caster reading.

(b) - Positive frame angle must be subtracted from positive caster reading.

Sec. 3A

Page 112

FRONT END ALIGNM ENT

G M C S E R V I C E M A N U A L

(c) - Negative frame angle must be subtracted from negative caster reading.

(d) - Positive frame angle must be added to negative caster reading.

Example: L-4000 with power steering has a left wheel caster reading of 2° p o si tive, but the frame angle is negative

(high in the rear) 1/2°; therefore

1 /2 ° negative frame angle plus 2° positive caster gives 2V the "corrected ca ster” for that wheel.

Referring to "Specifications,” we find that 2

y/P

positive caster is %° over maximum specified setting.

5. Repeat steps 2 through 4for the right wheel.

6. If the caster is not within specifications, caster can be corrected by adding or removing caster shim s between the axle and spring.

KING PIN INCLINATION

King pin inclination is the amount that top of king pin is inclined toward center of vehicle. King pins are inclined ( D, fig. 1), to decrease friction between tire s and road when turning. Precision in struments must be used to check king pin inclin ation when axle is installed in vehicle. When axle is removed, check can be made on bench as follows:

Place two uniform blocks on level surface, rest spring seats on blocks. Using a square, mea sure "K" and "L" (fig. 1). "K" minus ”L” equals king pin inclination in inches. If axle is bent or twisted, refer to "FRONT AXLE" (SEC. 3B) in this manual for corrective information. Straighten ing axle center to correct king pin inclination will also change camber. Recheck camber after co r recting king pin inclination.

IMPORTANT: Caster, camber, and toe-in dimensions are for vehicle carrying its design load whereby the frame in most instances would be level. If alignment check is to be made with frame

NOT LEVEL the frame angle (fig. 2) must be determined and added to the caster angle to obtain a true caster reading.

FRONT END ALIGNMENT SPECIFICATIONS

NOTE: Use in Conjunction with Alignment Chart, Figure 1, page 110.

TRUCK MODELS

E G /E M /E S - P S

4500

E G / E M / E S /

SM/SG/SS5500

ALL 4000

E G / E M / E S /

S M / S G / S S /

5500

E M / E G / E S /

SM6500

AXLE MODELS

B — M inus— A Cam ber (In c h e s )..

C — Camber (Degrees P o s itiv e )* ...

D— King Pin Inclination (D egrees).

E — Minus F —Toe-In (In ch es)

Caster (Degrees P o sitiv e )*.............

K — Minus

—

King Pin (In c h e s )...

F050 F055

33/64

2 0

7-1/6

V l°

Vs - %

23/4

l/2

51/ i4

F-070

33/64

2 0

± /4°

7-1/6

Vs - V k

W a

± Vz

6% 4

F-070

33/64

1/2° +

7-1/6

V l°

23/4 ± 1/2

63/64

(* ) Note: When Power Steering is used, Standard or Optional Caster is the same as called out.

G M C S E R V I C E M A N U A L

Sec. 3B

Page 113

Axle steering knuckles are constructed as shown in figure 2. Wheel bearings, springs, ste er ing, and brake parts which are mounted on front axle are described in their respective section in this manual. Front axle specifications are given at end of this section.

M AINTENAN CE O N VEHICLE

Following maintenance operations should be performed at intervals determined by severity of service:

1. Inspect spring U-bolts for tightness. If loose, tighten as directed in "FRONT SPRINGS"

(SEC. 3C).

2. Inspect and tighten all ball stud nuts.

3. Examine steering knuckle bearing caps for tightness and evidence of lubricant leakage. Tighten or replace parts as required.

4. Inspect and tighten king pin draw key nuts.

Loose draw keys will permit king pin to turn in axle center, thus enlarging king pin hole. If hole becom es too greatly enlarged, replacement of axle center may be necessary. If draw key holes become enlarged beyond use of new key, replace axle cen ter. IT IS NOT SAFE TO REAM AND BUSH DRAW

KEY HOLES.

5. Check vertical movement of knuckle on king pin as directed under "Axle Overhaul" later.

STOP SCREWS

Stop screws shown in figure 1 for F-040,

F-050 and F-055 axles are installed on steering arm.3 and stop against axle center. Stop screw s for

F-070 axles are installed in the steering knuckles and stop against the axle center. If stop screw s are set in too far, road shock may impose excessive load on steering gear, and worm shaft nut may bottom on housing end cover before stop screw s contact axle center.

Place each wheel on wheel alignment instru ment and adjust stop screw s as shown in figure 1.

When oversize tires are installed, the turning clearance should be checked. A minimum clearance of 5/8" should be maintained between ch assis and tir e s. If specified clearance does not exist, read just knuckle stop screw s to obtain the proper clearance.

FRONT AXLE REPLACEMENT

All component parts of the front axle a ssem bly except axle center can be replaced without re

SECTION 3B

fy n a n t A x lz

moving assem bly from vehicle if necessary. Minor straightening with suitable equipment can be a c complished with assem bly in vehicle. When the front axle requires a complete overhaul, the a s sembly can be replaced as described in following procedures:

REMOVAL

1. Jack up and support vehicle frame to re lieve load from front springs.

2. Remove wheels and hubs. Disconnect brake lines to axle. Disconnect drag link from steering arm.

3. While supporting axle center with suitable jack, remove spring U-bolts. Lower assembly and remove from under vehicle.

INSTALLATION

1. Place assem bly on dolly and roll into p o si tion under vehicle. Raise axle up against springs, making sure spring center bolts enter alignment holes in spring seats. Be sure caster axle shim s, if used, are in place between spring and axle with thick edge of caster spacer facing proper direction as indicated in figures 2 and 3 of "FRONT SPRINGS"

(SEC. 3C) of this manual. Attach axle to springs, tightening the U-bolts as described in "FRONT

SPRINGS" (SEC. 3C) of this manual.

2. Install hubs and bearings as described in

"FRONT HUBS AND BEARINGS" (SEC. 3D). Con nect drag link as directed in STEERING SYSTEM

(SEC. 9). Connect brake lines. If hydraulic brakes are used, bleed as described in "HYDRAULIC

S ec. 3B

Page 114

FRONT AXLE

G M C S E R V I C E M A N U A L

BRAKES" (SEC. 5A) of this manual.

3. Check stop screw s and adjust as previously described. Check front end alignment factors and adjust as necessary.

FRONT AXLE OVERHAUL

Steering knuckles, king pins, and bushings or thrust washers and thrust bearings can be replaced without removing front axle from vehicle. Minor axle straightening can also be accomplished with out removing assem bly from vehicle. Prelim inary inspection can be made while axle is still mounted.

These inspections should aid in determining the amount of repair n ecessary. Check front end align ment as directed previously under "FRONT END

ALIGNMENT" (SEC. 3A). Inability to correctly align wheels indicates that axle center or steering knuckle is distorted, tie rod bent, or knuckle bush ings are worn beyond lim its.

STEERING KNUCKLE

DESCRIPTION

The king pin is held in place with a tapered draw key, installed as shown in figure 2. The draw key is retained in place by a lock washer and nut.

Steering knuckles are equipped with bushings of polycarbonate construction and they can be washed in conventional solvents without damage.

Upper and lower ends of knuckles are sealed with king pin bearing caps and gaskets and an Oring seal at the bottom of upper bushings, to p re vent lubricant leakage and to exclude dirt and moisture. Some models are equipped with steering knuckle bushing spacer (fig. 2). The vertical thrust loads are carried by thrust bearing or thrust wash er installed between lower face of axle center and steering knuckle lower yoke.

REMOVAL

1. Jack up axle and remove hubs and bearings as directed in "FRONT HUBS AND BEARINGS"

(SEC. 3D). Remove brake backing plate from ste er ing knuckle. Remove tie-rod as directed in STEER

ING SYSTEM (SEC. 9) of this manual.

2. Remove steering arm from steering knuckle.

3. Remove king pin draw key nut and washer.

Thread nut on draw key far enough to protect threads. Strike nut with hammer to loosen draw key. Remove nut, then drive pin out with brass drift and hammer.

4. Remove cap screw s attaching upper and lower king pin bearing caps and gaskets to steer ing knuckle, then remove caps and gaskets.

5. Using brass drift and hammer drive king pin out of axle.

NOTE: On some models, bushing spacer will be removed at same time as king pin.

6. Remove steering knuckle thrust bearing or thrust washers, shim s, and O-ring.

7. Refer to "Inspection and Repair" later in this section for inspection and repair procedure.

INSPECTION A N D REPAIR

Wash all parts in cleaning solution. Cap gas kets should be discarded and replaced with new parts. Soak thrust washers and bearings in cleaner to dissolve lubricant; then brush with soft brush to remove grit if necessary.

1 Steering Knuckle

2 Cap Screw

3 Upper King Pin

Bearing Cap

4 King Pin Bearing Cap

Gasket

5 Lubrication Fitting

6 Shim

7 Draw Key

8 Stop Screw Lock Nut

9 Stop Screw

10 Thrust Bearing

Lubrication Fitting

Lower King Pin

Bearing Cap

Spacer - Steering

Knuckle Bushing

(Some Models)

Cap Screw

King Pin Bearing Cap

Gasket

Lower Bushing

O-ring Seal

Upper Bushing

King Pin

-3 079

Figure 2— Typical Steering Knuckle Construction

CAUTION: Avoid turning bearings in

races when bearing assemblies are dirty,

since small particles of grit will damage

bearings. "Specifications" at end of this

section itemize the various fits and toler ances which apply to all front axles cov

ered by this manual. It is recommended

that all parts which do not meet these

specifications be replaced.

King pin repair kits are available. The kits include parts which normally require replacement at overhaul.

G M C S E R V I C E M A N U A L

THRUST WASHERS OR BEARINGS

Examine thrust washers or bearings for ex c e ssiv e wear or damage. If thrust washer dust caps are damaged, replace. Replace all parts which show excessive wear.

STEERING KNUCKLE BUSHINGS

Replace steering knuckle bushings if wear is indicated, or if results given previously under

"Front Wheel Camber" indicate replacement is n ecessary.

BUSHING REPLACEMENT

Removal

Bushings are split, and of Polycarbonate con struction, and are hand push fit in knuckle. To re move, slide bushings out of bore in knuckle yoke.

Installation

Before installing bushings, remove nicks and burrs in knuckle yokes and polish with medium grit abrasive paper or cloth. Apply lubricant sp eci fied in LUBRICATION (SEC. 0) of this manual, to all parts. Push bushings into knuckle bores with split in bushings aligned with lubrication fitting.

KING PIN INSPECTION

Check diameter of king pin. Also check for minute cracks or other damage. If inspection re veals excessive wear, replace king pin.

AXLE CENTER

There are two conditions which, if either ex ists, w ill necessitate replacement of axle center:

1. If king pin holes in axle center ends are worn to such an extent that a new oversize king pin fits loosely, axle center must be replaced.

2. If axle center has been twisted or bent more than 5 degrees from original shape, center should be replaced. As a general rule, when an extrem e bent condition ex ists, minute fractures which may be invisible will occur, and failure un der ordinary operating conditions will result. Check axle center for twist with alignment instruments, or on a bench as illustrated in "FRONT END

ALIGNMENT" (SEC. 3A) in figure 3. If equipment is available, use Magna-Flux method to check axle center for minute fractures.

NOTE: AXLE CENTERS SHOULD ALWAYS

BE STRAIGHTENED COLD. UNDER NO CIRCUM

STANCES SHOULD HEAT BE APPLIED.

STEERING KNUCKLES

After steering knuckles have been thoroughly cleaned, examine knuckles for distortion, cracks,

Sec. 3B

Page 115

FRONT AXLE

or fractures. If Magna-Flux equipment is avail able, use this method to inspect knuckles for frac tures which otherwise would not be visible. Replace steering knuckles if inspection reveals defects which would affect serviceability.

INSTALLATION

1. Before assem bly, thoroughly clean all parts; then coat king pin with light coat of engine oil.

2. Position steering knuckle on axle, then slide thrust bearing into place.

NOTE: On models shown in inset of figure 2 place ste el washer between bronze w ashers, with lubricating grooves facing steel washer. Always place larger dust shield over top of w ashers.

3. Install a new O-ring seal at bottom of upper bushing.

4. Align king pin holes in steering knuckle yoke, axle end, thrust bearing or thrust washer, then partially install king pin through top.

5. With axle center held firm ly, place a jack under steering knuckle; then raise until all clea r ance between knuckle lower yoke, thrust bearing or thrust washer and axle center is taken up. Check clearance between top of axle center and knuckle upper yoke. If clearance exceeds 0.005", place a shim between axle center and knuckle upper yoke.

6. Install king pin, with m illed slot in side of pin registering with draw key hole in axle center.

Install king pin from top, inserting through ste e r ing knuckle yoke, shim, thrust bearing or thrust washer and axle center end. P re ss pin down until milled slot in pin lines up with draw key hole.

7. Insert draw key into axle center, r e g ister ing with king pin, then install lock washer and nut.

Tighten nut firm ly. It nut bottoms on knuckle be fore king pin is secure, replace draw key or use a draw key with more taper.

8. On models using steering knuckle bushing spacer, install spacer at lower end of king pin.

9. Install new gaskets, then install upper and lower king pin bearing caps with cap screw s. Tight en cap screw s to torque listed in "Specifications."

10. Lubricate king pins thoroughly through lu brication fittings as directed in LUBRICATION

(SEC. 0). Try action of steering knuckle for bind ing condition.

11. Install steering arm s to knuckles. Install tie-rod as directed in STEERING SYSTEM (SEC.

9) of this manual. Install brake backing plate a s sem bly. Install hubs and bearings as directed in

"FRONT HUBS AND BEARINGS" (SEC. 3D) of this manual.

12. Check front end alignment and stop screw adjustment as previously directed.

S ec. 3B

Page 116

FRONT AXLE

G M C S E R V I C E M A N U A L

SPECIFICATIONS

FRONT AXLE SPECIFICATIONS

AXLE MODEL

King Pin— Length..................................................................

Diameter at Bushings.......................................

Steering Knuckle Bushings— Length.................................

I.D ........................................

Thrust W ashers— Bronze (th ick n e ss)...............................

Steel (th ic k n e ss)...................................

F050

F055

623/64"

1.1090"

1.1094"

1 % "

1.1094"

1.1124"

Steering Knuckle Th ru st— M axim um ................................

Shim s A va ila b le .....................

0.005"

Torque Specifications

King Pin N ut...................................................................... - - -

King Pin Bearing Cap C a p - S c r e w ................................ 20-30 in.-lbs. 50-70 in.-lbs. 60-70 in.-lbs.

F070

757/64

1.2492"

1.2496"

1.2526"

G M C S E R V I C E M A N U A L

Sec. 3C

Page 117

SECTION 3C

f y n c - n t

DESCRIPTION

Front springs on all ser ie s are vari-rate leaf type. Springs are attached to front axle center with

U-bolts and secured at frame side rails as shown in figure 1. U-bolts may also secure shock ab sorbers and tow eyes (when used). Spring eyes on all se r ie s are equipped with replaceable bush ings. The front spring rear hangers on some ve hicles have a floating cushion. The cushion is held in place by the front spring rear hanger rebound bolt, and can be reversed to extend wear life of spring end-to-cushion metal contact area. Refer to figure 1. Front springs which employ rubbermounted bushings with solid eye bolt, require no lubrication at bushing.

GENERAL SPRING MAINTENANCE

LUBRICATION

Spring leaves are lubricated at time of a s sembly and require no further lubrication unless spring is disassembled.

TIGHTENING

IMPORTANT: U-bolt nuts must be retightened to initial torque listed in "Specifications” at end of this section, after 500 m iles. Thereafter, U-bolts should be checked at regular intervals. U-bolts must be kept TIGHT at all tim es to hold axle in place at springs. Otherwise, axle may shift, caus ing misalignment; also, spring leaf failure in the vicinity of the spring center bolt could result.

The center bolt serves only to hold the spring together while in shipment and during installation, and as a locating point when assembling spring to axle. After assem bly, it is strictly the function of the U-bolts to hold the spring and axle in align

CONDITION

Spring Noise

Spring Sag or

Bottom

Spring Breakage ment, and the importance of keeping the U-bolts tight, cannot be overemphasized.

Check, and tighten if necessary, all spring bracket bolt nuts and bracket pin clamp bolts. Re bound clips should be tightened just enough to hold spring leaves in alignment without restricting free movement of leaves.

REPAIR OPERATIONS

FRONT SPRING REMOVAL (Refer to Fig. 1)

1. Raise vehicle frame to take weight off the spring. Make sure vehicle is supported safely.

2. Support axle on floor jack.

3. Remove spring shackle U-bolt nuts, then lower axle.

4. At front of vehicle, remove spring eye bolt, nut, and washer; withdraw eye bolt from bracket and spring eye.

5. On all L-4000 S eries, remove bolt, bolt retainer, and rebound pin at rear hanger. On all

”E," ”S ,” and "PS” S eries, remove nut, lockwasher, rebound bolt, and spacer at rear hanger.

6. Remove shock absorber bracket (if used)

(figs. 2 and 3), spring caster spacer, tow eye (if used) and dowel pins (when used). Also, front spring rear hanger cushion (when used). Remove spring.

NOTE: Refer to figures 2 and 3 for correct position of caster spacer at time of installation.

INSPECTION

1. Thoroughly clean spring eye bushings, bolts, and pins.

2. Insert bolts or pins into bushings in spring eyes, and check for loosen ess. If excessive lo o se ness is evident, bolt pin or bushing must be r e placed.

SERVICE DIAG NO SIS CHART

POSSIBLE CAUSE

1. Loose U-bolts.

2. Loose or worn shackle bushings.

3. Lack of lubrication.

4. Defective shock absorber.

1. Inoperative shock absorbers.

2. Broken spring leaf.

3. Severe operation or overloading.

1. Loose U-bolts.

2. Normal fatigue.

3. Overloading.

CORRECTION

1. Tighten to recommended torque.

2. Replace shackle bushings.

3. Lubricate as required.

4. Replace shock absorber.

1. Replace shock absorbers.

2. Replace leaf or spring assy.

3. Check load capacity rating.

1. Tighten to recommended torque.

2. Replace spring.

3. Check load capacity rating.

Sec. 3C

Page 118

FRONT SPRINGS

G M C S E R V I C E M A N U A L

■=r---- FRONT BRACKET

' NUTS

3 5 - 5 5 Ft. Lbs. Torque

( E 4 5 0 0 - S 5 5 0 0 M o de ls)

3 0 - 4 0 Ft. Lbs. Torque

( E 5 5 0 0 -6 5 0 0 , S 6 5 0 0 M o de ls)

SPRING

EYEBOLT (TORQUE 250-300 FT. LBS.)

FRONT M O U N T IN G -A L L TILT CAB MODELS

Figure 1 — Front Spring M oun tings

3. Inspect spring assem bly for broken or fractured leaves. Number 1 and 2 leaves can be replaced, however if other leaves are broken, re place complete spring assem bly. Replace broken leaves as directed later in this section.

4. Inspect spring for loose or broken rebound clips. Rebound clips should be tight enough to hold spring leaves in alignment, but not tight enough to restrict free movement of leaves.

5. Check for broken, loose, or sprung spring center bolt. Replace or tighten as necessary.

BUSHING REPLACEMENT

Rubber-Type Eye Bushing (With Spring

Off Vehicle) All Series Except PS-4500

Remove and replace front eye bushing using bushing remover, and installer tool set J-21058 as shown in figures 5 and 6.

Series PS-4500 (With Spring on Vehicle)

Removal

1. Raise vehicle to take weight off spring and remove spring eye nut and bolt.

G M C S E R V I C E M A N U A L

B U M P E R

U -B O L T S P A C E R

U -B O L T

S H O C K A B S O R B E R

Sec. 3C

Page 119

FRONT SPRINGS

S P R IN G

A S S E M B L Y

C A S T E R S P A C E R

A X L E C E N T E R

S H O C K

A B S O R B E R B R A C K E T

U -B O L T N U T S

T-4856-11

FRONT

Figure 3 — Front Spring Center M oun ting

(All 4 0 0 0 - P S 4 5 0 0 M odelsI

2. Continue to raise vehicle until spring eye clears hanger.

3. Using J-21978-1 remover adapter J-21058 nut and screw and J-21830-4, -7 receiver and bridge, remove bushing from spring eye (fig. 7).

Installation

1. Using installer adapter J-21978-2 andtools called out in Step 3 of "Removal" procedure, in stall bushing (fig. 7) with offset of bushing at top of spring eye as shown in figure 9.

2. Lower vehicle to position spring eye in hanger.

3. Install spring eye bolt and nut. Tighten nut to 320-420 foot-pounds torque, then lower vehicle.

S eries PS-4500 (With Spring Off Vehicle)

If bushing is replaced with spring off vehicle, use a p ress and adapters J-21978-2 to remove and install bushing.

Figure 5 — Rem oving Rubber Type Eye B ushing

(All Series Except PS4500)

SPRING LEAF REPLACEMENT

1. Mark down one side of springs to assure original position of leaves, then place spring a s sembly in a vise or arbor p ress near center bolt.

2. When bolted type is used, remove rebound clip, nuts, bolts, and spacers.

3. File off peened end of center bolt, then re move nut and bolt.

4. Release vise or arbor press slowly to avoid possible injury. Separate spring leaves and clean thoroughly, using a wire brush if necessary.

5. Replace any broken rebound clips by cut ting old rivet, and riveting new clip to spring leaf.

6. Replace broken leaf and stack leaves in correct order, applying a thin film of graphite grease to each leaf. Align center bolt holes in spring leaves with long drift, then com press spring leaves in vise or arbor p ress.

7. Install center bolt and nut and tighten firm ly. Peen end of bolt to prevent nut loosening.

8. Remove spring from vise or arbor p ress.

Align spring leaves by tapping with hammer. In stall rebound clip, spacers, bolts, and nuts; tighten

J-21058

Front Spring Hanger

Fram e

R ear Spring Hanger

Rebound B olt

Wear Cushion

Rebound Pin

Spring

8 Spring U -B o lt

9 Shock A bsorber B racket

10 Spring Pad

11 C aster Spacer

12 Dowel

13 A xle

14 Eye Bushing t

-4854

Figure 4 — Front Spring Installation

(“E” and “S ” M odels 4500-6500 Series)

Figure 6 — Installing Rubber Type Eye Bushing

(All Series Except PS4500)

Sec. 3C

Page 120

FRONT SPRINGS

G M C S E R V I C E M A N U A L

Figure 7— Rem oving Rubber Type Eye B ush in g (PS4500)

Figure 8 — Installing Rubber Eye Bushing IPS4500)

enough to hold spring leaves in alignment, but not enough to restrict free movement of leaves.

FRONT SPRING INSTALLATION

(Refer to Fig. 1)

1. On all se r ie s, place rear end of spring in rear hanger, then install rebound pin, pin retainer, and pin retainer bolt, or rebound bolt spacer, spacer bolt, lock washer and nut.

2. Raise front end of spring into frame for ward hanger brackets; then install eye bolt, eye bolt washer, and nut.

3. With dowel pins (when used) tow eye (when

Figure 9 — Installed Position of Offset B ush in g (PS4500)

used) and caster spacer (when used) on axle pad, raise axle to springy making sure spring center bolt or dowel pin engages hole in axle pad.

NOTE: Install caster spacers with thick edge facing proper direction as shown in figures 2 and

3. If caster spacer is incorrectly installed it will result in hard steering.

4. Install shock absorber bracket, at spring,

U-bolt spacer, U-bolt and shock absorber (when used). Install U-bolts and nuts.

5. Tighten front spring eye bolt nut, bracket pin nuts, U-bolt nuts, rebound pin or bolt nuts, to torque listed in "Specifications" at end of this section.

6. Lubricate as instructed in LUBRICATION

(SEC. 0) of this manual.

7. Lower vehicle to floor.

SHOCK ABSORBERS

Shock absorbers are non-adjustable and non repayab le. Maintenance requirements involve re placement of the rubber mounting grommets, and tightening all shock absorber pin nuts at regular intervals. If a shock absorber becom es inoperative, the complete unit must be replaced.

CAUTION: When replacing shock ab

sorbers, check the model number stamped

on the unit to make sure it is the same

model as the one removed.

Refer to next page for "Specifications."

G M C S E R V I C E M A N U A L

Sec. 3C

Page 121

FRONT SPRINGS

SPECIFICATIONS

TORQUE SPECIFICATIONS

FT. LBS.

U-BOLT NUTS

All 4000 S e rie s............................................................................................................................................................................................................135-150

PS4500 .......................................................................................................................................................................................................... 105-130

E-5500-6500 Series, S6500 Series............................................................................................................................................ 90-110 Lube Before Ass.

E-4500, S5500 S e rie s .................................................................................................................................................................. 90-100 Lube Before Ass.

FRONT EYEBOLT-TO-BRACKET NUT

E4500, S5500 S e rie s.................................................................................................................................................................................................. 250-300

E5500-6500 Series, S6500 S e rie s............................................................................................................................................................................ 250-300

REAR BRACKET- TO- FRAME BOLT NUTS

FRONT BRACKET- TO- FRAME BOLTS

FRONT SPRING REAR REBOUND BOLT NUT

PS4500.............................................................................................................................................................................................................................. 75-95

SHOCK ABSORBER BRACKET- TO- FRAME

IMPORTANT

U-bolts must be retightened to initial torque

listed in "Specifications" after 500 miles.

Sec. 3D

Page 122

G M C S E R V I C E M A N U A L

SECTION 3D

cJluhl and (iea'Unai.

DESCRIPTION

Front hubs are mounted on steering knuckle spindle on opposed tapered roller bearing as illu s trated in figure 1. Refer to "Service Parts Identi fication" decal on dash compartment door to de termine type of axle used on a specific vehicle.

Mounting parts (mainly bearings, spindle nuts, and seals) shown in figure 1, are of primary import ance. Brake drum mounting bolts, studs, and nuts differ in type and method of installation on various ser ie s vehicles.

BEARING M AINTENANCE

All wheel bearings are adjustable for wear.

Satisfactory operation and long life of bearings depend upon proper adjustment and correct lubri cation. If bearings are adjusted too tight, they will overheat and wear rapidly. Loose adjustment will cause pounding and w ill also contribute to steering difficulties, uneven tire wear, and inefficient brakes.

Bearing adjustment should be checked at regular inspection periods.

Front hubs and bearings should be cleaned, inspected, and lubricated whenever hubs are re moved, or at intervals indicated in LUBRICATION

(SEC. 0) of this manual.

New hub oil sea ls should be installed when servicing bearings if there is the slightest indica tion of wear or damage. An imperfect seal may perm it bearing lubricant to reach brake linings, resulting in faulty brake operation and n ecessitat ing premature replacement of linings.

BEARING ADJUSTMENT CHECK

Before checking wheel bearing adjustment make sure brakes are fully released. Jack up the

F040 A XLE w / D IS C W HEELS

F050 A N D F055 A XLES w / D ISC W HEELS

F050 A N D F055 A XLES w / C A ST WHEELS

F070 AXLE D EM O U N T A B LE w /DISC W HEELS

1 Hub Cap or C losure Plate

2 Bearing Adjusting Nut

3 Adjusting Nut Washer

4 Cap Screw

5 Gasket

6 Wheel Bolt

7 Outer Bearing Cup

F070 A XLE FLANG E M O U N T ED w /DISC WHEELS

8 Outer Bearing Cone and R oller

9 Wheel Bolt Nut

10 Brake Drum

11 Hub to Brake Drum Bolt

12 Lock Nut

13 Inner Bearing Cup

14 Inner Bearing Cone and R ollers

15 Oil Shield or Deflector

16 Inner Oil Seal

17 Wheel (Cast Type)

18 Steering Knuckle

19 Wheel (Budd Type)

20 Hub

21 Wheel Clamp

Figure 1 — Front H ubs a n d B ea rin gs

front axle until wheels clear floor.

Check bearing play, by grasping tire at top and pulling back and forth, or by using a pry bar under tire. If bearings are properly adjusted, movement of brake drum in relation to backing plate will be barely noticeable and wheel will turn freely. If movement is excessive, adjust as follows:

FRONT WHEEL BEARING ADJUSTMENT

1. With the wheel raised and axle safely sup ported, remove hub cap, or hub cap closure plate and gasket.

2. Remove cotter pin securing adjusting nut to spindle.

3. Back off the adjusting nut, then using a torque wrench, tighten adjusting nut to 40 foot pounds on F-040, F-050, and F-055 axles, and 60 foot-pounds on F-070 axle, at the same time turn wheel in both directions to be sure all bearing surfaces are in contact.

4. Back off adjusting nut % the nearest cotter pin hole in spindle, or sufficient ly to allow the wheel to rotate freely within lim its

5. Install new cotter pin and make sure that wheel or hub turns freely.

6. Install hub cap or hub closure plate with new gasket, and tighten cap screw s firm ly.

7. Lower wheel to floor and remove jack.

FRONT HUB A N D BEARING

REPLACEMENT

G M C S E R V I C E M A N U A L

Sec. 3D

Page 123

FRONT HUBS A N D BEARINGS

hub as directed in LUBRICATION (SEC. 0) of this manual. If seal is leather, soak in oil before in stalling. On all other type oil seals, coat lip of seal with wheel bearing grease or equivalent be fore installing.

2. Place inner bearing in hub. Coat oil seal bore in hub with a thin layer of non-hardening se a l ing compound, then p ress seal in until seal case seats against shoulder in hub or against inner bearing cup. On types having spring-loaded liptype oil seal, seal must be installed with lip point ing inward.

3. On trucks so equipped, make sure the oil deflector and oil shield are in place on spindle.

4. Carefully install hub assembly on spindle, being careful not to damage inner oil seal.

5. Place outer bearing cone and roller a s sembly on spindle, pressing firm ly into hub with fingers. Install adjusting nut washer and adjusting nut.

6. Install tire and rim or tire and wheel a s sem bly.

7. Adjust bearings and complete the install ation as previously directed under "Front Bearing

Adjustment." Adjust brakes as directed in BRAKES

(SEC. 5) of this manual.

CLEANING, INSPECTION, AN D

REPAIR

REMOVAL (Fig. 1)

1. Jack up front wheel and remove tire and rim assem bly if cast wheels are used. Remove tire and wheel assem bly if ventilated disc or Budd type wheels are used.

2. On some trucks remove the hub cap.

NOTE: On F-040 axle hub cap is threaded into outer end of hub. On other vehicles remove cap screw s, lock washers, hub closure plate, and gas ket. Discard gasket.

3. Remove cotter pin, bearing adjusting nut, and adjusting nut washer.

4. Pull hub and drum assem bly straight off steering knuckle spindle, using care to prevent outer bearing from dropping on floor. Remove outer bearing cone and roller assem bly from hub.

5. Pull inner oil seal out of hub; then remove inner bearing from hub.

6. Clean, inspect, and repair parts as n eces sary, as directed later in this section under "Clean ing, Inspection, and Repair."

INSTALLATION (Fig. 1)

1. Lubricate bearings, spindle, and inside of

CLEANING

1. Immerse bearing assem blies in suitable cleaning solvent. Clean with stiff brush if n eces sary to remove old lubricant. Blow bearings dry with com pressed air, directing air stream across bearings. Do not spin bearings while blowing them dry.

2. Thoroughly clean all lubricant out of in side of hub and wipe dry. Make sure all particles of gasket are removed from outer end of hub, and that all sealing compound is cleaned out of oil seal bore in inner end of hub.

3. Clean lubricant off steering knuckle spindle, wash bearing adjusting nut and washer in cleaning solvent and wipe dry.

INSPECTION

1. Inspect bearings for excessive wear, chip ped edges, and other damage. Slowly roll rollers around cone to detect any flat or rough spots.

Replace damaged parts. If either the cone and roll er assem bly or the cup of the roller bearings are damaged, the complete bearing assembly must be replaced.

2. Examine bearing cups which are still in stalled in hub. If cups are pitted or cracked, they must be replaced as directed later under "Repair."

3. Examine brake drums for scoring or other

Sec. 3D

Page 124

G M C S E R V I C E M A N U A L

FRONT HUBS A N D BEARINGS

damage. Non-demountable brake drums can be re finished while mounted on hubs. (NOTE: Refer to

"HYDRAULIC BRAKES" (SEC. 5A) under "Brake

Drums.") If n ecessary to replace demountable brake drum refer to "Repair" later in this section.

4. Examine wheel studs or rim clamp studs for damaged threads and replace, if necessary, as directed later under "Repair."

5. Discard old oil sea ls and obtain new oil sea ls to be used at assem bly.

REPAIR

Bearing Cup Replacement

1. Bearing cups are removed by using a mild steel rod through opposite end of hub and driving against inner edge of bearing cup. Alternately drive on opposite sides of cup to avoid cocking cup and damaging inside of hub.

2. To install new cups, position cup in hub and drive into place, using a suitable driver or by using a mild steel rod against outer edge of cup.

If drift is used, alternately drive against opposite sides to assure driving cup in squarely. Cups must seat against shoulder in hub.

Brake Drum Replacement

1. Demountable Type. The demountable type drum may be separated from the hub and removed from the vehicle without disturbing the hub. The drum is held to the hub by countersunk, slotted screw s, which are easily removed with a screw driver.

2. Non-Demountable Type. Non-demountable type hub and drum assem bly is such that replace ment cannot be accomplished with the hub a ssem bly installed on the vehicle.

a. Separate the drums and hub by removing the drum-to-hub retaining bolts, hub stud nuts, or by pressing out the wheel studs, as applicable.

b. Position brake drum to hub assembly, mak ing certain that all drain holes are in alignment.

c. Apply a light, even coating of sealing com pound to the hub oil deflector contact surface, and position deflector to drum.

d. Install drum-to-hub retaining bolts, hub stud nuts, or press wheel studs into drum.

Wheel Bolt Replacement

Wheel bolts are serrated and may also be swaged in place; however, replacement procedure remains the same for both types of installation.

P re ss bolts out of hub flange, using suitable p ress, then p ress new bolts into place, making sure bolts are a tight fit. If all bolts were removed, be sure that hub oil deflector is in position under bolt heads.

IMPORTANT: If any one wheel experiences a single stud failure caused by a loose running wheel, all studs should be replaced.

A loose running wheel may cause only one stud to break, but several more studs may become fatigued to the point, of failure, but not actually breaking. Replacing only the one broken stud and remounting wheel will then set the stage for a second and possibly more serious failure. If holes in wheel have become elongated, or enlarged, re place wheel.

Hub Stud Replacement

Hub studs can be removed and replaced by using a conventional stud remover and replacer.

Make sure that studs are firmly bottomed in holes and that threads are not damaged during installation.

G M C S E R V I C E M A N U A L

Sec. 4A

Page 125

SECTION 4

HeaA, S u A n e fiA ia n

This section is divided into three sub-sections as shown in index below:

Section

Rear Axle and Controls ..............................................

Rear S p r in g s ....................................................................

Rear Hubs and B e a r in g s ..............................................

Propeller Shafts .............................................................

Page No.

125

145

149

155

SECTION 4A

***Reasi A x le a*t& G osttkoii.***

DESCRIPTION

Rear axles used on all vehicles covered by this publication are full floating type, using Hotch k iss or leaf spring drive.

Rear axles are Hypoid or spiral bevel pinion gear type. Pinion is straddle mounted between roller bearing and two adjustable tapered roller bearings. Differential is supported by adjustable tapered roller bearings in differential carrier.

Housing is either banjo or bowl type, with spring seats and brackets, also brake mounting brackets welded to housing. This type construction provides exact alignment and location of the axle assembly at time of assem bly and installation.

Axle shafts are full-floating type. Inner end of shaft is splined and engages sim ilar splines in differential side gear. Outer end of shaft is flanged and is attached to the wheel hub by studs, tapered dowels, and nuts.

REAR AXLE CONTROLS

Paragraphs following are intended to provide information relative to several system s used to shift 2-speed axles into high or low speeds.

ELECTRIC SHIFT

The electric shift control system con sists of a control switch, speedometer adapter, shift units, and interconnecting wiring harness.

CONTROL SWITCH

The control switch, mounted on transm ission shift lever consists of a shift button which is p osi tioned by the driver to operate a shift unit at axle.

The driver selects the axle ratio by moving con trol button (fig. 1) to select "Low” and "High" axle range. Movement of control button com pletes c ir cuit to one field of shift unit motor when in "High" and to opposite field when in "Low." Refer to ap plicable "Wiring Diagrams" booklet.

SHIFT UNIT

The shift unit and automatic switch assembly is mounted on differential carrier (fig. 2). This unit, controlled by the control switch, shifts the axle into "Low" or "High" range.

When the control switch button is in "Hi" range, wiring carries current to one field of the unit motor. The armature and drive screw turn in a clockwise direction and move the nut down (fig.3).

When the nut has traveled a sufficient distance to wind the torsion spring, a contact bumper on the nut breaks an electrical connection on the auto-

Sec. 4A

Page 126

G M C S E R V I C E M A N U A L

REAR AXLE A N D CONTROLS

T -2359 i

Figure 2 — Two-Speed Electric Shift Unit

Installed (Eaton Axle Show n)

matic switch so that motor is no longer energized and the armature stops rotating. To make sure that the nut cannot travel back on the screw due to vibration, a ball screw detent spring, holds the nut at the end of its travel on the screw.

The nut moves the spring winding lever down pivoting on winding and actuating lever shaft, winds the torsion spring for high. Thus an increased load is put on the spring, and in this position the axle is ready to snap into high speed ratio as soon as the load on the axle gears is relieved.

The torsion spring is assembled in the unit so that it is under approximately 50 to 90 pounds pressure, depending upon the size of the axle.

When the spring winding lever is moved so that the spring is wound, the p ressure of the spring is r a is ed to approximately 90 to 140 pounds, depending upon size of axle.

The additional pressure is used to shift the axle. When the shift is completed, the ends of the spring come together leaving the original tension on the spring. Thus pre-load tension holds the axle in either selected gear.

When the shift button is in "Lo" range, the motor is energized so that the motor armature and drive screw rotate to drive nut in opposite d irec tion for shift into "Low" range, in the same manner as previously described for "High" range operation.

SPEEDOMETER ADAPTER

The speedometer adapter is mounted to back of speedometer and is electrically connected to control switch. When the control switch button is placed into "Lo" range position, an electro-magnet shifts the adapter mechanism to compensate for the difference in gear reduction between "High" and "Low" range in the axle. When shift button is in "Hi" range position, current is released from electro-m agnet, and a spring holds the adapter mechanism in "High" range position.

Speedometer adapters used on these vehicles are 12 volt type. Voltage of the unit is stamped on the housing below the wire terminal. Care should be used to select unit of same voltage as vehicle.

WIRING SYSTEM

Reference should be made to optional equip ment wiring diagrams in "Wiring Diagrams" book let. The ignition switch must be on before electric shift mechanism will operate.

A separate circuit breaker in the circuit pro tects the shift circuit in the event of a short. Refer to applicable "Wiring Diagrams" booklet for cir cuit breaker connections.

V ACU U M SHIFT

Vacuum operated power shift system is used on some vehicles equipped with 2-speed rear axle.

A typical system arrangement is shown in figure 4.

Vacuum power shift system utilizes engine intake manifold vacuum and atmospheric pressure for its operation. Units used in vacuum power shift system are: Control Button, located on gearshift lever; Control Valve, mounted on frame side rail at left-hand side; Vacuum Check Valve, installed in vacuum line at dash junction; Speedometer Adap ter and Adapter Shift Diaphragm, mounted at speed ometer head under instrument panel; Rear Axle

Power Shift Chamber, mounted on differential ca r rier; and interconnecting vacuum lines and fittings.

P O S IT IO N IN H IG H P O S IT IO N IN L O W t

-2441

Figure 3 — Position of Drive Screw in H ig h a n d Low R a n g e

SYSTEM OPERATION

LOW SPEED

With shift control button in "Lo" position, control valve opens one side of shift chamber at

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rear axle to vacuum and opposite side to atm os- phere. In "Lo" speed position, vacuum is supplied to speedometer adapter causing rod to move inward shifting speedometer into low ratio.

H IG H A X LE P O SIT IO N

1 Control Cable

2 Cable Trunnion

3 Atmosphere Port

4 Speedometer Shift Port

5 Vacuum Port

6 Atmosphere Closed

- Vacuum Open

7 Atmosphere Open

- Vacuum Closed

8 Atmosphere Open to Axle

9 Vacuum Open to Axle

L O W A X LE P O SIT IO N

10 Atmosphere Open

- Vacuum Closed

11 Atmosphere Closed

- Vacuum Open

12 Poppet Lever

13 Operating Lever

T P M -7 5 9 1

Figure 5 — O p e ra tin g Positions of V a cu u m Shift Control V a lv e

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HIGH SPEED

With shift control button on gearshift lever up, in "Hi" position, rear axle power shift cham ber is subjected to vacuum through the control valve. With vacuum present on one side of the shift chamber diaphragm, the atmospheric p res sure on the opposite side of the diaphragm forces the diaphragm to move toward the vacuum side.

Movement of the diaphragm is transmitted to the rear axle sliding clutch shift fork through the shift rod, and the axle gears are shifted into high speed. At the sam e tim e, vacuum is removed from the speedometer adapter causing the spring to move the diaphragm and rod, shifting speed ometer into high speed.

SHIFTING

When shifting from "Lo" to "Hi" the operator pulls on control button, which is attached to valve through a cable. This ra ises the cable trunnion and operating lever up as shown in figure 5. The ten sion springs are therefore moved "over center" causing poppet lever to rotate, lifting one poppet valve and lowering the opposite valve.

When shifting from "Hi" to "Lo" the operator p resse s on control button. This moves the cable trunnion and operating lever downward, as shown in figure 5. The tension springs are therefore moved "over center" causing poppet lever to ro tate, lifting one poppet valve and lowering the opposite valve.

M AINTENANCE O N VEHICLES

At regular intervals, the following lubrication, inspection, and maintenance procedures should be accomplished and corrective m easures taken when ever necessary.

LUBRICATION

Lubrication intervals, method of filling and draining, also type of lubricant and capacities for all axles are covered in LUBRICATION (SEC. 0).

Examine housing cover, pinion oil seal re tainers, and axle shaft flanges for lubricant leaks.

Tighten bolts or nuts, or replace gaskets and seals as necessary to correct leaks.

MOUNTING

Check for axle misalignment. Select a point at one side of vehicle and a corresponding point at opposite side. Measure distances between points selected and identical points at each end of axle assem bly. If distances are not equal, axle m is alignment is indicated and rear spring should be checked for correct installation.

Refer to "REAR SPRINGS" (SEC. 4B) for spring

U-bolt tightening instructions, also for torque rod inspection and maintenance.

Figure 6 — Clearance Betw een A x le Shaft F la n g e a n d Stud Nut

AXLE SHAFT FLANGE MOUNTING

Axle shaft flanges are retained to hubs by hub caps or stud nuts and dowels.

1. Check tightness of stud nuts at regular in tervals. Tighten 1/2" nuts to 50-60 foot-pounds torque, or 5/8" nuts to 90-110 foot-pounds torque.

2. The studs must be straight and dowels of correct taper must be used. There should always be a slight clearance between nuts and driving flange when nuts are drawn up (fig. 6). No clea r ance at this point indicates excessive wear at studs, dowels, or holes in flange. Replacement of worn parts is the only remedy.

3. If stud nuts are not tightened to torque specified, play between flange and studs will cause bent or broken studs, also worn tapered holes in flange of axle shaft.

BENT HOUSING CHECK

A check for bent axle housing can be made with unit in vehicle in following manner; however, conventional alignment instruments can be used if available.

1. Raise rear axle with a jack until wheels clear floor. Block up axle under each spring seat.

2. Check wheel bearing adjustment and adjust if necessary, then check wheels for looseness and tighten wheel nuts if necessary. Refer to "REAR

HUBS AND BEARINGS" (SEC. 4C).

3. Place a chalk mark on outer side wall of tires at bottom. Measure across tires at chalk marks with a toe-in gauge.

4. Turn wheels half-way around so that chalk marks are positioned at top of wheel. Measure across tires again. If measurement at top is 1/8" or more sm aller than previous measurement noted at bottom of wheels, axle housing has sagged and is bent. If measurement at top exceeds bottom dimension by 1/8", axle housing is bent at ends.

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5. Turn chalk marks on both wheels so that marks are level with axle and toward rear of ve hicle. Take measurement with toe-in gauge at circuit breaker is faulty.

6. At ch assis junction, remove both w ires, then test circuit through red wire with white stripe.

chalk marks; then turn both chalk marks to front and level with axle and take another measurement.

If measurement at front exceeds rear dimension

Reconnect both w ires to terminal.

7. At ch assis junction, remove wire from term inal. Place axle shift lever switch in "Lo" by 1 /8 ” or more, axle is bent to the rear. If the measurement condition is the reverse, the axle is bent forward.

position and test circuit.

8. At ch assis junction, remove wire from term inal. Place axle shift lever switch in "Hi" position and test circuit.

ELECTRIC SHIFT M AINTENANCE

A N D DIAG NO SIS

The only general maintenance necessary on

The preceding tests should readily localize any trouble within the system . When checking the wiring harness for shorts or open circuits, exam ine for broken insulation.

the shift control system is periodic lubrication of unit as described in LUBRICATION (SEC. 0). The wiring connectors should be kept tight, and w ires to the various units should be kept in good condition.

The co n tro l o r ign ition sw itch can be b e st tested by substituting a new unit.

DIAGNOSING TROUBLE

If the vehicle shifts normally, but the speed ometer adapter fails to operate, make the test to

If the electric shift fails to operate properly, determine whether the adapter is getting current the system should be tested and the trouble diag nosed as described in following paragraphs. A test light consisting of a 12-volt bulb with two w ires a in "Lo” range. If current is present, replace the adapter. When the trouble is traced to the shift unit, it should be replaced.

few feet long with small battery clips on the ends.

Refer to Wiring Diagram and test in following sequence:

1. Disconnect two w ires from shift unit at rear axle. Place engine control or ignition switch in "ON" position, also place axle shift switch at shift lever in "Hi" position.

2. Connect one lead of test light to ribbed wire and opposite lead to ground. One of the following conditions should exist.

a. Should light come on and stay on, the c ir cuit is satisfactory and any trouble will probably be found in the shift unit. Repeat check for "Lo" position as directed in step 3 following.

b. If the light fails to come on, this indicates that the circuit is open between the control switch and the shift unit and further tests will be required.

c. If the light com es on but cycles, this indi cates that there is a short between the control or ignition switch and shift unit, and further tests will be required.

3. Remove test light lead from ribbed wire and connect to smooth w ire, also place axle shift switch in "Lo" position. Observe conditions as outlined in sub-paragraphs above.

4. Connect one lead of test light to control switch side of circuit breaker and opposite lead to ground. Should light come on, and stay on, the circuit is satisfactory. However, if the light fails to come on the circuit between the control switch and circuit breaker is either open or shorted.

5. Connect one test lead to load side of circuit breaker and opposite lead to ground. Should light

V A CU U M SYSTEM MAINTENANCE

All lines and units in vacuum power shift s y s tem must be kept free of vacuum leaks. When vac uum leaks exist, rear axle shift mechanism will operate sluggish and in some instances may not shift axle. If this condition exists make tests to determine location of leaks.

VACUUM LEAKAGE TEST

1. Disconnect flexible lines one at a time, at axle shift chamber and insert a vacuum gauge in line, using a "Tee" fitting.

2. Start engine and place axle shift button in

"Hi" or "Lo" depending upon location of vacuum gauge. Run engine long enough to obtain maximum vacuum, then stop engine and note rate of vacuum drop on gauge. If drop exceeds 1 inch to 10 min utes, leakage is excessive.

3. If leakage is indicated, coat all vacuum come on, and stay on, the circuit breaker is sa tis factory. However, if the light fails to come on the

Figure 7 — V a cu u m Tubing Connection Seal

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line connections with hydraulic brake fluid. If leak exists, fluid will be drawn into connection with en gine idling and control lever in "LOCK" position.

4. Remove line having leaking connection.

Slide tube nut back on tube and remove all particles of seal ring from tube and from inside of nut. Slip new seal ring over tube end. Insert tube into fitting and seat solidly. Slide seal ring (do not roll) into fitting (fig. 7). Thread tube nut into fitting and tighten slowly and firm ly.

5. Repeat above test on opposite vacuum line, being sure to change shift button.

6. If vacuum drop is still excessive after all connections have been checked, leakage in one of the units is indicated. Remove each unit and over haul or replace as required.

AIR CLEANER

Air cleaner rem oves dirt particles from at mosphere which p asses into the control valve and other units. Air cleaner should be removed and cleaned at regular intervals.

REAR AXLE SERVICE DIAGNOSIS

SYMPTOM

PROBABLE

REMEDY

NOISE ON DRIVE

E xcessive Pinion Gear B a c k la s h ................. Adjust

Worn Pinion and Bevel G e a r ....................... Replace

Worn Pinion B earin gs ...................................... R ep la ce

Loose Pinion Bearings .................................. Adjust

E xcessive Pinion End P l a y ............................. Adjust

Worn Differential Bearings ....................... Replace

Loose Differential B e a r in g s .......................... Adjust

E xcessive Bevel Gear R u n -O u t................. Replace

Low Lubricant Level ............................... Replenish

Wrong or Poor Grade L u b r ic a n t............... Replace

Bent Axle Housing ............... Straighten or Replace

NOISY ON COAST

Axle noises heard on drive will usually be heard also on coasting; although not as loud ............ Adjust or Replace

Pinion and bevel gear too tight (audible when decelerating & disappears when driving) . Adjust

INTERMITTENT NOISE

Warped Bevel G e a r ........................................ Replace

Loose Differential Case B o l t s .................... Tighten

SYMPTOM

PROBABLE

REMEDY

CONSTANT NOISE

Flat Spot on Pinion or Bevel Gear Teeth ............................... Replace

F lat Spot on B e a r i n g s ...................................... R ep lace

Worn Pinion S p l i n e s ..................................... Replace

Worn Axle Shaft Dowel H o le s .................... Replace

Worn Hub Studs ........................................... Replace

Bent Axle Shaft ............................................. Replace

NOISY ON TURNS

Worn Differential Side Gears and Pinions ................................................ Replace

Worn Differential S p id e r ............................. Replace

Worn Differential Thrust Washers . . . . Replace

Worn Axle Shaft Splines ............................. Replace

FAILS TO SHIFT

INTO HIGH OR LOW

Defective Electrical Circuit .................... Correct

Defective Shift Unit ..................................... Replace

Lack of Air P r e s s u r e .................................. Correct

Low V acuu m ................................................... Correct

REPLACEMENT A N D OVERHAUL

AXLE REPLACEMENT

REMOVAL

1. Jack up rear of vehicle until load is r e moved from springs, then place blocks under frame to prevent accidental dropping of vehicle.

2. Disconnect hydraulic or air brake lines, whichever is used. Refer to BRAKES (SEC. 5).

3. Disconnect electric wiring or line from shift chamber if vehicle is equipped with a 2-speed axle.

4. Disconnect propeller shafts as directed in

"PROPELLER SHAFTS" (SEC. 4D).

5. Disconnect torque or radius rods, if used, as directed in "REAR SPRINGS" (SEC. 4B).

6. Disconnect spring U-bolts as directed in

"REAR SPRINGS" (SEC. 4B).

7. Roll axle out from under vehicle, then r e move wheels, hubs, and bearings as directed in

"REAR HUBS AND BEARINGS" (SEC. 4C).

8. Whenever another axle is to be installed instead of the one removed, it may be necessary to remove two speed shift unit, and brake chambers.

Refer to respective sub-sections for instructions.

INSTALLATION

1. If brake chambers or two-speed shift unit has been removed, they should be reinstalled as directed in respective sections.

2. Install hubs, wheels and tire s as directed

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in "REAR HUBS AND BEARINGS" (SEC. 4C). Roll axle into position under vehicle.

3. Connect springs to axle as directed in

"REAR SPRINGS" (SEC. 4B).

4. Reconnect the torque rods as directed in

"REAR SPRINGS" (SEC. 4B). On some vehicles torque rods are adjustable to secure proper axle alignment.

5. Reconnect propeller shafts as directed in

"PROPELLER SHAFTS" (SEC. 4D).

6. Reconnect electric wiring or line at shift chamber if vehicle is equipped with a 2-speed axle.

7. Reconnect air brake lines as directed in

BRAKES (SEC. 5).

8. Check lubricant level and fill with type and g ra d e of lu b rican t in the m anner in str u c te d in

LUBRICATION (SEC. 0). Some types of axles r e quire additional lubricant at pinion cage when filled initially or after overhaul.

9. Remove blocks and lower vehicle to the ground. Retighten spring U-bolts as instructed in

"REAR SPRINGS" (SEC. 4B).

10. After all installation procedures have been completed, check air or vacuum lines for leaks, also test brakes for proper application.

DIFFERENTIAL CARRIER

REPLACEMENT

In some instances it may be desirable to r e move the differential carrier assembly from the axle housing, while the housing remains installed under the vehicle.

To a ssist in handling the differential carrier assem bly, a roller jack should be available; also, a pan for draining lubricant.

Inspect axle housing for lubricant leaks before cleaning, then steam clean thoroughly to remove all dirt or other foreign matter.

REMOVAL

1. Remove plug at bottom of housing to drain lubricant.

2. Remove axle shafts as directed under head ing "Axle Shaft Replacement" in this section.

3. On 2-speed axles disconnect lines from shift chamber or wiring from shift electric unit.

4. Disconnect propeller shaft from yoke as directed in "PROPELLER SHAFTS" (SEC. 4D).

5. Remove cap screw s or stud nuts, and lock washers, except two near top. Loosen two at top and leave installed to prevent carrier falling.

6. Support carrier on roller jack, remove top stud nuts or cap screw s, then work carrier free of housing. A sm all pinch bar may be used to keep carrier straight in housing bore, while carrier is withdrawn. End of bar must be rounded to prevent damage to carrier flange.

INSTALLATION

1. Install new differential carrier to housing gasket over studs or align bolt holes in gasket with holes in housing. On axles using cap screw s, in stall four temporary studs which will simplify locating carrier and gasket and a ssist in drawing carrier into place.

2. Roll carrier into place using roller jack.

Start carrier over studs and into housing, using flat washers under four equally spaced stud nuts.

3. Tighten all nuts evenly and alternately until carrier is in position. Replace temporary flat w ashers. Install lock washers, then tighten all nuts to specified torque.

4. Connect propeller shaft to rear axle yoke as directed in

"PROPELLER SH AFTS” (SEC.

4D).

5. On 2-speed axles connect wiring to electric shift unit or line to shift chamber.

6. Install axle shafts as directed under head ing "Axle Shaft Replacement" in this section.

7. Fill to level of filler plug opening with lub ricant recommended in LUBRICATION (SEC. 0) of this manual.

AXLE SHAFT REPLACEMENT

REMOVAL

Procedure for removal of axle shafts is the same with axle assembly removed or installed in the vehicle.

1. Remove nuts from studs attaching axle shaft flange to wheel hub.

2. Strike center of flange with a lead hammer to loosen flange and split tapered dowels from studs.

3. Remove split tapered dowels from studs.

In some instances it may be necessary to spread dowels, while being removed.

4. Grasp axle shaft flange and pull outward to remove. Remove and discard gasket.

INSTALLATION

1. Install new gasket over hub studs and against hub.

2. Dip splined end of shaft in axle lubricant, and insert shaft through hub.

3. Turn shaft as necessary to index shaft splines with differential side gear splines.

4. As shaft is pushed inward, rotate as nec essary to align flange holes with hub studs, then p ress shaft inward until flange is against hub.

5. Install split tapered dowel over each stud.

Install and tighten 5/8" nuts to 90-110 foot-pounds torque or 1/2" nuts to 50-60 foot-pounds torque.

6. Observe that clearance exists between nut and flange (fig. 6). If no clearance exists, this in dicates excessive wear at studs, dowels, or flange holes. Replace worn parts if necessary.

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Figure 8 — Propeller Shaft Yoke H oldin g Bar

PINION OIL SEAL REPLACEMENT

Several types of oil seal installation are used on axles covered by this publication. One type has the seal assembly installed directly into differen tial carrier, while another has the seal installed in a retainer which is attached to carrier.

REMOVAL

1. Remove propeller shaft from yoke at axle as directed in "PROPELLER SHAFTS" (SEC. 4D).

2. Hold propeller shaft yoke with holding bar

(fig. 8) while removing yoke retaining nut and washer.

3. Use suitable puller in manner typically i l lustrated in figure 9 to remove propeller shaft yoke.

4. On axle where seal and retainer is pressed into carrier, use available removing tool such as punch or pry bar. Remove flat washer from coun terbore in carrier.

5. On axles where seal and retainer assembly are attached to carrier by cap screw s, remove screw s and washers, then lift assembly from car rier. NOTE: Some axles also have a cork seal installed in a groove in pinion cage, which should be replaced.

INSTALLATION

1. Before installing new seal, be sure that differential carrier is cleaned of all deposits, such as oil, dirt, etc.

2. On axles where seal and retainer is p r e ss ed into carrier, install flat washer in carrier, then install strip sealer around carrier counterbore and against washer.

3. Coat outer surface of seal retainer with sealing compound, then position assem bly in car rier. Use suitable available tool to p ress or drive retainer into carrier until seated against flat washer.

4. On axles where seal and retainer assembly is attached to carrier by cap screw s, install cork seal in groove or gasket on pinion cage.

NOTE: Be sure that gasket does not cover any oil passage holes in pinion cage.

5. Install oil seal and retainer assembly over pinion and against pinion cage. Secure with cap

Figure 9 — Propeller Shaft Y oke Puller (Typical)

Figure 1 0 — Electric Shift Unit Seal M a rk in g s

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screw s and lock washers, tightened securely.

6. Coat lip of oil seal with axle lubricant, then install propeller shaft yoke, washer, and nut. Hold yoke with holding bar (fig. 8) while tightening nut to recommended torque.

3. Remove lock nuts and the two w ires from shift housing. Note that the long or black ribbed wire is attached to the bottom terminal.

ELECTRIC SHIFT UNIT REPLACEMENT

REMOVAL

1. Remove two shift housing to carrier stud nuts and lock washers (fig. 2).

2. Remove shift unit assem bly.

INSTALLATION

1. Check condition of rubber seal between shift unit and carrier. Seal must be in good con dition to prevent lubricant leaking into shift unit.

NOTE: Seal bears lettering "BOTTOM - FOR

WARD TANDEM" and "BOTTOM - SINGLE AND

REAR TANDEM," as indicated in insert of figure

10. Be sure seal is properly installed.

1 Motor Cover to Housing Screw (with Washer)

2 Motor to Cover Nut

3 Motor Cover Cable Clip

4 Motor Cover

5 Motor Cover Gasket

6 Electric Motor

7 Motor Grommet

8 Shift Unit Housing

9 Switch Terminal Nut (outside)

10 Switch Terminal Washer (outside)

11 Switch Terminal Bushing

12 Bearing (with snap ring)

13 Bearing Lock Nut

14 Bearing Cover Gasket

15 Bearing Cover

16 Bearing Cover to Housing Screw (With Washer)

17 Automatic Switch Assembly

18 Switch to Housing Screw (inside)

19 Switch Terminal Nut (inside)

20 Drive Screw Assembly

21 W7inding and Actuating Lever Shaft

22 Shift Fork Actuating Lever Assembly

23 Torsion Spring

24 Spring Winding Lever Assembly

25 Shift Housing Cover Gasket

26 Shift Housing Cover and Detent Spring

27 Lubricant Plug

28 Housing Cover to Housing Screw (with Washer)

Figure 11 — Electric Shift Unit C om pon ents (Eaton a n d Corporation)

TP-8598 -1

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Figure 12— Position of Drive N ut W hen Disassem bling

Figure 13— Rem oving Shaft, Actuating Lever, and Spring

2. Install w ires to outside term inals. The long black ribbed wire is attached to bottom terminal.

Harness is clipped to cable clip on housing.

3. With seal between carrier and shift unit in place, install shift unit over carrier studs. Make certain that the swivel block of the shift fork ac tuating lever fits into the slot in carrier shift fork.

Tighten stud nuts firm ly.

4. Check installation by making a "Lo" and

"Hi" range shift. Ignition or control switch must be turned on before check can be made.

NOTE: The shift unit motor is designed to be reversible and runs equally well in either d irec tion. If the terminal w ires are reversed, the unit will shift to "Low" when the control switch button is in "Hi" position, and will shift to "High" when the button is in "Lo" position.

REMOVAL OF ROCKWELL SHIFT UNIT

It is necessary to partially disassem ble the

Rockwell electric two-speed unit to remove it from axle housing. This may be accomplished in the following manner:

1. Remove five screw s from shift unit housing cover (25) (refer to fig. 18), then remove cover.

This also drains the lubricant. After cover is re moved, note that drive screw nut is either at top or bottom (fig. 3) depending on whether axle is in

"HIGH" or "LOW" range position.

2. Loosen shift unit-to-differential carrier stud nuts (fig. 16) to remove preload from shift unit spring.

3. Turn drive screw by hand to run nut to mid way position on drive screw, sim ilar to figure 12.

This is necessary to prevent damage to drive nut contact bumper.

4. Pull out lever shaft (fig. 16). Disconnect torsion spring from push rod, then remove spring and spring winding lever.

5. Remove shift unit-to-differential housing

Figure 14— R e m o v in g Drive Screw B ea rin g

Figure 15 — R e m o v in g M oto r W ires

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stud nuts, then remove shift unit from axle.

6. Remove wire cable clip from shift unit cover. Note to which terminal each wire is attach ed, then disconnect the two w ires from shift unit term inals.

ELECTRIC SHIFT UNIT OVERHAUL

The following information is provided on the assumption that shift unit has been tested and r e moved as previously instructed.

DISASSEMBLY (EATON AND CORP.)

Key numbers in text refer to figure 11.

1. Remove six screw s (28) and lock washers w hich attach c o v e r (26) to sh ift m otor h ousin g (8).

Drain lubricant from housing. Remove gasket (25).

2. After removing cover (26), the drive screw

(20) nut will be at either top or bottom depending upon the position in which the control switch was last left.

3. By turning drive screw, run nut from top or bottom to the center of the screw (fig. 12).

IMPORTANT: The previous step is essential to prevent damage to drive nut contact bumper, and is also necessary in assem bly.

4. Remove shift fork actuating lever (22), tor sion spring (23), and spring winding lever (24) as an assem bly by pulling shaft (21) up. Swing the assem bly away from the drive nut and lift out of the housing (fig. 13).

5. Remove three screw s and lockw ashers (16) which attach bearing cover (15). Remove cover and gasket (14).

6. Push down on drive screw assembly (20) until bearing assembly (12) is free of housing.

7. Insert screwdriver in drive slot of screw

(fig. 14), then remove bearing lock nut (13) and bearing with snap ring (12). Drive screw assembly

(20) can then be lifted out of housing.

8. Remove the two lock nuts (19) from switch term inals (17). Pull off motor w ires (fig. 15).

9. Remove three screw s and lock washers (1) which attach motor cover (4) to housing. Pull out motor (6) with cover (4) attached to motor with two cover nuts (2). Remove grommet (7).

10. Remove two jam nuts (9) and fiber washers

(10) from outside of housing. On inside remove switch center screw (18). Pull out automatic switch

(17) as shown in figure 17.

11. Do not disassem ble the shift fork actuating lever (22), torsion spring (23), and spring winding lever (24) unless necessary to replace one of the parts. If necessary to disassem ble, mount assem bly in vise as shown in figure 18. Turn spring winding lever (24) clockwise and pull to separate.

DISASSEMBLY (ROCKWELL) (Refer to Fig. 18)

1. Remove three screw s and lockw ashers (16) which attach bearing cover (15) to bottom of shift

Figure 16— Shift Unit Cover Removed(Rockwell Axles)

unit housing. Remove cover and gasket (14).

2. Push down on drive screw assembly (20) until bearing assem bly (12) is free of housing.

3. Insert screwdriver in drive slot of screw

(fig. 14); then remove bearing lock nut (13) and bearing with snap ring (12). Drive screw assembly

(20) can then be lifted out housing.

4. Remove the two lock nuts (19) from switch term inals (17). Pull off motor w ires (fig. 15).

5. Remove three screw s and lock washers (1) which attach motor cover (4) to housing. Pull out motor (6) with cover (4) attached to motor, with two cover nuts (2). Grommet (7) can then be re moved.

6. Remove two jam nuts (9) and fiber washers

(10) from outside of housing. On inside remove switch to housing screw s (18). Remove automatic switch.

7. Do not disassem ble torsion spring (23), and spring winding lever (22) unless necessary to r e place one of the parts. If necessary to disassem ble,

Figure 1 7 — D isa sse m b lin g Torsion Sp rin g from Lever

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mount assem bly in vise as shown in figure 19.

Place a short piece of rod in hub of spring winding lever as a safety factor to prevent injury should torsion spring slip out of control. Next, place two lengths of tubing over ends of spring, pull spring ends apart, then raise spring above spring winding lever (fig. 20). To assem ble, reverse above pro cedure.

CLEANING AND INSPECTION

Clean all parts except motor in cleaning so l vent. Inspect as follows:

Automatic Switch

The switch assembly is serviced only as an assem bly. The switch should have clean free mov ing points which close firmly under spring tension.

1 Motor Cover to Housing Screw (with Washer)

2 Motor to Cover Nut

3 Motor Cover Cable Clip

4 Motor Cover

5 Motor Cover Gasket

6 E lectric Motor

7 Motor Grommet

8 Shift Unit Housing

9 Switch Term inal Nut (outside)

10 Switch Term inal W asher (outside)

11 Switch Term inal Bushing

12 Bearing (with Snap Ring)

13 Bearing Lock Nut

14 Bearing Cover Gasket

15 Bearing Cover

16 B earing Cover to Housing Screw (with Washer)

17 Automatic Switch A ssem bly

18 Switch to Housing Screw (inside)

19 Switch Term inal Nut (inside)

20 D rive Screw A ssem bly

21 Winding and Actuating L ever Shaft

22 Spring Winding Lever

23 T orsion Spring

24 Shift Housing Cover Gasket

25 Shift Housing Cover and Detent Spring

26 Lubricant Plug

27 Housing Cover to Housing Screw (with Washer)

28 Housing to C arrier Seal

Figure 18 — Electric Shift Unit C om pon ents (Rockwell)

G M C S E R V I C E M A N U A L

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Drive Screw

The drive screw assembly is serviced only as an assem bly. While holding the nut, rotate the screw from one end to the other. It should rotate freely. When the nut gets to either end of the screw, the screw should continue to turn, but the nut should not jam or run off the ends.

Electric Motor

The motor (serviced only as an assembly) is reversib le. With the motor housing connected to one battery terminal, and either one of the two motor w ires connected to the other battery term inal the motor will run in one direction. With the other motor wire connected to the battery, motor w ill run in the opposite direction.

The motor has a stall torque of approximately

6 inch-pounds. Clamp a sm all crescent wrench on the rectangular drive on the armature shaft. Place motor in vise, and grasp wrench handle with one hand. Connect one motor wire to a battery terminal and connect motor housing to the other battery term inal. The wrench should tend to turn with a torque of about 6 inch-pounds. Allow wrench to turn VERY SLOWLY, making sure that this pull or torque is present the FULL 360 degrees turn of the wrench. If one armature is burned out, the torque will disappear for a sm all part of the 360 degrees. Do not overheat the motor while making test. Motor must be replaced as an assembly, and is lubricated for life of motor. The motor used is

12-volt type which is the same as truck electrical system . When installing a new motor use care to select motor of proper voltage. Voltage is stamped on motor housing and on side cover of shift unit.

M iscellaneous Parts

Gaskets should be replaced at assembly.

Inspect bearing. If balls are rough or chipped, replace with new bearing and snap ring assem bly.

Pack bearing assembly with clean grease (Chassis

Grease) - Symbol "C" in LUBRICATION (SEC. 0).

Inspect torsion spring (23, fig. 11 and 18) for breaks or wear at lever contact points. Make c e r tain that correct replacement spring is used.

ASSEMBLY (EATON AND CORP.)

Key numbers in text refer to figure 11.

1. Install automatic switch assembly (17) into housing. Use flat head screw (18) to attach switch to housing. On outside of housing, install two bush ings (11), fiber washers (10), and jam nuts (9) over switch terminal screw s. Tighten nuts firm ly.

2. Install motor assembly grommet (7), then install gasket (5) on housing. Install motor (6) and cover (4) into housing. Install three screw s and lock washers (1) and two stop nuts (2). Install motor cover cable clip (3) under outer screw.

Tighten screws and nuts firm ly.

Figure 19— Rem oving Torsion Spring (Rockwell)

3. Attach motor w ires to switch term inals.

The red or longer wire attaches to bottom term inal. Tighten inside terminal nuts (19) firm ly.

4. With a screwdriver inserted into slot of drive screw (20), install bearing (12) on end of screw with shielded side of bearing toward inside.

Retain bearing with bearing lock nut (13).

5. Run nut to center of screw, then insert slotted end of screw into housing, meshing slotted end with armature shaft.

NOTE: Fiber bumper contacts on drive nut must be toward switch.

6. Install gasket (14) and cover (15) with three screw s and lock washers (16). Tighten screw s firm ly.

7. If the assem bly consisting of shift fork ac tuating lever (22), torsion spring (23), and spring winding lever (24) has been separated, reassem ble.

With shift fork actuating lever (22) in vise, assem ble parts as shown in figure 21. Turn the spring

Figure 2 0 — R e m o v in g Torsion Spring (Rockwell)

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and fiber contact bumper down toward switch, position the slots of winding lever over the drive nut. Install the shaft (21) through center of the assembly into depression in housing.

9. Install new gasket (25) on housing. Install cover (26) with spring detent against drive nut.

Retain cover with screw s and lock washers (28).

10. Remove oil plug (27). With unit standing with motor up, lubricate in accordance with in structions given in LUBRICATION (SEC. 0). Re install plug and tighten firm ly.

Figure 21 — A sse m b lin g Torsion Spring and Levers (Eaton)

winding lever (24) with one end of spring, in clock w ise direction until end of spring is past shift fork actuating lever; then push in on assembly until positioned as shown in figure 17.

8. Dip above assem bly in lubricant. With drive nut on drive screw assembly in center of screw,

ASSEMBLY (ROCKWELL)

Key numbers in text refer to figure 18.

Tighten screw s and nuts firm ly.

1 Compression Nut

2 Screw

3 Valve Cover

4 Cover Gasket

5 Trunnion Screw

6 Valve Body

7 Body Gasket

8 Lower Valve Body

9 Tension Spring

10 Operating Lever

11 Trunnion

12 Retaining Washer

Figure 2 2 — Sectional a n d D isa sse m b le d V ie w s of Control Va lve

13 Poppet Lever

14 Pivot Pins

15 Poppet Spring

16 Poppet Stem

17 Poppet (Valve)

T P M -7 5 9 0

3. Attach motor w ires to switch term inals.

The red or longer wire attaches to bottom term inal. Tighten inside terminal nuts (19) firm ly.

4. With a screwdriver inserted into slot of drive screw (20), install bearing (12) on end of screw with shielded side of bearing toward inside.

Retain bearing with bearing lock nut (13).

5. Run nut to center of screw, then insert slotted end of screw into housing, meshing slotted end with armature shaft.

NOTE: Fiber bumper contact on drive nut must be toward switch.

6. Install gasket (14) and cover (15) with three screw s and lock washers (16). Tighten screws firm ly.

NOTE: R em ain d er of a sse m b ly of sh ift unit used on Rockwell axles must be completed when unit is installed on housing as described previous ly in the section under "Two-Speed Shift Unit

Replacement."

V A CU U M CONTROL VALVE

Control valve (fig. 22) requires very little maintenance, unless cleaning of air cleaner has been neglected and valve has become contamin ated as a result of neglect. However, should tests indicate that valve is faulty it should be repaired or replaced.

REMOVAL

1. Remove manifold to valve vacuum line, air cleaner line, and speedometer shift line from re spective valve ports.

2. Remove two axle shift chamber lines from valve ports.

3. Loosen cable clamp nut at top of valve.

4. Remove two mounting screw s, separate valve from mounting surface, and loosen cable trunnion screw.

5. Remove valve from control cable.

DISASSEMBLY (Fig. 22)

1. Remove four screw s, and separate cover, cover gasket, valve body assembly, body gasket, and lower body.

2. Remove two tension springs from ends of poppet lever and trunnion pin.

3. Remove two retaining washers, poppet springs and poppet valve assem blies from valve body. Remove d iscs from valve stem s.

INSPECTION

1. Check poppet valve seats in valve body and lower valve body for evidence of nicks or scratches which may cause vacuum leak.

2. Inspect poppet lev ers, springs, operating lev ers, trunnion pin, and pivot pin for wear or other damage.

G M C S E R V I C E M A N U A L

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REAR AXLE AN D CONTROLS

3. Inspect poppet discs and replace if not in new condition, since these item s are included in a repair kit.

ASSEMBLY (Fig. 22)

During assem bly operations apply a light film of Lubriplate, or equivalent, to all friction su r faces.

1. Place rounded end of operating levers over ends of pin in cable trunnion.

2. Align poppet lever between holes at pointed end of operating levers, and align to valve body.

NOTE: Be sure parts are assembled with trun nion pin off-center toward operating lev ers. Install pivot pins, driving pin in until ends are flush with valve body.

3. Install new poppet discs to ends of poppet stem s. Install poppet springs.

4. Install poppet valve stem s through holes in body and through elongated holes in poppet lever.

Install new retaining washers.

5. Install tension springs. One end of spring attaches to trunnion pin and opposite end to notch in poppet lever arm.

NOTE: Test operation of valve by moving trunnion up and down several tim es by hand, while noting if "over center" action of the tension springs cause poppets to operate freely and without binding.

6. Install new gasket to lower valve body and align body with valve body.

7. Hold these two parts in place while p osi tioning new gasket and valve cover to top of valve body. Install and tighten four screw s.

BENCH TEST

The following test will determine if the valve has been correctly assembled and is operating properly without serious vacuum leakage.

1. Attach vacuum source to vacuum port and install a shut-off valve in line.

2. Attach a vacuum line to each of the valve ports leading to axle shift chamber. Each line should have a vacuum gauge.

3. Supply 20 inches of mercury vacuum to valve with valve trunnion in "up" position. One gauge should read 20 inches of mercury and op posite gauge should read zero.

4. Push valve trunnion down and close speed ometer adapter outlet port. Reading on vacuum gauges will now be opposite to previous reading.

5. Check "snap over" position of cable trun nion, which should occur when trunnion is not le s s than 1/8" from valve body in each direction.

6. Whenever tests outlined in previous para graphs indicate that leakage is greater than 1 inch in 15 seconds, the valve must be inspected for faulty seats.

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Figure 2 3 — Two-Speed Axle Vacuum Shift Cham ber

Installed (Corporation Axle)

INSTALLATION

1. At cable button clamping bracket, loosen cable jacket clamp nut allowing cable to turn freely.

2. Insert cable into hole at top of valve cover and insert cable into hole in cable trunnion. Install and tighten cable securely, using trunnion screw.

3. Mount valve in the original location using mounting screw s. Tighten cover tube nut.

4. Attach intake manifold, air cleaner, speed ometer shifter changer, and shift chamber lines to valve in their original location.

5. With cable button pushed down, position operating button bracket to shift lever so that clearance exists between bottom of button and bracket.

SHIFT CHAMBER (CORP. AXLE)

REMOVAL (Fig. 23)

1. Remove hose clamps, then remove vacuum hose from cylinder. Tag each hose so that it will be replaced in proper position.

2. Remove three bolts and lock washers at taching cylinder to differential carrier, then r e move cylinder and housing assembly.

DISASSEMBLY (Fig. 24)

1. Remove screw s attaching two halves of cylinder to each other, then separate two halves.

2. Using two wrenches, remove outer push rod nut, then separate push rod from diaphragm.

3. Push piston rod in to relieve spring load, then remove snap ring from inside of piston rod.

Pull push rod and spring assembly from piston rod.

4. Should inspection indicate necessity, oil seal can be driven from housing at this tim e.

Figure 2 4 — Sectional V iew of Two-Speed Axle V acuum Shift Cham ber (Corporation Axle)

G M C S E R V I C E M A N U A L

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ASSEMBLY (Fig. 24)

1. Install washer, long spacer, spring, washer, short spacer, and nut on push rod.

2. Tighten adjusting nut until dimension over washers at each end is 2 -2 7 /3 2 ” (fig. 25). Install and tighten lock nut, being careful not to change dimension.

3. Lubricate inside of piston rod then install push rod and spring assem bly.

ring.

4. Compress push rod spring and install snap

5. Install push rod assem bly in housing.

6. Install new diaphragm and plates to push rod and tighten nut securely.

NOTE: Apply sealing compound around push rod hole in diaphragm plates.

7. Install outer half of cylinder to inner half and secure with screw s tightened securely.

8. Attach assembly to differential carrier, using new gasket. Tighten cap screw s securely.

9. Attach hoses to cylinder, being sure con nections are tight.

Figure 2 5 — Adjusting Push Rod (Corporation)

SHIFT CHAMBER (ROCKWELL AXLE)

REMOVAL AND DISASSEMBLY (Fig. 26)

1. Remove hose clamps, then remove vacuum hose from chamber. Tag each hose so that it can be identified and installed in proper position.

1 Diaphragm

2 Shift Chamber Assembly

3 Oil Seal

4 Differential Carrier

5 Push Rod Spring

6 Push Rod

7 Piston Rod

8 Lock Screw and Nut

9 Shift Fork

10 Sliding Clutch

11 Clutch Poppet

12 High Speed Gear

13 Cross Shaft

14 Low Speed Gear

15 Mounting Sleeve

16 Adjusting Shims

17 Stud and Nut

18 Snap Ring

19 Nut

Figure 2 6 — Sectional V ie w of Tw o -Spe ed A xle Shift C h am b er Installation (Rockwell)

T -3 4 7 1

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Figure

2 7 —

Two-Speed Axle V acuum Shift

C ham ber Installed (Rockwell)

2. Remove ten screw s attaching cover to chamber, then remove cover from body of cham ber.

3. Remove nut from end of push rod, then r e move diaphragm and plates assembly from push rod.

1 Diaphragm Body

2 Diaphragm Return

Spring

3 Diaphragm and Rod

Assembly

4 Mounting Bracket

5 Screws

t p m

-9 0 8 3

Figure 2 8 — Speedom eter A dapter Shift D ia p h r a g m

4. Remove two nuts and lock washers from studs (fig. 27) attaching chamber mounting flange to mounting sleeve and carrier. Remove chamber assem bly.

5. Force push rod in to relieve spring load, then remove snap ring (18) from inside of piston rod. Pull push rod and spring assembly from piston rod.

6. Piston rod and shift fork cannot be removed unless carrier assembly is removed from housing.

Refer to respective axle section for procedure.

ASSEMBLY AND INSTALLATION (Fig. 26)

1. If disassembled, assem ble push rod by in stalling parts in following order: washer, spring, washer, spacer, and nut. Stake nut securely to p re vent loosening.

2. Position push rod and spring assembly into piston rod. Compress spring sufficiently to install snap ring (18).

3. Apply sealing compound on the diaphragm plates around holes. Position diaphragm between two plates with diaphragm bead in grooves of plates.

4. Secure plates together with bolt, locking plate, and nut (19). Make sure that diaphragm is properly located, then tighten nut just enough to form a vacuum-tight seal.

5. Install chamber inner shell with flange over studs (fig. 27). Install lock washers and nuts, tighten nuts securely.

6. Position diaphragm assem bly over push rod, then install nut. Tighten nut securely.

7. Install cylinder outer shell to inner shell with diaphragm between sh ells. Install and tighten screw s firm ly.

8. Attach hose in their original location, using hose clamps.

CHECK VALVE

Check valve, in intake manifold line, is used to prevent vacuum lo ss or drop when engine is accelerated or is pulling under heavy load. Check valve also effectively retards lo ss of vacuum when engine is stopped. Refer to "HYDRAULIC BRAKES"

(SEC. 5A) of this manual for service maintenance information.

AIR CLEANER

An air cleaner is used at atmospheric inlet line to filter air entering control valve and shift units.

MAINTENANCE

At regular intervals remove air cleaner and im m erse in cleaning solvent to remove all accum ulated dirt or other foreign material. Drain clean ing solvent from element. Reinstall dry.

G M C S E R V I C E M A N U A L

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SPEEDOMETER ADAPTER

SHIFT DIAPHRAGM

When shift control lever is moved to "HI" position, cavity behind speedometer adapter shift diaphragm (fig. 28) is subjected to atmosphere through the shift control valve. Spring movement of diaphragm is transmitted to the speedometer adapter lever by the diaphragm rod, shifting the speedometer adapter gears into high ratio. When the control lever is moved to "LO" position, the control valve admits vacuum to the cavity behind the diaphragm and forces diaphragm and rod in ward, shifting the speedometer adapter gears into low ratio.

REMOVAL AND DISASSEMBLY

1. Disconnect vacuum line from the shift diaphragm body.

2. Remove two screw s attaching diaphragm bracket to speedometer adapter. Lift diaphragm and bracket to unhook diaphragm rod from adapter lever and remove diaphragm and bracket assembly.

3. Remove four screws attaching body to bracket. Remove body, spring, and diaphragm and rod assembly from bracket.

INSPECTION

1. Examine diaphragm for cracks or other damage. Replace assembly if diaphragm is damaged.

2. Check condition and tension of diaphragm spring. If spring is corroded or if tension is not sufficient to return diaphragm to release position, replace assem bly.

ASSEMBLY AND INSTALLATION

1. Position the diaphragm and rod assembly, spring, and body on diaphragm bracket and attach with four screw s. Screws must be tightened suf ficiently to make the assembly air-tight with two pounds of air pressure.

2. Position diaphragm and bracket assembly at speedometer adapter, hooking diaphragm rod into adapter lever. Attach diaphragm bracket to adapter with two screw s and washers.

3. Connect vacuum line to diaphragm body.

Tighten connection firm ly.

See next page for Torque Specifications.

Sec. 4A

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REAR AXLE TORQUE SPECIFICATIONS

IT E M

D R IV E PIN IO N Y O K E NUT

Eaton

T O R Q U E (F T . L B .) lVfi"-18..................................................................................................................325-450

M M 2 ..................................................................................................................400-600

1 H M 8 ..................................................................................................................500-700

Rockwell r - 2 0 ................................................................................................. 300-400

1 H M 8 ..................................................................................................................700-900

"-18................................................................................................................800-1100

Corporation

P/s "-18.................................................................................................................. 160-280

D IF F E R E N T IA L C A R R IE R TO H O U SIN G

Eaton

V i" -\l

Cap S cre w ................................................................................................... 75-85

5/8" - l l Cap S cre w ............................................................................................... 160-175

5/s"-18 Stud N u t.................................................................................................. 220-240

Rockwell

W - 2

0 Stud N ut.................................................................................................... 80-105

5/s"-18 Stud N ut.................................................................................................. 160-205

Corporation

7/ie"-20 Cap S c re w .................................................................................................. 75-90

9/ie"-1 8 .................................................................................................................. 130-170

O IL S E A L R E T A IN E R & PIN IO N C A G E

Eaton

9/ie"-12.................................................................................................................. 115-125

Rockwell

7/ie"-1 4 ...................................................................................................................... 55-70

......................................................................................................................80-105

9/ie"-12.................................................................................................................. 115-150

Corporation

W '- \3

(H 1 35 )...................................................................................................... 160-170

V i"-U

(H 1 50 )........................................................................................................ 80-105 fc"-13 (T 1 5 0 )........................................................................................................ 80-105

5/8" - l l (H I 1 0 )...................................................................................................... 160-170

S H IF T C H A M B E R

Stud N u t - 3/8"-24................................................................................................... 30-35

A X L E S H A F T F L A N G E

Stud N u t - 1/? " ......................................................................................................... 50-60

Stud Nut—H " ....................................................................................................... 90-110

Cap S c r e w - 5/ie"-24............................................................................................... 11-18

G M C S E R V I C E M A N U A L

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Page 145

H e a A S i

P rogressive type, two-stage rear springs, as used on all 4000 and PS4500 Series (fig. 1), have a straight-ended main leaf which rests against the cam surface of the front and rear hangers, thereby allowing the springs a full fore and aft float to effect spring length changes. The second or third leaf has hooked ends which contact rebound pins in the spring hangers to prevent excessive fore and aft travel in event of radius leaf rod failure.

The radius leaf rods maintain axle alignment and transmit driving and braking forces to the fram e. A spacer is used at bottom of each spring p ile to separate the last leaf from the radius leaf which is half-leaf formed with an eye and bushed for attachment to the front hanger.

Two slanted U-bolts attach the spring pile and radius leaf to the axle housing. Vari-rate type rear springs shown in figure 2 are used on all "E," and "S" Series veh icles. The spring eye is bushed and bolted to a bracket at front and is cam -sup ported at rear. Cam action of the spring leaf pro duces a variable deflection rate as contact point changes under varying load.

NOTE: Refer to "Service Diagnosis Chart" in "FRONT SPRINGS" (SEC. 3C) of this manual.

GENERAL SPRING MAINTENANCE

LUBRICATION

Spring leaves are lubricated at time of a s sem bly and require no further lubrication unless spring is disassem bled. Spring eye or radius leaf

SECTION 4B

i g m o

bushings that are rubber-mounted do not require lubrication.

TIGHTENING

At regular intervals, spring U-bolts should be checked and tightened if necessary to torque listed in "Specifications" at end of this section.

IMPORTANT: U-bolts must be kept TIGHT at all tim es to hold axle inplace at springs. Other w ise, axle may shift, causing misalignment; also, spring leaf failure in the vicinity of the spring center bolt could result.

CAUTION

U-bolts must be retightened to initial torque listed in "Specifications" after 500 m iles when new, or when spring repairs are made.

NOTE: The center bolt serves only to hold the spring together while in shipment and during in stallation, and as a locating point when assembling spring to axle. After assem bly, it is strictly the function of the U-bolts to hold the spring and axle in alignment, and the importance of keeping the

U-bolts tight cannot be overemphasized.

REPAIR OPERATIONS

REAR SPRING REMOVAL (Figs. 1, 2, and 3)

1. Raise vehicle frame to take weight off the spring. Make sure vehicle is supported safely.

Figure J— Rear Sp rin gs Installed (Series 4 0 0 0 a n d P S4 5 0 0 ) (Typical)

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REAR SPRINGS AND SUSPENSION

AUXILIARY SPRING

ASSEMBLY

Figure 2 — Rear Springs Installed (Typical for

“ £ ”

and “S” Models)

Remove rear wheels to provide access to spring assem bly.

2. Safely support axle on floor jack.

3. Install a C-clamp on radius leaf as shown in figure 3, to relieve load on radius leaf eye bolt on 4000 and PS4500 Series vehicles.

4. On 4000 and PS4500 Series (fig. 1), at front and rear hanger, remove rebound pin retainer bolt, then remove retainer. Install suitable puller

Figure 3 — U sin g C -C lam p at R adius Leaf

into tapped hole at end of rebound pin, then remove pin.

5. On "E," and "S" S eries, remove rebound bolt nut and washer, then remove rebound bolt

(fig. 2).

6. Remove spring U-bolt nuts, shock absorber bracket (when used) U-bolt anchor plate and Ubolts and U-bolt spacer, then lower axle slightly.

7. Remove spring eye or radius bolt nut and washer, then remove spring eye bolt from spring eye or radius leaf.

NOTE: When tapered shim is used, the p osi tion of shim thin and thick edge should be noted so that shim can be installed properly at assem bly.

8. Inspect spring. Replace bushing, repair or replace spring unit as outlined later in this section.

SPRING LEAF REPLACEMENT

NOTE: Auxiliary springs should be d isassem bled in an arbor p ress. When assembling springs, make sure spacer is installed between the auxil iary and main spring.

1. Mark one side of spring assembly to assure original position of springs when assembling.

2. Place spring in a vise and remove spring clip, bolt, nut, and spacer.

3. File peened end of center bolt and remove center bolt nut.

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J-2 1 0 5 8

Figure 4 — Rem oving Rubber-Type Eye B ushing

4. Open vise slowly and carefully to let spring assem bly expand. Wire brush and clean spring leaves.

5. Replace weak or broken spring leaf.

6. Align center bolt holes in spring leaves using a long drift.

7. Compress spring leaves in a vise, then re move drift and install a new center bolt.

8. Install nut on center bolt and tighten s e curely. Peen end of bolt to prevent nut from loo s ening.

9. Align springs by tapping with a hammer.

Install spring clip, bolts, spacers, and nuts.

SPRING EYE OR RADIUS LEAF BUSHING

REPLACEMENT (WITH SPRINGS REMOVED)

Steel Backed Rubber Bushings

Remove and replace radius leaf eye bushing using bushing remover and installer (J-21058 Tool

Set) as shown in figures 3 and 4.

REAR SPRING INSTALLATION

(Refer to Figs. 1, 2, and 3)

1. Set spring assem bly and tapered shim or spacer (if used) at axle pad.

IMPORTANT: Tapered shim must be installed on axle in same position that was noted at removal.

NOTE: If auxiliary springs are used, place spring assem bly and spacer in position.

2. Install U-bolt spacer over center bolt.

3. Seat U-bolts in spacer grooves, then s e cure spring to axle by installing anchor plates, shock absorber bracket (when used) and nuts on

U-bolts. Tighten nuts to torque listed in "Speci fications" at end of this section.

4. On "E," and "S" S eries, lower frame until spring enters hanger with spring eye and hanger hole aligned at front and spring touches cam sur face of hanger at rear.

5. On 4000 and PS4500 S eries, lower frame until ends of spring enter the hanger and touch the cam surface of hanger. Compress radius leaf with

Figure 5 — Installing Rubber-Type Eye B ushing

a C-clamp (fig. 3) until radius leaf eye and hanger holes are aligned.

6. On 4000 and PS4500, torque nut to torque listed in "Specifications." On "E," and "S" Series, torque the eye bolt to torque listed in "Specifica tions."

7. On 4000, and PS4500 Series, remove Cclamp from radius leaf.

8. On 4000, and PS4500 S eries, install re bound pin at front and rear hangers. Install re bound pin retainer and secure with retainer bolt.

9. On "E," and "S" S eries, install rebound bolt, washer and nut at rear hanger. Tighten re bound bolt nut to torque listed in "Specifications."

10. Install wheels.

11. Remove blocking and lower frame to place weight on springs. Check U-bolt nuts for proper torque. Refer to "Specifications."

CAUTION

U-bolts must be retightened to initial torque listed in "Specifications” after 500 m iles when new, or if spring repairs are made.

AUXILIARY SPRINGS

Some vehicles have auxiliary rear springs which are necessary for certain types of oper ation. When used, the auxiliary spring leaves or leaf (Single Leaf Auxiliary) are installed above the regular rear spring assem bly and are held in place by long U-bolts. Brackets are installed on frame and are contacted by the auxiliary spring to pro vide added stability required for these unusual conditions.

SHOCK ABSORBERS

Shock absorbers (when used) are non-adjustable and non-repairable. Maintenance operations

Sec. 4B

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are limited to replacement of rubber mounting grommets and periodically tightening all mountings. If a shock absorber becomes inoperative, the complete unit must be replaced.

CAUTION: When replacing a shock absorber, check the model number stamp ed on the unit to make sure it is the same model as the one removed.

SPECIFICATIONS

REAR SUSPENSION SPECIFICATIONS

SPRIN G EYE BU SH IN G —(4000 and PS4500) (Steel Backed Rubber T y p e )..................................................................................... (W idth) 3.270"-3.300"

(O .D .) 1.750"-1.755"

(I.D .) 0.940"-0.950"

(W idth) 2.725"-2.750"

(.O D .) 1 .3 7 5 M .38 0 '

RADIUS LEA F BU SH IN G —(A ll 400 0 -P S -4 50 0 ) (Steel Backed Rubber T y p e )................................................................................ (I.D .) 0.625"-0.632"

TORQUE SPECIFICATIONS

SPRIN G U-BOLT NUTS

All 4000 S e rie s.................................................

(A ll E and S M odels)......................................

PS-4500 Models...............................................

REAR SPRIN G REBOUND BO LT NUT

(A ll E and S M odels)....................................

SHOCK A BSO RBER NUTS

(Upper Nut All 4000 S e rie s).........................

(Low er Nut All 4000 S e rie s).........................

REAR SPRIN G EYE TO

Front Hanger Bolt Nut (All 4000 S e r ie s )..

(A ll E and S Series) Radius Leaf Bolt Nut.

REBOUND PIN RETA IN ER BOLT

(4000 and PS 4500 S e rie s)............................

FT. LB S .

220

300

175

450

TORQUE

320

225

500

G M C S E R V I C E M A N U A L

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fleoA

DESCRIPTION

Rear hubs on all se r ie s trucks are mounted to axle housing tube on opposed tapered roller bear ings as shown in figure 2. Hubs, bearings, and oil seals are identified with the type of rear axle.

Refer to "Service Parts Identification Decal" to determine type of axle used on a specific vehicle.

Mounting parts (mainly bearings, seals, and sleeves) are of primary importance. Brake drum mounting bolts, studs, and nuts differ in type and their method of installation on the various series vehicles will vary.

BEARING MAINTENANCE

All wheel bearings are adjustable for wear.

Satisfactory operation and long life of bearings depend upon proper adjustment and correct lubri cation. If bearings are adjusted too tight, they will overheat and wear rapidly. Loose adjustment will cause pounding and will also contribute to steering difficulties, uneven tire wear, and inefficient brakes.

Bearing adjustment should be checked at regular inspection periods.

Hubs and bearings should be cleaned, inspect ed, and lubricated whenever hubs are removed, or at intervals indicated in LUBRICATION (SEC. 0) of this manual.

New hub oil seals should be installed when servicing bearings if there is the slightest indi cation of wear or damage. An imperfect seal may perm it bearing lubricant to reach brake linings, resulting in faulty brake operation and n ecessitat ing premature replacement of linings.

SECTION 4C

a n d feea'dnaA.

ADJUSTMENT

1. Jack up axle and remove axle shaft as directed in "REAR AXLES" (SEC. 4A) of this manual.

2. Remove bearing lock nut and nut lock.

3. With a wrench, tighten adjusting nut to torque listed in "Specifications," while the wheel is being rotated in both directions to correctly position the bearings.

4. Back off the adjusting nut 1/8 to 1/4 turn.

5. Install bearing adjusting nut lock, referring to figure 1.

a. If vehicle is equipped with type shown in

View A, figure 1, align nearest slot in adjusting nut with short tang on nut lock and bend tang into slot on nut. Install lock nut with slots outward and tighten to torque listed in "Specifications." Then bend tangs of nut lock into slots in lock nut and adjusting nut.

b. If vehicle is equipped with type shown in

View B, figure 1, align flat on adjusting nut with nearest lip of nut lock. Make sure wheel turns freely; then install nut lock and lock nut. Tighten lock nut to torque listed in "Specifications." Bend one lip of nut lock over one flat on each nut.

6. After completing bearing adjustment, r e check adjustment to make sure wheel turns freely.

Final bearing adjustment should be within 0.001" to 0.007" end play.

LOCKNUT

A D JU ST IN G

NUT

BEARING

BEARING ADJUSTMENT

NUT

LOCK

W ASH ER

BEARING ADJUSTMENT CHECK

Before checking wheel bearing adjustment, make sure brakes are fully released and do not drag. Jack up axle until tire s clear the floor. Re move axle shafts as directed in "REAR AXLES"

(SEC. 4A) of this manual.

Check bearing play by grasping tire at top and pulling back and forth, or by using a pry bar under tire. If bearings are properly adjusted, movement of brake drum in relation to backing plate or brake spider will be barely noticeable and wheel will turn freely. If movement is excessive, adjust as follows:

NUT

LOCK

AD JU STIN G

NUT

BEARING

Figure 1 — Rear W h e e l B e a rin g A d ju stin g Nuts

T - 8 9 6

Sec. 4C

Page 150 G M C S E R V I C E M A N U A L

REAR HUBS AND BEARINGS

H I 10, H I 35, A X L E S — w / D IS C W H E E L S

H I 50, T 1 50, G 1 6 1 , G 3 6 1 A X L E S - w / C A S T W H E E L S

1 6 1 2 1 , 16 2 2 1 , 1 7 1 2 1 , 17 22 1 A X L E S - w / C A S T W H E E L S

1 6 1 2 1 , 1 6 2 2 1 , 17 1 2 1 , 17221 A X L E S - w / D I S C W H E E L S

1 Axle Shaft 20 Stud

2 Cap Screw

3 Dowel

4 Lock Nut

5 Washer

6 Gasket

7 Axle Shaft Spacer

21 Lock Nut

22 Oil Shield

23 Inner Bearing Cup

24 Inner Bearing Cone and Rollers

8 Nut Lock

9 Lock Nut

25 Oil Deflector

26 Inner Oil Seal

27 Seal Ring

10 Adjusting Nut 28 Oil Seal Sleeve

11 Adjusting Nut Washer

29 Inner Nut

12 Outer Bearing Cone and R ollers

30 Outer Nut

31 Wheel Rim Clamp

13 Outer Bearing Cup

14 Snap Ring

15 Hub

32 Wheel Rim Clamp

Stud

33 Wheel Rim

34 Wheel Rim Spacer

16 Wheel Nuts

17 Wheels

18 Brake Drum

19 Bolt

35 Hub Cap

36 Axle Shaft Flange

Stud T-

3 4 0 0 - 1

Figure 2 — Rear H ubs, Bearings, a n d O il Seals

G M C S E R V I C E M A N U A L

Sec. 4C

Page 151

REAR HUBS AND BEARINGS

7. Install axle shaft as directed in "REAR

AXLES" (SEC. 4A) of this manual.

nately drive on opposite sides of spacer to avoid cocking bearing cup in hub.

8. Clean, inspect, and repair parts as follows:

REAR HUB AND BEARING REMOVAL

(Refer to Figure 2)

CLEANING, INSPECTION, AND REPAIR

1. Jack up rear axle and remove tire and rim assem bly on vehicles having cast wheels. Remove tire and wheel assembly from trucks having vent ilated disc or Budd type wheels.

2. If brake drum is demountable type, remove brake drum.

3. Remove axle shaft as directed in "REAR

AXLES" (SEC. 4A) of this manual.

TYPES D AND E

1. Remove lock nut, nut lock, and adjusting nut from axle housing tube.

2. On Type E in figure 2, lift wheel (hub) and drum assem bly straight off axle housing, using care to prevent outer cone and roller assembly from dropping out of hub. Remove outer bearing cone and roller from hub.

3. On Type D figure 2, carefully pull hub a s sembly straight off axle housing, using care to prevent outer cone and roller assembly from drop ping out of hub. Remove outer bearing cone and roller from hub.

4. Pull inner oil seal out of hub, then lift out inner bearing cone and roller assem bly. Discard oil seal.

5. Clean, inspect, and repair parts as directed later under "Cleaning, Inspection, and Repair."

TYPES A, B AND C

1. Raise tang of nut lock out of slot in lock nut; then using wheel bearing nut wrench listed in

SPECIAL TOOLS at end of this manual, remove lock nut.

2. Remove nut lock, bearing adjusting nut, and washer from axle housing.

3. Carefully pull wheel (hub) and drum a s sembly or hub off axle housing.

4. Using a mild steel rod through outer end of hub, drive against inner bearing cup to drive inner cone and roller assembly and oil seal out of hub.

Drive alternately on opposite sides of cup to p re vent cocking of cup in hub. Discard oil seal.

5. Using a mild steel rod through inner end of hub, tap outer bearing cup outward away from the snap ring just enough to remove tension on snap ring.

6. Remove the snap ring, using Tru-arc or snap ring p liers through inner end of hub.

7. Using a mild steel rod against outer end of axle shaft spacer, drive outer bearing out of hub.

Care must be taken to engage edge of spacer with punch and not damage bearing seat in hub. Alter-

CLEANING

2. Thoroughly clean all lubricant out of inside of hub and wipe dry. Make sure all particles of gasket are removed from outer end of hub, and that all sealing compound is cleaned out of oil seal bore in inner end of hub.

3. Clean lubricant off axle housing tube.

4. Wash sm all parts such as nuts, spacers, and nut locks in cleaning solvent and wipe dry.

INSPECTION

1. Inspect bearings for excessive wear, chip ped edges, or other damage. Slowly roll the rollers around cone to detect any flat or rough spots. Re place damaged parts. If either the cone and roller assembly or the cup of the roller bearings are damaged, the complete bearing assembly must be replaced.

2. Examine bearing cups which are still in stalled in hub. If cups are pitted or cracked, they must be replaced as directed later under "Repair."

3. Examine oil seal sleeve (when used) on which the hub inner oil seal lip wipes for evidence of wear or roughness. If any damage is evident, sleeve must be replaced. Oil seal sleeves are re placed as directed later under "Repair."

4. Examine axle shaft flange studs (Views D and E, figure 2) for damaged threads or bent studs.

Clean up threads or replace studs as necessary.

On Views A, B and C, figure 2, check for damaged threads in tapped holes in outer end of hub. If threads are damaged, holes can be filled, drilled, and tapped, otherwise hub must be replaced. On hubs having internal splines, check condition of splines in outer end of hub. If any damage is evi dent, replace hub.

5. Examine brake drums for scoring or other damage. Non-demountable brake drums can be re finished while mounted on hubs. If necessary to replace brake drum refer to "Repair" later in this section.

6. Examine wheel studs or rim clamp studs for damaged threads and replace, if necessary, as directed later under "Repair."

7. Discard old oil seals and obtain new oil seals to be used at assembly.

Sec. 4C

Page 152

G M C S E R V I C E M A N U A L

REAR HUBS AND BEARINGS

REPAIR

Bearing Cup Replacement

2. To install new cups, position cup in hub and drive into place, using a suitable driver or by using a mild steel rod against outer edge of cup.

If drift is used, alternately drive against opposite sides to assure driving cup in squarely. Cups must seat firmly against shoulder in hub.

Inner Oil Seal Sleeve Replacement

1. To remove oil seal sleeve (when used) tap sleeve around entire circum ference with hammer to stretch the metal; then use a blunt chisel to cut into the sleeve inner flange. This will loosen the sleeve sufficiently to permit removal.

IMPORTANT: Do not damage axle housing tube when chiseling on sleeve.

2. Slide new sleeve over axle housing tube; then using axle oil seal sleeve driver set J-3822-02, drive sleeve into place. Use care not to damage surface on sleeve which will be contacted by the inner oil seal.

Brake Drum Replacement

1. Demountable Type. The demountable type drum may be separated from the hub and removed from the vehicle without disturbing the axle shaft and hub. The drum is held to the hub by counter sunk, slotted screw s, which are easily removed with a screwdriver.

2. Non-Demountable Type. Construction of the non-demountable type hub and drum assembly is such that replacement cannot be accomplished with the hub assem bly installed on the vehicle.

a. Separate the drums and hub by removing the drum-to-hub retaining bolts, hub stud nuts, or by pressing out the wheel studs, as applicable.

b. Position brake drum to hub assembly, mak ing certain that all drain holes are in alignment.

c. Apply a light, even coating of sealing com pound to the hub oil deflector contact surface, and position deflector to drum.

d. Install drum-to-hub retaining bolts, hub stud nuts, or p ress wheel studs into drum, as ap plicable.

Wheel Bolt Replacement

Wheel bolts are serrated and may also be swaged in place; however, replacement procedure rem ains the same for both types of installation.

Press bolts out of hub flange, using suitable p ress, then p ress new bolts into place, making sure bolts are a tight fit. If all bolts were removed, be sure that hub oil deflector is in position under bolt heads.

IMPORTANT: If any wheel experiences a single stud failure, caused by a loose running wheel, all wheel studs should be replaced.

A loose running wheel may cause only one stud to break, but several more studs may become fatigued to the point of failure, but not actually breaking. Replacing only the one broken stud and remounting wheel will then set the stage for a second and possibly more serious failure. If holes in wheel have become elongated or enlarged, re place wheel.

Hub Stud Replacement

Hub studs can be removed and replaced by using a conventional stud remover and replacer.

Make sure that studs are firmly bottomed in holes and that threads are not damaged during installation.

REAR HUB AND BEARING

INSTALLATION

(Refer to Figure 2)

After completing cleaning, inspection, and r e pair operations, lubricate bearings, axle housing tube, and inside of hub as directed in LUBRICA

TION (SEC. 0) of this manual. Coat lip of oil seal and surface contacted by seal lip with wheel bear ing grease or equivalent.

TYPE D AND E (Fig. 2)

1. Position inner bearing cone and roller in hub or wheel (hub) and drum assem bly. Coat oil seal case with a thin layer of non-hardening sea l ing compound; then press seal in hub until seal lip seats against hub. Seal lip must point inward and driving tool used must exert force on outer edge of oil seal.

2. Make sure oil seal sleeve is in place on axle housing. Place wheel (hub) and drum a ssem bly or hub on axle housing tube using care not to

'damage the inner oil seal.

3. Place outer bearing cone and roller assem bly on axle housing tube and p ress firmly into place. Install bearing adjusting nut, nut lock, and lock nut on axle housing tube.

4. Install tire and rim assem b lies or tire and wheel assem blies. Adjust wheel bearings as p re viously described under "Bearing Adjustment."

5. Install axle shafts as directed in "REAR

AXLES" (SEC. 4A). Adjust brakes as directed in

BRAKES (SEC. 5) of this manual.

TYPES A, B AND C (Fig. 2)

1. From inner end of hub place axle shaft spacer in hub, install outer bearing cone and roller

G M C S E R V I C E M A N U A L

Sec. 4C

Page 153

REAR HUBS AND BEARINGS

assembly; then install outer bearing cup with thin edge of cup toward outer end of hub until it clears the snap ring groove, using a suitable sleeve. In stall the snap ring in groove in hub.

2. Using a punch, drive axle shaft spacer to force outer bearing cup back against the snap ring.

IMPORTANT: This procedure must be follow ed to assure a wheel bearing adjustment that will not work loose.

3. Place inner bearing cup in hub with wide side of cup toward inside of hub. P ress cup into hub until it seats against shoulder in hub, using a suitable sleeve.

4. P re ss new oil seal into hub flush or until it seats against bearing cup, on types shown in Views

B, and C in figure 2, make sure seal ring is in place in axle housing.

5. Carefully install wheel (hub) and drum a s sembly or hub.

6. Install adjusting nut washer, adjusting nut, nut lock, and lock nut on axle housing tube. Install brake drum if previously removed.

7. Install tire and rim assem b lies or tire and wheel assem b lies. Adjust wheel bearings as pre viously described under "Bearing Adjustment."

8. Install axle shafts as directed in "REAR

AXLES" (SEC. 4A). Adjust brakes as directed in

BRAKES (SEC. 5) of this manual.

SPECIFICATIONS

TORQUE SPECIFICATIONS

ADJUSTING NUT FT. LBS.

All Axles Except Corp. H-110......................................................................................50

Corp. H-110............................................................................................................ 75-100

LOCK NUT

W Rockwell and Eaton.......................................................................................100-150

W Corp. T, H-150....................................................................................................... 135

W Corp. H-110............................................................................................................ 250

Sec. 4C

Page 154

_______________________G M C S E R V I C E M A N U A L

REAR HUBS AND BEARINGS

IMPORTANT

At installation, always coat the oil seal bore in hub with a thin layer of non-hardening sealing compound and always be sure that the oil seals are properly seated.

G M C S E R V I C E M A N U A L

Sec. 4D

Page 155

DESCRIPTION

SECTION 4D

Pnxm>elle'i SU ajjti

Power is transmitted from transm ission to rear axle through one or more propeller shaft and universal joint assem blies (fig. 1). The number of propeller shafts and universal joint assem blies vary with vehicle wheelbases and combination of transm ission and rear axle equipment.

onto end of yoke. Fixed yoke may be either welded to propeller shaft tube or it may be splined to a stub shaft and secured with a nut and cotter pin as shown in figure 2. It is recommended that a scribe mark be made on slip yoke and shaft to pro vide for alignment of yokes later at assembly.

PROPELLER SHAFTS (Fig. 1)

All propeller shafts are tubular type. A splined slip joint is provided in each drive line. If a single propeller shaft is used, slip joint is at transm is sion end of shaft; if two or more shafts are used, slip joint is at forward end of rear shaft. End of slip yoke is sealed by a cork washer, held in place by a steel washer and a dust cap which threads

UNIVERSAL JOINTS (Fig. 1)

Two types of universal joint assem blies are used on vehicles covered by this manual. Refer to

"Specifications" at end of this section for type of joint used on any vehicle with standard equipment.

Refer to applicable Parts Book for universal joint application with optional transm ission and axles.

Universal joints are described as follows:

Joint bearing cages are retained in yoke flanges on propeller shaft by snap rings. Bearings

T Y P IC A L S IN G L E PROPELLER S H A F T IN S T A L L A T IO N

1 Tube Assem bly

2 Bearing R ollers

3 Bearing

4 Universal Joint Journal

5 Snap Ring

T Y P IC A L D O U B L E PROPELLER SH A F T IN S T A L L A T IO N

6 Yoke

7 "U" Bolt Nut

9 Grease Retainer Guard

10 Grease Retainer

11 Rubber Cushion

12 Center Bearing Support

13 Center Bearing

14 Dust Cap

15 Cushion Retainer

T P M - 3 6 0 3 - 2

Figure 1— Typical Propeller Shaft a n d U niversal Joints

Sec. 4D

Page 156

PROPELLER SHAFTS

G M C S E R V I C E M A N U A L

CONDITION

Propeller Shaft Vibration

Universal Joint Noise

SERVICE DIAG NO SIS CHART

POSSIBLE CAUSE

1. Propeller Shaft Out of Balance.

2. Parking Brake Drum Out of Balance.

3. Distorted or Damaged Yokes.

4. Yokes Out of Parallel to Each Other.

1. Center Bearing Worn.

2. Worn Universal Joint Bearings.

3. Improper Lubrication.

4. Loose Flange Bolts.

CORRECTION

1. Check for Foreign Material on Propeller Shaft.

2. Replace Drum.

3. Install New Yokes.

4. Change Propeller Shaft.

1. Replace Center Bearing.

2. Replace Bearings.

3. Lubricate as Directed.

4. Tighten to Specifications.

at opposite end of propeller shaft are attached to journal cro ss with snap rings and U-bolts, lock washers and nuts. A visual inspection must be made of vehicle to determine at which end of pro peller shaft U-bolts and lock rings are used and at which end of propeller shaft lock rings only are used. Needle rollers are installed in bearing cages and oil sea ls are installed on inner ends of cages.

Repair Kits

Universal joint repair kits are available for all types of universal joints. Each kit contains a journal, bearings and seals, and retaining com ponents which should always be replaced when overhauling a universal joint.

CENTER BEARING (Fig. 2)

Center bearings are used to support center portion of drive line when two or more propeller shafts are used. Bearing is ball type, mounted in a rubber cushion which is attached to frame c r o s s member by the center bearing support. The two center bearings shown in cross section in figure

2 are of the same construction except for shape and location of dust slinger. View B illustrates center bearing used at shaft end with slip yoke;

View A illu strates center bearing used at shaft end with fixed yoke. Bearing is prelubricated and per manently sealed. Cavities in grease retainers on both sides of bearing are packed with waterproof grease to exclude dirt and water.

LUBRICATION

Journals of universal joints are drilled and provided with lubrication fittings through which lubricant travels to all four oil reservoirs, then through a sm all hole in side of each reservoir, direct to needle bearings. Bearings are protected against lubricant leakage and entrance of foreign matter by seals. Splines of slip joint are lubricated through lubrication fitting installed in slip yoke.

NOTE: Universal joints and slip yoke splines should be lubricated periodically as specified in

LUBRICATION (SEC. 0) of this manual.

PROPELLER SHAFT REMOVAL

Disconnecting propeller shaft perm its removal of transm ission or rear axle without disturbing unit at opposite end of shaft. On some vehicles, propeller shaft may be removed at any flange joint by removing nuts from bolts holding flanges. On other vehicles, propeller shafts must be discon nected at universal joints as described later in this section. Propeller shaft should be supported oefore removing to prevent damage by dropping. To r e move complete drive line, on models in which center bearings are used, it is necessary to d is connect center bearing bracket from hanger and remove propeller shaft guards (when used) from supports. Refer to figure 3.

DISASSEMBLY OPERATIONS

SLIP JOINT DISASSEMBLY

With propeller shaft removed, scribe a mark on slip yoke and shaft to insure assembly is in exactly same relative position. When clearly mark ed, unscrew dust cap and withdraw shaft. Remove cork washer, steel washer, and dust cap from shaft.

UNIVERSAL JOINT DISASSEMBLY

1. On universal joints using snap rings to re tain bearings on journal cross, remove snap rings

(fig. 1).

2. On universal joints using U-bolts to retain bearings on journal cross, remove nuts and washers from U-bolts, then remove U-bolts (fig. 1).

3. Strike one side of yoke with hammer to force one bearing out of yoke. Strike opposite side of yoke to force opposite bearing out.

5 4

G M C S E R V I C E M A N U A L

Sec. 4D

Page 157

PROPELLER SHAFTS

1 Nut

2 Yoke

3 Dust Shield

4 Rubber Cushion

5 Cushion Retainer

6 Center Bearing Support

7 Grease Retainers

8 Slingers

wss

1 ■ 1

j\J"

J J _

\yrww)

bv j

9 Bearing Assembly

10 Propeller Shaft

11 Dust Shield

12 Washer t

-3061

Figure 2 — Typical Propeller Shaft Center Bearings

CAUTION: Use care not to permit bearings to drop on floor, or irreparable damage may result.

4. Journal can now be tilted to permit removal of yoke from journal.

5. Remove the other two bearings in same man ner to permit removing journal from opposite yoke.

CENTER BEARING DISASSEMBLY

The following procedure covers disassembly of center bearing with propeller shaft removed from vehicle. Key numbers in text refer to figure 2.

1. Remove retainer (5) from support (6), then remove support from cushion (4).

2. On type shown in View A, figure 2, remove cotter pin and nut securing yoke (2) on shaft, then pull yoke off shaft. On type shown in View B, r e move dust shield (11) from shaft.

3. Remove rubber cushion (4) from bearing (9), then pull bearing assembly from shaft.

4. Remove grease retainers (7) from bearing, and remove slingers (8).

IMPORTANT: Do not attempt to disassem ble

Sec. 4D

Page 158

PROPELLER SHAFTS

G M C S E R V I C E M A N U A L

Propeller Shaft Guard

Propeller Shaft

Center Bearing

Support

Dust Cap

Washer (Steel)

Washer (Cork)

Bolt

Rear Axle

T P M -9 1 4 2 -1

Figure 3 — Propeller Shaft Guards Installed (“S ” Series

Sh o w n )

ball bearing. This is a sealed bearing and cannot be disassem bled without being destroyed.

5. If dust shields (3) are damaged, use a ch isel to break welds and remove shields.

If excessive clearance is noted, discard journal and bearings and replace with new parts contained in universal joint repair kit.

CLEANING AND INSPECTION

PROPELLER SHAFT

Thoroughly clean old grease and dirt from shaft splines, then check splines for wear, warpage, and cracks. If shaft is worn, warped, or crack ed, replace with new shaft. Welding of broken shaft is not recommended, since this operation requires special balancing facilities.

UNIVERSAL JOINT

Wash all parts in cleaning fluid. Make sure clean lubricant to rollers and turn on trunnion of journal to check wear. Refer to LUBRICATION

(SEC. 0) for type of lubricant.

lubricant passages in journal cross are clean. Soak needle bearings and cages in cleaning fluid to soften p articles of hardened grease, then wash in cleaning fluid, using a stiff brush if necessary to remove all old lubricant. Check each bearing for missing ro ll er s. Refer to "Specifications" at end of this s e c tion for correct number of ro llers. After needle bearing assem blies are thoroughly clean, apply

SLIP JOINT

Using a suitable cleaning fluid, clean all dirt and old grease from slip yoke, slip yoke splines, and shaft splines. Carefully inspect slip yoke splines for wear or evidence of twisting. Check clearance between slip yoke splines and shaft splines. If backlash is excessiv e, replace parts.

CENTER BEARING

Wash all parts except ball bearing and rubber cushion in suitable cleaning fluid.

DO NOT IMMERSE SEALED BEARING IN

CLEANING FLUID.

Wipe bearing and cushion clean with a cloth dampened with cleaning fluid.

Check the bearing for wear or rough action by rotating inner race while holding outer race. If wear or roughness is evident, replace with new bearing.

Examine rubber cushion for evidence of hard ening, cracking, or deterioraton. Replace with new part if damaged in any way.

Grease retainers and slingers are serviced only as a part of the bearing assembly.

ASSEMBLY OPERATIONS

CENTER BEARING ASSEMBLY

Key numbers in text refer to figure 2.

1. If removed, install new dust shields (3) on shaft or yoke. Tack weld or stake shields in place.

2. Press a grease retainer (7) over each side of bearing outer race. Pack cavities in retainers with waterproof grease recommended in LUBRI

CATION (SEC. 0) of this manual.

3. Install one slinger (8) over end of shaft.

Start bearing and retainer assem bly straight on shaft, then using a suitable sleeve to exert force on bearing inner race, p ress bearing and slinger against shoulder on shaft. Install the other slinger

(8) over shaft and position against bearing.

4. Install rubber cushion (4) over bearing a s sembly, making sure bearing is centered in hole in cushion.

5. Position support (6) around cushion and in stall cushion retainer (5).

6. On type shown in View B, figure 2, p ress dust shield (11) onto shaft against slinger (8). On type shown in View A, install yoke (2) on shaft.

IMPORTANT: Centerline through yoke flanges must be aligned with centerline of yoke flanges on other end of shaft. Install nut (1), tighten firmly, and secure with cotter pin.

SLIP JOINT ASSEMBLY (Fig. 1)

1. Position dust cap on shaft, then install steel washer and new cork or felt washer on shaft. Coat shaft splines with lubricant specified in LUBRICA

TION (SEC. 0) of this manual.

2. Align arrows or markings on splined shaft and slip yoke and insert shaft into slip yoke. Make certain yokes on both joints are exactly aligned.

IMPORTANT: Journal c r o sses must be in same plane, otherwise serious vibration will occur, with resultant damage to both shaft and connected units.

G M C S E R V I C E M A N U A L

Sec. 4D

Page 159

PROPELLER SHAFTS

3. Thread dust cap onto end of slip yoke.

Tighten dust cap by hand only; use of wrench will damage cork or felt washer.

4. Install lubrication fitting in slip yoke.

UNIVERSAL JOINT ASSEMBLY

NOTE: Make sure sea ls are in place on inner end of bearing cages. Apply lubricant recommend ed in LUBRICATION (SEC. 0) to needle rollers in each bearing to provide initial lubrication.

1. Install lubrication fitting in journal.

2. Install journal in yoke, then install bearing assem blies in yoke over journal trunnions. Use a plastic or rawhide hammer to tap bearings into place.

3. On universal joints using snap rings to r e tain bearings, p ress bearings in far enough to clear snap ring grooves, then install snap rings.

Hold journal and lightly tap yoke to seat bearings outward against snap rings.

4. On universal joints using U-bolts, install

U-bolts, washers, and nuts on journal bearing a s sembly and tighten nuts to torque listed in "Speci fications."

PROPELLER SHAFT INSTALLATION

If propeller shaft has been removed at flange joint, position propeller shaft at joint, and install bolts, washers, and nuts. If propeller shaft has been removed at universal joints, assem ble uni versal as previously described under "Universal

Joint Assembly." Where complete drive line has been removed on models having center bearing, connect center bearing support to crossm em ber.

On "S" models, install propeller shaft guards to frame supports. Refer to figure 3 for typical pro p eller shaft installation on "S" models. A visual inspection must be made of vehicle to determine the number of propeller shaft guards and center bearings used.

See following page for "Specifications."

Sec. 4D

Page 160

PROPELLER SHAFTS

G M C S E R V I C E M A N U A L

SPECIFICATIONS

UNIVERSAL JOINT APPLICATION

The following tabulation lists universal joints used with standard equipment only. Refer to parts book for universal joints used with optional equipment.

JOI NT SERIES

1350

1410

1480

UNIVERSAL JOINT SPECIFICATIONS

JOURNAL NEEDLES

DI AMETER

PER BEARING OF NEEDLES

0.7730"-0.7735"

0.7/30"-0.7735"

0.8942 0.8947"

0.0783"-0.0785"

0.0936 0.0938"

LENGTH OF

NEEDLES

0.625"

0.765"

TORQUE SPECIFICATIONS

U N IV ER SA L JO IN T U-BO LT NUT

x 24 Nut 1350. 1410 ..................................................................................................................................... 20-24 ft. lbs.

7/ie"-20 Nut 1480.................................................................................................................................................. 32-37 ft.-lbs.

PR O PELLER S H A FT TO HANGER ATTACH IN G PA RTS

7/ie" x 20 N u t.......................................................................................................................................................... 25-30 ft. lbs.

A TTACH IN G PA RTS TO REAR A X LE OR TRA N S.

7/is" x 20 N u t.. 1350.1410 ................................................................................................................................. 50-60 ft. lbs.

Vz"

x 20 Nut. 1480 ........................................................................................................................................... 60-70 ft.-lbs.

Propshaft Support to Fram e ................................................................................................................................ 40-50 ft. lbs.

G M C S E R V I C E M A N U A L

Sec. 5A

Page 161

SECTION 5 fetvcJ zei

This group is divided into three sections as shown in Index below:

Section

Hydraulic B r a k e s ....................................................

Air Brakes ..............................................................

Parking Brake .......................................................

Page No.

161

208

254

BRAKE SYSTEM EQUIPMENT

There are four different brake system s used on vehicles covered by this manual.

1. Straight Hydraulic brakes are used as standard equipment on all 4500 Series trucks.

2. Vacuum A ssisted Hydraulic brakes are used as standard and/or optional equipment on trucks covered by this manual as follows: a. Dash mounted master cylinder with remote mounted vacuum booster:

Standard - L4000, DL4000, S5500, and S6500

S eries.

Optional - P4500 Model and L4000, DL4000

S eries (Heavy Duty). b. Dash mounted vacuum booster (with integral master cylinder):

Standard - E5500, 6500 S eries.

Optional - E4500, E5500, 6500 Series

(Heavy Duty).

SECTION 5A

3. Air A ssisted Hydraulic brakes are used as standard equipment on LA a.nd DLA 4000 Models.

4. Full Air brakes are available on all models covered by this manual when specified on the sales order or as optional equipment, except:

4500 S eries and ES, SS5500 Models.

5. Optional Equipment is available in both system s. Such item s as vacuum reserve tank, heavy duty boosters, vacuum gauges, trailer brake connections, air parking brake, moisture ejector, etc., are factory installed options.

IMPORTANT: The following brake maintenance schedules, adjustments, procedures, and replacement techniques are required and are applicable to normal vehicle usage. Unusual or severe operations require greater attention to the normal maintenance approach commensurate with the u sage severity.

***<M*idbaulic fenakeA.***

Contents of this section are listed in Index below:

GENERAL

Subject Page No.

Brake System Maintenance .................. . . .

162

Brake Adjustments ................................ . . . 162

Bleeding B r a k e s ....................................... . . .

165

Brake Pedal and Linkage .....................

. . . 167

Master Cylinders .................................... . . .

170

Wheel C y lin d e r s ....................................... . . .

175

Hydraulic L i n e s ....................................... . . . 179

Vacuum Power C y lin d e r s .....................

. . . 180

Vacuum Power Cylinder Air Cleaner . . . .

181

Vacuum Check Valve ............................

. . . 183

Vacuum R eserve Tank ......................... . . .

184

Vacuum G a u g e ..........................................

. . . 184

Vacuum P u m p ........................................... . . .

184

Air Power C y l i n d e r ................................ . . .

185

Brake Shoes and Linings .....................

. . . 187

Brake Shoe R e lin in g ................................ . . .

199

Brake Drums ........................................... . . .

199

The vacuum power assisted system used on vehicles covered by this manual is described as a

"one to one" system ; that is the volume of hydraulic fluid output of the vacuum booster is the same as the input volume. This type system eliminates the need for compensating lines and also the need for

"pumping" the brake pedal in the event of loss of vacuum power a ssist.

The vacuum system on these vehicles contains a check valve which maintains enough vacuum in the booster chamber to permit at least one power a ssisted brake application after lo ss of vacuum occurs.

The various components of the brake system , such as shoe and lining assem blies, pedal and link age, power boosters, master cylinders, wheel cyl-

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

Air Cleaner

Vacuum Gauge

Master Cylinder

Vacuum Line From Engine

(From Vacuum Pump on D iesel)

Brake Pedal

Vacuum Power Cylinder

Vacuum Line From Engine to Control Valve

Hydraulic Line From

Master Cylinder

Hydraulic Line to Wheels

10 Atmosphere Line From

Air Cleaner

Figure I — Typical V acuum and Hydraulic Lines Installed (Remote M ounted Booster)

inders, lines, gauges, reserve tanks, etc., are covered under respective headings in this section.

For illustration of typical system installation see figure 1.

BRAKE SYSTEM M AINTENANCE

1. Maintain proper level of hydraulic brake fluid in master cylinder. Refer to LUBRICATION

(SEC. 0) for recommended fluid and checking in tervals. At least once a year, drain and flush en tire brake system and refill with new fluid.

2. Adjust brake shoes at regular intervals.

After two or three adjustments, check brake linings for wear. Reline brakes before lining is worn suf ficiently to permit lining rivets to damage brake drums.

3. Keep brake pedal and linkage well lubri cated to assure free movement and rapid release of brakes.

4. Inspect entire brake system regularly for fluid leakage. Leakage must be corrected immed iately.

5. Make sure brake shoes are free on their mountings, that shoe return springs are not weak or broken, and that backing plates are not sprung or loose on axle or steering knuckle.

6. Service remote mounted vacuum power cylinder air cleaner, referring to LUBRICATION

(SEC. 0) for recommended intervals and for ser v ice instructions. Air cleaners on dash mounted booster and master cylinder assem bly are integral part of complete assem bly and can be serviced only when assem bly is removed from the vehicle as part of unit overhaul.

7. Tighten all vacuum and atmosphere line fittings and connections.

8. Perform "Power Brake System Tests" as directed later under "Power Cylinders." These tests may reveal sub-standard performance before the condition becom es bad enough to cause driver complaints or brake failure on the road.

BRAKE ADJUSTMENTS

There are six different type brakes used on these vehicles:

1. Type "F" manual adjusting - FRONT.

2. Type "FA" automatic adjusting - FRONT.

3. Type "FR-3" manual adjusting - REAR.

4. Type "FR-3A" automatic adjusting - REAR.

5. Duo-Servo automatic adjusting - FRONT.

6. Twin-Action automatic adjusting - REAR.

G M C S E R V I C E M A N U A L

BRAKE ADJUSTMENT MODEL CHART

FRONT BRAKES

Type "F"

(Manual)

L4000 Series

6500 Series

(exc. "S")

Type "FA"

(Automatic)

S6500

Duo-Servo

(Automatic)

4500 Series

5500 Series

REAR BRAKES

Type "FR-3"

(Manual)

6500 Series

(exc. "S")

Type "FR-3A"

(Automatic)

S6500

Twin-Action

(Automatic)

L4000 Series

4500 Series

5500 Series

MANUAL ADJUSTMENT

All manual brake adjustments to compensate for normal lining wear can be made without re moving wheels and brake drums. Adjustment points are accessib le through openings in brake backing plate or are external type.

Sec. 5A

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HYDRAULIC BRAKES

NOTE: Wheel bearings must be properly ad justed before attempting to adjust brake shoes.

Refer to "HUBS AND BEARINGS" (SEC. 3D for

FRONT and SEC. 4C for REAR).

Brake shoe adjustment points for front brakes

(Type "F") are illustrated in figure 2. Adjustment points for rear brakes (Type "FR-3") are shown in figure 3.

Type "F" (Fig. 2)

1. Jack up front end of vehicle until wheels clear floor- Place wrench on one adjusting cam stud to adjust shoe. Rotate wrench in direction of forward wheel rotation to decrease lining-todrum clearance. Reduce clearance until brake drag is felt as wheel is turned in forward direction by hand.

2. Move wrench slightly in opposite direction until brake drag is relieved, then move wrench an additional 7 to 10 degrees to provide running clea r ance. (7 to 10 degrees is equal to 1 to 1/ inches of travel at end of an 8-inch wrench.)

3. Place wrench on opposite adjusting cam stud and adjust second shoe by repeating Steps 1 and 2.

W H EEL CYLINDER

BOLT

BLEEDER

VA LVE

FRONT SH O E

A D J U ST IN G STUD

WHEEL

CYLINDER BOLTS

ADJU STIN G

TOOL

BLEEDER VALVE

C O N N E C T O R

TUBE

COPPER

G A SK E T S

C O N N E C T O R

TUBE

REAR SH O E

A D JU ST IN G STUD

Figure 2 — Type “ F” Brake Adjustm ent

REAR AXLE

BRAKE LINE

Figure 3 — Type “ F R -3 " Brake A djustm ent

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

Type "FR-3" (Fig. 3)

1. Jack up vehicle until wheels are clear of floor. Remove adjusting hole covers from backing plate.

2. At one adjusting slot, insert adjusting tool

(J-4707) or sim ilar tool through slot and engage adjusting wheel and decrease lining clearance until lining drags on drum.

3. Relieve drag by rotating adjusting wheel in opposite direction. Back off adjustment as follows:

For worn lining - 3 notches (clicks).

For new lining - 5 notches (clicks).

4. At other adjusting slot, repeat Steps 2 and

3 to adjust other shoe.

5. Install hole covers in backing plate.

AUTOMATIC ADJUSTMENT

Duo-Servo

As the brakes are applied, when vehicle is traveling in reverse, the shoes contact the drum and revolve with the wheel until the web of the primary shoe contacts the anchor pin. This motion causes the secondary shoe to move away from the anchor pin, thus increasing the distance between the actuating lever pivot point and the anchor pin.

Since the actuating link maintains a constant length, the actuating lever assem bly pivots on the second ary shoe hold-down pin location and the pawl end of the lever rocks down against the adjusting screw star wheel. If the lining is worn enough to allow sufficient movement of the secondary shoe, the pawl will advance the star wheel one or two teeth.

If the brake linings are not worn enough to require an adjustment, the restricted movement of the secondary shoe prohibits over-adjustment.

When the brakes are released, the pull-back springs return the shoes to the rest position. At the same time, the actuating lever return spring moves the linkage to the rest position. The contour of the actuating lever pawl allows the lever to ratchet back to the rest position and in effect "take a new bite" on the star wheel. As a result of this action, the linkage is in position to make the next adjustment as it is needed.

Under normal operating conditions it is not necessary to make any manual adjustment to this type brake. However, when it is necessary to re move a brake drum it may also be necessary to

"back-off" the adjustment in order to pull edge of drum past linings. In such ca ses, insert a screw driver or awl through hole in backing plate and hold adjusting lever or pawl away from adjusting screw. Then turn screw with proper brake tool to loosen adjustment. See figures 4 and 5.

Twin-Action

Brake shoe adjustment takes place when brakes are applied with a firm pedal effort while the ve hicle is backing up. Applying the brakes moves adjusting levers which turn the star wheels and rotate the adjusting screw s outward from the anchor brackets. This action adjusts the shoe until clearance between the lining and drum is within proper lim its.

Should low pedal heights be encountered, it is recommended that numerous forward and reverse stops be performed with a firm pedal effort until a satisfactory pedal height results.

A ccess holes are located in the flange plate.

These holes are for service purposes in the event retracting of the brake shoes is required to remove the drum. In order to back off the adjusting screw s,

Figure

4 — Ba cking O ff

Adjusting

Screw

(Cross-Section View)

Figure 5 — Backing

Off

Adjusting Screw (Outside V ie w )

G M C S E R V I C E M A N U A L remove the cover from the a ccess hole and insert a screw driver. Place a corner of the screwdriver blade in the hole in the adjusting lever and push

Sec. 5A

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HYDRAULIC BRAKES

the lever away from the star wheel. Using a brake adjusting tool, back off the star wheel. See figures

4 and 5.

BLEEDING BRAKES

Use only Hydraulic Brake Fluid recommended in LUBRICATION (SEC. 0). When other than rec ommended fluid has been used, drain and flush the entire hydraulic system , using clean alcohol or a hydraulic brake system cleaning fluid. D isassem ble, clean, and inspect hydraulic units. Replace all rubber parts. Refill system with recommended fluid.

The need for bleeding air from system is gen erally indicated by a springy, spongy pedal action.

The presence of air in system is a result of low fluid level in master cylinder, or of some part of the system having been disconnected. Bleeder valves are provided on the power cylinder (some models), master cylinder (some models) and at wheel cylinders. Type "F" and type "FA” front brakes have two cylinders per wheel and each has a bleeder valve. Type ”FR -3” and type "FR-3A" rear brakes have two cylinders per wheel with a bleeder screw at the top cylinder only. Duo-Servo front brakes have one cylinder per wheel and each has a bleeder screw. Twin-Action rear brakes have two cylinders per wheel with a bleeder screw at the top cylinder only. Refer to figure 7 for bleed ing sequence by truck model.

Master cylinder is accessib le under the hood on conventional models, through access door in seat riser on tilt cab models and through a ccess door in floor on "P" model. Bleeder valves at wheel cylinders are accessib le at inner sides of the backing plates.

It is recommended that brake system is bled in a definite sequence to obtain best result. Figure

7 illustrates various combinations of brake equip ment used, with bleeder valves numbered in the recommended sequence in which they should be bled.

IMPORTANT: Note that neither master cylin der nor power cylinder on some models is equip ped with a bleeder valve. If bleeding at the wheels only does not produce satisfactory results, it will be necessary to disconnect line from master cyl inder and bleed it through output port. Then r e connect line and disconnect power cylinder output line and bleed. Reconnect line and check oper ation of brakes. If still not satisfactory, rebleed wheel cylinders in sequence shown.

There are two methods of bleeding hydraulic brake system s used on these vehicles; pressure bleeding and manual bleeding. Both are acceptable and adequate (except on split system s) but p res sure bleeding is recommended, if equipment is available.

CAUTION: Before starting pressure

bleeding operations, stop engine and des

troy vacuum in system before opening any

bleeder valve. _____ ______

Figure 6 — Brake Bleeding Tool for

Split System Master Cylinder

P a ge^166

______________________ G M C S E R V I C E M A N U A L

HYDRAULIC BRAKES

F R O N T — F R O N T —

DU O SERVO

P 4 5 0 0

F R O N T —

TW IN-A C TIO N

/ T q

T \ DASH M O U NTED

CYLINDER

u

DUO-SERVO

4 5 0 0 (EXC. P)

T W IN -A C TIO N

F R O N T ----

“F"

L 4 0 0 0

F R O N T —

TW IN -A C TIO N

S 5 5 0 0 A N D S 6 5 0 0

F R O N T —

©

DASH

M O U N T ED

CYLINDER

DUO-SERVO

E 5 5 0 0

“F”

Figure 7 — H ydraulic Brake Bleedin g Sequence Chart

E 6 5 0 0

“ FR-3’

T-5637

SPLIT SYSTEM ("S" MODELS)

The split system on "S" Models consists of two separate brake system s split as follows:

1. Main System - front wheel brakes plus one cylinder on each rear wheel brake.

2. Secondary System - one cylinder on each rear wheel brake.

The system on both models con sists of a dash mounted master cylinder and two frame mounted power cylinders.

It does not matter which system (main or s e c ondary) is bled first, however, each must be bled separately. Because the two system s have a com mon push rod and act simultaneously, THE SPLIT

BRAKE SYSTEM CANNOT BE BLED MANUALLY.

THE PRESSURE BLEEDING METHOD MUST BE

USED.

Figure 6 illu strates a tool which can be made locally for use in p ressu re bleeding the split brake system (both standard and optional).

Tool (J-23339) may also be used for this pur p ose. It is a special adapter designed to fit the m aster cylinder used on the "S" Models. This tool is not illustrated.

PRESSURE BLEEDING

Refer to figure 7 for bleeding sequence.

1. Make sure fluid level in p ressure tank is up to petcock above outlet and that tank is charged with 40 to 50 psi air pressu re.

2. Clean dirt from around master cylinder filler cap or cover. Remove standard cover and install special cover required to fit the model cyl inder used. Connect p ressure tank hose to filler

G M C S E R V I C E M A N U A L

Sec. 5A

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HYDRAULIC BRAKES

cap or cover opening. Bleed air from hose before tightening connection. Open valves at both ends of hose.

3. First bleed master cylinder valve on models where used. Slip end of bleeder hose over bleeder valve No. 1 and place other end in a glass jar con taining enough hydraulic fluid to cover end of hose.

Open bleeder valve with wrench and observe flow of fluid from hose. Close bleeder valve as soon as bubbles stop and fluid flows in a solid stream .

4. Bleed valve No. 2 (on power cylinder where used), then bleed wheel cylinders in sequence shown in figure 7. After bleeding wheel cylinders, repeat bleeding operations at power cylinder (whereused).

5. If, after bleeding, the pedal "feel" is not s a tis f a c t o r y , it i s re co m m en d e d that the r e sid u a l check valve in the master cylinder or the check valve in the power cylinder piston be inspected (on those models which have check valves). Improper operation of either or both of these valves will re sult in the same pedal "feel" as air in the system .

Refer to applicable procedures for repair. If these valves are operating properly, or if "feel" is not satisfactory on models not using check valves, then air is still present in system and bleeding again will be necessary.

MANUAL BLEEDING

Manual bleeding is the same as p ressure bleeding, except that the brake fluid is forced through the lines by pumping the brake pedal in stead of by air p ressure. Fluid in master cylinder must be replenished after bleeding at each valve.

Brake pedal should be pumped up and down slowly, and should be on downstroke as valve is closed.

BRAKE PEDAL A N D LINKAGE

There are three basic types of brakepedaland linkage installations used on vehicles covered by this manual. They are illustrated in figures 8, 9, and 10.

Figure 8 illustrates the type installation used with a dash mounted m aster cylinder and a remote booster cylinder (P4500 and 5500 Models).

Figure 9 illustrates the type installation used with a dash mounted combination master and boos ter cylinder (4500 Series except "P," 5500 S eries, and 6500 Series).

Figure 10 illustrates the type installation used with the m aster cylinder mounted under the cab and a push through brake pedal (all tilt cab models).

BRAKE PEDAL REPLACEMENT

(ALL EXCEPT TILT CAB)

These models have a suspended type brake

Figure 8 — Brake Pedal and Master Cylinder

Installation (P4500 and 5500 M odels)

g c

Page 168_______________________

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HYDRAULIC BRAKES

2 3

10 3 11

1 Clutch Pedal

Shaft Lever

2 Clamp Bolt and Nut

3 Bushings

4 Bolt

5 Pedal Sleeve

6 Lock Washer

7 Nut

8 Pedal Return Spring

9 Pedal Support Bracket

Pedal Bumper

Spring Washer

Clutch Pedal and Shaft

Brake Pedal Assembly

Bolt

Push Rod

T - 3 4 0 8

Figure 9 — Clutch and Brake Pedal Installation (E4500,

5 5 0 0 , 6 5 0 0

and

S 5 5 0 0 , 6 5 0 0 )

pedal mounted in a bracket which is secured on the underside of the instrument panel.

As indicated on figures 8 and 9, the brake pedal pivots on the outside of sleeve, and clutch pedal shaft extends through inside of sleeve. Nylon bushings are installed in each end of brake pedal tube, forming the contact between pedal tube and pedal sleev e. Clutch pedal shaft is carried in nylon bushings installed in each end of sleeve. The brake m aster cylinder is mounted on the engine side of the dash (double barrei on some models, single barrel on others). Adjustable push rods, extending through dash into m aster cylinder bores, are at tached by special bolts to brake pedal lever and to clutch pedal shaft lever (on models with hy draulic clutch controls).

In released position, each pedal is held against a rubber bumper by pedal return springs. The fol lowing pedal replacement procedures cover both clutch and brake pedals.

PEDAL REMOVAL (Figs. 8 and 9)

In order to remove the brake pedal, the clutch pedal must also be removed.

1. Remove bolts attaching brake and clutch m aster cylinder push rods to pedal levers.

2. Unhook pedal return springs.

3. Loosen clamp bolt securing clutch pedal shaft lever on end of clutch pedal shaft and remove lever from shaft. Remove spring washer, bushings, and clutch pedal and shaft from sleeve.

4. Remove bolt attaching pedal sleeve to panel-to-dash brace. Remove sleeve from brace, at the same time removing brake pedal and bush ings.

PEDAL INSTALLATION

Before installing pedals, check bushings in brake pedal and in pedal sleeve for evidence of wear or deterioration. Bushings are split type and can easily be removed and replaced.

1. Install bushings in pedal tube. Position brake pedal at underside of instrument panel-todash brace. Insert pedal sleeve through brace and pedal and attach sleeve to brace with bolt and nut.

2. Install bushings in sleeve. Insert clutch pedal shaft through sleeve and install spring wash er and pedal shaft lever on end of shaft. Tighten lever clamp bolt firm ly.

3. Connect pedal return springs.

4. Connect master cylinder push rods to brake and clutch pedals, using special shoulder bolts, lock washers, and nuts. Tighten nuts to 2 5-30foot pounds torque.

5. Adjust push rod to provide rod to piston clearance as directed under "PushRodAdjustment."

BRAKE PEDAL REPLACEMENT

(TILT CAB)

(Refer to Figure 10)

REMOVAL

In order to remove the brake pedal on tilt cab models, it is necessary to first remove the clutch

G M C S E R V I C E M A N U A L

Sec. 5A

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HYDRAULIC BRAKES

1 Pedal Upper Half

2 Pedal Upper and Lower

Seals

3 Upper to Lower Pedal

Connector Bolt

4 Pedal Lower Half

5 Pedal Return Spring

6 Pedal Bumper

7 Pedal Support Sill

8 Pin and Bushing Assy.

9 Pedal to Push Rod Bolt

10 Clevis

11 Adjusting Nut

12 Push Rod

13 Boot

14 Mounting Bracket

15 Bracket to Master

Cylinder Gasket

16 Master Cylinder

T-2552

Figure 10— Brake Pedal and Master Cylinder Installation (Tilt Cab Models)

pedal assem bly to obtain enough clearance to r e move brake pedal.

1. Remove clutch pedal (for details see "Clutch

Pedal and Bushing Replacement" in "CLUTCH CON

TROLS" (SEC. 7D) of this manual.

2. Remove upper to lower pedal connector bolt. Remove pedal upper half.

3. Remove pedal return spring.

4. Remove pedal to push rod bolt.

5. Remove lock ring and washer from outside end of pin and bushing assem bly.

6. Remove grease fitting from bushing.

7. Remove bolts which fasten bushing a ssem bly to cab sill.

8. Simultaneously slide pedal assem bly and bushing assembly out of cab sill in opposite direc tions, twisting each as necessary to clear sill and other obstructions.

INSTALLATION

1. Simultaneously insert bushing assembly from outer side of cab sill and brake pedal assem bly from inner side of cab sill, twisting each as necessary to allow pedal pin to slide completely through bushing and bushing assembly to slide completely through cab sill.

2. Install bolts which fasten bushing assembly to cab sill. Tighten securely.

3. Install grease fitting.

4. Install washer and lock ring on outside end of pin and bushing assem bly.

5. Install pedal to push rod bolt.

6. Install pedal return spring.

7. Insert pedal upper half through sea ls and fasten upper and lower pedal halves with bolt.

8. Install clutch pedal (for details see "Clutch

Pedal andBushing Replacement" in "CLUTCH CON

TROLS" (SEC. 7D) of this manual).

PUSH ROD ADJUSTMENT

Instructions covering push rod adjustment varies according to model. The amount of free play and the location for measuring free play dif fers, dependent on vehicle model and type of equip ment used.

Push rod adjustment is very important on all models and tolerances given should be adhered to.

If the push rod is too long, brakes will not release completely. If the push rod is too short excessive pedal travel will be required to apply the brakes.

IMPORTANT: If any doubt exists relative to push rod adjustment, always remember it is better to have push rod adjusted too short than for it to be too long.

TILT CAB MODELS (Refer to Fig. 10)

1. Set emergency brake or block wheels.

2. Tilt cab (see instructions in Section 1).

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

3. Pull back boot on push rod. Visually check to see if piston is seated firm ly against piston snap ring in cylinder bore. If piston is NOT against snap ring, push rod is too long and should be shortened.

4. To adjust, loosen lock nut and turn rod in or out of rod end as necessary. Adjust so that a slight movement of brake pedal at pad is necessary before end of push rod contacts piston.

5. Tighten lock nut.

6. Check operation of brakes.

P4500 (Refer to Fig. 8)

1. Loosen lock nut on push rod.

2. Turn push rod in or out of push rod end as necessary so that free pedal travel measured at center of pedal pad is between 0.060” and 0.250”.

3. Tighten lock nut.

4. Check operation of brakes.

ALL MODELS WITH DASH MOUNTED

POWER CYLINDER (STD. OR OPT.)

(Refer to Fig. 20)

1. Loosen lock nut on push rod.

2. Turn push rod in or out of push rod end as necessary to obtain free play of 0.250” before push rod causes movement of power cylinder hub.

NOTE: The free play is ”at push rod" NOT at pedal pad. The push rod is part of the power cyl inder assem bly and the free play is related to the power cylinder not the brake pedal.

3. Tighten lock nut.

4. Check operation of brakes.

DESCRIPTION

There are four different type brake master cylinders used on these vehicles; single barrel

(models with mechanical clutch controls), double barrel (models with hydraulic clutch controls), split system , and those which have a master cy l inder integral with the dash mounted type vacuum power booster.

On conventional cab models, all types are mounted on the engine side of the fire wall. The single barrel cylinder is fastened by two bolts; the double barrel cylinder u ses three bolts. The boos ter type cylinder has four studs as part of the vac uum chamber. These studs pass through the fire wall and the assem bly is fastened with four nuts on these studs, inside the cab. The master cylinder is fastened to the booster assembly on two studs with nuts.

On tilt cab models the double-barrel cylinder is mounted under the cab on a bracket with three bolts.

On "P" Models the double-barrel cylinder is mounted on a dash panel with three bolts.

On "S” Models the split system type master cylinder is used. It is mounted on engine side of the fire wall and is fastened by four bolts.

Some master cylinders have bleeder screw s and others do not (refer to brake bleeding sequence chart, figure 6).

FILLER CAPS

MASTER

CYLINDERS

the result of changes in temperature as well as changes in fluid level as the result of normal brake operation. These caps are fastened to the top of the master cylinder by a single bolt down through the center which fits in a threaded hole in the master cylinder body (see fig. 12).

F iller caps used on those cylinders which are integral with a dash mounted vacuum booster are identical to caps used on regular master cylinders except that they are round instead of rectangular.

Filler cap used on split system is a single cap covering both reservoirs and is fastened by a single bolt in the center as shown in figure 13.

Brake fluid level in all master cylinders should be checked periodically by removing filler cap and making visual inspection. On conventional models the master cylinder is accessib le by lifting the hood to the engine compartment on the left side of vehicle. On tilt cab models the m aster cylinder is accessible by removing the metal plate on the riser panel below the front of the driver’s seat.

On "P" Models the master cylinder is accessible by removing a metal cover from outside the ve hicle at the front, or from inside the vehicle, on the dash, between windshield and instrument panel.

Location differs with body manufacturer. On "S”

Models the master cylinder is accessib le by lifting the hood to the engine compartment on the left side of the vehicle.

M AIN TEN AN CE (ALL TYPES)

F iller cap on single and double barrel cylin ders is rectangular and incorporates a combination seal and diaphragm made of rubber. The purpose of this is to prevent dirt from entering the reservoir, to prevent brake fluid from leaking out and to a l low for expansion and contraction of fluid level as

F iller caps on all master cylinders are de signed to vent the fluid reservoir without perm it ting lo ss of fluid. B y-pass port between cylinder bore and reservoir and vent hole in filler cap must be kept open to assure proper operation. An ob structed by-pass port will prevent return of fluid to reservoir, preventing full release of brakes.

G M C S E R V I C E M A N U A L

B y-p ass ports may be obstructed by one of the fol lowing causes:

1. Clogged with dirt - - remove master cy l inder and disassem ble and clean all parts.

2. Swollen primary cup due to the use of wrong fluid - - overhaul master cylinder, drain and flush entire brake system , and refill with proper fluid.

3. Pedal binding on shaft, preventing full re turn of piston - - free up and lubricate pedal.

4. Improper push rod adjustment - - adjust push rod.

MASTER CYLINDER REPLACEMENT

TILT CAB MODELS

Removal

1. Tilt cab forward and place a suitable con tainer under master cylinder to catch fluid when hydraulic lines are disconnected. DO NOT RE

USE THIS FLUID.

2. Disconnect hydraulic lines from outlets of brake and clutch cylinders.

3. Pull push rod boots off master cylinder.

Boots will remain on push rods when master cyl inder is removed.

4. Remove three bolts attaching master cyl inder to support bracket and remove master cyl inder assembly.

Installation

1. Position master cylinder assem bly at sup port bracket and guide push rods into pistons. At tach cylinder with three bolts. Tighten bolts firm ly.

2. Connect hydraulic lines to brake and clutch cylinder outlets.

3. Place push rod boots over ends of master cylinder brackets.

4. Adjust push rods as directed under "Brake

Pedal and Linkage."

5. Fill master cylinder reservoir and bleed brake system as directed under "Bleeding Brakes."

CONVENTIONAL MODELS

(SEPARATE MASTER CYLINDER)

Removal

1. Place a suitable container under master cylinder to catch fluid when hydraulic lines are disconnected. DO NOT RE-USE THIS FLUID.

2. Disconnect hydraulic lines from outlet of brake cylinder (also clutch lines on dual cylinders).

3. Pull push rod boot off master cylinder tube which extends through dash. Boot will remain on push rod when master cylinder is removed.

4. Remove three bolts and lock washers (two on single barrel cylinders) attaching master cyl-

Sec. 5A

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HYDRAULIC BRAKES

inder to dash (nuts are welded to inner side of dash) and remove m aster cylinder assembly.

Installation

1. Place gasket over each cylinder tube. P o si tion m aster cylinder assem bly at dash, while an assistant inside cab guides push rod into piston.

Attach cylinder to dash with three bolts and lock washers (two on single barrel cylinders).

2. Connect hydraulic line to brake (and clutch on dual) cylinder outlet.

3. Inside cab, place push rod boot over end of cylinder tube.

4. Adjust push rod as directed under "Brake

Pedal and Linkage."

5. Fill master cylinder reservoir and bleed brake system as directed under "Bleeding Brakes."

CONVENTIONAL MODELS

(WITH DASH MOUNTED BOOSTER)

Removal

1. Place a suitable container under master cylinder to catch fluid when hydraulic line is d is connected. DO NOT RE-USE THIS FLUID.

2. Remove two nuts from studs on booster chamber and pull master cylinder off studs.

3. If complete booster assembly is to be re moved, omit Step 2. Instead, remove nut and bolt which fastens push rod to brake pedal inside cab.

4. Remove four bolts which fasten booster and support bracket assembly to cab fire wall.

5. Pull booster assem bly (with master cylin der and support bracket attached) away from fire wall and remove from engine compartment.

Installation

1. Place booster assem bly (with master cyl inder and support bracket attached) in position on fire wall from engine compartment side.

Sec. 5A

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G M C S E R V I C E M A N U A L

1 R eservoir Cover

2 M aster Cylinder Housing

3 Piston Return Spring

4 Primary Cup

5 Piston Assem bly

6 Snap Ring

7 Boot

8 Check Valve (Brake Cylinder Only)

9 Check Valve Seat (Brake Cylinder Only)

10 Bleeder Valve (Brake Cylinder Only)

Figure 12— D ouble Barrel Master Cylinder Components

2. Fasten booster support bracket to fire wall with four bolts.

3. Attach push rod to brake pedal.

4. If master cylinder only is to be installed omit Steps 1, 2, and 3. Instead, place master cyl inder in position on studs on booster chamber and fasten with two nuts.

5. Connect hydraulic brake line to master cylinder.

6. Fill master cylinder reservoir with proper fluid and bleed brake system as directed under

"Bleeding Brakes."

7. Adjust brake pedal push rod as necessary.

"S" MODELS

(SPLIT MASTER CYLINDER)

Removal (Refer to Fig. 11)

1. Wipe master cylinder and lines clean with a clean cloth. Place dry cloths below master cyl inder to absorb any fluid spillage.

2. Disconnect hydraulic lines at master cyl inder. Cover line ends with clean, lint-free mater ial to prevent foreign matter from entering system .

3. Disconnect battery ground strap or stop light wires and brake warning switch wire.

4. Remove nuts, bolts, and washers which fasten master cylinder to dash. Pull master cylin der straight off push rod and remove from engine compartment.

5. Remove and discard m aster cylinder push rod boot.

6. Remove master cylinder cover and pour out fluid from reservoirs. Pump the remaining fluid out by depressing piston.

Installation (Refer to Fig. 11)

1. Assem ble new boot on brake pedal push rod.

2. Place master cylinder in position in engine compartment. Make certain that push rod and boot are in proper position.

3. Fasten master cylinder to dash with nuts, bolts, and washers.

4. Connect brake lines to master cylinder.

5. Fill the reservoirs with recommended brake fluid.

6. Follow instructions in this manual under heading of "Bleeding Brakes."

G M C S E R V I C E M A N U A L

7. If necessary, adjust the brake pedal freeplay as directed.

8. Connect battery ground strap or stop light w ires and brake warning switch wire (whichever was disconnected at removal).

9. Test brakes and make any necessary ad justments if operation is not satisfactory.

MASTER CYLINDER OVERHAUL

The following procedures cover disassem bly, cleaning, inspection and repair, and assem bly of components used in both the brake and clutch cy l inder bores on double barrel master cylinders and on brake cylinder bores on single barrel cylinders.

The m a ste r c y lin d er a s s e m b ly u se d w ith dash mounted power booster is integral with the booster and has a different internal construction. They can be removed and installed on the vehicle as d es cribed in "Master Cylinder Replacement." Over haul of this type master cylinder is covered in the unit overhaul manual as part of the complete a s sembly overhaul.

OVERHAUL (EXCEPT SPLIT-TYPE)

(Refer to Figure 12)

1. Clean all dirt from outside of unit, using a non-petroleum solvent.

2. Remove snap ring from groove in both cyl inder bores.

3. Remove piston assem bly, primary cup, return spring and retainer assem bly, check valve and check valve seat from brake cylinder bore.

4. Remove piston assem bly, primary cup, and return spring and retainer assem bly from clutch cylinder bore.

5. Remove cover from cylinder housing.

6. Remove bleeder screw (if used).

Cleaning

Im m erse all parts in denatured alcohol and wash thoroughly. Wipe sm all parts dry and blow out inside of reservoir and cylinder bores. Make sure intake and by-pass ports in cylinder housing and bleeder holes in piston are clean.

CAUTION: DO NOT use kerosene or

gasoline for cleaning master cylinder

components.

Inspection and Repair

Master cylinder repair kits are available which contain all the parts ordinarily required when overhauling master cylinders. Refer to ap plicable Parts Book for part number of repair kit.

In addition to replacement of parts contained in repair kit, master cylinder should be inspected and repaired, if necessary, as follows:

Sec. 5A

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HYDRAULIC BRAKES

1. Examine cylinder bores. If scored or rust ed, recondition by honing. Be sure to use proper size hone. (Refer to "Specifications" for nominal diameter of cylinder bores.) Do not hone more than necessary to remove sco res and smooth up cylin der. Remove burrs caused by honing from around by-pass and intake ports.

2. Check piston fit in cylinder bore. Clearance between piston and cylinder wall should be within

0.001" to 0.005" when checked with feeler gauge.

Assem bly (Fig. 12)

1. Before assembling, coat inside of cylinder bores and dip all internal parts in hydraulic brake fluid.

In sta ll com p on en ts in b rak e cy lin d er b o re of double barrel cylinders as follows: a. Install check valve seat in cylinder bore, then position check valve on seat.

b. Install return spring (shortest of the two) in bore with large diameter end of spring over check valve.

c. Install primary cup in cylinder bore with lip of cup toward outlet end. Make sure end of r e turn spring seats inside the cup.

d. Insert piston and secondary cup assembly into cylinder bore, with open end of piston toward open end of cylinder.

e. P re ss piston into cylinder bore, com press ing spring, and install snap ring in groove in bore.

Make sure snap ring is fully seated in groove.

3. Install components in clutch cylinder bore as follows: a. Install return spring (longest of the two) in cylinder bore, large diameter end first.

b. Install primary cup in cylinder bore with lip of cup toward outlet end. Make sure end of spring seats inside the cup.

c. Insert piston and secondary cup into cylin der bore, with open end of piston toward open end of cylinder.

d. P re ss piston into cylinder bore, com press ing spring, and install snap ring in groove in bore.

Make sure snap ring is fully seated in groove.

4. Install cover on cylinder reservoir.

5. Install bleeder screw (if used).

OVERHAUL (SPLIT-TYPE)

D isassem bly (Refer to Fig. 13)

1. Remove cylinder cover bolt and gasket.

2. Lift off reservoir cover and cover seal.

Pour out any excess fluid and stroke piston to force fluid through outlet ports.

3. Remove piston stop bolt and gasket from bottom of reservoir housing.

4. Use snap ring p liers and remove retainer ring from groove in end of cylinder bore.

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

1 Primary Piston Seal Cup

2 Primary Piston

3 Cover Seal

4 Reservoir Cover

5 Gasket

6 Cover Bolt

7 Intake Port

8 B y-P ass Port

9 Reservoir Housing

10 Tube Seat

11 Secondary Piston Return

Spring

12 Secondary Piston P ressure

Cup

13 Floating Secondary Piston

14 Secondary Piston Seal Cup

15 Gasket

16 Stop Bolt

17 Primary Return Spring

Retainer

18 Primary Return Spring

19 Primary Piston Stop Pin

20 Primarv Piston P ressure

Cup

21 Stop Plate

22 Retainer Ring t

-5245

Figure 13— Split System Master Cylinder (S5500 - S6500)

5. Remove stop plate.

6. All internal parts should slide easily out of cylinder bore. If they do not, apply com pressed air carefully at front outlet port. If parts do not remove easily, examine bore carefully for exten sive damage which may eliminate the possibility of reconditioning the m aster cylinder.

Cleaning and Inspection

Clean all parts in denatured alcohol or brake fluid. If reservoir housing is degreased, finish clean to remove all trace of other solvents. Inspect cylinder bore for scratches or corrosion. Minor blem ishes can be removed with crocus cloth or a clean-up hone. DO NOT OVERSIZE CYLINDER

MORE THAN 0.007-INCH OVER NOMINAL INSIDE

DIAMETER.

Check by-pass ports in both reservoirs to make sure they are open and free of burrs. Probe parts with soft copper wire 0.020-inchin diameter, or sm aller. Do not use steel wire to check parts.

This may scratch bore of master cylinder or cause burrs in port.

Remove and discard all rubber parts. All rub ber parts are included in repair kit which is avail able from regular service parts sources.

Assembly (Refer to Fig. 13)

1. Coat all parts with a liberal amount of brake fluid.

2. Install rubber seal cup on secondary piston with cup lip facing rear (open end of cylinder).

NOTE: All other cup lips face opposite direc tion (closed end of cylinder).

3. Stack and install secondary piston spring, pressure cup and piston in cylinder bore.

in cylinder bore.

6. Install stop plate in cylinder bore.

7. Compress all parts in cylinder bore and install retainer ring in groove.

8. Install reservoir cover and seal.

4. Install piston stop bolt and gasket, making sure screw enters cylinder bore behind rear of piston.

5. Assem ble and install primary piston parts

G M C S E R V I C E M A N U A L

Sec. 5A

Page 175

HYDRAULIC BRAKES

BRAKE PIPE DISTRIBUTION A N D SWITCH ASSEMBLY

All models with split brake system are equip ped with a brake pipe distribution and switch a s sembly (refer to fig. 11). The hydraulic brake lines are routed from the master cylinder, through the switch assem bly, to the front and rear brakes. The switch is wired electrically to the brake alarm indicator light on the instrument panel. In the event of fluid loss in either the main or secondary brake system , the indicator light will come on when the brakes are applied. If this light com es on during vehicle operation, it is an indication that there is a failure somewhere in the brake system . The truck should be removed from service as soon as p ossible and the trouble corrected.

This light also com es on when the ignition key is held in the "START" position. As soon as the key is released to the "ON" position, the light goes out. The purpose of this is to assure the driver that the warning light is not burned out.

BRAKE PIPE DISTRIBUTION A N D

SWITCH ASSEMBLY REPLACEMENT

(Refer to Figure 11)

REMOVAL

1. Disconnect battery cable.

2. Disconnect electrical lead from pressure differential switch.

3. Place dry rags below the switch to absorb any fluid spilled during removal of switch.

4. Disconnect four hydraulic lines from con nections at switch. If necessary, loosen line con nections at main cylinder. Cover open line ends with clean, lint-free material to prevent foreign matter from entering the system .

5. Remove mounting screw and remove switch from vehicle.

INSTALLATION

1. Make sure new switch is clean and free of dust and lint. If any doubt exists, wash switch in suitable solvent, and dry with air.

2. Place switch in position and secure to brac ket with mounting screw.

3. Remove protective material from open hydraulic brake lines and connect lines to switch.

If necessary, tighten brake line connections at main cylinder.

4. Connect switch electrical lead.

5. Connect battery cable.

6. Bleed the brake system s as outlined in this manual.

TESTING DISTRIBUTION

AND SWITCH ASSEMBLY

1. Determine if bulb is functioning by turning key in ignition switch to "START" position.

2. Check main cylinder to make sure both reservoirs have enough fluid. Add if necessary.

3. Turn key in ignition switch to "ON" position.

4. Open wheel cylinder bleed screw at one rear wheel.

5. Depress brake pedal and hold down. The brake warning light should come on due to p r e s sure difference between front and rear system s.

Approximately 200-250 psi differential is needed to operate brake light switch.

6. Close bleed screw , then release brake pedal. Refill rear reservoir, if needed.

NOTE: Caution should be taken to prevent air from entering hydraulic system during checks on switch.

7. The recommended interval for checking switch is 24 months, or 24,000 m iles, any time major brake work is done, or any time brake oper ation is abnormal.

WHEEL CYLINDERS

There are four different type wheel cylinders used on vehicles covered by this manual. Front brakes are either Type "F," "FA,” or Duo-Servo.

Rear brakes are either Type "FR-3,” "FR-3A,"or

Twin-Action.

Since wheel cylinders can be disassembled and repaired without removing them from the ve hicle the procedures are covered in this manual along with "Replacement" procedures.

WHEEL CYLINDER REPLACEMENT

TYPES "F" AND "FA"

Removal

1. Jack up axle and remove brake shoes as directed under "Brake Shoe Removal."

2. Disconnect axle brake tube from inlet con nector at upper cylinder. Remove inlet connector attaching connecting tube fitting to upper cylinder,

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L and remove bolt attaching connecting tube fitting to lower cylinder. Remove connecting tube and fitting assem bly.

3. Remove one large and two sm all bolts at taching each cylinder to backing plate, then remove cylinders from backing plate.

Installation

NOTE: The two wheel cylinders mounted on each brake are identical; however, cylinders on right- and left-hand brakes have opposite cylinder castings. Clean mating surfaces of cylinders and backing plate to insure proper alignment.

TYPE "FR-3" AND "FR-3A"

Removal

1. Jack up axle and remove brake shoes as directed under "Brake Shoe Removal."

2. Disconnect axle brake tube from upper cyl inder at inner side of backing plate. Remove wheel cylinder connecting tube at inner side of backing plate.

3. Remove two bolts and lock washers attach ing each wheel cylinder to backing plate. Remove wheel cylinders and heat shields, then remove heat shields from cylinders.

1. Place each cylinder on backing plate and attach with one large and two sm all bolts and lock washers.

2. Position wheel cylinder connecting tube and fittings assembly and attach fitting to lower open ing in upper cylinder with inlet connector, using new copper gasket on both sides of fitting. Attach fitting to lower opening in lower cylinder with special bolt, using new copper gasket on both sides of fitting. Tighten inlet connector and special bolt firm ly.

3. Install bleeder valve in upper opening in each cylinder.

4. Install brake shoes as directedunder "Brake

Shoe Installation." Bleed brake system as directed under "Bleeding Brakes."

Installation

NOTE: Upper and lower wheel cylinders on both right- and left-hand brakes are interchange able. Cylinders must be positioned on backing plate so that the long stroke end of the cylinder faces the shoe toe (adjustment end of shoe) or the adjusting slot in backing plate. Make sure mating surfaces of cylinders, heat shields, and backing plate are clean to assure proper alignment.

1. Position heat shield on each wheel cylinder and install on backing plate, and attach each cy l inder with two bolts and lock washers.

2. Attach connecting tube to upper opening in lower cylinder and to lower opening in upper cyl inder. Connect axle brake tube to lower opening in lower cylinder, and install bleeder valve in upper opening in upper cylinder.

3. Install brake shoes as directedunder "Brake

Shoe Installation." Bleed brake system as directed under "Bleeding Brakes."

DUO-SERVO

Removal

1. Jack up axle and remove wheel, brake drum, and brake shoes as directed later under

"Brake Shoe Removal."

2. Disconnect metal brake tube from flexible hose at frame, disconnect hose from frame, then unscrew hose fitting from wheel cylinder housing.

3. Remove cap screw s and washers attaching wheel cylinder to backing plate and remove cylin der assembly.

TWIN-ACTION

Removal

1. Jack up axle and remove brake shoes as directed later under "Brake Shoe Removal."

2. Disconnect brake tube from rear wheel cyl inder connector at inner side of backing plate. Re move brake tube connecting wheel cylinders at outer side of backing plate. Remove dust shield from upper end of each cylinder.

3. Remove cap screw s and lock washers at taching wheel cylinders to backing plate, then r e move wheel cylinders and heat shield. Remove brake line connectors from cylinder housings.

Installation

1. Position wheel cylinder on backing plate and attach with cap screw s and lock washers.

2. Thread brake hose fitting into wheel cylin der housing using a new copper gasket on hose fitting. Insert fitting at other end of hose through frame and secure with toothed lock washer and nut or with spring lock, depending upon type used. Con nect metal brake tube to hose fitting inside frame side rail.

3. Install brake shoes as directedunder "Brake

Shoe Installation." Bleed brake system as directed under "Bleeding Brakes."

Installation

NOTE: Forward and rearward wheel cylinders are not interchangeable. Rearward cylinder has threaded inlet opening near center of cylinder bore. Forward cylinder has threaded bleeder valve opening at extreme outer edge of cylinder bore.

Cylinders must be positioned with connecting tube openings toward each other.

G M C S E R V I C E M A N U A L

Sec. 5A

Page 177

HYDRAULIC BRAKES

TYPE “ F” A N D TYPE “ F A ” - F R O N T

TYPE “ FR -3 ” A N D TYPE “ F R -3 A ” - R E A R

1 Boot

2 Brake Shoe Guide

3 Piston

4 Piston Cup

5 Cup Filler

6 Piston Spring

7 Cylinder

8 Brake Shoe Anchor

Slot

9 Push Rod

T - 4 5 6 6

Figure 14— W heel Cylinders Used with Type

“F”, “F A ”, “FR-3”, and “FR -3 A ” Brakes

1. Position heat shields on cylinders, place wheel cylinders on backing plate, and attach with cap screw s and lock washers. Tighten cap screw s firm ly. Install dust shield on upper end of each cylinder.

2. Install connecting tube between the two cyl inders and tighten connections firm ly. Connect brake tube to inlet opening in rearward cylinder at inner side of backing plate. Install bleeder valve in threaded opening in forward cylinder.

3. Install brake shoes as directed under "Brake

Shoe Installation." Bleed brake system as directed under "Bleeding Brakes."

WHEEL CYLINDER REPAIR

TYPES "F" AND "FA” (Fig. 14)

Disassem bly

Pull boot off end of cylinder, then remove boot and piston. Pull boot off piston. Brake shoe guide is pressed into piston and cannot be removed. Re move piston cup, cup filler, and spring from cyl inder. Remove bleeder valve from cylinder.

Inspection and Repair

1. Repair kits are available which contain the

Figure 15— Checking Fit of Piston in Wheel Cylinder

parts to be replaced when overhauling wheel cyl inders. Refer to Parts Book for repair kit part numbers.

2. Inspect cylinder bore for scores, scratches, or corrosion. Light scratches or slightly corroded spots may be polished out with crocus cloth. Never use emery cloth or sandpaper. If scratches or corrosion are too deep to be polished out, replace cylinder.

3. Check fit of new pistons in cylinder bore, using a feeler gauge (fig. 15). Clearance should be within 0.0025" to 0.0065" on "F" and "FA" type cylinders. Replace cylinder if clearance exceeds the maximum.

Assembly

Before assem bling wheel cylinder, be sure each part has been cleaned in denatured alcohol.

CAUTION: DO NOT use kerosene or

gasoline for cleaning wheel cylinder parts.

Dip each internal part in hydraulic brake

fluid before assembling.

1. Insert piston spring, cup filler, and cup into cylinder bore. Cup filler bumper and cup lip must face closed end of cylinder.

2. Assem ble boot on piston, making sure the boot snaps over the brake shoe guide.

3. Install piston and boot, inserting piston into cylinder and engaging boot lip in groove in edge of cylinder. Position brake shoe guide so slot in guide is parallel with flat mounting surface of cylinder.

DUO-SERVO (Fig. 16)

Disassembly

Pull boots off ends of cylinder and remove push rods from boots. Push pistons, cups, and spring out of cylinder. Remove bleeder valve from cylinder.

Sec. 5A

Page 178

HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

BOOT.

Figure 16— Duo-Servo W heel Cylinder

Inspection and Repair

1. Repair kits are available which contain the parts to be replaced when overhauling wheel cyl inders. Refer to Parts Book for repair kit part numbers.

3. Check fit of new pistons in cylinder bore, using a feeler gauge. Clearance should be within

0.002" to 0.004". Replace cylinder if clearance exceeds 0.004". Refer to figure 15.

Assem bly

Before assem bling wheel cylinder, be sure each part has been cleaned in denatured alcohol.

1 Connecting Rod

2 Seal

3 Wheel Cylinder Body

4 Piston

5 Cup

6 Connector Insert

7 Spring Assembly

T-2699

Figure 17 - T w in -A c t io n W heel Cylinder

CAUTION: DO NOT use kerosene or

gasoline for cleaning wheel cylinder parts.

Dip each internal part in hydraulic brake

fluid before assembling.

Insert pistons, cups, and spring into cylinder bore. Assem ble push rods in boots and install boots over ends of cylinder. Install bleeder valve.

TYPES "FR-3" AND "FR-3A" (Fig. 14)

D isassem bly

Pull boots off ends of cylinders and remove push rods from boots. Push pistons, cups, and spring out of cylinder. Remove bleeder valve from upper cylinder.

Inspection and Repair

1. Repair kits are available which contain the parts to be replaced when overhauling wheel cyl inders.

IMPORTANT: Only genuine GMC parts should be used. Non-genuine parts may deteriorate and swell in a short time, resulting in faulty brake operation.

2. Inspect cylinder bore for scores, scratches, or corrosion. Light scratches or slightly corroded spots may be polished out with crocus cloth. Never use emery cloth or sandpaper. If scratches or cor rosion are too deep to be polished out, replace cylinder.

3. Check fit of new pistons in cylinder bore, using a feeler gauge as shown in figure 15. Clear ance should be within 0.001" to 0.005" on "FR-3" type. Replace cylinder if clearance exceeds the maximum.

Assembly

Before assembling wheel cylinder, be sure each part has been cleaned in denatured alcohol.

CAUTION: DO NOT use kerosene or

gasoline for cleaning wheel cylinder parts.

Dip each internal part in hydraulic brake

fluid before assembling.

1. Install pistons, piston cups, and spring, with cup lips toward inside of cylinder.

2. Assem ble push rods and boots, then install on cylinder. Seat boots evenly in cylinder grooves.

Align push rod slots as shown in figure 14.

3. Install bleeder valve in upper cylinder.

TWIN-ACTION (Fig. 17)

D isassem bly

Pull boots off ends of cylinder and remove push rods from boots. Push pistons, cups, and

G M C S E R V I C E M A N U A L

Sec. 5A

Page 179

HYDRAULIC BRAKES

spring out of cylinder. Remove cups from pistons.

Remove bleeder valve from upper cylinder.

Inspection and Repair

1. Repair kits are available which contain the parts to be replaced when overhauling wheel cyl inders. Refer to Parts Book for repair kit part numbers.

2. Inspect cylinder bore for scores, scratches, or corrosion. Light scratches or slightly corroded spots may be polished out with crocus cloth. Never use emery cloth or sandpaper. If scratches or cor rosion are too deep to be polished out, replace cylinder.

3. Check fit of new pistons in cylinder bore, using a feeler gauge. Clearance should be within

0.002” to 0.004". Replace cylinder if clearance exceeds 0.004". Refer to figure 15.

Assem bly

Before assem bling wheel cylinder, be sure each part has been cleaned in denatured alcohol.

CAUTION: DO NOT use kerosene or

gasoline for cleaning wheel cylinder parts.

Dip each internal part in hydraulic brake

fluid before assembling.

Figure 18— U sing Special Tool (J-4705) for Installing

W heel Cylinder Cup (Twin-Action Only)

1. Install new cup on each piston so open end of cup w ill be toward flat end of piston. Use special tool (J-4705) to guide cup over piston (fig. 18).

This applies to old style assem b lies only.

2. Assem ble boots on push rods, being sure bead on boot engages groove in push rod. Install boots and push rods on cylinders, engaging bead on outer edges of cylinder housing.

HYDRAULIC LINES

Hydraulic brake system units are intercon nected by flexible hose and special metal tubing.

Flexible hose is used between master cylinder (on cab) and frame connection, between frame and front wheel cylinders, and between frame and rear axle brake line. Whenever hydraulic lines have been disconnected for any reason, brake system must be bled, after connecting lines, as directed under "Bleeding Brakes."

FLEXIBLE HOSE

At front wheels on type "F" and type "FA," hose fitting is threaded into wheel cylinder connec tor, with a copper gasket used between shoulder on hose fitting and connector. On Duo-Servo a con nector is not used. Fitting at other end of hose is inserted through hole in frame and secured by a toothed lock washer and nut or by a spring lock.

Brake tube connector or tee fitting threads into end of hose fitting.

At rear axle, fitting at one end of hose is threaded into axle tee, with a copper gasket used to seal the connection. Other end of hose is insert ed through frame bracket and secured by a toothed lock washer and nut or by a spring lock. Brake tube connector or tee fitting threads into end of hose fitting.

To remove hose, disconnect end at frame or frame bracket, then unscrew hose fitting from wheel cylinder or rear axle tee. When installing hose, always use a new copper gasket at wheel cylinder and rear axle tee. When frame end of hose is secured by a nut, always hold hose fitting with a wrench while tightening nut to prevent twisting hose.

METAL TUBING

When necessary to replace metal brake tubing, always use special metal tubing which is designed to withstand high p ressure and to resist corrosion.

Ordinary copper tubing is not satisfactory for use as hydraulic brake lines. When replacing tubing, always use the same size as that removed.

TUBE FLARING

In order to insure a proper flare, a special flaring tool must be used. When using tool, in structions furnished by the tool manufacturer should be followed. Always inspect newly formed flares for cracks or malformations which might cause leaks.

Sec. 5A

Page 180

HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

Vacuum power cylinders are used as standard equipment or are available as optional equipment on all vehicles with hydraulic brakes covered by this manual.

All the power cylinders used on these vehicles, both remote mounted and dash mounted (integral with master cylinder) are the type used in the "one to one" hydraulic system . That is, the hydraulic fluid volume output is equal to input.

The power cylinder is a combined vacuumhydraulic power unit, utilizing vacuum and atm os pheric p ressure for its operation.

The vacuum source on gasoline engine models is the engine intake manifold. The vacuum source on Toro-Flow D iesel Models is the vacuum pump.

The combination of vacuum in front of the diaphragm and atmospheric pressure behind the diaphragm results in the power application of the brakes.

V A C U U M POWER BRAKE

SYSTEM TESTS

V ACU U M POWER CYLINDERS

VACUUM TEST

With engine stopped, hand brake applied and transm ission in neutral, apply brakes several tim es to destroy all vacuum in system .

Depress brake pedal, and while holding foot pressure on pedal, start engine. If vacuum system is operating, pedal will tend to fall away under foot p ressu re when engine starts, and le s s p ressure will be required to hold pedal in applied position.

If no action is felt, vacuum system is not func tioning.

Inspect vacuum lines for leakage, and for re striction caused by bent or kinked tube or hose.

If no fault is found in lines, trouble is in power cylinder control valve, necessitating overhaul of power cylinder.

HYDRAULIC TEST

Stop engine and again destroy all vacuum in system . Depress brake pedal and hold foot p res sure on pedal. If brake pedal gradually falls away under foot pressure hydraulic system is leaking, either internally or externally.

Inspect all hydraulic line connections for leak age and make the necessary repairs. If no external leaks are evident, inspect master cylinder and wheel cylinders and replace parts as necessary.

If the condition still exists, an internal leak in power cylinder is indicated, necessitating over haul of power cylinder.

POWER CYLINDER REPLACEMENT

The installed location of vacuum power cyl inders varies by model.

■

C Y LIN D E R

FILTER)

' r —j j ' *

FRO M M ASTER

C Y LIN D E R

T O W H E E LS

! P O W E R

' c y l i n d e r

FROM M ASTER

C Y LIN D E R

/ / FRO M V A C U U M

/ / S O U R C E

I L I A T M O SP H ER E

lin e

FROM V A C U U M

S O U R C E

[C O N T R O L

! V A L V E

FRO M AIR

FILTER

(A TM O SPH E R E )

• *.

"^SS^STEP

SU P P O R T

* 5 ^

V A C U U M

C O N N E C T IN G

TUBE

CO N V EN TIO N A L MODELS

BLEEDER

V A L V E C O N T R O L

3 V A L V E

V A C U U M

C O N N E C T IN G j |

TUBE

TO W H EEL . . ^

CYUNDEBS

TILT CAB MODELS

Figure 19 — Pow er C ylinder Installed

G M C S E R V I C E M A N U A L

Sec. 5A

Page 181

HYDRAULIC BRAKES

Conventional - behind cab step, immediately below left-hand door. Vacuum reserve tank is lo cated in this sam e area, when used. See figure 19.

Tilt Cab - between frame side rails in front of the radiator and behind the front bumper. See figure 19.

P4500 - on the outside of the left-hand frame side rail just ahead of the second frame c r o ss member.

"S" Models - on the outside of the left-hand frame side rail.

Some Models (both standard and optional) use the combined m aster-booster cylinder type which is mounted on the dash panel in the engine compartment. See figure 20.

REMOVAL (REMOTE MOUNTED)

1. For easier accessibility, it is recommended that cab step be removed on conventional models and that cab be tilted forward on tilt cab models.

2. Clean away as much road dirt and grease as possible to prevent contamination of vacuum or hydraulic system s.

3. Have suitable container available to catch hydraulic brake fluid which will flow from system .

DO NOT RE-USE THIS FLUID.

4. Disconnect all hydraulic, vacuum, and at mospheric lines and hoses from power cylinder.

5. Remove bolts and nuts which fasten cylin der to vehicle frame and support brackets. Remove power cylinder.

INSTALLATION (REMOTE MOUNTED)

1. Place power cylinder in position and fasten with nuts and bolts to vehicle frame and support brackets.

2. Connect all hydraulic, vacuum, and atm os pheric lines and hoses to power cylinder.

3. Bleed master cylinder and vacuum power cylinder as directed under "Bleeding B rakes” in this manual. If ONLY the power cylinder has been removed, it should not be necessary to bleed the wheel cylinders IF the master cylinder and power cylinders are bled first AND lines to wheel cylin der have not been disturbed.

4. Start engine and test operation of brake sy s tem as directed. Refer to "Trouble-Shooting" chart in this manual if operation is not satisfactory.

V A C U U M POWER (

There are three different types of air cleaners used on vehicles with vacuum assisted hydraulic brakes.

SERVICING AIR CLEANERS

The air cleaner used on P4500, S5500, and

REMOVAL (DASH MOUNTED)

. 1. Clean away as much road dirt and grease as possible to prevent contamination of vacuum or hydraulic system s.

2. Have suitable container available to catch hydraulic brake fluid which will flow from system .

DO NOT RE-USE THIS FLUID.

3. Disconnect hydraulic line from master cyl inder outlet.

4. Disconnect vacuum hose from vacuum check valve in booster chamber.

5. Inside cab, disconnect push rod from brake pedal.

6. Remove four bolts which fasten booster and support bracket to fire wall and remove boos ter and master cylinder assembly with support bracket from engine compartment.

INSTALLATION (DASH-MOUNTED)

1. Place power cylinder booster (with master cylinder and support bracket attached) in position on fire wall in engine compartment.

2. Install four bolts which fasten support bracket to fire wall in engine compartment.

3. Connect vacuum line to check valve in booster chamber.

4. Connect hydraulic line to master cylinder.

5. Inside cab, connect push rod to brake pedal.

6. Fill master cylinder with proper fluid. If

ONLY power cylinder has been removed it should not be necessary to bleed wheel cylinders. Bleed m aster cylinder as directed under "Bleeding Brakes."

7. Adjust brake pedal as directed.

8. Start engine and check operation of brake system as directed. Refer to "Troubleshooting" chart in this manual if operation is not satisfactory.

NDER AIR CLEANER

S6500 Models is the metal cup type which uses a hog's hair type element. This cup is a friction fit on the air intake pipe and can be removed by pull ing straight off. It can be cleaned and reused. Re fer to LUBRICATION (SEC. 0) in this manual for service intervals and cleaning instructions. If

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

Figure 2 1 — Power Cylinder Air Cleaner Installed (Conv.)

cleaner has become so laden with an accumulation of dirt, that satisfactory cleaning cannot be done, replace it with a new cleaner.

The air cleaner used on the conventional and all Tilt-Cab Models is a plastic encased, synthetic element type filter and cleaning is NOT recom mended. When cleaner becom es so laden with dirt, that tapping it against some solid surface (such as a work bench) will not remove foreign matter, then a new cleaner should be installed.

The air cleaner used with dash mountedpower cylinders is an integral part of the assem bly. This air cleaner is a cylindrical piece of polyurethane foam which is fastened on the power cylinder push rod. This air cleaner can be removed from the assem bly, cleaned,^and replaced.

LOCATION OF AIR CLEANERS

The air cleaner on the P4500 Model vehicles is located on the dash panel in front of the driver’s seat and is readily accessib le.

The air cleaner on "S" Models is located on the fire wall under the dash on the driver’s side.

The air cleaner on the conventional models is located in the left rear corner of the cab, directly behind the driver's seat. The air cleaner on the

Tilt-Cab models is located in front of the radiator near the vacuum power cylinder and is accessible by tilting cab forward. To remove cleaner from conventional or tilt cab, unfasten nut and bolt hold ing cleaner to bracket and pull cleaner off air hose

(see fig. 21).

The air cleaner on models equipped with dash mounted boosters is located in the booster hub on the push rod. To remove this air cleaner it is nec essary to disconnect push rod from brake pedal and remove push rod from booster assem bly. This requires approximately 225 lbs. pulling force and therefore some sort of leverage is needed. This can be done without removing booster from the vehicle. It must be done from inside the cab or body. The nylon push rod retainer will be broken upon removal, therefore a new retainer should be available before removing push rod. Remove filter from push rod, clean as directed in LUBRICATION

(SEC. 0) in this manual, and replace on push rod.

Reinstall push rod and connect to brake pedal.

Refer to figure 22 for illustration of this type of filter.

Figure 2 2 — Pow e r C ylinder A ir Cleaner (D a sh -M o u n te d Booster)

gec 5A.

G M C S E R V I C E M A N U A L ______________________

Page‘i83

HYDRAULIC BRAKES

V A CU U M CHECK VALVE

On all vehicles with vacuum power assisted hydraulic brakes a check valve is used somewhere in the vacuum line between the engine intake mani fold (gasoline) or the vacuum pump (Diesel) and the vacuum power cylinder (see fig. 23).

Purpose of check valve is to seal vacuum in power cylinder (and in vacuum reserve tank, when used), assuring sufficient vacuum for at least one power brake application in case the engine stalls.

Check valve can be tested for leakage by d is connecting power cylinder vacuum line from valve fitting and connecting a vacuum gauge, using a length of hose between gauge and check valve. Start engine, run at idle for a few seconds, and note reading on gauge. Stop engine and observe rate of vacuum drop. If drop exceeds 1 inch in 15 seconds, leakage must be considered excessive, and check valve must be repaired or replaced.

There are three basically different type vac uum check valves used. One is repairable and two are not. The repairable type has a cast metal body and is used on Tilt Cab and P4500 Model trucks.

The non-repairable types have a sealed plastic body and are used on all other models.

Check valves (plastic, non-repairable type) used with dash mounted boosters are integral with vacuum chamber assem bly. Check valves used on

"S" Models and som e conventional Models are mounted separate from booster cylinders.

Removal and installation of valves on P4500,

"S" Models, conventional, and Tilt Cab Models is the sam e. Disconnect all lines and hoses and r e move bolts or screw s which fasten valve to vehicle.

Discard malfunctioning valves removed from con ventional and "S" Models and replace with new valve. These are non-repairable. Valves removed from Tilt Cab and P4500 Models can be repaired.

To remove check valve from dash mounted power cylinders disconnect vacuum supply hose from check valve manifold assembly and pull man ifold assem bly out of grommet in vacuum booster chamber. Discard malfunctioning valves since this type cannot be repaired. When installing this type valve always use a new rubber grommet. Coat grommet lightly with grease prior to installation.

Valve on the P4500 Model is mounted on dash panel below master cylinder assembly and on op posite side of panel.

Valve on the tilt cab model is at the front of the engine and is mounted on a bracket attached to the frame crossm em ber on diesel models. On gas oline models, the valve is fastened t6 a bracket which is bolted on cab rear support, inside the channel on left-hand side (see fig. 23).

Valve on conventional and "S" Models is lo cated in the engine compartment and is fastened to a bracket attached to the fire wall (see fig. 23).

As previously stated, check valve on models using dash mounted booster is part of vacuum chamber assem bly.

REAR CAB

SUPPORT

M O U N T IN G

BRACKET

TO EN G IN E OR

V A C U U M PUMP

CHECK

VALVE

TO EN G IN E O R * —

V A C U U M PUMP

ifS m r i

I j j r o P O W E R

' M

CYLINDER

CHECK VALVE

TO POW ER

CYLINDER

C O N V E N T IO N A L M O D E L S

Figure 2 3 — V a cu u m Check V a lv e s Installed

TILT C A B M O D E L S

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G M C S E R V I C E M A N U A L

V A C U U M RESERVE TANK

A vacuum reserve tank is used as standard equipment on "S” 5500 and 6500 Models and as op tional equipment on all other models using vacuum assisted hydraulic brakes. This tank has a mini mum capacity of 1,000 cubic inches and is installed in the vacuum line between the vacuum check valve and the power cylinder.

On conventional cab models, the tank is in stalled immediately below the left-hand door, be hind the cab step.

On tilt cab models, the tank is installed be hind the engine, in front of the rear axle, and be tween frame side rails.

side of the left-hand side rail just to the rear of the batteries.

To replace tank, disconnect lines and brackets connecting tank to vehicle.

The vacuum gauges used on vehicles covered by this manual all operate on the same principle and are factory set and sealed units which are not adjustable or repairable. If a gauge fails to oper ate or operates improperly, it must be replaced.

All vacuum gauges are located in the instrument panel.

A vacuum gauge is standard equipment on some models and optional on others.

If a vapcuum gauge is suspected of operating improperly, it may be checked by comparing read ings with a test gauge which is known to be accur ate. Observe readings on vehicle gauge at engine idle speed and at various, specific engine rpm up

V A C U U M G AUG E

to maximum. Install test gauge in convenient loca tion in vacuum line and observe readings on test gauge at same, specific engine rpm. The manu facturer’s specifications permit a variation of - 1inch of mercury at 5 inches and - 2 inches of mer cury at 20 inches. Any variation beyond these lim its is an indication that the vehicle vacuum gauge should be replaced. Before condemning a gauge which does not register, or registers im properly, make certain that all vacuum lines in the system are free of dirt and/or kinks and that all connections are tight. System leakage can result in registration on gauge which is not normal. Also, on models with diesel engine, make certain that vacuum pump is properly installed and operating.

VA CU U M PUMP

GENERAL DESCRIPTION

The vacuum pump is a rotary, sliding vane type pump in which the rotor is eccentrically lo cated with respect to the housing. The pump is dependent upon oil as a means for lubrication of the bearings and also for providing a seal.

The vacuum pump is operated directly by a belt and pulley drive from the engine and operates at all tim es while the engine is running. The lubri cation of the pump is accomplished by connection with the oil pressure system of the engine.

the drive pulley, be certain that correct pulley is used. If pulley diameter is too large the pump ca pacity will be decreased; if the pulley is too small pump speed will exceed maximum recommended and premature pump failure will result. Refer to

Parts Catalogue for proper replacement pulley.

SYSTEM TESTS

The following tests or checks can be made on the vacuum pump while it is operating.

DISCHARGE OF OIL AND AIR

The oil plus the air which enters through the vacuum port, is discharged through the housing just below the point of minimum rotor to housing clearance. The oil and air leaves the pump through the opening on the pump base which is connected to the engine crankcase by a discharging hose.

DRIVE PULLEY

Maximum pump speed, for good life expect ancy, is 4,000 rpm. If it is necessary to replace

LUBRICATION

After the pump has been running for a few minutes, check the oil and air discharge line near the pump discharge port. If the line is not warming up, stop the pump and check for restrictions in the oil supply line.

VACUUM

Let the pump and engine operate at their norm al operating speed for several minutes so as to warm the oil circulating through the pump. Check the vacuum gauge. The pump should maintain at

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

least 26 inches of mercury vacuum. Let the engine idle. The pump should maintain at least 20 inches of mercury vacuum with the engine idling. If the pump does not maintain the vacuum values given above, inspect the pump for belt slippage or lack of lubrication. Also inspect the vacuum lines and fittings for leaks. If vehicle is not equipped with vacuum gauge, temporarily connect one in intake line.

BINDING IN THE PUMP

After the pump has been running for several minutes, stop the pump, loosen the belt adjusting device and remove the belt. With the vacuum port of the pump open to atmosphere, rotate the pump in the direction indicated on the front end plate, and check for points at which the pump tends to be binding. If binding occurs, the pump should be re moved from the installation, disassem bled, and inspected for faulty parts.

OIL LEAKS

After the pump has been operating for several minutes, inspect between the housing and the end plates for signs of oil leakage. This check should be made both with the vacuum port open and closed to atmosphere.

V A CU U M PUMP REPLACEMENT

(Refer to Figure 24)

REMOVAL

1. Loosen adjusting arm bolt and nut.

2. Loosen tension on drive belt and remove belt from drive pulley.

3. Disconnect air intake hose.

4. Disconnect oil inlet hose.

5. Disconnect oil and air discharge hose.

6. Remove four bolts which secure vacuum pump to support base.

7. Remove pump and discard gasket.

INSTALLATION

1. Position new gasket on pump base.

1 Crankshaft Pulley

2 Drive Belt

3 Drive Pulley

4 Adjusting Arm

5 Adjusting Bolt

6 Air Intake

7 Oil Inlet Line

8 Pump Body

9 Body to Base Bolt

10 Mounting Base

11 Base to Bracket Bolt

12 Mounting Bracket

13 Air and Oil

Discharge Hose

14 Bracket to Engine

Bolt

T-2943

Figure 2 4 — V acuum Pum p Installed (Typical)

2. Position pump on base and secure with four bolts.

3. Connect oil and air discharge hose.

4. Connect oil inlet hose.

5. Connect air intake hose.

6. Install belt on drive pulley and pull to proper tension (120-130 pounds (new belt) or 80-90pounds

(used belt)) using a strand tension gauge placed at the center of the greatest belt span.

7. Tighten adjusting bolt and nut.

AIR POWER CYLINDERS

Air power assisted hydraulic brakes are standard equipment on models LA4000 and DLA-

4000. These models use an air power cylinder to activate the standard type hydraulic brake. A reg ular air com pressor is used as the air supply source.

NOTE: Full air brakes are also available on these same models, as optional equipment. Refer to "AIR BRAKES" (SEC. 5B) of this manual.

AIR POWER BRAKE SYSTEM

OPERATION

An air-operated power unit is used on LA and

DLA-4000 models in place of a vacuum-assisted power unit. With the air power unit, the hydraulic brake system remains unchanged.

The air power unit consists of three basic elements:

1. An air cylinder which includes a cylinder,

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G M C S E R V I C E M A N U A L

Line To

C ontrol V a lv e

To W h e e l

C y lin d e rs

M a s t e r C y lin d e r

Line To

W h e e l C y lin d e r

A ir T a n k To

C ontrol V a lv e

Line

To C on trol

V a lv e

kJf

..,

To Trailer

B ra k e s

A ir Tank

P o w e r C y lin d e r!

Figure 2 5 — Typical Installation for Air-Assisted

Hydraulic Brakes on Tilt Cab M odels

a piston, and a push rod that connects the power piston to the hydraulic piston.

2. A hydraulic cylinder which includes a hy draulic piston with built-in check valve and a re sidual pressure check valve.

3. An air p ressure control valve which con tro ls the power output of the air pressure cylinder in accordance with the hydraulic pressure develop ed within the brake master cylinder.

The com pressed air supply line is attached to the control valve. Air is exhausted from the ex haust port in the control valve through an exhaust tube directed downward to prevent the entrance of dirt or water into the power cylinder.

The hydraulic input line from the master cyl inder is attached to the fluid inlet port located in the control valve. The outlet port, located in the end cap, is connected to the wheel cylinders of the vehicle brakes.

When the brake pedal is depressed, hydraulic fluid is transmitted from the master cylinder to the control valve. /The force on the control valve piston moves the valve diaphragm assembly, which closes the atmospheric port and opens the com pressed air port. The com pressed air admitted to the air cylinder moves the air piston and push rod to displace fluid to the wheel cylinders and apply the brakes.

When pressure on brake pedal is removed, the force of the brake shoe return springs, the air piston return spring and the brake pedal return spring cause movement in the opposite direction of all components and the brakes are released.

Opening of the atmospheric port in the control valve allows com pressed air to vent to atmosphere.

LUBRICATION

Refer to LUBRICATION (SEC. 0) for type of lubricant, recommended periods of application, and method of applying.

AIR POWER BRAKE SYSTEM TESTS

OPERATING TEST

1. Build up air pressure in system to normal operating p ressu re. If vehicle is equipped with trailer brake controls, trailer line shut-off cocks must be closed while making tests.

2. Apply brakes, then listen for sound of ex hausting air pressure as brakes are released.

Rapid release of air pressure indicates that power unit is operating.

3. Depress brake pedal and hold foot pressure on pedal. If pedal gradually falls away, leakage in hydraulic system is indicated. Make further test as directed under "Hydraulic P ressure T est.”

AIR PRESSURE TESTS

1. Remove lubrication pipe plug from rear end of cylinder shell and connect an air pressure test gauge at this point. Build up air pressure in system to maximum lim it.

2. Coat all air line connections with soap suds to check for leakage. Leakage can som etim es be corrected by tightening the connection. If this fails to correct leakage, new fittings, metal tubing, or flexible hose must be used.

3. Hold a jar of water up under exhaust tube so that end of tube is im m ersed in water. Watch for bubbles to appear in water. The appearance of

G M C S E R V I C E M A N U A L bubbles indicates a leaking control valve poppet air inlet seal.

4. Make a brake application and hold foot p res sure on pedal, and observe action of air p ressure gauge at rear of power unit. Power unit should hold maximum p ressure registered on gauge without perceptible lo ss until the brake pedal is released.

L oss of air p ressure indicates a leaking control valve poppet exhaust seal, or leakage past the power cylinder piston.

5. Depress and momentarily hold brake pedal to several positions between fully released and fully applied positions. P ressu res registered on gauge at rear of power unit should vary according to degree brake pedal is depressed.

6. Make a full brake application, then observe action of air p ressure gauge when brakes are re leased. If gauge does not return to zero or is slow in returning, a sticking control valve hydraulic piston is indicated.

HYDRAULIC PRESSURE TEST

1. Connect a hydraulic pressure gauge capable of registering at least 1200 pounds pressure to bleeder valve opening at one of the wheel cylinders.

Do NOT remove air p ressu re gauge installed at rear of power cylinder.

2. Apply brakes until approximately 60 pounds is registered on air gauge at rear of power cylin der. Observe reading on hydraulic p ressure gauge.

P ressu re should be 950 to 1100 pounds with 60 pounds air p ressure applied to power cylinder. If air system pressure is higher or lower than 60 pounds, hydraulic p ressu re will be proportionately higher or lower. Hold brakes applied for at least one minute, observing action of p ressure gauge.

3. A low pressure reading or a drop in hy draulic pressure indicates leakage in hydraulic lines, wheel cylinders, or power cylinder. Inspect hydraulic lines and wheel cylinders; repair or re place damaged parts.

4. After repairs have been made (if n eces

Sec. 5A

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HYDRAULIC BRAKES

sary), repeat test described in paragraph 2 above.

If p ressure is still too low or if p ressure drops, an internal leak in the power unit slave cylinder is indicated. This n ecessitates removing and over hauling the power cylinder.

AIR POWER CYLINDER

REPLACEMENT

REMOVAL (Refer to Fig. 25)

1. Tilt cab forward.

2. Clean away as much road dirt and grease as possible to prevent contamination.

3. Having suitable containers, catch hydraulic fluid which drains from system when hydraulic lines are disconnected. Disconnect lines. DO.NOT

RE-USE THIS FLUID.

4. Disconnect air lines.

5. Remove bolts which attach air power cyl inder to mounting brackets and remove cylinder from vehicle.

INSTALLATION

1. Place air power cylinder in position and fasten to mounting brackets with bolts.

2. Connect air lines.

3. Connect hydraulic lines.

4. Check master cylinder and add fluid if necessary.

5. Bleed hydraulic system as necessary.

6. Start engine, build up air p ressure and check operation of brakes.

AIR POWER CYLINDER

AIR CLEANER

Air cleaners used with air assisted power hydraulic brakes are part of the air com pressor system and are covered in LUBRICATION (SEC.0) of this manual.

BRAKE SHOES

TYPE “F” FRONT BRAKE

(Refer to Figure 26)

Two identical brake shoes are arranged on backing plate so that their toes are diagonally opposite. Two single-end wheel cylinders are arranged so that each cylinder is mounted between the toe of one shoe and the heel of the other. The two wheel cylinder pistons apply an equal amount of force to the toe of each shoe. Each cylinder casting is shaped to provide an anchor block for the brake shoe heel.

Each shoe is adjusted by means of an eccen-

A N D LININGS

trie cam which contacts a pin pressed into brake shoe web. Each cam is attached to the backing plate by a cam and shoe guide stud which protrudes through a slot in the shoe web and in conjunction with flat washers and C-w ashers, also serves as a shoe hold-down. Two return springs are connected between the shoes, one at each toe and heel,

With vehicle moving forward, both shoes are forward acting (primary shoes), self-energizing in forward direction of drum rotation. With veh id e in reverse, both shoes are reverse acting since neither is self-energized in the reverse direction of drum rotation.

Sec. 5A

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G M C S E R V I C E M A N U A L

1 Wheel Cylinder

2 Brake Shoe Return

Spring

3 Backing Plate

4 Brake Shoe

5 Brake Lining

6 Brake Shoe Adjusting

Cam

7 Brake Shoe Guide

Washer

8 Brake Shoe Guide

C-W asher

9 Adjusting Cam and

Shoe Guide Stud

10 Shoe Guide Anti-

Rattle Washer

11 Adjusting Cam Spring

Figure 2 6 — Type “F” Front Brake Assem bly

BRAKE SHOE REMOVAL (Fig. 26)

1. Jack up axle and remove hub and brake drum assem bly as directed in "FRONT HUBS AND

BEARINGS" (SEC. 3D) of this manual.

2. Remove both brake shoe return springs, using brake spring p liers.

3. Remove C-washers and flat washer from each adjusting cam and hold-down stud. Lift shoes off backing plate.

CLEANING AND INSPECTION

1. Clean all dirt out of brake drum. Inspect drum for roughness, scoring, or out-of-round.

Replace or recondition brake drum as necessary.

Refer to "Brake Drums” later in this section.

2. Inspect wheel bearings and oil seals as di rected in "FRONT HUBS AND BEARINGS" (SEC.

3D) of this manual.

3. Check backing plate attaching bolts to make sure they are tight. Clean all dirt off backing plate.

4. Inspect brake shoe return springs. If broken, cracked, or weakened, replace with new springs.

5. Check cam and shoe guide stud and friction spring on backing plate for corrosion or binding.

Cam stud should turn easily with an 8-inch wrench, but should not be loose. If frozen, lubricate with kerosene or penetrating oil and work free.

6. Examine brake shoe linings for wear. Lin ings should be replaced if worn down close to rivet heads. Refer to "Brake Shoe Relining" in this section.

BRAKE SHOE INSTALLATION

1. Install anti-rattle spring washer on each cam and shoe guide stud, pronged side facing ad justing cam.

2. Place shoe assembly on backing plate with cam and shoe guide stud inserted through hole in shoe web; locate shoe toe in wheel cylinder piston shoe guide and position shoe heel in slot in anchor block.

3. Install flat washer and C-washer on cam and shoe guide stud. Crimp ends of C-washer to gether.

4. After installing both shoes, install brake shoe return spring. To install each spring, place spring end with short hook in toe of shoe, then using brake spring p liers, stretch spring and s e cure long hook end in heel of opposite shoe.

5. Install hub and brake drum assembly as directed in "FRONT HUBS AND BEARINGS" (SEC.

3D) of this manual.

6. Adjust brake as previously directed under

"Brake Adjustments.”

DUO-SERVO FRONT BRAKE

(Refer to Figure 27)

The Duo-Servo front brakes used on these vehicles are self-adjusting. Primary linings (shoe toward front of vehicle) are shorter than second ary linings (shoe toward rear of vehicle).

Self-adjusting actuating lev ers are attached to the secondary (rear) shoes on all models and oper ate when the brakes are applied while the vehicle is traveling in reverse.

BRAKE SHOE REMOVAL

1. Jack up vehicle and remove wheel.

2. If drum cannot be removed readily, back off adjustment as described under heading of

"Brake Adjustments."

3. Block up brake pedal so it will not be de pressed while drums are removed. Wheel cylinder boots are recessed in grooves on cylinders, elim inating need for clamps.

G M C S E R V I C E M A N U A L

Sec. 5A

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HYDRAULIC BRAKES

1 Shoe Guide Plate

2 Anchor Pin

3 W heel C ylind er

4 P rim ary Shoe Return

Spring

5 Brake Backing Plate

6 Prim ary Brake Shoe and Lining

7 H old-Down W asher

8 H old-Down Pin

9 C onnecting Spring

10 Adjusting Nut

11 A djusting Screw

12 A djusting Socket

13 Actuating L ev er

14 L ev er Return Spring

15 L ev er O verrid e

Spring

16 H old-Down Spring

17 A djusting L ever

Pivot

18 Secondary Brake

Shoe and Lining

19 Actuating Link

20 Secondary Shoe

R eturn Spring

r u n

Figure 2 7 — D uo-Servo Front Brake (Automatic Adjuster)

4. Unhook primary shoe return spring first from anchor pin and secondary shoe return spring from actuating link. Refer to figure 28.

5. Remove actuating lever return spring.

6. Disengage actuating link end first from anchor pin, then from adjusting lever pivot.

7. Remove hold-down pins and springs. Refer to figure 29.

8. Remove the actuating lever assem bly.

NOTE: The actuating lever, adjusting lever pivot and lever override spring are removed as an assem bly. It is not recommended that they be disassem bled for service purpose unless one or more of the components is damaged. It is much easier to assem ble and disassem ble the brakes by leaving this assem bly intact.

9. Remove brake shoe guide plate.

10. Pull top of shoes away from anchor pin and wheel cylinder push rods and remove shoes from backing plate.

11. Move top of brake shoes toward one another crossing them until adjusting screw assem bly and spring fall off, permitting shoes to separate.

CLEANING AND INSPECTION

1. Clean all dirt out of brake drum. Inspect

Figure 2 8 — U nh o oking Brake Shoe Return Spring

drum for roughness, scoring, or out-of-round.

Replace or recondition drum as necessary. Refer to "Brake Drums" in this section.

2. Carefully pull lower edge of wheel cylinder boots away from cylinders and note whether inter ior is excessively wet with brake fluid. E xcessive fluid indicates leakage past piston cups, requiring overhaul of wheel cylinder.

NOTE: A slight amount of fluid is nearly a l ways present and acts as lubricant for pistons.

3. Check all backing plate attaching bolts to make sure bolts are tight. Clean all rust and dirt

Figure 2 9 — R e m o v in g H o ld D o w n Sp rin g s a n d Pins

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

Figure 3 0 — Installing Primary Shoe Return Spring

from brake shoe contact surfaces on backing plate using fine emery cloth.

4. Inspect brake shoe return springs. If broken, cracked, or weakened, replace springs.

5. If lining is worn to the extent that replace ment is necessary, replace lining as directedunder

"Brake Shoe Relining."

BRAKE SHOE INSTALLATION

1. Inspect new brake shoe and lining a ssem blies and make sure there are no nicks or burrs on edges of shoes which contact backing plate.

NOTE: Keep hand clean while handling brake

Figure 3 2 — Checking Operation of Actuating Lever

shoes. Do not permit oil or grease to come in con tact with linings.

2. Connect brake shoes together with connect ing spring and place adjusting screw assem bly in position.

CAUTION: Make sure the proper

adjusting screw assembly is used (left-

or right-hand). The adjusting screw a s 

sembly must be installed with the star

wheel (adjusting screw) nearest to the

secondary shoe. The connecting spring

must be installed with the long end hooked

on the secondary shoe, so that the spring

coils will not interfere with movement of

star wheel.

Figure 3 1 — Brake Shoe Contact Surfaces a n d B a ck in g Plate

3. Spread brake shoes apart at top and place against backing plate so that primary shoe (short lining) is toward front of vehicle. Secondary shoe

(long lining) is toward rear of vehicle.

4. Insert brake shoe webs into slots in wheel cylinder rods.

5. Secure primary shoe to backing plate with hold-down pin, spring and washers.

6. Place the actuating lever assem bly (includ ing pivot and override spring) in position on s e c ondary shoe and attach both shoe and actuating lever assembly to backing plate with hold-down pin, spring, and washers.

---- 7. Install guide plate over anchor pin.

8. Install actuating link.

G M C S E R V I C E M A N U A L

Sec. 5A

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HYDRAULIC BRAKES

CAUTION: DO NOT hook the actuating

link over the anchor pin with a regular

spring hook tool. This may damage the

wheel cylinder boot. Place the actuating

link over the anchor pin first and then

fasten link to actuating lever assembly by

holding this assembly in the full "DO W N”

position.

9. Install primary shoe return spring in shoe and pull over anchor pin. Refer to figure 30.

IMPORTANT: Return spring for primary shoe is always installed AFTER actuating link, regard le s s of right or left, so that it will be in the OUT

SIDE position on the anchor pin.

10. Install secondary shoe return spring in shoe and pull over actuating link.

11. Pry shoes away from backing plate and lubricate shoe contact surfaces with special lubri cant (S-17). Be careful to keep lubricant off linings.

Refer to figure 31.

12. Check operation of self-adjusting mech anism by hand operating. If there is any binding, locate trouble and correct. Refer to figure 32.

13. Expand adjustment as far as possible to still permit brake drums to clear linings. Install brake drums.

14. Install wheels, lower vehicle to ground and finish adjustment by applying brakes as many tim es as required, while vehicle is traveling in reverse, until proper pedal height is attained.

TYPE “FA” FRONT BRAKE

(Refer to Figure 33)

The type "FA" front brake is the same as the type "F" brake except for method of adjustment.

The type "FA" brake has an automatic adjusting mechanism.

An automatic adjuster lever is pivot-pinned on the inner side of shoe web and rests against the manual adjuster cam. A drum contact plug is mount ed on the pivot pin on the outside of the shoe web and is centered in the shoe table and lining. A spring loaded, serrated wedge slides on the pivot pin and under the drum contact plug between the plug pin and a wedge guide which is also pinned on the shoe web. A torsion spring is hooked over the contact plug pin, the lever pivot pin, and the edge of the shoe web. This torsion spring holds the a s sembly stable and keeps the plug surface flush with the lining surface.

As the lining wears, the brake drum depresses the contact plug and it moves the adjuster lever away from the shoe table. In this gradual action, the spring loaded wedge moves to keep the gap between the plug pin and the wedge guide closed.

1 Brake Shoe and

Lining Assembly

2 Contact Plug

3 Backing Plate

4 Brake Shoe Return

Spring

5 Wheel Cylinder

6 Torsion Spring

7 Wedge

8 Wedge Spring

9 Flat Washer, Spring

Washer, and "C"

Washer

Figure 3 3 — Type “F A ” Front Brake Installed

This holds the lever (and the brake shoe) in the adjusted position.

At the point of maximum lining wear, the plug pin bottoms on the inner side of its oversized hole in the shoe web, stopping automatic adjustment.

BRAKE SHOE REMOVAL

(Refer to Figure 34)

1. Jack up axle and remove hub and brake drum assem bly as directed in "FRONT HUBS AND

BEARINGS" (SEC. 3D) in this manual.

2. Remove both brake shoe return springs, using brake spring p liers.

3. Remove C-washer, flat washer, anti-rattle washer and another flat washer from each pin and remove shoes from backing plate.

DISASSEMBLE AUTOMATIC ADJUSTER

(Refer to Figure 34)

1. Unhook wedge spring from wedge and re move spring.

2. Unhook torsion spring from shoe web, work spring coil off lever pivot pin and slide end of torsion spring off contact plug pin.

3. Pull adjuster lever from opposite side of shoe web.

4. Pull contact plug through shoe table.

5. Lift off retainer washer, wedge, and guide.

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______________________ G M C S E R V I C E M A N U A L

HYDRAULIC BRAKES

Connector Tube

Spring Washer

Bolt

Flat Washer

Backing Plate

Bleeder Valve

Wheel Cylinder

Brake Shoe

Flat Washer

Anti-rattle

Washer

C-washer

Return Spring

Wedge Guide

14 Contact Plug

15 W edge Spring

16 Torsion Spring

17 Retainer Washer

18 Wedge

19 Adjuster Lever

20 Brake Lining

21 Rivet

T-4578

CLEANING AND INSPECTION

1. Clean all dirt out of brake drum. Inspect drum for roughness, scoring, or out-of-round.

Replace or recondition brake drum as necessary.

Refer to "Brake Drums" in this section.

2. Inspect bearings and oil sea ls as directed in "FRONT HUBS AND BEARINGS" (SEC. 3D) in this manual.

3. Check backing plate attaching bolts to make sure they are tight. Clean all dirt off backing plate.

4. Inspect brake shoe return springs. If broken, cracked, or weakened, replace with new springs.

5. Check cam and shoe guide stud and friction spring on backing plate for corrosion or binding.

Cam stud should turn easily with an 8-inch wrench, but should not be loose. If frozen, lubricate with kerosene or penetrating oil and work free.

6. Check all automatic adjuster components and replace any which are worn or damaged. Re place springs if broken, cracked, or weakened.

7. Check wheel cylinders as instructed under

"Wheel Cylinder Repair" in this section. Replace with new cylinders if necessary.

8. Examine brake shoe linings for wear. Lin ings should be replaced if worn down close to rivet heads. Refer to "Brake Shoe Relining” in this section.

Figure 3 4 — Type “F A " Front Brake Com ponents

ASSEMBLE AUTOMATIC ADJUSTER

(Refer to Figure 34)

1. Place the wedge guide on the shoe web (side away from mounting plate) with the serrations facing away from the shoe table.

2. Lay the wedge on the shoe with the serra tions against matching serrations on the wedge guide. Align wedge slot with pivot pin hole.

3. Insert contact plug from drum side of shoe, guiding its shank through the hole in the shoe table and over the wedge guide and wedge.

4. Place adjuster lever on opposite side of shoe web and insert pins through holes in shoe web and mating hole in contact plug shank.

5. Place retainer washer over wedge pivot pin.

6. Slide "U” hook of torsion spring on pin over contact plug shank. Attach end of wedge spring to this hook, then install coil of torsion spring over the pivot pin and pull the spring hook over the edge of shoe web.

7. Connect wedge spring oh raised hook on the wedge "fork."

8. Fully retract the wedge against the lever pivot pin, pressing on the contact plug to permit this movement. If the plug now protrudes more than 0.005" above lining, clamp shoe in vise jaws bear against the adjuster lever and dress down the

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

plug. This can be done with a file, taking care to not create a "flat spot" on the lining. (An alternate method is to block adjuster lever in extended p osi tion and grind plug with lining.) If fully extended plug is more than 0.005" BELOW lining surface, replace with new plug.

BRAKE SHOE INSTALLATION

1. Place brake shoes over hold-down pins on backing place and install a flat washer, an anti rattle washer, a flat washer, and a C-washer (in that order) on each pin. Note that each shoe has a

"heel" and "toe." The "heel" fits in the anchor slot of wheel cylinder, the "toe" fits in the piston end of wheel cylinder.

2. After installing both shoes on backing plate, install return springs. To install each spring, place spring end with short hook in "toe" of shoe, then using brake spring p liers, stretch spring and secure long hook end in ,Theel" of opposite shoe.

3. Center each shoe, before installing drum, by sliding shoe up or down in its anchor slot until the leading and trailing edges of the lining are equi distant from the inner curl of the brake mounting plate.

4. Back off manual adjustment cam.

5. Install hub and brake drum as directed in

"FRONT HUBS AND BEARINGS" (SEC. 3D) in this manual.

INITIAL MANUAL LINING ADJUSTMENT

1. Rotate adjuster cam stud in the direction of forward drum rotation. Tighten adjustment until the lining drags on the brake drum.

2. Back off the adjuster cam stud while ro tating drum forward, until drag is just relieved.

3. Adjust the second manual shoe adjuster cam stud in the sam e manner, forward to tighten and reverse to relieve drag, and perm it automatic adjustment to take over.

TYPE “FR-3” REAR BRAKE

(Refer to Figure 35)

Each brake is equipped with two double-end wheel cylinders which apply hydraulic pressure to both the toe and the heel of two identical, selfcentering shoes. The shoes anchor at either toe or heel, depending upon the direction of drum ro tation. Brake anchor supports and backing plate are bolted to the axle housing flange. The supports have removable slotted anchor pins at the shoe h eels, and adjusting screw s at the shoe toes. Ad justing screw s act as anchors in the reverse direc tion of rotation. Each adjusting screw is threaded into or out of its support by means of an adjusting wheel. Adjusting wheels are accessible through adjusting slots in the backing plate.

1 Wheel Cylinder Heat

Shield

2 Upper Wheel Cylinder

3 Anchor Pin

4 Return Spring (Short)

5 Guide Washer

6 Guide Bolt

7 Guide Bolt Nut Lock

Wire

8 Brake Shoe and

Lining Assembly

9 Return Spring (Long)

10 Adjusting Wheel

Lock Spring

11 Adjusting Wheel

12 Lower Wheel

Cylinder

13 Backing Plate

TPM-9116

Figure 3 5 — Type “FR-3” Rear Brake Assem bly

BRAKE SHOE REMOVAL

1. Jack up axle and remove hub and brake drum assembly as directed in "REAR HUBS AND

BEARINGS" (SEC. 4C) of this manual.

2. Install wheel cylinder clamps to hold piston in cylinders.

3. Using special brake spring tool (J-8049), remove brake shoe return springs.

4. Remove lock w ires, nuts, and washers from brake shoe guide bolts, then remove brake shoe assem b lies.

5. Remove screw s attaching adjusting wheel lock springs to anchor supports. Thread each ad justing screw from the shoe side of its anchor support by turning adjusting wheels, then lift ad justing wheels out of slots in anchor supports.

CLEANING AND INSPECTION

1. Clean all dirt out of brake drum. Inspect drum for roughness, scoring, or out-of-round.

Recondition or replace drum as necessary. Refer to "Brake Drums” in this section.

2. Clean all dirt out of anchor pin holes and adjusting screw openings in anchor supports.

3. Inspect wheel bearings and oil seals as directed in "REAR HUBS AND BEARINGS" (SEC.

4C) of this manual.

4. Inspect brake shoe return springs. If broken,

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L cracked, or weakened, replace with new springs.

5. Inspect threads on adjusting screw s and in adjusting wheels for wear or damage. Replace as necessary.

6. Examine brake shoe linings for wear. Lin ings should be replaced if worn down close to rivet heads. Refer to "Brake Shoe Relining” in this section.

BRAKE SHOE INSTALLATION

1. Install adjusting screw s and wheels in anchor supports dry; use no lubricant. Insert each adjusting wheel in slot in anchor support, insert threaded end of adjusting screw in anchor support, then turn adjusting wheel to thread adjusting screw into anchor support. Insert anchor pins into holes in anchor supports, with slots in pins facing slots in supports.

2. Install brake shoes with cut-away end of shoe web next to adjusting screw and with ends of shoes engaging slots in wheel cylinder push rods and anchor pins. Install flat washer and nut on each brake shoe guide bolt. Tighten nuts finger-tight, then back off nuts only far enough to allow move ment of shoes without binding.

3. Install brake shoe return springs, hooking one end of each spring in brake shoe web, then hook other end over anchor pins with special brake spring tool (J-8049).

4. Remove wheel cylinder clamps.

5. Install hub and brake drum assem bly as directed in "REAR HUBS AND BEARINGS" (SEC.

4C) of this manual.

6. Adjust brakes as directed under "Brake

Adjustments."

TW IN-ACTION TYPE REAR BRAKE

(Refer to Figure 36)

BRAKE SHOE REMOVAL

1. Raise the vehicle and place on jack stands.

2. Remove brake drums.

NOTE: If brake drums are worn severely, it may be necessary to retract the adjusting screw s.

3. Using Tool (J-22348), remove the brake shoe pull-back springs (fig. 37).

NOTE: Since wheel cylinder piston stops are incorporated in the anchor brackets, it is not nec essary to install wheel cylinder clamps when the brake shoes are removed. However, the brake pedal must not be depressed while the drums are removed.

4. Loosen the adjusting lever cam cap screw and while holding the star wheel end of the adjust ing lever past the star wheel, remove the cap screw and cam.

1 Hold-Down Pin

Spring Lock

2 Hold-Down Pin

3 Adjusting Screw

13 Wheel Cylinder

14 Brake Shoe Return

Spring

15 Brake Shoe Anchor

4 Adjusting Lever 16 Lever Return Spring

5 Adjusting Lever Pin 17 Adjusting Lever Pin

6 Hold-Down Spring Cup

7 Lever Override

Spring

8 Brake Shoe and

Lining

Sleeve

18 Hold-Down Spring

19 Brake Backing Plate

20 Hold-Down Pin

Retainer

9 Adjusting Lever

Pivot

21 Hold-Down Pin

Spring

10 Adjusting Lever Cam 22 Adjusting Lever

11 Adjusting Lever Bolt Link

12 Wheel Cylinder

Shield

T-2698

Figure 3 6 — Twin-Action Rear Brake

Assem bly (Automatic Adjuster)

Figure 3 7 — R e m o v in g Pull Back Sp rin gs

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

T-2726

Figure 3 8 — Rem oving Brake Shoe Hold D ow n Pins

5. Remove the brake shoe hold-down springs and pins by com pressing the spring with Tool (J-

22348) and, at the sam e time, pushing the pin back through the flange plate toward the tool. Then, keeping the spring com pressed, remove the lock

(C-washer) from the pin with a magnet (fig. 38).

6. Lift off the brake shoe and self-adjuster lever as an assem bly.

7. The self-adjuster lever can now be removed from the brake shoe by removing the hold-down spring and pin. Remove lever return spring also.

NOTE: The adjusting lever, override spring and pivot are an assem bly. It is not recommended that' they be disassem bled for service purposes unless they are broken. It is much easier to a s sem ble and disassem ble the brake leaving them intact.

8. Thread the adjusting screw out of the brake shoe anchor and remove and discard the friction spring (not shown in figure 36).

9. Clean all dirt out of brake drum. Inspect drums for roughness, scoring or out-of-round.

Replace or recondition drums as necessary.

10. Carefully pull lower edges of wheel cyl inder boots away from cylinders. If brake fluid flows out, overhaul of the wheel cylinders is nec essary.

NOTE: A slight amount of fluid is nearly al ways present and acts as a lubricant for the piston.

11. Inspect flange plate for oil leakage past axle shaft oil se a ls. Install sea ls if necessary.

12. Check all flange plate attaching bolts to make sure they are tight. Clean all dirt and rust

Figure 3 9 — Brake Shoe and Automatic Adjuster Assem bly

from shoe contact faces on flange plate using emery cloth.

13. Thoroughly clean adjusting screw s and threads in the anchors.

BRAKE SHOE INSTALLATION

1. Put a light film of lubricant on shoe bearing surfaces of brake flange plate and on threads of adjusting screw .

2. Thread adjusting screw completely into anchor without friction spring to be sure threads are clean and screw turns easily. Then remove screw s, position a new friction spring on screw and reinstall in anchor.

3. A ssem ble self-adjuster assembly and lever return spring to brake shoe and position adjusting lever link on adjusting lever pivot.

4. Position hold-down pins in flange plate.

5. Install brake shoe and self-adjuster assem blies onto hold-down pins. Insert ends of shoes in wheel cylinder push rods and legs of friction springs.

NOTE: Make sure the toe o fth e sh o e is against the adjusting screw (fig. 39).

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G M C S E R V I C E M A N U A L

Figure 4 0 — M ea su rin g Points for Brake Shoe Centering

6. Install cup, spring, and retainer on end of hold-down pin. Using Tool (J-22348) com press the spring. With spring com pressed, push the holddown pin back through the flange plate toward the tool and install the lock on the pin.

7. Using Tool (J-22348) install brake shoe return springs.

8. Holding the star wheel end of the adjusting lever as far as possible past the star wheel, posi-

Figure 41 — P ositionin g A djustin g Lever

Figure 4 2 — Wire G a u g e Position for Correct

Adjusting Lever Adjustment

tion the adjusting lever cam into the adjusting lever link and assem ble with cap screw.

9. Check the brake shoes for being centered by measuring the distance from the lining surface to the edge of the flange plate at the points shown in figure 40. To center the shoes, tap the upper or lower end of the shoes with a plastic mallet until the distances at each end become equal.

10. Locate the adjusting lever 0.020" to 0.039" above the outside diameter of the adjusting screw thread by loosening the cap screw and turning the adjusting cam.

NOTE: To determine 0.020" to 0.039", turn the adjusting screw 2 full turns out from the fully r e tracted position. Hold a 0.060" wire gauge at a 90° angle with the star wheel edge of the adjusting lever. Turn the adjusting cam until the adjusting lever and threaded area on the adjusting screw just touch the wire (figs. 41 and 42).

11. Secure the adjusting cam cap screw and retract the adjusting screw .

12. Install brake drums and wheels.

13. Adjust the brakes by making several for ward and reverse stops until a satisfactory brake pedal height results.

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

TYPE “FR -3A ” REAR BRAKE

The type "FR-3A" rear brake is the same as the type "FR-3" brake except for method of ad justment. The type "FR-3A" brake has an auto matic adjusting mechanism. Refer to figure 43.

Brake shoe adjustment takes place when the brakes are applied with firm pedal effort while vehicle is backing up. When brakes are applied

(backing up) the heel of the brake shoe moves away from the forward-acting anchor, an action which places a cocking motion in the link-crank system .

An adjustable eccentric on the shoe web provides a hinge for a short link which carries this motion to an adjuster crank fastened on the forward acting anchor pin by a C-washer. From the adjuster crank, motion transfers through the long link to the star wheel crank assem bly mounted on the op posite anchor bracket so that a pawl on the crank m eshes with the star wheel. The motion pivots

(cocks) the crank back, the force overcoming the adjuster spring connected between a finger of the crank and the brake shoe return spring pin. If the lining clearance perm its sufficient movement, the crank pawl picks up the next tooth on the star wheel.

Unintentional back-off of the star wheel is prevented by a friction ring located on the star wheel screw. This ring applies sufficient drag to prevent an automatic back-off, but not enough to prevent manual adjustments at the star wheel.

1 Brake Shoe and

Lining Assembly

2 Hold-down Bolt,

Washer, Nut, and

Lock Wire

3 Crank Link (Long)

4 Eccentric and Screw

5 Shoe Return Spring

(Short)

6 Adjuster Crank

7 Crank Link (Short)

8 Wheel Cylinder

Cover

9 Wheel Cylinder

10 Backing Plate

11 Adjuster Spring

12 Starwheel

13 Starwheel Crank

14 Shoe Return Spring

(Long)

15 Anchor Pin

16 "C" Washer

T-4579

Automatic adjustment is completed upon brake release, as the adjuster spring returns the star wheel crank, advancing the star wheel one tooth.

Completion may be delayed by anchoring pressure against the star wheel screw; in this case, it is completed as the anchor p ressure is relieved by the next forward brake application.

Figure 4 3 — Type “FR -3 A ” Rear Brake Installed

4. Remove short crank links by rotating ad juster cranks until link "U" hooks clear the eccen trics on shoe webs, then remove the sm aller "U" hooks from the adjuster cranks.

BRAKE SHOE REMOVAL

(Refer to Figure 44)

1. Jack up axle and remove hub and brake drum assem bly as directed in "REAR HUBS AND

BEARINGS" (SEC. 4C) of this manual. It m aybe n ecessary to back off adjuster star wheels slightly to free grooved drums.

5. Spread adjuster crank C-washers and lift off cranks.

6. Remove bolt which fastens star wheel crank to anchor support and remove crank.

7. Remove adjuster eccentric screw and ec centric from brake shoe.

8. Remove two long shoe return springs and two short return springs by sliding looped ends off pins.

CAUTION: DO NOT back off adjust

ment so much that star wheel is jammed

against the friction ring on the star wheel

screw; this may damage the friction ring.

9. Remove lock w ires, hold-down nuts, and washers from hold-down bolts and lift off brake shoes.

2. Unhook the two automatic adjuster springs.

3. Remove the two long crank links by pivoting back the star wheel cranks until their slots align with the link "U" hooks. Lift out links, then slide their ”S" hooks from the adjuster cranks.

10. Thread each star wheel screw out of anchor support from shoe side of support. Lift star wheels from support slots.

NOTE: DO NOT attempt to remove a friction ring from a star wheel screw; if necessary, re place with a new screw and friction ring assembly.

Sec. 5A

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HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

2 Brake Lining

3 Brake Shoe

4 Hole Cover

5 Starwheel Crank

6 Adjuster Spring

7 Starwheel

8 Bolt

9 Spring Washer

11 Bleeder Valve

12 Wheel Cylinder Cover

13 Wheel Cylinder

14 Anchor Pin

15 Shoe Return Spring (Short)

16 Adjuster Crank

17 C-washer

18 Hold-down Washer

20 Lock Wire

21 Shoe Return Spring (Long)

22 Crank Link (Long)

23 Starwheel Screw

24 Hold-down Bolt

25 Crank Link (Short)

26 Eccentric Screw

27 Eccentric

- 4 5 8 0

CLEANING AND INSPECTION

1. Clean all dirt out of brake drum. Inspect drum for roughness, scoring, or out-of-round.

Recondition or replace drum as necessary. Refer to "Brake Drums" in this section.

2. Clean all dirt out of anchor pin holes and adjusting screw openings in anchor supports.

3. Inspect wheel bearings and oil seals as directed in "REAR HUBS AND BEARINGS" (SEC.

4C) of this manual.

4. Inspect brake shoe return springs. If they are broken, cracked, or weakened, replace with new springs.

5. Inspect threads on adjusting screw s and in adjusting wheels for wear or damage. Replace as necessary.

6. Check all automatic adjuster components and replace any which are worn or damaged. Re place springs if broken, cracked, or weakened.

7. Check wheel cylinders as instructed under

"Wheel Cylinder Repair" in this section. Replace with new cylinders if necessary.

Figure 4 4 — Type “FR -3A" Rear Brake Components

8. Examine brake shoe linings for wear. Lin ings should be replaced if worn down close to rivet heads. Refer to "Brake Shoe Relining" in this section.

BRAKE SHOE INSTALLATION

1. Insert star wheels in anchor support slots and thread in star wheel screw from the shoe side, friction ring end toward the shoe. For new linings, back off screw s, taking care to not jam star wheels.

NOTE: DO NOT LUBRICATE STAR WHEEL

SCREWS.

2. Position one brake shoe with its "toe" (cut away portion of web) located in the adjuster slot and the "heel" in the anchor pin slot of anchor sup ports.

3. Install brake shoe hold-down bolt, holddown washer and hold-down nut. Tighten nut fingertight and then back off nut one turn and insert nut lock wire.

4. Install the other brake shoe in same man ner as described in paragraphs 2 and 3.

5. Install long brake shoe return springs in shoe web, longest shank at adjuster, and hook springs over pins.

6. Install short brake shoe return springs in shoe web and hook springs over pins at anchor end.

7. P lace adjuster eccentrics on shoe webs and fasten with self-tapping screw . Tighten screw only finger-tight to permit final adjustment later.

8. Place adjuster cranks on anchor pins, their long arms toward shoes, bushing toward backing plate, so that they rotate freely while resting against return spring hooks.

9. Install and crimp adjuster crankC-washer.

10. Place star wheel crank on anchor support and fasten with crank bolt.

11. At each adjuster crank assem ble the short link sm all hook into the short arm of the crank from the lower side and hook the other end of link around the eccentric on the shoe web.

12. Assem ble long link "S" hook to long arm of adjuster crank from upper side, rotate star wheel crank so that slot lines up with link "U" hook.

Insert "U" hook and rotate star wheel crank back to approximate adjusting position.

13. Install adjuster spring with short hook on star wheel crank finger so that its long shank hook assem b les on the outer groove of the pin from the wheel cylinder side.

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

INITIAL MANUAL LINING ADJUSTMENT

1. If shoes have been relined, back off star wheel adjustments.

2. Center each shoe; insert a pry tool against backing plate curl and shoe (do not mar lining).

Slide shoe up or down in anchor slots until leading and trailing edges of the lining are equidistant from the inner curl of the brake backing plate.

3. On each shoe web, rotate hex eccentric, as required, until linkage aligns star wheel crankpawl with center line of star wheel screw. A SMALL

DRILL POINT RECESS ON THE ANCHOR SUP

PORT IS THE ALIGNING MARK.

4. When aligned, lock eccentrics by tightening self-tapping screw s to 19 foot-pounds torque.

5. Install hub and drum as described in "REAR

HUBS AND BEARINGS" (SEC. 4C) of this manual.

6. Remove both adjustment slot covers from back of backing plate.

7. Insert adjusting tool and turn each star wheel until lining drags on drum while drum is rotated. To tighten adjustment, move tool handle toward axle while using inner side of adjuster slot as fulcrum for the tool, rotating the star wheel teeth away from the axle.

8. Back off star wheels while rotating drum forward, until drag is just relieved. Provide ad ditional running clearance by backing off 8 to 10 more notches and replace slot covers. Automatic adjustment now takes over.

BRAKE SHOE RELINING

Brake linings on these models are riveted to the brake shoes and may be replaced. These lin ings may be purchased in replacement sets of four linings and sufficient rivets of correct sp ecifica tions. Refer to Parts Book for lining replacement kits. When replacing linings, make sure that shoes are clean and that linings are installed in a manner that will prevent gaps between lining and shoe.

Conventional lining replacement equipment should be used. Make sure lining fits firmly against shoe, and that rivets are properly upset.

BRAKE DRU M S

Brake drum installations are illustrated in

"FRONT HUBS AND BEARINGS" (SEC. 3D) and

"REAR HUBS AND BEARINGS" (SEC. 4C) of this manual. Procedures for replacing brake drums are also included in the above mentioned sections.

Whenever brake drums are removed for serv icing brakes, inspect drums. If found to be scored, rough, or out-of-round, drums should be machined.

Machining or grinding of brake drums in crea ses the inside diameter of the drum and chang es the lining to drum fit. When machining drums, it is recommended that the following maximum oversizes not be exceeded:

(a) Drums with standard diameter up to 14" can be machined up to 0.060" oversize.

(b) Drums with standard diameter over 14" can be machined up to 0.080" oversize.

When it is found that machining to these max imum lim its does not provide a suitable braking surface, discard the worn drum and replace with a new standard drum.

DO NOT EXCEED THESE LIMITS. THIS IS A

SAFETY PRECAUTION.

Sec. 5A

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G M C S E R V I C E M A N U A L

3. Weak brake hose.

4. Leaking conduits.

5. Leaking wheel cylinder.

6. Leaking m aster cylinder.

7. Leaking m aster cylinder check valve.

8. Air in system .

9. Plugged m aster cylinder filler cap.

10. Improper brake fluid.

11. Low fluid level.

TROUBLESHOOTING CHART

LOW PEDAL OR PEDAL GOES TO TOE BOARD

PROBABLE CAUSE

E xcessive clearance between linings and drum.

2. Automatic adjusters not working.

REMEDY

Adjust brakes.

2. Make forward and reverse stops; if pedal stays low, repair faulty adjusters.

3. Replace with new hose.

4. Repair or replace faulty parts.

5. Clean and rebuild.

6. Clean and rebuild.

7. Install new check valve.

8. Bleed system .

9. Clean filler cap vent holes; bleed system .

10. Flush system and refill with recommended brake fluid.

11. F ill reservoir with brake fluid; bleed system .

SPRINGY, SPONGY PEDAL

PROBABLE CAUSE

Air trapped in hydraulic system .

2. Improper brake fluid.

3. Improper lining thickness or location.

4. Drums worn too thin.

5. Master cylinder filler vent clogged.

6. Weak hose.

REMEDY

Remove air by bleeding.

2. Flush, refill and bleed system . Use recom mended brake fluid.

3. Install specified lining or replace shoe and lining.

4. Replace drums.

5. Clean vent or replace cap; bleed brakes.

6. Install new hose.

EXCESSIVE PEDAL PRESSURE REQUIRED TO STOP

PROBABLE CAUSE

Brake adjustment not correct.

2. Incorrect lining.

3. Grease or fluid soaked lining.

4. Lining not in full contact.

5. Improper fluid.

6. Frozen master or wheel cylinder pistons.

7. Brake pedal binding on shaft.

8. Linings installed on wrong shoes.

9. Glazed linings.

10. Bellmouthed, barrel-shaped or scored drums.

REMEDY

Adjust the brakes.

2. Install specified linings.

3. Repair grease seal or wheel cylinder. Install new linings.

4. Grind lining to proper radius.

5. Flush out system; fill with recommended fluid; bleed.

6. Recondition or replace all cylinders.

7. Lubricate.

8. Install primary and secondary linings correctly.

9. Sand surface of linings.

10. Replace or resurface drums in R.H. and L.H.

pairs.

G M C S E R V I C E M A N U A L

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HYDRAULIC BRAKES

LIGHT PEDAL PRESSURE - - BRAKES TOO SEVERE

PROBABLE CAUSE

1. Brake adjustment not correct.

2. Loose backing plate on front axle.

3. A sm all amount of grease or fluid on linings.

4. Charred linings.

5. Incorrect lining.

6. Wheel bearings loose.

7. Lining loose on shoe.

8. E xcessive dust and dirt in drums.

9. Bad drum.

REMEDY

1. Adjust the brakes.

2. Tighten plates.

3. Replace the linings.

4. Sand the surfaces of the linings.

5. Install factory specified linings.

6. Adjust wheel bearings.

7. Replace lining or shoe and lining.

8. Clean and sand drums and linings.

9. Turn drums in pairs or replace.

BRAKE PEDAL TRAVEL DECREASING

PROBABLE CAUSE

1. Master cylinder compensating port plugged.

2. Swollen cup in master cylinder.

3. Master cylinder piston not returning.

4. Weak shoe retracting springs.

5. Wheel cylinder pistons sticking.

REMEDY

1. Open, use air or .015 wire. Remove any burr in bore.

2. Replace rubber parts flush system . Refill with recommended fluid.

3. Rebuild master cylinder.

4. Replace springs.

5. Clean cylinder bores and parts. Replace bad parts.

PULSATING BRAKE PEDAL

PROBABLE CAUSE

1. Drums out-of-round.

2. Loose brake drums on hub.

3. Worn or loose wheel bearings.

4. Bent rear axle.

REMEDY

1. Refinish drums.

2. Tighten.

3. Replace or adjust.

4. Replace axle.

BRAKES FADE

PROBABLE CAUSE

1. Incorrect lining.

2. Poor lining contact.

3. Thin drum.

4. Dragging brakes.

REMEDY

1. Replace lining with lining recommended.

2. Grind lining to proper radius; adjust.

3. Replace drum.

4. Adjust.

ALL BRAKES DRAG WHEN ADJUSTMENT IS KNOWN TO BE CORRECT

PROBABLE CAUSE

1. Pedal does not return to stop.

REMEDY

1. Lubricate the pedal.

Sec. 5A

Page 202

HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

ALL BRAKES DRAG WHEN ADJUSTMENT IS KNOWN TO BE CORRECT (Cont'd.)

PROBABLE CAUSE REMEDY

2. Improper fluid.

3. Compensating or bypass port of master cylinder closed.

4. Use of inferior rubber parts.

2. Replace rubber parts and fill with recom mended brake fluid.

3. Open by air or .015 wire. Remove any burr in bore.

4. Install proper parts.

ONE WHEEL DRAGS

PROBABLE CAUSE

1 .

Weak or broken shoe retracting springs.

2. Brake shoe to drum clearance too sm all.

3. Loose wheel bearings.

4. Wheel cylinder piston cups swollen and d is torted or the piston stuck.

5. Pistons sticking in wheel cylinder.

6. Drum out-of-round.

7. Obstruction in line.

8. Distorted shoe.

9. Defective lining.

1 .

REMEDY

Replace the defective brake shoe springs and lubricate the brake shoe ledges.

2. Adjust.

3. Adjust wheel bearings.

4. Rebuild cylinders.

5. Clean or replace pistons; clean cylinder bore.

6. Grind or turn both front or rear drums.

7. Clean out or replace.

8. Replace.

9. Replace with specified lining.

PULLS TO ONE SIDE

PROBABLE CAUSE

1. Grease or fluid soaked lining.

2. Loose wheel bearings,.loose packing plate on rear axle or front axle or loose spring bolts.

3. Linings not of specified kind or primary and secondary shoes reversed.

4. T ires not properly inflated or unequal wear of tread. Different tread non-skid design.

5. Linings charred.

6. Water, mud, etc., in brakes.

7. Wheel cylinder sticking.

8. Weak or broken retracting springs.

9. Out-of-round drums.

REMEDY

1. Replace with new linings.

2. Adjust the wheel bearing, tighten the backing plate on the rear and front axles and tighten spring bolts.

3. Install specified linings. Install shoes correctly.

4. Inflate the tires to recommended p ressu res.

Rearrange the tires so that a pair of non-skid tread surfaces of sim ilar design and equal wear will be installed on the front wheels, and another pair with like tread will be installed on the rear wheels.

5. Sand the surfaces of the lining.

6. Remove any foreign material from all of the brake parts and inside of the drums. Lubricate the shoe ledges and rear brake cable ramps.

7. Repair or replace wheel cylinder.

8. Check springs — replace bent, open-coiled or cracked springs.

9. Resurface or replace drums in left- and righthand pairs (both front and both rear).

G M C S E R V I C E M A N U A L

Sec. 5A

Page 203

HYDRAULIC BRAKES

PULLS TO ONE SIDE (Cont’d.)

PROBABLE CAUSE

10. Brake dragging.

11. Weak ch a ssis springs, loose U-bolts, loose steering gear, etc.

12. Loose steering.

13. Unequal camber.

14. Clogged or crimped hydraulic line.

REMEDY

10. Check for loose lining. Adjust.

11. Replace spring, tighten U-bolts, adjust steering gear, etc.

12. Repair and adjust.

13. Adjust to "Specifications."

14. Repair or replace line.

15. Wheel cylinder size different on opposite sides.

15. Replace with correct cylinders.

16. Loose king pin.

16. Replace king pins or bushings.

17. Bad drum.

17. Refinish drums in pairs.

ONE WHEEL LOCKS

PROBABLE CAUSE

1. Gummy lining.

2. Tire tread slick.

REMEDY

1. Reline.

2. Match up tire treads from side to side.

WET WEATHER: BRAKES GRAB OR WONTT HOLD

PROBABLE CAUSE

1. Linings too sensitive to water.

2. Dirty brakes.

3. Bent backing plate - - opening.

4. Scored drums.

REMEDY

1. Reline.

2. Clean out.

3. Straighten.

4. Grind or turn in pairs.

BRAKES SQUEAK

PROBABLE CAUSE

Backing plate bent or shoes twisted.

2. Metallic particles or dust imbedded in lining.

3. Lining rivets loose or lining not held tightly against the shoe at the ends.

4. Drums not square or distorted.

5. Incorrect lining.

6. Shoes scraping on backing plate ledges.

7. Weak or broken hold down springs.

8. Loose wheel bearings.

9. Loose backing plate, anchor, drum, wheel cylinder.

10. Linings located wrong on shoes.

REMEDY

Straighten or replace damaged parts.

2. Sand the surfaces of the linings and drums. Re move all p articles of metal that may be found in the surfaces of the linings.

3. Replace rivets and/or tighten lining by re riveting.

4. Turn or grind or replace drums.

5. Replace lining.

6. Apply brake lube to ledges. Replace with new shoe and linings, if distorted.

7. Replace defective parts.

8. Tighten to proper setting.

9. Tighten.

10. Install linings correctly.

Sec. 5A

Page 204

HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

BRAKES CHATTER

PROBABLE CAUSE

1. Incorrect lining to drum clearance.

2. Loose backing plate.

3. Grease, fluid, road dust on lining.

4. Weak or broken retractor spring.

5. Loose wheel bearings.

6. Drums out-of-round.

7. Cocked or distorted shoes.

8. Tapered or barrel-shaped drums.

REMEDY

1. Readjust to recommended clearances.

2. Tighten securely.

3. Clean or reline.

4. Replace.

5. Readjust.

6. Grind or turn drums in pairs.

7. Straighten or replace.

8. Grind or turn in pairs.

SHOE CLICK

PROBABLE CAUSE

1. Shoes lift off backing plate and snap back.

2. Hold down springs weak.

3. Shoe bent.

4. Grooves in backing plate pads.

REMEDY

1. Change drums side to side or grind drums

(in pairs).

2. Replace springs.

3. Straighten.

4. Grind and lubricate.

TROUBLE SHOOTING POWER HYDRAULIC BRAKES (Vacuum A ssist Units)

NOTE: The same types of brake troubles are encountered with power brakes as with standard brakes. Before checking the power brake system for source of trouble, refer to trouble diagnosis of standard hydraulic brakes.

After these possible causes have been eliminated, check for cause as outlined below.

NOTE: Make the following test before checking hard pedal for the cause. With the engine stopped, depress the brake pedal several tim es to eliminate all vacuum from the system . Apply the brakes, and while holding the foot pressure on the brake pedal, start the engine. If the unit is operating correctly, the brake pedal will move forward when the engine vacuum power is added to the pedal pressure. If this test shows that the power unit is not operating, the trouble may be one of the following:

BRAKE SYSTEM LOSES FLUID

PROBABLE CAUSE

1. External Leak: Leaking-pipe connections, hose, wheel cylinders, master cylinder head nut, etc.

2. Internal Leaks: Past secondary seals into power unit. Check vacuum hose for fluid.

REMEDY

1. Clean parts. Tighten. Replace defective parts.

2. Rebuild master cylinder.

G M C S E R V I C E M A N U A L

Sec. 5A

Page 205

HYDRAULIC BRAKES

NO BOOST — HARD PEDAL

PROBABLE CAUSE

Bent, broken obstructed tube. Collapsed hose.

2. Stuck check valve.

3. Air inlet blocked.

4. Air valve stuck.

5. Faulty diaphragm.

6. Faulty piston seal.

7. Leaks internally.

8. Leaking vacuum tank.

SLOW BRAKE PEDAL RETURN

PROBABLE CAUSE

1. E xcessive seal friction in power unit.

2. Faulty valve action.

3. Broken return spring.

BRAKES GRABBY

PROBABLE CAUSE

1. Broken valve spring.

2. Sticking vacuum valve.

3. Reaction diaphragm leakage.

REMEDY

Replace defective parts.

2. Replace valve.

3. Replace filter. Open passages.

4. D isassem ble unit - - clean - - replace defective parts.

5. Replace diaphragm.

6. Replace seal.

7. Rebuild.

8. Repair tank.

1. Rebuild unit.

2. Rebuild unit.

3. Replace spring.

1. Rebuild unit.

REMEDY

2. Clean and lubricate.

3. Rebuild unit.

Sec. 5A

Page 206

HYDRAULIC BRAKES

G M C S E R V I C E M A N U A L

SPECIFICATIONS

FRONT BRAKES

TRUCK SERIES 4500

5500

T y p e ................................................................ Duo-Servo

Adjustm ent.................................................... Automatic

S iz e .................................................................

Lining W idth..................................................

14 x

IVi

21/?"

Lining Th ickn ess..........................................

Lining A rea—Sq. In. per a xle ....................

136.1

REAR BRAKES

TRUCK SERIES All Except

6500

T y p e ................................................................ Twin-Action

Adjustm ent.................................................... Automatic

S iz e ................................................................. 1 5 x 4

Lining W idth.................................................. 4"

Lining Th ickness...........................................

Lining A re a - S q . In. per a xle ....................

249.0

B R A K E C O N T R O L S

Wheel Cylinder Bore

TRUCK

SERIES

Front

LV4000

P/s"

LA4000

P/a"

4500

S5500

7/s"

E5500

/%"

Vs"

E6500

P/s"

S6500

'P/4"

*M aster cylinder is part of dash mounted booster

Rear

P/2"

lVz"

P/s"

L4000

E6500

“ F"

Manual

1 5 x 3

Vie

199.0

E6500

“ FR-3”

Manual

1 5 x 6

Vz"

379.6

Master

Cyl. Bore

P/4"

* l 3/4"

SG500

“ FA ”

Automatic

1 5 x 3

.31"

199.0

S6500

“ FR-3A”

Automatic

1 5 x 6

Vz"

379.6

MODEL

NO.

C-4055

C-4056

C-4074-A

C-4074-B

C-4074-C

C-4090

2504183

(A ir operated)

STANDARD

OPTIONAL

Std.

Opt.

Std.

Opt.

Std.

Opt.

Std.

TRUCK

SERIES

LV4000

P4500

LV4000

E4500 (Conv.)

E5500 (Conv.)

E6500

E5500

E6500

E5500 (Cowl)

E4500 (Cowl)

S5500

S6500

LA4000

DLA4000

POWER CYLINDERS

TYPE

MOUNT

Remote

OVERALL

DI AMETER

11.7"

Remote

Dash

11.7"

Dash

Remote

11.7"

13.0"

4.625"

CYLI NDER

BORE

.84"

.91"

POWER

DI APHRAGM

STROKE

3.00"

4.40"

4.75"

HYDRAULI C

PISTON

STROKE

—

4.50"

.97"

.91"

.97"

1.125"

4.75"

4.45"

3.90"

4.50"

3.75"

G M C S E R V I C E M A N U A L

SPECIFICATIONS (CONT.)

VACUUM PUMP SPECIFICATIONS

Model (exc. D LV4000)............................................................................. 4GA

Model (D LV4000)..................................................................................... 4GB

Rotation........................................................................................... Clockwise

D rive.......................................................................................... Belt & Pulley

Front Bearing (B a ll)

I.D .......................................................................................0.7872"-0.7874"

0 . D 1.8501"-1.8504"

Rear Bushing (Not Serviced Separately)

1.......................................................................................... D 0.7500"-0.7505"

Front End Plate

Recess for Baffle Plate— Dia.............................................. 2.250"-2.251,/

Recess for Ball Bearing—Dia........................................ 1.8495"-1.8505"

Recess for Oil Seal— Dia.................................................... 1.498"-1.500"

Recess for Felt W asher— Dia............................................. 1.240M .260"

Shaft Hole— Dia................................................................... 0.826"-0.831"

Rotor Vane

Q uantity...................................................................................................... 3

Length................................................................................... 3.179"-3.181"

W idth..................................................................................... 1.050"-1.070"

Th ickn ess..............................................................................0.246"-0.249"

Baffle Plate

Outside Diam eter................................................................ 2.251"-2.253"

Shaft Hole Diam eter........................................................... 0.790"-0.800"

Oil Seal

Outside Dia........................................................................... 1.501M .505"

I.D. to fit Shaft Dia. o f.................................................................... 0.781"

T h ickn ess............................................................................. 0.703"-0.734"

T yp e ........................................................................................... Double Lip

Housing

Inside Diam eter............................................................... 3.5715"-3.5725"

Length (between machined e n d s)................................... 3.310"-3.315"

Rotor

Length................................................................................... 3.181^-3.182"

M aterial...................................................................................... Aluminum

Rotor Shaft

Length....................................................................................................... 9"

Diam. at Rear Bushing................................................... 0.7485"-0.7495"

Diam. at Ball Bearing.....................................................0.7867"-0.7872"

Sec. 5A

Page 207

HYDRAULIC BRAKES

Sec. 5B

Page 208

G M C S E R V I C E M A N U A L

SECTION 5B

A it Qn&k&i

INDEX

Subject Page No.

Brake System Equipment .................................... 208

Brake System Maintenance ................................ 208

Brake Adjustments ...............................................209

Slack A d j u s t e r s ...................................................... 212

Brake Chambers (Standard) .............................213

Air T a n k s .................................................................214

Air Tank Check Valve ........................................215

Safety Valve ..........................................................215

Pressure Protection Valve ................................ 216

Quick R elease Valve ........................................... 216

Moisture Ejector Valve .................................... 216

Brake Application V a l v e s .................................... 217

Air Lines ................................................................. 219

Air Pressure Gauge ........................................... 220

Low Air Pressure S w i t c h .................................... 221

T railer Brake C o n t r o l s ........................................221

I.C.C. Brake System E q u ip m e n t......................221

Trailer Brake Hand Control V a l v e s ...............221

Subject Page No.

Trailer Emergency Air Supply Control Valves 222

Tractor Protection (Breakaway) Valves . . . 223

Double Check Valve and Stop Light Switch . . 223

Front Brake Limiting Valve and Two-Way

Control Valve .................................................. 224

DD3 Brake Actuator System .............................226

Inversion V a l v e ......................................................230

Push-Pull Control Valve .................................... 231

Synchro V a l v e ......................................................... 231

Anchorlok Brake C h a m b e r s................................ 232

Front Brake Shoes and Anchor Pins .............. 233

"S" Cam Rear Brakes ........................................234

Brake Drums ......................................................... 236

Stopmaster Brakes ...............................................236

"Fail-Safe" Brakes ...............................................244

S p e c ific a tio n s ......................................................... 248

Troubleshooting Chart - General .................. 249

Troubleshooting Chart - S t o p m a s te r ...............252

BRAKE SYSTEM EQUIPMENT

The air brake system com prises a group of devices, some of which maintain a supply of com p ressed air, some of which direct and control the flow of the com pressed air, and others which trans form the energy of com pressed air into the mech anical force and motion n ecessary to apply the brakes. Refer to figure 1 for typical schematic diagram.

Information in this section covers all stand ard air brake equipment, as well as other units which are used as optional equipment on some models.

There are two basically different types of air actuated brakes used on vehicles covered by this manual. One type is the cam -type brake which is energized by an air chamber and slack adjuster arrangement. The other is called Stopmaster, which is a complete assem bly consisting of two air chambers connected to two brake shoes through tubes containing push-rod-and plunger assem b lies.

All information relative to Stopmaster brakes is found under the heading of "Stopmaster Brakes" in this section. Unless otherwise specified, all pedals, valves, controls, etc., covered in this manual apply to both cam -type and Stopmaster type brake system s.

Refer to AIR COMPRESSOR AND GOVERNOR

(SEC. 6T) for information relative to air com p resso rs and governors.

BRAKE SYSTEM M AINTENAN CE

Normal operation of braking system n e c e ssi tates periodic te sts, inspection, and adjustments to assure safe, efficient operation. Test, inspection and adjustment procedures for each air brake con trol unit are described under individual headings in this section. Since the vehicles covered by this

Maintenance Manual will be used in a wide variety of operation types, it is im possible to fix mainten ance intervals (either time or mileage) which will satisfactorily suit all conditions. Therefore, any such intervals stated in these maintenance pro cedures must be related to the type of usage to which a particular vehicle is put. Obviously, a truck used in city "stop and start" driving will r e quire different service operations and intervals than one hauling "over the road" for long distance.

With this in mind, all service intervals should be related to a specific vehicle.

Compression and subsequent cooling of air causes the moisture in the air to condense. This moisture co llects in air tank and should be drained daily. Drain cocks are provided at bottom of air tanks for this purpose. Satisfactory draining is accomplished only by leaving the drain cocks open after com pressed air has escaped and until all drainage stops.

Some vehicles are equipped with a moisture ejector valve (optional), which elim inates the need for daily drainage of air tanks. For description of

G M C S E R V I C E M A N U A L

Sec. 5B

Page 209

AIR BRAKES

C O N S T A N T PRESSURE LIN ES

D ELIVERY LIN ES

1 Slack Adjuster

2 Standard Brake Chamber

3 Limiting and Quick Release

Valve

4 Air Compressor

5 Air Intake

6 Governor

7 Emergency Parking

"Push-Pull" Valve

8 Trailer Brake Hand

Control Valve

9 Two-Way Valve

10 Low Air Buzzer Switch

11 Air Gauge

12 Application Valve

13 Double Check Valve

14 Tractor Protection Valve

15 Trailer Brake Service Line

16 Trailer Brake Emergency

Line

17 Air Tanks

18 Stopmaster Brake

Chambers

19 Check Valve

20 Moisture Ejector Valve

21 Drain Valve

22 Safety Valve t

-3469

Figure 1 — Schematic D iagram of Typical Air Brake System

how this valve works, refer to procedures under heading of "Moisture Ejector Valve."

The complete air system should be checked for leakage at regular intervals. Build up air p res sure in system to governor cut-out point, then with engine stopped and brakes released, observe rate of air p ressure drop registered by the dash air p ressure gauge. The rate of drop should not ex ceed two pounds per minute. With engine stopped and brakes fully applied, observe rate of air p res sure drop registered by the dash gauge. Rate of drop should not exceed three pounds per minute.

If leakage is excessive, leakage test should be made at air line connections and at all air brake control units as directed under individual headings later in this section.

In cold weather, particular attention should be given to draining of moisture from air system .

BRAKE ADJUSTMENTS

Brake adjustments to compensate for normal lining wear are made at slack adjuster at each wheel. Adjustment must be made before the brake chamber push rod travel reaches the maximum working stroke listed in "Specifications" at end of this section.

On 5500 and 6500 "cowl" models, an adjustable

Sec. 5B

Page 210

AIR BRAKES

G M C S E R V I C E M A N U A L

1 Application Valve

2 Valve Mounting Bracket

3 Pedal Support Bracket

4 Pedal Return Spring

5 Pedal Stop Bumper

6 Brake Pedal

7 Push Rod End

8 Adjusting Nut

9 Push Rod

10 Boot

T - 3 4 6 8

Figure 2 — Brake Pedal and Linkage (Cow l M odels)

push rod is used between the brake pedal and the brake application valve. On "L" models, an ad justable stop screw is provided to control the pedal push rod to application valve relationship. These adjustments are not normally required except when the application valve, pedal, or push rod have been removed and reinstalled.

On E6500 Models the brake pedal is part of the application valve assem bly and adjustment is by means of a stop screw (Midland-Ross valve) or a stop button (Bendix-Westinghouse valve).

PUSH ROD ADJUSTMENT

(5500, 6500 COWL MODELS) (Fig. 2)

Push rod adjustment controls the exhaust opening between the hollow end of the application valve piston and the exhaust valve, and the pedal travel before brake application begins. If push rod is too long, it will prevent the piston from leaving the exhaust valve and brakes will not r e lease, or if it does not open far enough it can re sult in slow brake relea se. If push rod is too short, excessive pedal travel will be required to start brake application, and full brake application may not be obtained. With push rod installed (fig. 2), adjust as follows:

1. Loosen lock nut on push rod.

2. Using a pair of pliers, grasp and turn rod into rod end until pedal does not contact the pedal stop bumper with push rod bottomed in piston cup.

3. Place a .040” shim between the brake pedal and the pedal stop bumper, then adjust the push rod until it just contacts the piston cup.

Push Rod to Pedal Pin

Push Rod

Application Valve

Valve and Pedal Support

Bracket

Application Valve Piston

Cup

Pedal Stop Screw

Lock Nut

Pedal to Bracket

Pin

Pedal 7,563

Figure 3 — Brake Pedal and Linkage (Tilt Cab M odels)

4. Hold push rod while firm ly tightening lock nut.

5. Check brake operation for full application and release.

PEDAL STOP SCREW ADJUSTMENT

(TILT CAB MODELS - Fig. 3)

Pedal stop screw adjustment controls the ex haust opening between the hollow end of the appli cation valve piston and the exhaust valve. It also controls the pedal travel before brake application begins. If stop screw is turned down too far, it will prevent the piston from leaving the exhaust valve and brakes will not relea se. If it does not open far enough it can result in slow brake release. If stop screw is not turned down far enough, excessive pedal travel will be required to start the brake ap plication, and full application may not be obtained.

Adjust stop screw as follows:

1. Loosen lock nut on pedal stop screw.

2. Back stop screw out until there is free play between the push rod and the application valve piston cup.

G M C S E R V I C E M A N U A L

Sec. 5B

Page 211

AIR BRAKES

1 Line to Air Gauge

2 Valve Mounting Bolt and Nut (in Engine

Compartment)

3 Lines to Trailer

Brakes Hand Control

Valve

9 Application

4 Double Check Valve and Stop Light Switch

5 Line to Tractor

Protection Valve

6 Pedal Stop Button

7 Pedal Assembly

8 Pedal to Valve Bolts

Valve Assembly T-2126

Figure 4 —Brake Pedal and Application Valve

lnstalled(Conv. Cab) (Typical)

3. Turn stop screw down until all free play is removed; then back screw out l/2 turn and lock.

4. Hold stop screw while tightening lock nut.

5. Check brake operation for full application and release.

PEDAL STOP SCREW ADJUSTMENT

(CONVENTIONAL MODELS - Fig. 4)

On all conventional models, both Midland-Ross and Bendix-Westinghouse application valves (pedal assem bly included) are used. Midland-Ross has a stop screw and Bendix-Westinghouse has a stop button as part of the assem bly. This stop screw, or button, is used to adjust pedal to provide proper pedal travel. If travel is too great, application will be too slow and full application may not be obtained.

If travel is not great enough, brakes may not re lease completely. Adjust stop screw (button) as follows:

1. Loosen lock nut.

2. Turn stop screw (M-R) into pedal bracket until pedal roller does not touch exposed end of

Figure 5 —Brake P ed al Stop Installed ( " S ” Models)

valve piston; or (B-W) until plunger does not touch valve piston.

3. Turn stop screw (M-R) out of pedal bracket until roller JUST TOUCHES exposed end of valve piston; or (B-W) until plunger JUST TOUCHES valve piston. In other words, there should be NO

FREE PLAY between pedal and valve piston.

4. Tighten lock nut without moving stop screw

(or button).

5. Check brake operation for full application and release.

BRAKE PEDAL STOP ADJUSTMENT

(Refer to Figure 5)

A pedal "stop" is provided on all school bus models with air brakes to prevent driver from bending or breaking push rod as the result of exerting more p ressure than necessary on the brake pedal. It is important that this "stop" be properly adjusted whenever service procedures have been performed which might change the pedalto-valve relation. Adjust as follows:

1. Set emergency brake or block wheels.

2. Exhaust air from brake system .

3. Loosen lock nut and turn adjusting bolt and stop plate assembly down as far as possible away from brake pedal.

Sec. 5B

Page 212

AIR BRAKES

G M C S E R V I C E M A N U A L

4. Depress and hold brake pedal in full-down position.

5. Turn adjusting bolt and stop plate assembly up until plate contacts brake pedal, with pedal in full-down position.

6. R elease brake pedal and turn adjusting bolt and stop plate assembly up (toward brake pedal) three full turns.

7. Hold adjusting bolt and stop plate assembly and tighten lock nut.

8. Start engine and build up air p ressure in system .

9. Check operation of brake pedal. Make sure pedal contacts stop plate before piston bottoms in application valve.

BRAKE LINING WEAR ADJUSTMENT

(Refer to Fig. 6)

NOTE: On vehicles equipped with "Stopmaster" brakes, brake shoe adjustment is covered under

"Stopmaster Brakes" near end of this section.

Slack adjusters functioii as adjustable levers and provide a quick and easy method of adjusting the brakes to compensate for normal lining wear.

P ositive-locking type slack adjusters are used on all vehicles. Internal construction of all slack ad justers is as shown in figure 7; however, lever arm (body) may be offset to suit installation re quirements. Refer to "Air Brake Specifications" at end of this section to determine slack adjuster type used.

The most efficient brake action with "S" cam brakes, will be obtained when the arm travel of the slack adjuster is held to a minimum so that the full length of the lever is utilized during brake ap plication. Minor adjustment to compensate for normal lining wear should be confined to the slack adjusters.

Figure 7 —Slack Adjuster

Push rod travel should be maintained as short as possible without brakes dragging (refer to fig.

6). Push rod travel should be checked after every

2,000 m iles of operation to determine whether ad justment is necessary. Brake linings should be re placed before wear exposes rivet heads and causes drum damage.

1. With wheel jacked up, turn slack adjuster worm shaft until brake drags, then back off until wheel turns freely.

NOTE: Lock sleeve must be pushed in before jvorm shaft can be turned (fig. 7). Make sure sleeve is pushed in far enough to clear hex end of worm shaft before turning shaft.

2. Be sure wheel turns freely with brakes fully released. After completing adjustment, make sure lock sleeve comes out and engages hex end of worm shaft (fig. 7). Pry sleeve out with screw driver if necessary. Coat lock sleeve and end of worm shaft with wheel bearing grease to keep out dirt and moisture to assure free movement of sleeve at next adjustment.

SLACK ADJUSTERS

SLACK ADJUSTER OPERATING TEST

Apply brakes and make sure all slack adjust ers rotate freely and without binding. Release

G M C S E R V I C E M A N U A L

Sec. 5B

Page 213

AIR BRAKES

1 Adjusting Worm Shaft

2 Lubrication Hole Plug

3 Clevis Pin

4 Slack Adjuster

5 Adjusting Clevis

Mounting Bracket

7 Brake Chamber

Air Brake Hose

9 Front Axle

10 Brake Camshaft

11 Snap Ring

1 Air Brake Hose

2 Brake Chamber

3 Mounting Bracket

4 Slack Adjuster

5 Rear Axle

Snap Ring

7 Brake Camshaft

Lubrication Hole Plug

9 Clevis pin

10 Adjusting Clevis

1.2194

Figure 9 —Brake Cham ber and Slack

Adjuster Installed (Rear)

Figure 8 — Brake Cham ber and Slack

Adjuster Installed (Front)

brakes and make sure all slack adjusters return to released position freely without binding.

With brakes released, make sure the angle formed by slack adjuster arm and brake chamber push rod is greater than 90 degrees. All slack adjusters should be set at the same angle. With brakes applied, make sure the angle formed by the slack adjuster arm and brake chamber push rod is still slightly greater than 90 degrees and that all are at the same angle. If angle is le s s than 90 de attach with spacer and lock ring or cotter pin.

2. Connect brake chamber push rod yoke to slack adjuster with clevis pin and cotter pin. Refer to "Brake Chamber Installation" for adjustment of brake chamber push rod.

3. Adjust brakes as directed under "Brake

Adjustments."

BRAKE CHAMBERS (STANDARD)

grees with brakes applied, slack adjuster is going

"over center." Adjust brakes as previously des cribed under "Brake Adjustments."

All service information in the following par agraphs refers only to standard chambers. Cham bers used on rear brakes only on 6500 Series are covered under the separate heading of "Stopmaster

Brakes." "Stopmaster" and "Fail-Safe" brakes are also available on all Series 5500 as optional equip

SLACK ADJUSTER REPLACEMENT

(Refer to Figs. 8 and 9)

Removal

1. Remove clevis pin attaching brake chamber push rod yoke to slack adjuster.

2. Remove lock ring or cotter pin and spacer securing slack adjuster on camshaft. Slide slack adjuster off end of shaft.

ment. Chambers used as optional equipment for air operated emergency and parking brakes are cover ed under separate headings of "DD3 Brake Actuator

System" or "AnchorlokBrake Chambers." Standard chambers on rear brakes of Series 4000 tilt cab models, all Series 5500 models, and for front brakes are covered here.

Installation

1. If a new slack adjuster is being installed, make sure it is the same size and type as that removed. Make sure spacing washer is in place on camshaft. Slide slack adjuster onto camshaft and

An air brake chamber is used at each wheel to convert the energy of com pressed air into the mechanical force and motion required to apply the brakes. The yoke on the brake chamber push rod connects to a slack adjuster which is mounted on the brake camshaft. Push rod opening and four

S ec. 5B

Page 214

AIR BRAKES

G M C S E R V I C E M A N U A L equally spaced holes near clamping flange in non p ressu re plate provide for breathing and drainage.

For illustration of brake chambers installed see figure 8 (at front axle) and figure 9 (at rear axle).

Brake chambers have two different type clamp rings; (1) a two-piece ring with two bolts and (2) a one-piece clamp ring with two bolts at the clamp ring joint.

BRAKE CHAMBER OPERATION

As air p ressu re enters the brake chamber behind the diaphragm, the diaphragm forces push rod outward, thus applying force to the slack ad juster which rotates brake camshaft, applying brakes. When air p ressure is released from the brake chamber, the brake shoe return springs and the push rod spring return brake shoes, camshaft, slack adjuster, push rod, and diaphragm to re leased position.

BRAKE CHAMBER

SERVICEABILITY TESTS

1. Operating Test

Apply brakes and see that the brake chamber push rods move out promptly without binding. Re lease brakes and see that they return to released position without binding.

2. Leakage Test a. While full brake pressure is being deliver ed apply soap suds to clamp ring holding the dia phragm in place between the pressure plate and non-pressure plate. No leakage is perm issible. If leakage is evident, tighten clamp ring bolts.

b. With the brakes fully applied, check for leakage through the diaphragm by coating the push rod hole and drain holes in non-pressure plate with soap suds. No leakage is perm issible. If leak age is evident, replace the diaphragm.

BRAKE CHAMBER REPLACEMENT

1. Removal

Disconnect the air line from brake chamber.

Disconnect push rod yoke from slack adjuster.

Remove nuts from brake chamber mounting studs, then remove brake chamber assem bly.

2. Installation

Install the brake chamber on mounting bracket and secure with stud nuts and lock w ashers. Con nect push rod yoke to slack adjuster. Adjust the brakes as previously directed under "Brake Ad justments." Apply brakes and make sure push rod is correct length. Angle formed by push rod and slack adjuster should be greater than 90 degrees with brakes released, and with brakes applied after being adjusted, this angle should still be greater than 90 degrees; in other words, the slack adjuster should not go "over center" during brake application. If necessary, adjust yoke on push rod to obtain this condition. Push rod must not extend through yoke far enough to interfere with slack adjuster. Test brake chamber as directed under

"Serviceability Tests."

MAINTENANCE

It is recommended that all brake chambers be removed, disassem bled, inspected and thoroughly cleaned at the tim e that brakes are relined or at one year periods, whichever occurs first (also de pendent upon the type of operation and operator experience). Any parts worn, cracked, or deter iorated should be replaced.

AIR TANKS

The number of air tanks used and their mount ing locations vary from model to model. On tilt cab models one tank is mounted crossways between frame side rails behind front bumper and in front of first frame crossm em ber. On conventional cab models the tanks are mounted along the outside of the left frame rail, under the cab in the step area.

On "cowl" models the air tank is mounted on the outside of the left-hand frame side rail near the front of the vehicle. Standard air tank on all models except tilt cab is a divided tank which incorporates a wet tank and a dry tank in the same assembly, divided by a check valve which is built into the tank.

The purpose of the air tanks is to provide a place to store com pressed air so there will always be an ample supply available for immediate oper ation of the brakes. Tanks provide storage for sufficient com pressed air for several brake ap plications with engine stopped.

Another purpose of the air tanks is to provide a place where the air, heated during com pression, can cool and the water vapor can condense. Most of this condensation takes place in the "wet" tank; this is the tank into which the com pressed air is first discharged from the com pressor. Condens ation should be drained from all air tanks daily.

To drain tanks properly, leave drain cocks open until all air escapes and draining stops. Daily draining is not necessary on those models which have the optional moisture ejector valve.

All pressure for operation of the brakes and air com pressor governor is taken from the dry tank. A one-way check valve at inlet to second tank prevents loss of air p ressure from the second tank in the event of leakage in the first tank or air com p ressor discharge line.

Air tank U-bolts and support brackets to frame

bolts should be checked for looseness at regular intervals and tightened if necessary. Air tank may be cleaned inside using steam or hot water. If corrosion or other damage has weakened the tank, it must be replaced.

AIR PRESSURE CHECK VALVE

There are several different kinds of check valves used on vehicles covered by this manual.

Check valves located as separate units in the air lines (single check valve, double check valve, and double check valve with stop light switch) are to be serviced and repaired as covered in the Air Brake

Control Units Overhaul Manual X-5B-01.

Check valve prevents loss of air pressure from second air tank in the event of leakage in the first tank or in the air com pressor discharge line.

Arrow on valve body indicates direction of air flow through valve.

The rubber valve seat should be replaced if there is any evidence of deterioration or hardening

Valve spring should be replaced if weakened by rust or corrosion. Valve disc should be perfectly smooth and free of rust or corrosion. When in stalling check valve, make sure it is installed to perm it air flow from first tank into second tank as indicated by the arrow on valve body.

A fourth type check valve, which is an integral part of the divided air tank assem bly, is to be serviced and repaired as detailed in the following procedures (refer to fig. 10). This valve is built into the tank at the point where the "wet" tank por tion is divided from the "dry" tank portion (refer to fig. 11).

All check valves, regardless of type, should be removed, disassembled, and cleaned or replaced every six months, 50,000 m iles, or 1800 hours

(whichever occurs first).

G M C S E R V I C E M A N U A L

Sec. 5B

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AIR BRAKES

DIVIDED TANK CHECK VALVE SERVICE

(Refer to Fig. 10)

1. Drain air from all reservoirs.

2. Remove cap nut carefully. Nut com presses both valve spring and valve seat spring and parts will "fly off” if not removed carefully.

3. Remove springs, valve, and valve seat.

4. Inspect all parts for cracking, deterior ation, or swollen condition. Discard any bad parts.

5. Clean valve seat area.

6. Reassem ble, using new parts as necessary.

Install seat and O-ring assembly, valve, and springs.

7. Compress springs by pushing down on cap nut and thread cap nut into tank. Tighten cap nut.

8. Build up air p ressure in system and deter mine effectiveness of check valve by opening drain cock on "wet” portion of tank and note pressure retention in "dry” portion of tank.

SAFETY VALVE

A safety valve is installed in air tank to elim inate the possibility of air pressure building up in the system beyond a safe maximum in the event of failure of the air com pressor governor.

OPERATION

When pressure in the air tank is built up to exceed 145 to 155 psi, air pressure forces ball valve off seat, permitting air to escape through exhaust port to atmosphere. After pressure bleeds down, spring forces ball back onto the seat.

MAINTENANCE

Check safety valve periodically for leakage, using soap suds at exhaust port, with 90 pounds pressure in tank. Leakage should not exceed a 3inch bubble in 3 seconds. Once a year, safety valve should be disassem bled, cleaned with kerosene, and reset to blow off at 145 to 155 psi.

ADJUSTMENT (Fig. 12)

1. Loosen lock nut.

2. Adjust pressure by turning adjusting screw.

Turn clockwise to increase pressure or counter clockwise to decrease pressure.

3. Tighten lock nut.

"W ET” TA N K

CHECK V ALVE

DRY" TANK

OUTLET

PORT

Figure 1 0 - A ir Tank C h e ck Valve

INLET

PORT

^ DRAIN PORT TANK DIVIDER

Figure 11— D iv id e d Air Tank

Sec. 5B

Page 216

AIR BRAKES

G M C S E R V I C E M A N U A L

1 Body

2 Ball Seat

3 Ball Valve

4 Exhaust Port

5 Spring

6 Adjusting Screw

7 Stem

8 Lock Nut

9 Spring Cage

Figure 12— Safety Valve

PRESSURE PROTECTION VALVE

The p ressu re protection valve is used on some models. It is mounted in a delivery port of the ap plication valve. On som e ser ie s trucks it may be used with optional equipment (air shift, differential lock, etc.). In the optional application, it is located in the outlet air line of air tank between air tank and optional equipment.

The function of the valve is to close the air lines to horns, wipers, transm ission shift, differ ential lock, etc., when the pressure in the main air system falls below 65 psi (- 5 lbs.). Thus, in the event of p ressu re lo ss to 65 psi, there still will be sufficient p ressure left to apply service or em er gency brakes and stop the vehicle.

REPLACEMENT

Removal

1. Block vehicle wheels.

2. Exhaust air pressure from system .

3. Disconnect air lines to valve.

4. Remove valve from port of application valve (or air tank line).

AIR TA N K FRAME SIDE RAIL

MOISTURE

EJECTOR VALVE

CAB STEP

SUPPORT

LINE TO

W HEELS

DRAIN

VALVE

EXHAUST

PORT

T-2320

Figure 13— M oisture Ejector V a lve Installed (Typical)

Installation

1. Install valve in delivery port of application valve (or air tank line).

2. Connect air lines to valve.

3. Build up air p ressure in system and check for leaks.

4. Drain air p ressure in system below 65 psi and check to determine if valve has shut off supply to applicable units.

QUICK RELEASE VALVE

Quick release valve is used as standard equip ment at both the front and rear brakes on some models, and at front brakes only on other models.

The purpose of the quick release valve is to r e duce the time required to release the brakes by hastening the exhaust of air pressure from the brake chambers. The valve consists of a body cover and diaphragm so arranged as to permit air p ressure to flow through the valve in one direction.

When application pressure is reduced, the air p ressure which has passed through the valve is permitted to escape through the exhaust port.

SERVICEABILITY TESTS

1. Operating Test

Apply brakes and observe that when brakes are released, air pressure is exhausted freely through the exhaust port of the valve. Be sure the exhaust port is not restricted in any way.

2. Leakage Test

With brakes applied, coat the exhaust port with soap suds to check leakage. Leakage is caused either by dirt on exhaust seat, by a worn diaphragm, or by a damaged exhaust seat on valve cover.

QUICK RELEASE VALVE REPLACEMENT

Removal

Disconnect air lines from valve. Remove two bolts attaching valve to crossm em ber or axle bracket and remove valve assem bly.

Installation

Mount valve on crossm em ber or axle bracket and tighten mounting bolts firm ly. Connect air lines to valve, referring to "Air Lines” section for torque specifications for air line fittings. Build up air pressure in system , then test valve as di rected under "Serviceability Tests."

MOISTURE EJECTOR VALVE

DESCRIPTION AND OPERATION

The moisture ejector valve is mounted on a bracket attached to the cab step support close to the wet air tank. Moisture is ejected each time the brakes are released. Air pressure lifts actuator

G M C S E R V I C E M A N U A L which lifts plunger, moving inlet valve off seat.

This perm its flow of air from wet tank into column section of valve. When brakes are released, air pressure snaps actuator back in place, allowing air and moisture in column to escape past plunger seat through exhaust port of lower body to atmos phere. Spring then returns inlet seat and plunger seat to "OFF" position. This action takes place each time brakes are applied and released, there by operating a continuous process of moisture ejection from brake air system .

The moisture ejector valve is NOT standard equipment. It is offered as optional equipment only on all 5500 and 6500 S eries.

Sec. 5B

Page 217

AIR BRAKES

REPLACEMENT (Refer to Fig. 13)

Removal

1. Exhaust air from system .

2. Disconnect air lines at valve.

3. Remove bolts which fasten valve to bracket on cab step support and remove valve.

Installation

1. Position valve on bracket on cab step sup port and secure with attaching bolts.

2. Connect air lines at valve.

3. Build up air pressure in system . Check operation of valve while applying and releasing brakes. Check for leaks.

BRAKE APPLICATION VALVES

GENERAL

The brake application valves used on models covered by this manual all operate on the same basic principle. The physical shape of the valves and the methods of mounting differ according to model. There are three mounting types; tilt cab models, conventional cab models, and "cowl" models.

TILT CAB MODELS

The application valve is mounted on a support bracket in an inverted position inside the cab. The actuating push rod from the brake pedal extends up through the bracket into the valve piston cup as shown in figure 3. A breather tube is installed in the exhaust opening in place of filter screens and a hose connected to the tube carries the ex haust air down below the cab floor.

CONVENTIONAL CAB MODELS

The application valve on these models is fa s tened to the cowl (fig. 4). The valve has two studs as part of the assembly and one threaded bolt hole.

The valve is mounted inside the cab and studs ex tend through holes in cowl. Nuts and lock washers are installed on studs on engine compartment side along with one bolt to fasten valve securely to cowl. A pedal bracket and pedal assembly is fa s tened to the bottom of the application valve by three bolts. Pedal assembly contacts valve piston with an upward movement. The exhaust port is on the back side of the valve and exhaust air escapes into engine compartment.

"COWL" MODELS

On these models, brake application valve is mounted in a horizontal position on engine side of dash. Valve assem bly is attached to a mounting bracket which is bolted to the dash panel. Brake pedal is mounted inside the cab, with the actuating push rod extending through the dash panel into the valve piston cup as shown in figure 2.

APPLICATION VALVE REPLACEMENT

On all conventional cab models both Midland-

Ross and Bendix-Westinghouse application valves are interchangeable as complete assem blies (in cluding pedal). The component parts are not inter changeable. All valve ports, mounting holes and brackets are located in the same relative places to permit replacement of assem blies regardless of manufacturer. The following procedures covering removal and installation, apply to both Bendix-

Westinghouse and Midland-Ross valves.

TILT CAB MODELS

Removal

1. To remove pedal only, remove cotter pin and drive out pedal to bracket pin.

2. To remove pedal, valve and bracket as an assembly or valve only, block vehicle wheels or hold by some means other than air brakes.

3. Drain air pressure from brake system .

4. Disconnect air lines from valve.

port.

5. Disconnect exhaust hose from valve exhaust

6. Remove bolts which attach support bracket to cab and remove complete assembly or:

7. If valve only is to be removed, remove bolts which attach valve to support bracket and remove valve.

Installation

1. To install valve only, place valve in posi tion on support bracket and attach with bolts or:

Sec. 5B

Page 218

AIR BRAKES

G M C S E R V I C E M A N U A L

2. To install pedal, valve and support bracket as an assem bly, position in cab and attach a ssem bly to cab with bolts.

3. Connect exhaust hose to valve exhaust port.

4. Connect air lines to valve.

5. Start engine and build up air pressure in brake system .

6. Check for leaks.

7. Test operation of brakes.

NOTE: Various item s of special or optional equipment are often assem bled in outlet ports of the valve, such as low air pressure switch, double check valve, stop light switch, etc. These item s may be removed separately from the valve by d is connecting proper air lines, without the necessity of removing the valve from the vehicle. They may also be taken out WITH the valve as an assembly, if desired.

CONVENTIONAL CAB MODELS

Removal

1. To remove pedal only, remove cotter pin and drive out pedal to bracket pin.

2. To remove pedal and valve as an assembly block vehicle wheels or hold by some means other than air brakes.

3. Drain air pressure from brake system .

4. Disconnect air lines from valve both in cab and in engine compartment.

5. From engine side of cowl, remove one bolt and two stud nuts which fasten valve to cowl.

6. Remove pedal and valve assembly from inside cab.

Installation

1. Place pedal and valve assembly in position on cowl inside cab.

2. From engine compartment side of cowl, install one bolt and two stud nuts to fasten valve to cowl.

3. Connect air lines to valve, both in cab and in engine compartment.

4. Start engine and build up air pressure to operating level.

5. Check for leaks.

6. Test operation of brakes.

NOTE: Various item s of special or optional equipment are often assembled in outlet ports of the valve, such as low air pressure switch, double check valve, stop light switch, etc. These item s may be removed separately from the valve by d is connecting proper air lines, without the necessity of removing the valve from the vehicle. They may also be taken out with the valve as an assembly, if desired.

"COWL” MODELS

Removal

1. To remove pedal only, it is also necessary to remove the clutch pedal. Refer to "HYDRAULIC

BRAKES” (SEC. 5A) under heading of "Brake Pedal

Replacement (All Except Tilt Cab)"for instructions.

2. To remove valve only, block vehicle wheels or hold by some means other than air brakes.

3. Drain air pressure from brake system .

4. Disconnect air lines from valve.

5. Remove three bolts from valve and remove valve from mounting bracket, or remove two bolts from mounting bracket and remove valve, bracket and boot from firewall as an assem bly.

Installation

1. Place valve (or valve, mounting bracket and boot) in position and secure with bolts.

2. Connect air lines to valve.

3. Start engine and build up air pressure in brake system .

4. Check for leaks.

5. Test operation of brakes.

NOTE: Various item s of special or optional equipment are often assembled in outlet ports of the valve, such as low air pressure switch, double check valve, stop light switch, etc. These item s may be removed separately from the valve by d is connecting proper air lines, without the necessity of removing the valve from the vehicle. They may also be taken out WITH the valve as an assembly, if desired.

APPLICATION VALVE

SERVICEABILITY TESTS

OPERATION TESTS

Check the delivery pressure of the brake valve using an accurate test gauge connected into one of the air lines leading to the brake chambers. De p ress the pedal to several positions between the fQlly released and fully applied positions and check the delivered pressure on the test gauge to see that it varies proportionately with the movement of the pedal. When the pedal is fully applied, the reading on the test gauge should be approximately that of full reservoir pressu re. The reading on the test gauge should fall off to zero when application is released. Also, check p ressu res registered on the dash gauge. These should agree with test gauge readings within 5 pounds.

LEAKAGE TESTS

With the valve fully released, check the ex haust port or end of exhaust tube for leakage. No leakage is perm issible. Leakage evidenced by this

G M C S E R V I C E M A N U A L

Sec. 5B

Page 219

AIR BRAKES

test is probably caused by worn or deteriorated inlet valve seal or by binding or corrosion between the exhaust valve disc and the valve cage, prevent ing the inlet valve from fully closing.

Make and hold a high pressure application.

Coat the exhaust port and the top of the valve with soap suds. No leakage is perm issible.

Leakage evidenced by these te sts may be due to worn or deteriorated exhaust valve or leaking piston sea ls.

and the push rod to pedal pin with engine oil. Use oil sparingly. Do not drip oil on pedal pad.

2. Conventional Cab Models. Lubricate hinge pin and roller pin with engine oil. Use oil sparing ly. Do not drip oil on pedal pad.

3. Cowl Models. Lubricate nylon bushings on clutch and brake pedal shaft and sleeve sparingly with engine oil. Also oil push rod to pedal bolt.

Do not drip oil on pedal pad.

PREVENTIVE M AINTENANCE

BRAKE PEDAL

No regular, periodic maintenance is required.

At the time of each ch assis lubrication it is well to check pedal operation.

1. Tilt Cab Models. If the pedal does not move

"free and easy," lubricate the pedal to bracket pin

BRAKE APPLICATION VALVE

It is recommended that every year, or after

50,000 m iles, whichever occurs first (and also dependent upon the type of operation and operator experience) that the application valve be removed from the vehicle, disassem bled and various com ponents inspected for wear or deterioratioi).. In stall new parts where they are found to be worn or damaged. This applies to all valves on all models.

AIR LINES

Metal tubing and flexible hose are used to connect the various units in the air brake system .

Service instructions for both types follow:

METAL TUBING

Metal lines are of annealed copper tubing with three-piece com pression type fittings. Flared type fittings should never be used in air brake system s.

Connections should be tested at least every 5,000 m iles and tightened or replaced, if necessary.

When replacing metal tubing, tubing must be free of burrs, copper cuttings, and dirt. Blow tubing out with com pressed air. Any of the above mentioned p articles will destroy sealing seats in air control units. New tubing must be of the same size as the old tubing.

Always use a new sleeve when replacing tub ing. When tightening tube connector nuts, tighten to torque listed below to assu re an airtight con nection. Overtightening will cause leakage. Apply

S.A.E. #10 lube oil to ball sleev es, tubes, and male threads, then torque to minimum value and check for leaks. If leaking, back off tube nut approximate ly % turn and retorque to higher than minimum value.

Tubing Size

1/4 Inch

3/8 Inch

1/2 Inch

5/8 Inch

Torque Inch-Pounds

30 to 50

90 to 115

100 to 125

FLEXIBLE HOSE

Flexible hose is used at each brake chamber, between cab and frame, and at trailer connections where it is im possible to use metal tubing due to constant flexing during vehicle operation. Hose connections should be tested at least every 5,000 m iles and tightened or replaced if necessary. Any hose which is chafed, worn, or kinked should be replaced.

SERVICEABILITY TESTS

1. Operating Test

If any trouble symptoms, such as slow brake application or release, indicates a restricted or clogged air line, disconnect the suspected tube or hose at both ends and blow through it to make sure the passage is clear. Inspect tubing and hose for partial restriction such as would be caused by dents or kinks. If such condition is found, tubing or hose should be replaced.

2. Leakage Test

With air system fully charged and brake ap plied, coat all tubing and hose connections with soap suds to check for leakage. No leakage is p er m issible. Leakage is som etim es corrected by tightening the connection. If this fails to correct leakage, new fittings, metal tubing, or flexible hose must be installed.

TRAILER CONNECTIONS

On vehicles equipped with trailer connections, two air lines are used to connect the truck brake system to the trailer brake system . One of these lines is the "Service" line and the other is the

"Emergency" line. The emergency line delivers constant air pressure to the trailer air tank and operating valve, while the service line delivers air pressure to trailer brakes only while the trailer brakes are being operated, either by means of the

Sec. 5B

Page 220

AIR BRAKES

G M C S E R V I C E M A N U A L

Figure 14 — Trailer Hose Coupling

foot brake system or by the trailer brake hand control valve. Flexible hoses are used to make the connection between the truck and the trailer. Each hose is equipped with couplings for convenience in connecting and disconnecting the truck and trailer brake system s (fig. 14).

The emergency line is at the right side and is tagged "Emergency.” The service line is at the left side and is tagged "Service." When coupling tractor and trailer make sure that air lines are properly connected. Couplings on trailer are also tagged "Service" and "Emergency." See figure 15 for illustration of trailer connections mounted on the back of a conventional cab model.

1. Couplings

Figure 14 shows a sectional view of a single hose coupling, and a view of the two couplings connected. The design of the coupling is such that when the two are connected together, pressure is placed on two rubber gaskets, making an airtight seal. The rubber gaskets should be replaced every six months, or more often under severe operating conditions.

2. Dummy Couplings

Dummy couplings are mounted on rear of cab and serve as hangers for the trailer hose when they are disconnected from the trailer. Both hoses should always be connected to the dummy coup lings when not connected to the trailer.

3. Cut-out Cocks (When Used)

Cut-out cocks are used in the trailer brake lin es on vehicles not equipped with trailer break away valve. Purpose of cut-out cocks is to provide a means of closing off these lines when they are not being used. The cut-out cock is open when the handle is at a 90-degree angle to the body, and is

1 Trailer Hose

Couplings

2 Dummy Couplings

3 Brake and Electrical

Lines

4 Hose Support Springs

5 Electrical Connections

6 Tractor Protection

Valve

Figure 15— Trailer Brake Connections

closed when the handle is parallel with the body.

Stops are provided so the handle cannot be turned beyond its normal open and closed positions.

Cut-out cocks should be tested periodically for leakage. Connect cut-out cock to source of air pressure, build up 90 pounds pressure against it, and cover opening with soap suds. If leakage ex ceeds a 1-inch bubble in 3 seconds, cock should be repaired or replaced. In some Instances, leakage may be caused by dirt on the key. This condition can be remedied by cleaning the key and seat with gasoline, then grinding the key to its seat with grade 400 grinding compound. Thoroughly wash off all grinding compound and coat key lightly with a good grade of cup grease before assembling. If the key or body is badly scored, the complete cut-out cock should be replaced.

AIR PRESSURE GAUGE

The air pressure gauge in the instrument panel provides the driver with a means of checking s y s tem air pressure. The vehicle should never be put in motion until pressure reaches 65 pounds. If pressure reading drops to le s s than 65 pounds while vehicle is in motion, vehicle should be stop ped and the cause of air loss corrected. Dash

G M C S E R V I C E M A N U A L gauge should be checked regularly with an accurate test gauge. If pressure reading varies 4 pounds or more, replace gauge with a recalibrated unit.

LOW AIR PRESSURE SWITCH

Low air pressure switch is used with a buzzer as a low air alarm. Buzzer is also used as a part of engine alarm system . The switch is installed in a delivery port of the application valve or in a fitting which is installed in a delivery port of the application valve. Switch is adjusted and sealed by

Sec. 5B

Page 221

AIR BRAKES

the manufacturer and is not reparable. Switch has only one wire terminal, being internally grounded.

The low air pressure switch is an air-controlled switch in an electrical circuit, automatic ally controlling a buzzer in the cab. A tell-tale light is also used. Refer to applicable "Wiring

Diagram" in Manual X-6905 for electrical circuits.

The switch has a nominal pressure setting of

58 to 65 psi. If switch fails, it must be replaced.

When installing switch, do not use sealing com pound on threads, since the switch is grounded through its mounting and sealing compound will act as insulation.

TRAILER BRAKE CONTROLS

INDEPENDENT TRAILER

BRAKE APPLICATION

On vehicles equipped with trailer brake hand control valve, trailer brakes may be applied with out applying the truck brakes. When hand control valve lever is moved to applying position, air p ressure p asses through the hand control valve and double check valve into trailer brake service line, applying the trailer brakes. When hand con trol valve lever is returned to released position, air p ressure in the trailer brake service line is exhausted from exhaust port of the control valve, releasing the trailer brakes. Any desired degree of trailer brake application is obtained by regulat ing the position of the hand control valve lever.

I.C.C. BRAKE SYSTEM EQUIPMENT

Some vehicles are equipped with special I.C.C.

(Interstate Commerce Commision) brake system equipment in conjunction with the trailer brake controls. These controls are a tractor protection

(breakaway) valve and a trailer emergency air supply control valve. These controls are provided for the following purposes:

1. They protect the tractor air system from complete lo ss of air pressure in the event of a trailer breakaway or lo ss of air pressure in the trailer air system .

2. They automatically actuate the trailer brake emergency relay valve (on trailer) in case the tractor air system pressure falls below 45 psi.

3. They provide the driver with a manual means of actuating the trailer brake emergency relay valve (on trailer).

TRAILER BRAKE HAND

CONTROL VALVES

Three different trailer brake hand control valves are used on these models. Midland-Ross valve Model N-3973-H is used on all tilt cab models. The other two hand control valves are used optionally on conventional cab models. Bendix-

Westinghouse (Model TC-2) and Midland-Ross

(Model N-30060) are completely interchangeable.

All three valves are mounted on the steering column with the operating handle on the right-hand side (fig. 16). The valve graduates the delivered air pressure in proportion to the degree the oper ating handle is moved. That is the farther the handle is moved from "OFF" to "ON," the greater the air pressure delivered to the trailer brakes.

If, at any time during such an application a service brake application is also made with the foot-con trolled valve, whichever valve releases the greater air pressure will control the brakes.

On Midland-Ross valve Model N-30060 it is necessary to hold the handle in the desired position in order to apply trailer brakes. When handle is released, it automatically returns to the "OFF" position. The Bendix-Westinghouse valve (Model

TC-2) and the Midland-Ross valve on tilt cab

Models (N-3973-H) will remain in the placed position until manually moved. Other than this operation of all three valves is identical.

HAND CONTROL VALVE REPLACEMENT

Removal

1. Block vehicle wheels.

2. Drain air from brake system .

3. Disconnect air lines from valve.

4. Remove bolts attaching mounting bracket and valve to steering column.

5. Remove valve and bracket.

Installation

1. Position valve and mounting bracket on steering column. Fasten with bolts.

2. Connect air lines to valve.

3. Start engine and build up air pressure.

4. Check for leaks and operation of brakes.

Sec. 5B

Page 222

AIR BRAKES

G M C S E R V I C E M A N U A L

T railer Brake Hand

Control Valve

Air Lines to

Application Valve

Stop Light Switch and

Double Check Valve

5 Line to Tractor

Protection Valve

6 Brake Pedal

7 Steering Column

Bracket

8 Steering Column

T-2195

Figure 16— Trailer Brake H and Control Valve

Installed— Conventional M odels

TRAILER EMERGENCY AIR SUPPLY

CONTROL VALVES

The trailer emergency supply control valve, working in conjunction with the tractor protection

(breakaway) valve, controls the operation of the trailer brakes in EMERGENCY situations.

NOTE: THIS SYSTEM IS NOT DE

SIGNED TO BE USED AS A PARKING

BRAKE UNDER ANY CIRCUMSTANCES.

PUSH TO SUPPLY

TRAILER AIR

PULL FOR

EMERGENCY

T - 2 9 7 0

Figure 17— Emergency Control Valve Decal

There are two different model control valves used on these vehicles but both operate on the same principle. They are spring-loaded valves which w ill automatically act when pressure in the truck brake system falls below 45 psi.

Whenever the emergency air valve is actuated, either manually or automatically, truck air system pressure must be built up above 45 psi and valve knob must be manually held in to charge the trailer emergency line and release the trailer brakes.

This same type valve is also used with the

DD3 brake system which is optional equipment available on tilt cab models. For information r e l ative to the function of this valve with the DD3 system , see procedures given under that heading in this section. If a truck has BOTH the DD3 s y s tem and trailer brake controls, there w ill be TWO control valves and each will be properly identified.

There are two different valves used on con ventional cab models, one Bendix-Westinghouse and one Midland-Ross. These two valves are inter changeable on conventional cab models as com plete assem b lies. However on any given vehicle, it is necessary to use a breakaway valve of the same manufacturer with each control valve; you can NOT use a B-W control valve with an M-R break-away valve, and vice versa.

On conventional models this valve is located in the engine compartment on the firewall and is connected to the knob by a push rod. The knob is located in the instrument panel in the first hole on the left side and is identified by a decal on the panel which is illustrated in figure 17.

EMERGENCY CONTROL VALVE

REPLACEMENT

Removal

1. Drain air pressure from brake system .

2. Disconnect air lines.

3. Steel Tilt Cab - Remove screw s from plate which holds the valve to bracket at left of steering column. Remove valve.

Conventional Cab - Disconnect knob and push rod assembly from piston stem . Remove screw s which fasten valve to cowl. Remove valve from engine compartment side of cowl.

Installation

1. Position valve at mounting bracket (tilt cab) or cowl (conventional) and attach air lines.

2. Secure valve with screw s. Install plate where used.

3. On conventional cab models connect knob and push rod to valve stem .

4. Start engine and build up air pressure to operating level.

5. Check for air leaks.

6. Check the operation of trailer emergency brakes.

TRACTOR PROTECTION

(BREAKAW AY) VALVE

The tractor protection valve, used in conjunc tion with the trailer emergency air supply control valve, controls operation of the trailer brakes in

EMERGENCY situations.

This valve is located on the inner side of the cab back panel on tilt cab models and on the out side of the cab back panel on conventional cab models (fig. 15).

Both service and emergency trailer brake lin es are routed through this valve, and its basic function is to protect the tractor air brake system from lo ss of pressure in the event of pressure lo ss in the trailer system .

There are two optional valves used on conven tional cab models, one Bendix-Westinghouse and one Midland-Ross. They are interchangeable as complete assem blies but each must be used with a control valve made by the same Manufacturer.

You can NOT use a B-W breakaway valve with an

M-R control valve, and vice versa. The Bendix-

Westinghouse valve has two mounting bolt holes, while the Midland-Ross valve has three mounting bolt holes.

G M C S E R V I C E M A N U A L

Sec. 5B

Page 223

AIR BRAKES

SERVICEABILITY TESTS

Operating T ests

1. Pull out emergency air valve knob to ex haust air pressure from breakaway valve control line. Disconnect trailer emergency line from emergency outlet port at breakaway valve and connect an air p ressure test gauge to emergency outlet port.

2. Start engine and build up air pressure in system . Low air pressure buzzer should stop operating at 58 to 65 psi. With air pressure in operating range, push emergency air valve knob in. Test gauge should show full air system p res sure. Then pull knob out; test gauge should drop to zero.

3. Again build up air p ressure in system to operating range, then stop engine. Push emergency air valve knob in. Make a se r ie s of brake applica tions until low air buzzer sounds. Slightly open drain cock in the dry air tank to obtain a slow

(approx. 10 psi per min.) pressure drop in the tractor brake system . When truck air system drops to 45 psi (approx.), the emergency air valve knob should automatically come out and pressure on test gauge should rapidly drop to zero.

Leakage Tests

1. Build up air pressure in truck brake s y s tem to operating range. Push in emergency air valve knob to charge trailer brake system . Use soap suds to coat exhaust ports of emergency air valve and breakaway valve.

2. When emergency air valve leaks e x c e s s ively, install new piston O-rings. When breakaway valve leaks excessively, install new O-rings and plunger seal.

BREAKAWAY VALVE REPLACEMENT

Removal

1. Block vehicle wheels.

2. Drain air pressure from brake system .

3. Disconnect air lines.

4. Remove mounting bolts and valve.

Installation

1. Position valve on back of cab and install mounting bolts.

2. Connect air lines.

3. Start engine and build up air pressure to operating level.

4. Check for leaks.

5. Check operation of brakes.

DOUBLE CHECK VALVE AN D

STOP LIGHT SWITCH

A combination double check valve and stop light switch is used in brake system s on all con ventional models equipped with trailer brake con trols. Check valve is used to connect both the foot brake application valve and the trailer brake hand control valve to the trailer brake service line.

Check valve is installed in delivery port in brake application valve. Air line from trailer brake hand control valve connects to other end of check valve.

Trailer brake service line and truck stop light switch are connected to the two side outlet ports.

CHECK VALVE OPERATION

When brake application is made by the foot brake valve, air p ressure from the foot brake valve forces the shuttle valve over against the in let from the hand control valve and flows out the

Sec. 5B

Page 224

AIR BRAKES

G M C S E R V I C E M A N U A L holes in the valve guide into the trailer brake service line. When foot brakes are released and trailer brakes are applied by means of the hand control valve, air pressure from the hand control valve forces the shuttle valve over against the in let from the foot brake valve and flows out through the holes in the valve guide into the trailer brake service line.

CHECK VALVE SERVICEABILITY TESTS

1. Operating T ests a. Apply truck brakes and note that brakes apply promptly on both the truck and the trailer.

Release truck brakes and note that brakes on truck and trailer both release promptly.

b. Move hand control valve lever to applied position and note that brakes apply only on the trailer. Move control valve lever to released p osi tion and note that trailer brakes release promptly.

2. Leakage T ests a. Apply truck brakes and check for leakage at hand control valve exhaust port, using soap suds.

b. Apply trailer brakes only with hand control valve and check for leakage at truck brake appli cation valve exhaust port, using soap suds.

c. No leakage is perm issible in either of these te sts. If there is any leakage, replace the shuttle valve.

CHECK VALVE REPLACEMENT

Removal

1. Block vehicle wheels.

2. Drain air pressure from brake system .

3. Disconnect air lines from valve.

4. Screw valve out of brake application valve.

Installation

1. Screw valve into brake application valve.

2. Connect air lines.

3. Start engine and build up air pressure to operating level.

4. Check for leaks.

5. Check operation of brakes and stop lights.

A combination limiting and quick release valve and a two-way control valve are used in combin ation on some vehicles as shown in figure 18. This combination perm its full brake valve delivery p res sure to the front brakes when on dry roads, or at the option of the driver, lim its the pressure to the front brakes to 50 percent of the brake valve de livery pressure when on slippery roads.

The two-way control valve (handle or knob) is mounted on instrument panel within easy reach of the driver. On tilt cab models, a plate showing

"DRY ROAD" and "SLIPPERY ROAD" positions is mounted on the dash panel and a flip-type lever is used to select the desired position. On all other models, there is a knob on the dash panel marked

"FRT. BRAKE LIMIT." When pushed in the valve is in "DRY ROAD" position. Pull knob out for "SLIP

PERY ROAD" position. On conventional cab models the valve is located inside the cab. On "cowl" models the valve is inside the engine compartment.

In both cases, the valve is mounted on a bracket fastened to the firewall with two bolts.

The limiting quick release valve is mounted on frame crossm em ber near the front brake cham b ers. One air line from brake application valve is connected to the inlet port of the two-way valve and another connects to the brake valve port at top of limiting quick release valve (fig. 18). Another air line connects the side delivery port of the twoway valve to the port opposite the mounting pad of the limiting quick release valve. The two other

FRONT BRAKE LIMITING VALVE A N D

TW O -W A Y CONTROL VALVE

side ports of the limiting quick release valve are connected to the front brake chambers.

The limiting quick release valve, besides pro viding for a 50 percent reduction of front wheel brake pressure, also serves as a quick release valve when brakes are released.

SERVICEABILITY TESTS

1. Operating Tests a. Connect an air p ressure test gauge into the air line leading to the rear brake quick release or relay valve; disconnect air line at valve and connect gauge to line if no other convenient con necting point is available. Disconnect one front brake chamber line from port at side of limiting quick release valve and connect another test gauge to this port.

b. Place the handle or knob of the two-way valve in the "DRY ROAD" position and apply the truck brakes. Both test gauges should read the same. Place the handle of the two-way valve in the

"SLIPPERY ROAD" position and apply the truck brakes. The test gauge at the limiting quick release valve should read approximately one-half the amount shown on the test gauge connected to the rear axle air line.

2. Leakage Tests a. Place the handle or knob of the two-way valve in "DRY ROAD" position and with the truck

G M C S E R V I C E M A N U A L

L im itin g— Q u ick

Release V a lv e

Front

Brake

C h a m b e rs

Inlet

V a lv e

^

V a lv e J

C arrier 1^ *0

E xh au st

Port

P lu n g e r

Sec. 5B

Page 225

AIR BRAKES

Front

Brake

C h a m b e rs

D R Y R O A D P O S IT IO N

Lim itin g— Q u ic k

Release V a lv e

Inlet

V a lv e

C arrier

V a lv e

Disc

SLIPPER Y R O A D P O S IT IO N

Figure 18 — Front Brake Lim iting a n d T w o -W a y Control V a lve O peration

TPM-6583

Sec. 5B

Page 226

AIR BRAKES

G M C S E R V I C E M A N U A L brakes applied, coat the exhaust ports of the twoway valve and limiting quick release valve with soap suds. If leakage is excessive, replace valve.

b. Place handle of two-way valve in "SLIP

PERY ROAD" position and with truck brakes ap plied, coat exhaust port of two-way valve with soap suds. If leakage is excessiv e, replace valve.

TWO-WAY VALVE REPLACEMENT

IMPORTANT: Before disconnecting air lines, either scribe a line or put a daub of paint on one air line and corresponding port on valve. It is pos sible to connect the air lines to this valve in the opposite position, with the result that the brake application p ressu res would be opposite to that in tended; that is, with valve knob in "SLIPPERY

ROAD" position, brake application would be for

"DRY ROAD" conditions and vice versa.

Installation

1. Position valve in instrument panel or on fire wall and connect air lines.

2. On tilt cab models fasten valve and plate to instrument panel with screw s.

3. On other models, fasten valve and bracket to fire wall.

4. Start engine and build up air pressure.

5. Check for leaks.

6. Check operation of brakes.

LIMITING VALVE REPLACEMENT

Removal

1. Block vehicle wheels.

2. Drain air from brake system .

3. Disconnect air lines.

4. Remove bolts which fasten valve to vehicle.

Remove valve.

Removal

1. Block vehicle wheels.

2. Drain air p ressure from brake system .

3. Disconnect air lines.

4. On tilt cab models remove screw s and re move plate and valve from instrument panel.

5. On other models, disconnect rodfrom lever and remove bolts and valve from bracket.

Installation

1. Connect air lines.

2. Position valve and fasten with bolts.

3. Start engine and build up air pressure.

4. Check for leaks.

5. Check operation of brakes.

DESCRIPTION

DD3 BRAKE ACTUATOR SYSTEM

Standard air-operated chambers are used at the front wheels.

The DD3 brake actuator system con sists of three major units connected by air lin es. These are, the brake actuator (chamber), a push-pull control valve (for manual parking and emergency application), and an inversion valve (to direct the flow of air p ressure to either parking or locking chambers). Of these three units the actuator is used by either the service or parking system s, while the other units are used wholly by the park ing system to operate the foundation brake. These three units are used in conjunction with a standard foot control valve and a slack adjuster connection to standard cam-operated wheel brakes.

Since this DD3 system serves both parking and service brake system s, information on mechanical parking brake in sub-section for "PARKING BRAKE" applies to those vehicles which do not have DD3 parking brake.

The name of the system is derived from the description of the actuator (chamber). "DD" de notes the double diaphragm and the suffix "3" de notes the triple action for service, parking and emergency braking. The actuator functions norm ally as a service brake chamber but in addition has a means of mechanically locking a brake ap plication so it can be used for parking. The DD3 brake actuator is used only at the rear wheels.

SERVICE BRAKE OPERATION

Figure 19 shows schem atically how the system works. With the handle of the push-pull control valve pushed in, air pressure from the parking reservoir is delivered through the push-pull con trol valve to the control port of the inversion valve.

From there it is routed to the lock port of the DD3 brake actuator. Air pressure, actihg on the actua tor piston moves it forward to contact the rollers which roll up the ramp of the piston holding them away from the push plate shaft. This allows the push plate and shaft to move freely in both direc tions for normal service brake application and release.

PARKING OPERATION

To park, the handle of the push-pull control valve is pulled out. This action clo ses the inlet valve, closing off any further air supply to the push-pull valve control port (and from there through the inversion valve to the DD3 brake actuator lock port). At the same tim e, this "pulling out" action opens the exhaust valve of the push-pull control valve, which allows the lock port of the DD3 brake actuator to vent through the control port of the inversion valve and then through the push-pull

G M C S E R V I C E M A N U A L

CONTROL PORT

INLET VALVE SEAT

EXHAUST VALVE m | | RESERVOIR

[ j ATMOSPHERIC

Sec. 5B

Page 227

AIR BRAKES

PUSH-PULL VALVE

PISTON

CONTROL

PORT

SUPPLY

PORT

INLET

VALVE

EXHAUST

VALVE SEAT

EXHAUST PORT

INLET-EXHAUST

VALVE

INLET-EXHAUST

VALVE SEAT

EMERGENCY

RESERVOIR

PORT

INVERSION VALVE

PARKING

DIAPHRAGM PORT

DD3 BRAKE ACTUATOR

SHAFT

PISTON

RAMP

COLLAR RAMP

ROLLER

SPRING

PARKING RESERVOIR

AIR SUPPLY SOURCE

SERVICE RESERVOIR

LOCK PORT

PARKING AND

EMERGENCY PORT

SERVICE

PORT

RELAY A N D

Q U IC K R E

LEA SE V A LV E

BRAKE

A P P L IC A T IO N

V A LV E

Figure 1 9 — Schem atic D ia g ra m of D D 3 Brake Actuator System

T-l 190-1

Sec. 5B

Page 228

AIR BRAKES

G M C S E R V I C E M A N U A L control valve and the open exhaust port of the foot control valve.

When the DD3 brake actuator lock port is vented the roller spring forces the rollers against the ramp on the collar to engage them with the push plate shaft.

When the control port of the inversion valve is vented, the inversion valve piston moves for ward and opens the inlet exhaust valve. This opens the line from the parking reservoir and allows air pressure to flow into the parking port of the DD3 brake actuator. Full parking reservoir pressure is delivered and a parking brake application results.

With the rollers against the shaft, the shaft can move forward but is locked so that it cannot return for release. To release parking brake application it is necessary to have full pressure in the air system , "push in" on push-pull control valve (make sure it stays "in") and make a full 100 p si service brake application.

EMERGENCY OPERATION

The vehicle is equipped with an air pressure gauge (in the instrument cluster) and (as optional equipment) a low air p ressure buzzer. When the operator is aware of a lo ss of air pressure as in dicated by the gauge or the buzzer, and the service brakes will not stop the vehicle, a manual em er gency application of the parking brake should be made by pulling out the handle of the push-pull control valve. Brakes then operate as described under the heading of "Parking Operation."

In the event the operator does not respond to the warning system or if the system fails to func tion, or if the lo ss of air pressure is too sudden for action, and if the air pressure in the parking reservoir falls below 40 psi, the push-pull control valve will automatically "pop" out, causing p res sure in the DD3 actuator lock port to exhaust, which will result in an automatic parking (em er gency) brake application.

DD3 BRAKE ACTUATOR OPERATION

(Refer to Figure 19)

NORMAL RUNNING

Through the push-pull control valve and an inversion valve, air enters the actuator locking port and exerts p ressu re on the locking piston grommet. The resultant force moves the locking piston forward against the rollers and roller spring. The beveled, or ramp, end of the piston will pick up and hold the rollers away from the shaft. As long as air pressure remains against the locking piston grommet and the rollers are not in contact with the shaft, normal service brake applications will permit the shaft to move freely, back and forth, past the locking mechanism. When a normal service brake application is made, air enters the actuator service port and applies p res sure against the service diaphragm. The diaphragm moves the push plate and shaft out, applying the brakes. Upon the release of the service applica tion, the brakes are released.

PARKING

To park, air is exhausted from the locking port and air is applied against the parking dia phragm through the parking diaphragm port. When air is exhausted from the lock piston, the roller spring forces the rollers against the collar and shaft. Air entering the parking port exerts force on the parking diaphragm. The diaphragm moves the push plate and shaft out, applying the brakes.

With no air on the lock piston, the shaft becom es mechanically locked in the applied position as the rollers wedge between the shaft and collar.

NOTE: While in a parked position, when there is a lo ss of air pressure on the parking diaphragm, the output force on the shaft is reduced. However, the shaft will not retract since its output force is transferred to the mechanical lock mechanism.

RELEASE OF PARKING APPLICATION

To release a parking application of the DD3 brake actuator, it is necessary to re-apply air pressure to equal a shaft force approximately the same as was used in making the parking applica tion. This is necessary to release the locking ro ll ers so they can be moved away from the shaft when air is re-applied to the locking piston. This can be accomplished by making a 100 psi service application after the push-pull control valve is "in" to release the parking application.

To release a parking application, air enters the locking piston and the air on the parking dia phragm is exhausted. A full 100 p si service brake application will be necessary to force the shaft forward sufficiently to allow the locking rollers to disengage and unlock the shaft. Upon release of the service application, the return spring will return the shaft to the release position.

In the event of a lo ss of air from the service system and it becomes necessary to move the vehicle before service air can be restored, the brakes may be manually released as follows:

I MP O R T A N T : BLOCK WHEELS OF

VEHICLE BEFORE RELEASING BRAKES.

Exhaust any air pressure remaining in the parking reservoir by opening drain cock, then back off the slack adjuster at each rear brake chamber.

If necessary, disconnect slack adjuster from cham ber push rod clev is.

PREVENTIVE M AINTENANCE

DD3 BRAKE ACTUATOR

Depending on experience and type of operation, the drain slot in the actuator non-pressure plate should be checked and cleared periodically.

Brakes should be adjusted as is customary with any brake chambers. Push rod travel should be as short as possible without brakes dragging.

E xcessive travel not only shortens the normal service life of diaphragms but gives slow braking response, w astes air, and d ecreases brake torque output.

Push rod to slack adjuster alignment should be checked in both the applied and released positions, the rod should move out and return properly with out binding. Also, check the angle formed by the slack adjuster arm and push rod. It should be 90 or greater in any position, after adjustment.

It is recommended that every year, or after

50,000 m iles whichever occurs first (and also dependent upon type of operation, and operator experience) that brake actuators be removed from vehicle and disassem bled.

Disassem ble DD3 brake actuator, clean all parts and lubricate locking mechanism. A special barium base grease (or its equivalent) is recom mended as a lubricant.

When diaphragms or return spring or both are replaced, like parts in the corresponding brake actuator on the same axle should also be replaced.

OPERATING A N D LEAKAGE CHECKS

DD3 BRAKE ACTUATOR

OPERATING

With the brake actuator in the released p osi tion, make several service brake applications and note that actuators apply and release properly.

Operate parking push-pull control valve and ob serve that actuators apply. While actuators are in a parking position, drain air supply to parking diaphragm and note that actuators remain applied.

Replenish air supply to auxiliary diaphragm.

Operate push-pull control valve to release parking application, then make a 100 p si service applica tion to complete release of actuators. The magni tude of the service brake application to release the brakes may vary on different vehicles due to com pressor governor setting. A service application of approximately 100 psi will release the brakes.

LEAKAGE

With air system at maximum governor p res sure and DD3 brake actuators in the released position, check drain slot and around the push rod boot with a soapy solution to detect possible leak age past the locking piston grommet.

G M C S E R V I C E M A N U A L

Sec. 5B

Page 229

AIR BRAKES

Make and hold a service brake application and again check the actuator drain slot for service diaphragm leakage. Continue to hold the service application and coat around the service and park ing diaphragm clamping rings with the soapy solu tion to detect seal leakage.

Operate the actuator control valve to a park ing position and check the exhaust port of a service brake application to detect parking diaphragm leakage. This parking diaphragm leakage detection point could be the exhaust port of the foot brake valve, quick release valve or relay valve. While still in a parking position, the parking diaphragm clamping ring should be coated with the soap solu tion to detect seal leakage.

Should leakage be detected at the clamping rings in either of the above tests, the clamping ring nuts should be tightened evenly but only enough to stop leakage.

If the DD3 brake actuator does not function as described, or leakage is excessive, it is recom mended that it be repaired or replaced.

DD3 BRAKE ACTUATOR

REPLACEMENT

(Refer to Figure 20)

REMOVAL

1. Block and hold vehicle by some means other than air brakes.

2. With the brake actuators in the released position, disconnect or completely remove air brake hoses from parking and service ports of the actuator.

3. At this point, exhaust air from parking reservoir. This may be done by opening the drain cock in the reservoir tank or by pulling out the push-pull control valve button.

Figure 20— D D 3 Brake Actuator System

Installed at Rear Axle

Sec. 5B

Page 230

AIR BRAKES

G M C S E R V I C E M A N U A L

NOTE OF CAUTION: Air will be ex hausted out the line that was connected to the parking port, if the push-pull control valve is operated. If this line is not r e moved, it should be disconnected in such a way that it w ill not whip and cause damage as the air exhausts.

4. As a safety precaution, the service system should also be drained.

5. Disconnect air brake hose at actuator lock port.

6. Remove yoke pin cotter pin and knock out yoke pin.

7. Remove mounting nuts, then actuator.

INSTALLATION

IMPORTANT: DD3 brake actuators must be installed with the drain slot pointing down and towards the center line of the vehicle.

1. Mount actuator to mounting bracket and tighten securely.

2. Fasten actuator push rod yoke to slack adjuster with yoke pin. Lock yoke pin with cotter pin. The angle formed by the push rod and slack adjuster arm should be greater than 90°.

3. Connect air brake hoses to actuator taking precautions that the proper hose is installed in the correct port, and hoses are positioned for proper movement during coach operation.

4. Adjust brakes.

5. Build up air pressure in system and test operation of brakes.

6. Test for leaks.

INVERSION VALVE DESCRIPTION

The inversion valve is used in combination with the DD3 brake actuators and push-pull control valve in a parking and/or emergency system . When the push-pull control valve is operated, the in version valve operates permitting air in the park ing reservoir to apply the brakes. The inversion valve also operates automatically when air p res sure drops to a predetermined pressure (40 psi).

The inversion valve employs a 1-1/4" diam eter hole mounting. The valve serves as a manifold having a total of six (6) 1/4" pipe ports: three (3) control ports, two (2) delivery ports and one (1) supply port. These ports are identified. The con trol ports are marked "C,” supply "S" and the delivery ports are marked "D." The exhaust port is protected by a diaphragm.

INVERSION VALVE OPERATION

With no air p ressure in the system , the in version valve inlet valve is open and its exhaust is closed. On initial build-up, as air enters the parking reservoir to which the inversion valve supply port is connected, it will pass by the open inlet and out the delivery ports. When system air pressure reaches between 50 and 60 psi and the push-pull control valve is pushed in, air will pass into the inversion valve from the push-pull control valve. This air flows in one control port and exerts a force on the inversion valve piston. At a p res sure between 60 and 70 psi, the piston moves against the resistance of the two (2) piston springs.

The piston exhaust seat moves away from the inlet and exhaust valve, opening the exhaust passage.

The inlet valve spring and supply air in the inlet valve will cause it to seat. Air at the inversion valve delivery will now exhaust from the valve exhaust port.

PARKING OR EMERGENCY

The air at the inversion valve control ports is exhausted through the push-pull control valve exhaust when it is operated. The piston springs will then cause the piston to move and seat on the inlet and exhaust valve closing the exhaust p a ss age. The inlet valve is moved off its seat by the piston, so that supply air from the parking r e s e r voir will pass by the open inlet and out delivery ports.

When the application is released by pushing in on the push-pull control valve, air p asses into the inversion valve control port. The piston moves away from the inlet and exhaust valve, opening the exhaust passage through the piston. The inlet valve clo ses and air in the delivery ports will exhaust through the center of the piston stem and out the inversion valve exhaust port.

PREVENTIVE MAINTENANCE

The manufacturer recommends that every year or after 50,000 m iles the inversion valve be disassem bled, cleaned and lubricated. Lubricate with a barium base grease (or equivalent).

Rubber parts should be replaced and any other parts which show signs of wear or damage should also be replaced.

INVERSION VALVE

OPERATING A N D LEAKAGE CHECKS

OPERATING

With the air brake system built up to governor cut-out pressure and the brakes released, operate by pulling out the push-pull control valve button to apply the brakes. Note that the brakes apply.

Operate by pushing in the push-pull control valve to release the brake application and note that the delivered air from the inversion valve is exhausted out its exhaust port. The operation of the push-pull control valve will not necessarily

G M C S E R V I C E M A N U A L

Sec. 5B

Page 231

AIR BRAKES

complete the release of the brakes. A full 100 p si service brake application after the push-pull con trol valve is pushed in should complete the release.

LEAKAGE

Start leakage checks with system pressure up to governor cut-out and brakes released. Check the inversion valve exhaust port for possible leak age at (1) the large piston grommet; (2) the piston stem grommet or; (3) the inlet valve or its seat.

Slight leakage is perm issible. While the inversion valve is still in this position, the cap nut should be checked for leakage by the seal ring.

Actuate push-pull control valve by pulling out on the button to apply the brakes, then check the inversion valve exhaust port for exhaust valve or seat leakage.

If the inversion valve does not function as described or leakage is excessive, it is recom mended that it be repaired or replaced.

INVERSION VALVE REPLACEMENT

(Refer to Figure 20)

REMOVAL

1. Block and hold vehicle by means other than air brakes.

2. Drain service and parking reservoir air supply.

3. Disconnect air lines and air brake hoses from inversion valve.

4. Loosen mounting nut and remove valve.

INSTALLATION

1. Check and clean air lines to valve.

2. Mount valve securely with mounting nut and lock washer.

3. Connect air lines and air brake hoses.

4. Check for proper operation and leaks.

PUSH-PULL CONTROL VALVE

DESCRIPTION

The push-pull control valve is located in the dash panel. It is to the right of the steering co l umn. The valve has a black knob which moves in and out ("push-pull") for operation. The lettering on the knob is illustrated in figure 21. A red col ored ring on the knob, when exposed, indicates that parking brake is on. The valve has four ports; two delivery, one supply and one for connection to the service brake foot control valve. The push-pull valve directs the flow of air to the DD3 brake ac tuator through the inversion valve. The direction of flow is controlled within the valve by a combin ation inlet and exhaust valve in conjunction with the position of the knob ("push" for service, -

"pull" for parking).

Figure 2 1 — D D 3 Control Valve Knob

CONTROL VALVE OPERATION

For operation of the push-pull control valve, refer to figure 19 and the description given previ ously under "Service Brake Operation," "Parking

Operation" and "Emergency Operation."

CONTROL VALVE REPLACEMENT

REMOVAL

1. Secure vehicle by some means other than air brakes.

2. Exhaust air from parking brake system . It is unnecessary to exhaust service air.

3. Disconnect air lines from push-pull con trol valve. Mark lines to assure installation in correct valve ports when replacing valve.

4. Drive spirol pin out of button and remove button.

5. Remove mounting nut from valve body and remove valve from dash panel.

INSTALLATION

1. Position valve on dash panel and secure with mounting nut.

2. Place button on plunger shaft, line up hole in button with hole in plunger shaft and drive in spirol pin.

3. Connect air lines to push-pull control valve ports making sure lines are connected to correct ports.

4. Build up vehicle air pressure system , and check valve for operation and leaks.

SYNCHRO VALVE

The purpose of the Synchro valve is to activate the trailer emergency brakes when tractor em er gency push-pull control valve is pulled. It joins the trailer emergency brake system to the tractor parking and emergency brake system . It is used only on vehicles which have trailer brake connec tions and air operated emergency brakes (L4000 only).

Sec. 5B

Page 232

AIR BRAKES

G M C S E R V I C E M A N U A L

On tractors which have an air operated em er gency brake system (such as DD3), as opposed to those having a mechanically applied emergency brake, this valve is used to apply both tractor and trailer emergency system s simultaneously. The basic purpose of this type application is to prevent trailer "jack-knife" conditions, which can result from applying only tractor brakes while vehicle is in motion.

application will be necessary to complete release of tractor brakes.

2. Leakage Test. Using soap suds, check for leakage both with brakes applied and released. If any leakage is evident, remove valve from vehicle and repair or replace.

REPLACEMENT

The Synchro valve is mounted in the air line system controlling the trailer emergency valve. It is installed in the lines at the cab front cro ss sill, in or near the junction block in the sill. It is ac cessib le with cab tilted, or from underneath with cab in normal position. The supply of air from the

Synchro valve is connected to the control port of the tractor protection valve.

Removal

1. Block vehicle wheels or make a parking brake application (with DD3 system , parking brake is effective after air is exhausted).

2. Exhaust air from brake system .

3. Disconnect air lines from synchro valve and remove valve.

SERVICEABILITY TESTS

1. Operating Test. Pull knob of push-pull con trol valve (tractor emergency brake) and note that trailer emergency brakes also apply. Push knob of push-pull control valve and note that trailer em er gency brakes release. A 100 psi foot valve brake

Installation

1. Place valve in position and connect air lines.

2. Start engine and build up air pressure to at least 100 psi.

3. Push "in" on control valve knob and make a service brake application. This will release the parking brake application.

4. Test as directed in applicable procedure.

ANCHORLOK BRAKE CHAMBERS

"Anchorlok" brake chambers are used as optional equipment on all 5500 and 6500 Series trucks. Refer to figure 22.

The "Anchorlok" chamber is used as a service brake chamber, an emergency brake in case of air pressure lo ss and a spring-applied parking brake.

It con sists of two separate air chambers, each having its own diaphragm and push rod. In the front chamber, air p ressu re enters behind the diaphragm when brake pedal is pushed, causing a service brake application, just as in any standard chamber.

The rear chamber is subject to constant air p r e s sure in front of the diaphragm, com pressing the emergency parking spring. In the event of lo ss of air pressure in the rear chamber, or intentional exhausting of pressure by the driver, the spring will apply the brakes. Application will begin when pressure drops to approximately 45 psi and will be complete when pressure reaches approximately

25 psi.

STUD. NUT, A N D

W A SH ER STO W ED

AT SIDE O F CHAMBER

? 5 9

"> u> :’J

« -S)

_

Figure 2 2 — A n ch o rlok Brake C h am b er Installed

STUD, NUT, A N D

W ASH ER INSTALLED

(SPRING COM PRESSED)

Figure 2 3 — Spring C o m p re ssin g A sse m b ly

In the event of an automatic emergency ap plication (loss of air pressure) and it is necessary to move the vehicle before air pressure can be restored, the emergency parking spring can be com pressed mechanically to release brake. A spring "caging" tool is part of the chamber assem bly. Remove nut and release stud from its storage place on chamber body. Remove spring housing rubber cap and insert stud in hole. Secure stud in place (1/4 turn) and "cage" spring by tightening nut with wrench. Directions are also given for this operation on the body of the chamber (see fig. 23).

This same procedure is followed if the chamber is to be removed from the vehicle for service.

A manual emergency application (or parking application) may be made by the driver by pulling out the knob on the instrument panel which con trols manual application. Release of a parking or emergency application can be made by pushing in this same knob, provided there is at least 45 pounds pressure in the air brake system .

BRAKE CHAMBER REPLACEMENT

REMOVAL

1. Block vehicle wheels.

2. With brakes released, remove "springcaging" tool from its storage place. Remove spring housing rubber cap, insert stud in hole and turn

1/ 4 turn. Run nut down on stud until finger tight, then use wrench to turn nut at least three turns.

Spring is now "caged."

NOTE: If both chambers are to be removed, perform step 2 on each BEFORE proceeding further.

G M C S E R V I C E M A N U A L

Sec. 5B

Page 233

AIR BRAKES

3. Open air tank drain valves and exhaust pressure from brake system .

4. Disconnect air lines at chamber.

NOTE: If only the emergency parking chamber needs to be removed, this may be done at this point by removing rear clamp ring and lifting rear cham ber assembly off front (service) chamber.

5. Disconnect push rod clevis from slack ad juster.

6. Remove nuts and lock washers from mount ing studs.

7. Remove "Anchorlok" brake chamber from mounting bracket.

INSTALLATION

1. Place "Anchorlok" chamber in position on mounting bracket.

2. Install lock washers and nuts on studs.

3. Connect push rod clevis to slack adjuster.

4. Connect air lines at chamber.

5. Start engine and build up air pressure to operating level. Make sure knob is pushed in on emergency parking brake valve on instrument panel.

6. Back off nut from "caging" stud in end of chamber. Remove stud and replace in storage pocket on chamber housing. Install rubber cap over release stud hole.

7. Check operation of brakes.

8. Check for leaks.

FRONT BRAKE SHOES A N D ANCHO R PINS

BRAKE SHOES

(Refer to Figure 24)

One-piece molded lining is riveted to each shoe. Lining should be replaced before it becomes worn to the extent that the rivets will damage the brake drum. Make sure new lining fits firmly against shoe and that all rivets are properly upset.

When brake drums have been machined oversize, shim s should be used between lining and shoe or oversize lining used to maintain proper lining-todrum contact. Refer to "Brake Drums" in this s e c tion. Maximum braking efficiency can be obtained immediately if linings are trued-up with a conven tional lining grinder so they are properly central ized in relation to center of hub.

Whenever any part of the brake assembly has been removed and replaced, adjust brakes as di rected under "Brake Adjustments."

ANCH O R PINS

Anchor pin ends of shoes are secured on the anchor pins by lock rings. Shoe ends are not equip ped with bushings; if shoes or anchor pins become worn, parts must be replaced. Contact between cam ends of shoes and cam is made through ro ll ers. No lubricant should be applied at ro llers or cam head; anchor pin ends should be coated with

S-17 Special Lubricant or equivalent at assem bly.

Guide pins, two for each shoe, hold shoes in align ment on backing plate.

CAMSHAFTS

Front brake camshafts have constant lift type cams forged integral with shaft. Camshafts are mounted in camshaft and brake chamber brackets which are bolted to backing plate (fig. 24). Each

Sec. 5B

Page 234

AIR BRAKES

G M C S E R V I C E M A N U A L

1 Lock Ring

2 Spacer

3 Slack Adjuster

4 Camshaft Seal

5 Camshaft Bushing

6 Camshaft and Brake

Chamber Bracket

7 Backing Plate

8 Cam (integral with shaft)

9 Cam Roller

10 Brake Shoe

11 Brake Shoe Return Spring

12 Guide Pin Washer

13 Guide Pin "C" Washer

14 Guide Pin

15 Lock Ring

16 Anchor Pin t

-1584

Figure 2 4 — Front Brake Assem bly

bracket is equipped with two bushings and a lubri cation fitting. Space between bushings acts as a lubricant reservoir. Lubricant should be applied sparingly at intervals specified in LUBRICATION

(SEC. 0) in this manual.

CAUTION: Do not overlubricate camshaft, as ex cess lubricant will be forced into brake drums.

Slack adjuster, mounted on splined end of camshaft, is held in place by a lock ring. A spacer is used on each side of slack adjuster. Whenever camshaft has been removed, coat bushing surfaces with S-17 Special Lubricant or equivalent before installing. After installation, apply lubricant as directed in LUBRICATION (SEC. 0), and adjust brake as directed under "Brake Adjustments."

Refer to "Front Suspension" under "FRONT

HUBS AND BEARINGS" (SEC. 3D) for removal of wheels, hubs, and brake drums for access to brake shoes.

“S” C A M REAR BRAKES

"S” cam brake assem blies are used on rear axle of all tilt cab models and all 5500 Series m odels. All 6500 Series models use "Stopmaster" brakes at rear axle. Brake assem bly can be r e moved as a complete assembly; however, the var ious components must be replaced individually.

The brake assem bly is mounted on the brake spider, which is bolted to flange on axle housing.

Brake assembly shown in figure 25 is atypical

Wagner brake assembly.

BRAKE SHOES A N D ANCH O R PINS

(Refer to Figure 25)

Refer to "Rear Suspension" under "REAR

HUBS AND BEARINGS" (SEC. 4C) for removal of wheels, hubs, and brake drums for access to brake shoes.

Each brake shoe con sists of a shoe table with two shoe webs welded in place. At anchor end, shoe webs straddle the mounting flange on brake spider and pivot on anchor pins. Anchor pins are

G M C S E R V I C E M A N U A L

Sec. 5B

Page 235

AIR BRAKES

Section A - A

Looking in Direction of A rro w s

1 Brake Shoe

2 Brake Shoe Return

Spring

3 Cam (integral with shaft)

4 Camshaft Seal

5 Camshaft Bushing

6 Brake Spider

7 Dust Shield

8 Camshaft and Brake

Chamber Bracket

9 Camshaft

10 Snap Ring

11 Spacers 16

12 Slack Adjuster

13 Lock Ring

Anchor Pin

Leather Seal

Brake Shoe Roller

Roller Pin

Brake Shoe Lining

T P M -7 6 3 0

Figure 2 5 — Rear Brake Assem bly

held in place by a lock ring at each end. A leather seal is used between lock ring and shoe web at outer end and between dust shield and shoe web at inner end to retain lubricant and exclude dirt. Shoe ends are not equipped with bushings; if shoes or anchor pins become worn, parts must be replaced.

Refer to figure 26 for cross-section al view.

At cam end of each shoe, a roller installed between shoe webs on a roller pin makes the con tact between shoes and cam. Flats on end of roller pin fit into notches in shoe webs. Tension of brake shoe return spring holds shoe rollers firmly against cam. Return spring pins are staked in 8 places so that they will not slide out of shoe webs. No lubri cation is required at rollers or roller pins; parts should be assem bled clean and dry. Anchor pin ends should be coated with S-17 Special Lubricant or equivalent during installation.

A two-piece molded lining is riveted to each shoe. Linings should be replaced before wear ex poses the rivet heads and causes damage to brake drums. Both linings on each shoe are identical and can be installed at either end. New linings must be securely riveted to shoe with correct size rivets, and rivets must be properly upset. Maximum brak ing efficiency can be obtained immediately if lin ings are trued-up with lining grinder so they are properly centralized in relation to center of hub.

Whenever any part of the brake assembly has been removed and replaced, adjust brakes as di rected under "Brake Adjustments."

Sec. 5B

Page 236

AIR BRAKES

G M C S E R V I C E M A N U A L

CAMSHAFT

Rear brake camshafts have constant lift, Stype cam s forged integral with shaft. Camshaft is carried in a bushing in brake spider at outer end, and in a bushing in camshaft and brake chamber bracket at inner end. Camshaft and brake chamber bracket is bolted to brake spider in conjunction with the brake dust shield. Lubrication fitting in bracket provides a means of lubricating both bush ings; space between bushings serve as a lubricant reservoir. Seals, in outer end of camshaft bore in brake spider and in inner end of bracket, retain lubricant and exclude dirt. Apply lubricant at in tervals indicated in LUBRICATION (SEC. 0).

CAUTION: Do not overlubricate camshaft, as excess lubricant may be forced by the sea ls into the brake drums.

Slack adjuster, mounted on splined end of cam shaft, is held in place by a lock ring. A spacer is used on each side of slack adjuster. On the brake assembly shown in figure 25, the two spacers (11) are the same; on some models equipped with offset slack adjusters, the inner spacer is thicker than the outer spacer. Whenever camshaft has been r e moved, coat bushing surfaces with S-17 Special

Lubricant or equivalent before installing. After installation, apply lubricant as directed in LUBRI

CATION (SEC. 0), and adjust brakes as directed under "Brake Adjustments."

BRAKE DRUMS

Brake drum installations are illustrated in

"Rear S u sp en sion " in"REAR

HUBS AND BEARINGS"

(SEC. 4C), and in "Front Suspension" under "FRONT

HUBS AND BEARINGS" (SEC. 3D). By referring to the illustrations in the above sections, methods of replacing brake drums are readily discernible.

Whenever brake drums are removed for serv icing brakes, inspect drums. If found to be scored, rough, or out-of-round,drums should be machined.

(a) Drums with standard diameter up to 14" can be machined up to .060" oversize.

(b) Drums with standard diameter over 14" can be machined up to .080" oversize.

When it is found that machining to these max imum lim its does not provide a suitable braking surface, discard the worn drum and replace with a new standard drum.

DO NOT EXCEED THESE LIMITS. THIS IS

SAFETY PRECAUTION.

STOPMASTER BRAKES

The Stopmaster type brake differs from the conventional "S" cam type brake in several r e spects. The air chamber push rod is connected to the brake shoes through a series of wedges, ro ll ers, and plungers rather than through a slack ad juster and camshaft. Stopmaster brakes are used at the rear wheels only. Stopmaster brakes employ two different type air chambers; (1) a standard air chamber which is operated by air pressure and

(2) a "Fail-Safe" air chamber which can be oper ated either by air pressure or by spring pressure.

There are three basic variations of Stopmaster brakes shown in figure 27; standard, single axle

"Fail-Safe,” and tandem axle "Fail-Safe."

STOPMASTER STANDARD

SINGLE AXLE "FAIL-SAFE”

Figure 2 7 — Stopm aster Brake A ssem blies

TANDEM AXLE "FAIL-SAFE”

G M C S E R V I C E M A N U A L

Sec. 5B

Page 237

AIR BRAKES

AUTOMATIC ADJUSTER

All Stopmaster brakes have automatic adjust er mechanisms. The basic part of the adjuster

(refer to fig. 28) is a plunger assembly which is made up of the adjusting plunger, the actuator, and the adjusting bolt. The actuator is threaded in ternally to receive adjusting bolt. On the external iurface, there are buttress type teeth. The plunger guide is free to slide in a drilled hole in the spider housing and has teeth to match those on the exter ior surface of the actuator. A spring, gasket, and bolt are used to hold the guide in contact with the actuator.

Figure 29 is an illustration of an automatic

1 Adjusting Bolt and Shoe

Retainer Assembly

2 Actuator

3 Plunger Seal

4 Adjusting Plunger

5 Plunger Guide

6 Plunger Guide Spring

7 Plunger Guide Washer

8 Plunger Guide Bolt

Figure 2 8 — Automatic Adjuster Components

Brake Air Chamber Assembly

N on-Pressure Half

Brake Shoe Assembly

Adjusting Bolt Assembly

Identification Ring

Spanner Nut Retainer

Spanner Nut

Plunger Seal and Retainer

Adjusting Pawl (Plunger Guide)

Hollow Cap Screw

11 Gasket

12 Spring

13 Adjusting Sleeve (Actuator)

14 Adjusting Plunger

15 Wedge Spring Retainer

16 Roller

17 Plunger Housing

18 Anchor Plunger (Solid)

19 Guide Screw

20 Gasket

Figure 2 9 — A utom atic Adjuster A sse m b le d

21 Plunger Seal and Retainer

22 Roller Retaining Cage

23 Wedge Spring

24 Cotter Key

25 Washer

26 Wedge Shaft

27 Wedge Guide

28 Diaphragm Plate (Push Rod)

29 Rubber Boot

30 Pressure Half

Sec. 5B

Page 238

AIR BRAKES

G M C S E R V I C E M A N U A L adjuster assem bly installed. When the plunger a s sembly is moved outward to apply the shoe against the drum, the plunger guide will slide across the sloping sides of the teeth on the actuator. If the plunger assembly moves outward and exceeds the pitch distance, the teeth on the guide will engage the next teeth on the actuator. When the plunger returns, the actuator must rotate in order to allow the assem bly to return to the "in” position. This rotation is caused by the angle of the teeth. As the actuator rotates, it screw s the adjusting bolt. The distance for the plunger to move before adjusting is controlled either by the angle of the teeth, and/ or the number of teeth. This travel establishes the lining-drum clearance.

The plunger guide has two flat sides, which are a slip fit in a slot in the adjusting plunger.

This performs two functions: (1) it prevents the guide from turning, and (2) it prevents the adjust ing plunger from turning in the housing.

In order to function properly the adjusting bolt must not turn. If it rotates with the actuator, no adjustment would occur.

The combination of the number of teeth on the outside of the actuator and the number of threads per inch on the adjusting bolt establishes the actual

Figure 3 0 — Installin g A djusting Bolt

linear advance or rate of adjustment.

Procedures covering the removal and install ation of automatic adjuster components are given in the following paragraphs.

Any time the adjuster assem blies are r e moved for service they should be lubricated as directed in the following procedures.

The adjuster system should be disassem bled whenever brake shoes are relined and inspected for the general condition of all moving parts. It is advisable to use new plunger seals and plunger guide gaskets when removing and installing these parts.

REMOVAL (Refer to Fig. 28)

1. Remove brake shoes and brake chambers as detailed under applicable procedures.

2. Remove bolt and plunger guide gasket from housing.

3. Remove spring and plunger guide.

4. Unscrew adjusting bolt from actuator.

5. Using a screwdriver, pry plunger seal out of spider housing.

6. Remove actuator and adjusting plunger.

INSTALLATION (Refer to Fig. 28)

NOTE: Make sure that adjusting mechanism is installed at proper end of spider so that brake shoe ends are mounted in proper position. Also make certain that all parts are properly lubricated.

All threads on all components should be coated with lubricant to assure smooth, free operation.

The tip of the plunger guide and the entire plunger should also be coated. See LUBRICATION (SEC. 0) for type of lubricant to be used.

1. Install new seal on adjusting plunger and actuator.

2. Install adjusting plunger and actuator in spider housing.

3. Tap plunger seal into place in spider hous ing. See figure 36.

4. Screw adjusting bolt into actuator to the full length of threads, then back off 1/4 turn so that screw will not jam and fail to adjust when assembly is complete. See figure 30.

5. Install plunger guide in spider housing. The end of the guide with teeth is installed first and the flat sides of the guide must fit into the slot in the adjusting plunger to mesh with the outer teeth of the actuator.

CAUTION: The chamfered notch on the back end of the guide must be toward the plunger seal end of the housing, otherwise the automatic adjust ment feature will not functiom. When properly a s sembled, if adjusting bolt is turned in one direc tion, the brake will adjust and if turned in opposite direction a ratcheting effect will result. When a s sembled wrong, a ratcheting effect will result

G M C S E R V I C E M A N U A L

Sec. 5B

Page 239

AIR BRAKES

Figure 31 — Standard Stopmaster Air Cham ber Components

regardless of which direction adjusting bolt is turned.

6. Install spring, gasket and bolt.

7. Install anchor plunger components as d es cribed under "Brake Actuation Components.”

8. Install brake shoes and brake chamber as detailed under applicable procedures.

5. Remove bolt and nut which secure clamp ing ring.

6. Scribe a mark across the pressure housing and the non-pressure housing to assure proper reassem bly.

7. Remove diaphragm, rod, boot and guide from housings.

INITIAL ADJUSTMENT

If a new installation has just been made as described above, start engine and build up required amount of air pressure in system . Then pump the brake pedal until the automatic adjuster system adjusts enough to provide sufficient brake for safe driving. Final adjustment is made with the vehicle in motion, by pumping the pedal.

SERVICING STANDARD STOPMASTER

BRAKE CHAMBERS

It is recommended that all brake chambers be removed, disassem bled, inspected and thoroughly cleaned at the time that brakes are relined or at one year periods, whichever occurs first (also dependent upon type of operation and operator ex perience). Thorough cleaning, proper lubrication and replacement of any worn parts on a preventive maintenance basis will assure proper operation of the system at all tim es.

Instructions covering the removal and service of standard chambers follows (refer to fig. 31):

REMOVAL AND DISASSEMBLY

1. Disconnect air lines from chambers.

2. Using a punch, drive lock washer protru sions from notches in spanner nut and spider housing.

3. Using a spanner wrench or a punch and hammer, loosen spanner nut which secures air chamber to brake spider housing.

4. Remove air chamber assembly from brake spider housing.

CLEANING AND INSPECTION

1. Clean all metal parts thoroughly, using a suitable cleaning fluid. Blow dry with air or wipe dry with cloth. (Do not use solvent on diaphragm.)

2. Examine diaphragm and replace with new part if any signs of wear or deterioration are evident.

3. Inspect pressure housing for scratches, scores, or excessive wear. Examine all parts for obstructions and remove any foreign matter.

4. Examine diaphragm plate rod boot for de terioration or cracks. If deterioration or other damage is evident, replace. In order to replace boot it is necessary to remove the plastic guide from the end of the rod. If the guide is damaged or worn, it too should be replaced. Apply a liberal amount of rubber cement to boot flange and mating surface on non-pressure housing.

BRAKE CHAMBER ASSEMBLY

AND INSTALLATION

1. Install boot, rod, guide and diaphragm in non-pressure housing.

2. Position pressure housing on non-pressure housing so that scribe marks made at disassem bly are aligned.

3. Install clamping ring on assembly and s e cure with bolt and nut.

4. Install air chamber in brake spider housing until it ,rbottoms" in spider. Then back off not more than one full turn to position chamber ports in line with air tubes. The plastic guide will a s sure proper positioning of the wedge. At this point lock the air chamber in position by tightening the

Sec. 5B

Page 240

AIR BRAKES

G M C S E R V I C E M A N U A L

Figure 3 2 — Staking Air Cham ber Lockwasher

spanner nut against lock washer and the spider housing. Using a punch, drive edge of lock washer into notches provided in spider housing and span ner nut (see fig. 32).

BRAKE SHOE A N D LININGS

BRAKE SHOE REMOVAL (Refer to Fig. 33)

1. Jack up rear of vehicle and remove wheels.

2. Remove hub and brake drum assembly.

Refer to "Rear Suspension" under "REAR HUBS

AND BEARINGS” (Sec. 4C) of this manual.

3. Remove brake shoe return springs.

4. Lift brake shoe web out of shoe hold-down clip and out of notches in anchor and adjusting plungers. NOTE: Mark adjusting end of brake shoes to insure correct reassem bly.

SHOE RELINING

Each brake shoe con sists of a shoe table with a single web welded in place. A two-piece molded lining is riveted to each shoe. Lining should be replaced before wear exposes the rivet heads and, causes damage to brake drums. Both linings on each shoe are identical and can be installed at either end. New linings must be securely riveted to shoe with correct size rivets, and rivets must be properly upset. Maximum braking efficiency can be obtained immediately if linings are truedup with a lining grinder so they are properly cen tralized in relation to center of hub.

BRAKE SHOE INSTALLATION

(Refer to Fig. 33)

1. Position brake shoe webs inside hold-down clips with ends engaging slotted end of anchor plungers and slotted end of adjusting bolt.

NOTE: Brake shoes are constructed with a

4-inch radius on the adjusting end and a 3-inch radius on the anchor end. When installing shoes on brake assembly, make certain the end marked as suggested in "NOTE" of step 4 of "Removal” is mounted in adjusting plunger.

2. Install brake shoe return springs. Make certain hold-down clip applies pressure to shoe web to avoid cocked shoes.

BRAKE ACTUATION COMPONENTS

Actuation components can be serviced without removing spider from axle. Trouble diagnosis might indicate faulty internal parts which would not necessitate brake chamber disassem bly or new brake lining. Actuation components should be in spected for faulty or unacceptable conditions.

For service of automatic adjuster components see procedures under that subject on a previous page of this section. The following procedures cover the anchor end components and other ac tuation components.

REMOVAL (Refer to Fig. 33)

1. Remove brake chambers. Refer to proced ures covering standard and/or "Fail-Safe” cham ber service.

2. Loosen spanner nut, then unscrew non pressure housing from brake spider. This leaves wedge, roller and spring assem bly exposed.

3. Remove wedge, roller and spring assembly from actuation housing by pulling straight out.

4. Remove brake shoes. Refer to procedure covering this operation.

5. Remove plunger guides and washers.

6. Pry plunger seal from spider housing.

7. Remove anchor plunger.

8. Remove automatic adjuster components as described in applicable procedures.

DISASSEMBLY OF WEDGE ASSEMBLY

(Refer to Figs. 33 and 34)

1. Remove cotter pin and wedge return spring washer from wedge assembly.

2. Slide wedge spring off wedge.

3. Remove wedge retainer washer and rollers from roller retaining cage.

G M C S E R V I C E M A N U A L

Sec. 5B

Page 241

AIR BRAKES

1 Brake Shoe and

Lining Assembly

2 Adjusting Bolt Assy.

3 Adjusting Sleeve

(Actuator)

Plunger Seal and

Retainer

Adjusting Plunger

Brake Spider

(Plunger Housing)

Adjusting Pawl

(Plunger Guide)

8 Spring

9 Gasket

10 Hollow Cap Screw

11 Bolt

12 Brake Shoe Hold-

Down Clip

13 Guide Screw

14 Anchor Plunger

(Solid)

15 Brake Shoe Return

Spring

16 Dust Shield

17 Lock Washer

18 Bolt

19 Dust Cover

20 Wedge Shaft

21 Roller

9

22 Roller Retaining

Cage

23 Wedge Spring

Retainer

24 Wedge Spring

25 Washer

26 Cotter Pin

27 Identification Ring

28 Spanner Nut

29 "Failsafe" Air

Chamber

30 Standard Air Chamber

31 Lock Washer

32 Nut

T-2291

Figure 3 3 — Stopm aster Brake C om ponents (Autom atic Adjuster with “ F a il-Safe ”)

Sec. 5B

Page 242

AIR BRAKES

G M C S E R V I C E M A N U A L

P L U N G E R

1 Retaining Cage

2 "Ears" on Washer

3 Roller

4 Wedge Retainer

Washer

5 Wedge Return Spring

Return Spring Washer

7 Cotter Pin

Wedge

Figure 3 4 — W e d g e and Roller Assem bly

CLEANING AND INSPECTION

All components should be thoroughly cleaned prior to inspection and reassem bly.

1. Inspect wedge for bent or distorted condi tion. Examine bearing surfaces for scoring or wear. Replace wedge if there is evidence of wear or distortion.

2. Examine rollers for any wear or out-ofround condition. No scratches or scoring is p er m issible.

3. Examine wedge spring for fatigue or cor rosion. Replace spring if necessary.

4. Inspect actuation housing cylinder bores for scores, scratches, or corrosion. Light scratches or slightly corroded spots may be polished out with crocus cloth. Never use emery cloth or sand paper. If scratches or corrosion are too deep to be polished out, spider must be replaced.

Inspect plungers for scoring, scratches, or corrosion. Light scratches may be polished out with crocus cloth. If scratches or corrosion are too deep to be polished out, plunger must be re placed.

. Inspect plunger seal for any cracking or deterioration. Any deterioration is unacceptable and seal should be replaced.

ASSEMBLY OF WEDGE ASSEMBLY

(Refers to Figs. 33 and 34)

1. Install rollers in retaining cage.

2. Place washer in position on retaining cage.

3. Install wedge in retaining cage.

4. Position spring on wedge against washer and com press enough to install return spring washer and cotter pin.

INSTALLATION (Refer to Fig. 33)

1. Install new seals on anchor plungers as shown in figure 35.

2. Install plungers and sea ls in housing as shown in figure 36.

NOTE: Installation tool shown in figure 33 can

PLU N G E R

Figure 3 5 — Installing Seal

Anchor Plunger

be made locally according to dimensions shown in figure 37.

3. Insert plunger guide with new washer inside slots in anchor plungers.

4. Install automatic adjuster components as detailed in applicable procedure.

5. Install wedge assembly in actuation housing

(refer to fig. 38). Be sure rollers are seated cor rectly in retainer cage and make good contact with plungers.

NOTE: Spring retainer washer has "ears" on each side to be used as guides to assure correct installation (see fig. 34). Housing has "slots" to match "ears" on washer (see fig. 39).

. Install brake shoes as previously described

A N C H O R

PLUNGER

IN ST A LLIN G TO O L

G M C S E R V I C E M A N U A L

Sec. 5B

Page 243

AIR BRAKES

PLUNGER SEAL

T-2339

Figure 3 6 — Installing Anchor Plunger and Seal

under "Brake Shoe Installation" in this section.

7. Install brake chambers as described p re viously.

. Connect all air lines into both chambers.

9. Build up air p ressure in system and push parking brake knob in to admit air into outer cham bers (with "Fail-Safe" only).

10. With air in outer chambers, turn release bolt at each chamber (if "Fail-Safe") counterclock w ise as far as it will go (approximately 18 turns see fig. 42). Brakes are now in operating condition, either for service brakes or parking.

T-2340

Figure 3 8 — Installing W edge Assem bly

11. After brakes are in operating condition, adjust brakes and repeat operating and leakage tests as previously described.

Figure 3 7 — P lu n g er Seal Installin g Tool D im en sion s

Figure 3 9 — W e d g e C avity in H o u sin g (“ Slots” Show n)

Sec. 5B

Page 244________________________

G M C S E R V I C E M A N U A L

AIR BRAKES

GENERAL

“FAIL-SAFE” BRAKES

The Stopmaster "Fail-Safe" is a mechanical actuation feature for power brakes and is two-fold in purpose. It is used as an air-released , springapplied parking brake, as well as a safety feature in the event of air brake failure.

DESCRIPTION A N D OPERATION

BRAKE CHAMBERS (Fig. 40)

Two brake chamber assem blies are used at each wheel. Type used differs by model as shown in figure 27. The "Fail-Safe" brake chamber a s sembly con sists of an inner and outer chamber.

The inner chamber, containing a diaphragm and diaphragm plate rod, serv es as the service brake chamber and operates in the same manner as a conventional brake chamber. Movement of dia phragm plate rod is transmitted to the brake shoes

1 Spring Lock

2 Release Bolt

3 Spring and Cap

Assembly

4 Release Bolt Nut

5 Piston

Pressure Housing

7 Clamping Ring

Rubber Diaphragm

9 Diaphragm Plate

Rod

10 Rubber Boot

11 Wedge Rod Guide

In let Port

(Service B rakes)

Inlet Port

(P a rk in g Brake)

1 2

Wedge Rod (Part of

Wedge Assembly]

13 Non-Pressure

Housing

14 O-Ring

15 Rubber Washer

16 Spring

17 Rivet

18 Retainer Plate

19 Piston Seal

2 0

Expander

2 1

Spring Lock

Capscrew

- 2 1 9 9

Figure 4 0 — “ Fa il-S a fe ” Brake C ham ber A sse m b ly

through the mechanical actuating components as described later.

The outer chamber contains a spring-loaded piston which acts against the service brake cham ber diaphragm plate rod. During normal operation, constant air pressure is applied to the outer cham ber, this pressure, acting on the piston, holds the spring com pressed. When air pressure is released from the outer chamber by pulling out the knob on the parking brake control valve, spring pressure forces the piston toward the service brake cham ber; piston movement is transmitted through the service brake diaphragm plate rod to the brake actuating mechanism, applying the brakes.

This same action will take place in the event air pressure is lost from the system .

NOTE: The air tank supplying air pressure to the parking brake chambers is protected from the main air system by a one-way check valve; this tank will contain enough pressure for at least one parking brake release in case pressure is lost from the main air system .

In case of complete pressure lo ss, and p res sure in the protected tank is depleted, brakes will remain applied until air pressure is restored. If necessary to move the vehicle before air pressure can be restored, brakes can be released by turn ing the release bolts clockwise as far as possible

(approximately 18 turns) to com press the springs, as shown in figure 42. (This must be done at all

"Fail-Safe" chambers at each wheel.) After air pressure has been restored, service brakes will be operative immediately; however, the parking brake will remain inoperative until the spring r e lease bolts are backed out (counterclockwise) as far as possible to release the springs. Push park ing brake valve knob in to released position to ad mit air pressure into the parking brake chambers to hold springs com pressed while turning the r e lease bolts.

CAUTION: Under no circum stances should any service operations be attempted on the brake cham bers without first com pressing the springs by means of the release bolts. Applying air pressure

(at least 60 psi) to the parking brake chambers, either from the vehicle air system or from shop air supply, will hold springs com pressed and facilitate turning bolts.

MECHANICAL ACTUATING COMPONENTS

(Refer to Fig. 33)

When pressure is applied to the brake cham ber diaphragm plate rod, either by air pressure during a service brake application or by spring pressure from the parking brake chamber, move

G M C S E R V I C E M A N U A L

Sec. 5B

Page 245

AIR BRAKES

1 9 2 0

1 Spanner Nut Retaining W asher

2 Spanner Nut

3 Wedge Rod Guide

4 Tag Nut

5 Caution Tag

Nut

7 Lock W asher

Clamping Ring

9 W asher

10 Bolt

11 N on -P ressu re Housing

12 Push Rod Boot

13 Diaphragm Plate Rod

14 R u b b er D ia p h r a g m

15 "F ail-S afe" P re ssu re Housing

16 Housing to Cap Rubber W asher

17 Housing to Plunger "O" Ring

18 Air Chamber Piston Plunger

A ssem b ly

19 Air Chamber Cap A ssem b ly

20 R ele a se Bolt Spring Lock

21 C apscrew

22 Lock W asher

Figure 41 - “Fail-Safe” Air C ham ber Components

ment is transmitted to both ends of each brake shoe through wedges, rollers, and plungers which are installed in the actuating housing in the brake spider. One plunger for each shoe incorporates an adjusting wheel to provide a means of adjusting the brakes to compensate for normal lining wear.

All Stopmaster brakes have automatic adjuster mechanisms.

SERVICEABILITY TESTS

tom of chamber. Any small air leaks should be evident. No leakage is perm issible at either loca tion. If leakage occurs at clamping ring, tighten clamping ring. If leakage still p ersists, diaphragm may be deteriorated or not fitting properly between pressure and non-pressure housings (see figs. 40 and 41).

If air is escaping from drain holes only, it is an indication that diaphragm is faulty and should be replaced.

OPERATING TEST

1. Service Brakes

Make a brake application and check expansion of brake shoes against drum. Shoes should move freely and instantly when brake treadle is de pressed. Release treadle. Shoes should contract and release the brakes without any lag. Visually inspect entire lining area to see if lining is bearing properly on both sides.

2. Parking Brakes

Apply parking brakes by pulling knob of con trol valve to release air from chamber. Brakes should apply promptly and should hold on any grade on which vehicle is expected to operate. Release the brakes by pushing knob in. The brakes should release instantly and wheels turn freely.

LEAKAGE TEST

1. Service Brakes

With brakes applied, check air chambers for leakage at clamping ring by covering ring with soap suds. Also apply suds to drain holes on bot

2. Parking Brakes (Fig. 40) a. With parking brake released by air p r e s sure, apply soap suds on cap around release bolt.

Any leakage that is evident indicates a faulty piston seal. Seal should be replaced and suds applied again to be sure leakage has been corrected.

b. Soap suds should be applied at cap to p res sure housing joint. If leakage is evident, fault could be due to distorted cap caused by ca reless handling or deteriorated rubber washer between cap and housing.

c. Coat service brake relay valve exhaust port with soap suds. Leakage at this point indicates leakage past O-ring seal in the pressure housing.

If leakage occurs, replace O-ring with new part.

SERVICING “FAIL-SAFE” BRAKE

CHAMBERS

Brake chamber components can be removed from the vehicle for inspection and replacement of parts without removing the non-pressure housing and without disturbing the mechanical actuating mechanism.

Sec. 5B

Page 246

AIR BRAKES

G M C S E R V I C E M A N U A L

Figure 4 2 — Com pressing “Fail-Safe” Power Spring

REMOVAL AND DISASSEMBLY

Refer to figure 40 (also refer to figure 41 for components).

C A U T IO N : BEFORE ATTEMPTING BRAKE

CHAMBER REMOVAL, BLOCK WHEELS SE

CURELY, SINCE PARKING BRAKE WILL NOT BE

APPLIED.

1. With air pressure in parking brake cham ber (brake released), loosen release bolt spring lock and swing to one side; then turn release bolt clockwise as far as it will go (approx. 18 turns) to com press the power spring. Refer to figure 42.

2. Exhaust air pressure from parking brake chamber by pulling parking brake knob out.

3. Disconnect air lines from both chambers.

4. Mark pressure housing and non-pressure housing so that parts can be reassembled in the same relative position. Loosen clamping ring by unscrewing bolt. Hang clamping ring on non pressure plate tube.

5. Remove entire cap and spring assembly, p ressure housing, and rubber diaphragm (see fig.

43). Diaphragm plate rod and boot will remain in the non-pressure housing.

. Mount pressure housing in v ise.

Figure 4 3 — Rem oving “Fail-Safe” Assem bly

NOTE: Do not tighten vise jaws enough to d is tort pressure from cap assem bly. See figures 44 and

4 5

for illustration of this operation and dimen sions to make a "strap" wrench.

7. Remove washer and O-ring from pressure housing.

. Remove piston assem bly from cap by pull ing straight out. At tim es the spring, when fully com pressed, cocks slightly. It is then necessary to loosen the release bolt a few turns so that the piston can be withdrawn easily.

9. The piston, retainer plate, seal and expand er are held together by rivets. If any part of this assembly is defective the complete assembly must be replaced. Details are not serviced separately.

10. Cap and spring assem bly is serviced as a unit. If any of the parts become damaged or need replacing, it is necessary to replace the complete cap and spring assem bly.

CAUTION: Do not attempt to disassem ble the cap and spring assem bly. In the event any part of this assembly is defective, the complete assembly must be replaced. The component parts are not serviced separately.

CLEANING AND INSPECTION

(Refer to Figs. 40 and 41)

1. It is recommended that all brake chambers be removed, disassembled, inspected and thorough ly cleaned at the time brakes are relined or at one

G M C S E R V I C E M A N U A L

Sec. 5B

Page 247

AIR BRAKES

Figure 4 4 — Rem oving Pressure H ousing with “Strap” Wrench

year periods, whichever occurs first (also depend ent upon type of operation and operators experience).

2. Clean all metal parts thoroughly, using a suitable cleaning fluid. Blow dry with air or wipe dry with cloth.

3. Inspect piston cap for signs of damage or excessive wear. Piston should slide freely inside cap assem bly. Replace piston if badly worn or damaged.

4. Inspect inside walls of cap assembly for scratches, scores, or excessive wear. Slightly worn spots may be removed with crocus cloth. Inspect external threads on cap for rust or corrosion.

5. Inspect piston seal for cracking or deter ioration. Inspect expander and expander retaining plate for deterioration. Replace piston assembly, if necessary.

. Inspect pressure housing for scratches, scores, or excessive wear. Examine all parts for obstructions and remove any foreign matter.

7. Examine spring in cap for deterioration or rust. Inspect release bolt for signs of rust on the threaded portion. Unless spring or bolt is in very bad condition, replacement should not be necessary.

See "Caution" in Step 10 of "Removal and D isas sembly."

. Discard O-ring and rubber washer. Replace with new parts.

9. Examine diaphragm plate rod boot (in non pressure housing) for deterioration or cracks. If deterioration or other damage is evident, replace as follows: a. Pull diaphragm plate rod, wedge rod guide and boot out of wedge rod and mounting tube r e spectively.

b. Remove guide and boot from diaphragm plate rod and install new boot on plate rod. Replace wedge rod guide.

c. Apply a liberal amount of rubber cement to boot flange and mating surface on non-pressure housing.

d. Position plate rod on wedge rod and hold rubber boot flange tightly against housing surface.

Flange should seal tight to keep any moisture or foreign matter from falling into actuation com ponents.

NOTE: Be careful not to disturb wedge and roller mechanism inside actuation housing when repositioning plate rod on wedge rod.

BRAKE CHAMBER ASSEMBLY

AND INSTALLATION

Refer to figure 40 (also refer to figure 41 for components).

1. Install O-ring in groove in pressure housing.

2. Install piston assem bly in cap assem bly.

3. Position rubber washer in pressure housing at bottom of internal threads. Thread cap and spring assembly into pressure housing and tighten firmly against rubber washer. This may be done with "strap" type wrench (see figures 44 and 45)

Sec. 5B

Page 248

AIR BRAKES

G M C S E R V I C E M A N U A L or by putting pressure housing in vise and using a wrench on hex end of cap.

4. Position diaphragm over plate rod, then in stall p ressure housing and cap assem bly.

NOTE: Diaphragm should fit evenly between pressure housing and non-pressure housing. Align marks made on housings at disassem bly to insure proper air port location.

5. Pull clamping ring over flange of pressure and non-pressure housings. Install clamp bolt and nut and tighten firm ly.

. Connect all air lines and build up air p res sure in system to normal operating pressure. Push parking brake knob in to admit air to outer brake chamber.

7. Turn release bolt counterclockwise as far as possible (approx.

18 turns) to release spring

(see fig. 42). This will leave the parking brake chamber in operating condition.

NOTE: It is best to have at least 60 psi of air in chamber to hold spring tension off nut so a bet ter "feel" is obtained when the nut does bottom.

SPECIFICATIONS

FRONT BRAKES

FRONT AXLE MODEL *F070

Brake S iz e ................................................................................

Brake Shoe Lining

W idth......................................................................................

T h ickn e ss..............................................................................

Area (sq. in. per a x le )........................................................

1 5 x 3

7/ i

190

Brake Chamber

T yp e .......................................................................................

Diam eter................................................................................

523/32"

Adjust Travel to ................................................................... Short as possible w/o brakes dragging

Slack Adjuster

T yp e........................................................................................

Length Between Hole C enters...........................................

PL-18

W - W

*A ir brakes are optional equipment on LA, DLA4000. Standard brakes are Air-

Assisted Hydraulic.

TRUCK SERIES

REAR BRAKES (EXCEPT STOPMASTER)

L, DL4000(*) ALL MODELS(f)

Brake S ize ............................................

Brake Shoe Lining

W idth...............................................

Th ickn ess.......................................

Area (sq. in. per a x le )....................

Brake Chamber

1 5 x 6

3/ 4 "

15 x 5

3/4"

316.8

Typ e .................................................

Diam eter.........................................

l lA "

Adjust Travel t o .................................

Slack Adjuster

T y p e ................................................

Length Between Hole Centers.

(* ) With Eaton 16121 or 16221 opt. axle.

PL-24

5/2"

( f ) Includes L, DL4000 with Timken G161 or G361 opt. axle.

m *

Short as possible w/o brakes dra

PL-20

STOPMASTER BRAKE SPECIFICATIONS

TRUCK SERIES

Brake S iz e .................................................................................

Brake Shoe Lining

W idth.....................................................................................

Th ickn ess..............................................................................

Area (sq. in. per a xle )........................................................

Brake Chamber

Standard

Diameter (at clamp b and).............................................

"Fail-Safe”

Diameter (at chamber body).........................................

* “ Fail-Safe” chambers are optional on all 5500-6500.

5500— OPT

6500— STD

15 x 5

Crescent

315

5.66"

5.264"*

G M C S E R V I C E M A N U A L

Sec. 5B

Page 249

AIR BRAKES

GENERAL TROUBLESHOOTING CHART

NO BRAKES

PROBABLE CAUSE

1. No air pressure

2. Restricted tubing or hose

3. Defective brake valve

REMEDY

1. Check for leaks, broken lines, etc. Repair or replace as necessary

. Replace defective parts.

3. Repair or replace

INSUFFICIENT BRAKES

PROBABLE CAUSE

1. Low brake line pressure

2. Too much push rod travel

3. Worn linings or drums

4. Leaking chamber diaphragm

5. Slack adjusters out of adjustment

. Wrong size brake chambers

REMEDY

. Check for leaks, etc. and repair

. Adjust

3. Replace as necessary

4. Replace diaphragm

5. Adjust

. Replace according to "Specifications”

SLOW BRAKE APPLICATION

PROBABLE CAUSE

1. Low brake line pressure

2. Linkage binding

3. Too much push rod travel

4. Restriction in line

5. Leaking brake valve

. Worn linings or drums

7. Leaking chamber diaphragm

. Brake shoe anchor pins frozen

9. Foot control valve linkage improperly adjusted

10. Camshaft bushings binding or worn

REMEDY

1. Check for leaks, etc. and repair

. Lubricate linkage

3. Adjust

4. Remove restriction or replace line

5. Repair or replace

. Replace as necessary

7. Replace diaphragm

. Free up, replace or lubricate as necessary

9. Adjust

1 0

. Lubricate or replace

Sec. 5B

Page 250

AIR BRAKES

G M C S E R V I C E M A N U A L

SLOW BRAKE RELEASE

PROBABLE CAUSE

1. Linkage binding

2. Restriction in line

3. Too much push rod travel

4. Improper seating of valves in application valve.

5. Binding cam or camshafts

. Weak shoe return springs

REMEDY

1. Lubricate linkage

. Remove restriction or replace line.

3. Adjust

4. Repair or replace

5. Lubricate if possible; replace if not effective.

. Replace springs

GRABBING BRAKES

PROBABLE CAUSE

G r e a se or d irt on lin in g

2. Brake drum out-of-round

3. Defective application valve

UNEVEN BRAKES

PROBABLE CAUSE

1. Uneven slack adjuster settings

2. Linkage binding at one or more wheels

3. Linings worn uneven

4. Brake shoe return spring weak or broken

5. Defective brake chamber

. Defective brake drum

7. Unequal springs in brake chambers or between brake shoes

C lean or r e lin e .

. Turn or replace

3. Repair or replace

REMEDY

. Adjust properly

. Lubricate as necessary

3. Adjust or replace

4. Replace

5. Repair or replace

. Repair or replace

7. Replace in pairs.

SLOW PRESSURE BUILDUP IN RESERVOIRS

PROBABLE CAUSE

1. Clogged air cleaner

.2. Air leak

3. Faulty com pressor

4. Open or leaking reservoir drain cocks.

5. Defective com pressor governor

. Clean or replace

REMEDY

. Find and repair

3. Repair (see “ Air Com pressor” section in this manual)

4. Close, repair or replace.

5. Repair or replace

G M C S E R V I C E M A N U A L

Sec. 5B

Page 251

AIR BRAKES

AIR PRESSURE ABOVE NORMAL

PROBABLE CAUSE

1. Defective air gauge

2. Governor out of adjustment or defective

3. Restricted line between governor and com p ressor

4. Compressor unloader inoperative

. Replace

REMEDY

. Adjust, repair or replace

3. Clear line or replace

4. Repair or replace

QUICK LOSS OF PRESSURE WHEN ENGINE

IS STOPPED

(BRAKES NOT APPLIED)

PROBABLE CAUSE

1. Leaking lines or connections

2. Worn or leaking com pressor exhaust valve or one-way check valve.

3. Leaking governor

4. Leaking application valve

5. Open or leaking reservoir drain cock

(BRAKES FULLY APPLIED)

1. Leaking brake chamber

2. Leaking application valve

3. Leaking service line

4. Leaking chamber hoses

5. Dirt in two-way check valve. (If equipped with hand control valve and brakes are applied by the foot valve, dirt in the two-way check valve could cause a p ressure leak at the hand valve exhaust port.)

. Defective quick release valve

SAFETY VALVE "BLOWS OFF”

PROBABLE CAUSE

1. Safety valve out of adjustment

2. P ressure in system above normal

3. Governor out of adjustment

REMEDY

. Repair or replace

3. Repair or replace

4. Repair or replace

5. Close, repair or replace

. Repair or replace

3. Repair or replace

4. Repair or replace

5. Clean or replace

. Clean or replace diaphragm.

REMEDY

. Adjust

. See chart on "Air pressure above normal”

3. Adjust

Sec. 5B

Page 252

AIR BRAKES

G M C S E R V I C E M A N U A L

STOPMASTER TROUBLESHOOTING CHART

"FAIL-SAFE" PARKING BRAKE WILL NOT RELEASE

PROBABLE CAUSE

1. Air leak in "Fail-Safe" lines

2. Loose clamp ring or cap

3. Leakage at release bolt

4. Faulty piston O-ring seal

5. Foreign material in "Fail-Safe" chamber

. Improper wedge adjustment

7. Corroded "Fail-Safe" spring

REMEDY

. Check air system and correct leaks

. Tighten and check for air leaks

3. Replace piston and seal assem bly

4. Replace piston O-ring seal

5. Clean with solvent and lubricate

. Make wedge adjustment

7. Replace cap and spring assembly

"FAIL-SAFE" PARKING BRAKE WILL NOT APPLY

PROBABLE CAUSE

"Fail-Safe" spring not fully released

. Inoperative parking brake control valve or quick release valve

3. Foreign material in chambers or piston stuck in cap

4. "Fail-Safe" spring failure

5. Rollers not aligned with plungers or wedge not mated with diaphragm plate rod

. Brakes out of adjustment

REMEDY

Turn release bolt counterclockwise

. Check operation of valves as outlined in

Maintenance Manual and replace if necessary

3. D isassem ble and clean with solvent; lubricate piston and cap

4. Replace cap and spring assembly

5. Remove non-pressure housing and check installation of wedge

. Adjust brakes; check operation of automatic adjusters

AUTOMATIC ADJUSTERS INOPERATIVE

PROBABLE CAUSE

1. Guide installed backwards

2. Guide spring m issing or weak

3. Plunger seal failure

4. Adjusting bolt threaded into actuator too tight

5. Plunger guide washer omitted

REMEDY

1. Remove plunger guide components and reassem ble

2. Replace guide spring

3. Replace seal; clean and lubricate actuation parts

4. Back off bolt 1/4 turn

5. Replace washer

G M C S E R V I C E M A N U A L

SERVICE BRAKES INOPERATIVE

PROBABLE CAUSE

1. Low air p ressure

2. Faulty brake chamber diaphragm

3. Improper brake shoe adjustment

4. Improper wedge adjustment

5. Plunger seal failure

. Grease on linings

Sec. 5B

Page 253

AIR BRAKES

REMEDY

. Check system for leaks

. Replace diaphragm

3. Adjust brake shoes

4. Make wedge adjustment

5. Replace seal and clean and lubricate actuation parts

. Reline brakes and check seals

Sec. 5C

Page 254

G M C S E R V I C E M A N U A L

SECTION 5C

PanJiinxj, Rtovkel

EXTERNAL CONTRACTING BAN D TYPE BRAKE

External contracting band type parking brake is mounted at rear of transm ission (fig.

Brake drum is attached to the transm ission output shaft flange in conjunction with the propeller shaft universal joint flange. The band and lining assem bly is supported around the drum by a bracket on the adjustment side and an anchor bar on the stationary side. Both supports are attached to the transm ission case. The band contracts around the drum when brake is applied.

Linkage connecting parking brake lever to brake operating cam s varies on different models, however, adjustment is made at brake assembly in same manner.

BAND TYPE ADJUSTMENT (Fig. 1)

1. Place hand lever in fully released position.

Disconnect brake rod or cable from operating cams by removing cotter pin and clevis pin.

2. Remove lock wire from anchor adjusting screw and turn anchor screw as necessary to ob tain 0.010" to 0.015" between lining and drum.

Install lock wire in anchor screw.

3. Loosen lock nut on locating bolt and tighten adjusting nut on locating bolt until there is a c lea r ance of

0 2 0

" between lower end of lining and drum. Measure clearance about 1-1/2 inch from end of lining. When correct clearance is obtained, tighten lock nut on locating bolt.

4. Loosen lock nut on adjusting bolt and tighten adjusting nut on adjusting bolt to obtain clearance of

0 2 0

" between upper end of lining and drum.

Measure clearance about 1-1 /2 inch from end of lining. Tighten lock nut on adjusting bolt.

5. Adjust end on brake rod so that clevis pin may be freely inserted through operating cam s and rod end. Install clevis pin and cotter pin, then tighten lock nut on rod end.

rear off brake drum and anchor bar (fig.

), r e moving band and lining assem bly off over propeller shaft.

INSPECTION

1. Examine braking surface of drumfor rough n ess or scoring. If drum is worn or damaged, it must be replaced.

2. Inspect brake lining. If worn down close to rivet heads, new lining must be installed.

3. Examine tension and release springs; r e place if weak or broken.

BRAKE BAND INSTALLATION (Fig. 1)

1. Place band and lining assembly over pro peller shaft. Place anchor screw spring in depres sion of anchor bar, and com press spring as band

BRAKE BAND REMOVAL (Fig. 1)

1. Disconnect brake rod or cable from oper ating cam s. Remove clev is pin and operating cams from upper end of adjusting bolt.

2. Remove nuts, washers, and tension spring from lower end of adjusting bolt. Lift adjusting bolt straight up out of brake band brackets and support, stripping release springs and cam shoe from bolt as bolt is removed.

3. Remove nuts from locating bolt, then r e move bolt.

4. Remove lock wire from anchor screw, then back screw out until clear of anchor bar.

5. Slide band and lining assembly straight to

1 Brake Band

2 Cams

3 Links

4 C levis Pins

5 Cam Shoe

Lock Nut

7 Adjusting Nut

Locating Bolt

9 Tension Spring

10 Washer

11 Adjusting Nut

12 Lock Nut

13 Lock Washer

14 Brake Lining

15 R elease Springs

16 Brake Drum

17 Adjusting Bolt

18 Anchor Bar

19 Anchor Screw

20 Lock Wire

T P M - 9 8 7 3

Figure 1 — Contracting B a n d (External) P a rk in g B rake (TypicalI

anchor bracket is placed over anchor bar.

2. Install anchor screw through bracket and spring into anchor bar. Insert locating bolt up through band lower bracket and hole in support and install nuts temporarily.

3. Place operating cam s between links and install new clevis pin and cotter pin.

4. Insert threaded end of adjusting bolt down between operating cam s with hook toward rear of vehicle. As bolt is lowered into place it must pass through cam shoe, band upper bracket, upper r e lease spring, brake support, lower release spring, and band lower bracket. Install tension spring, flat washer, adjusting nut, lock washer (if used), and lock nut on adjusting bolt.

5. Adjust lining to drum clearance and con nect brake rod as directed under "Band Type Ad justment."

BRAKE DRUM REMOVAL

1. Remove brake band and lining assembly.

2. Remove nuts and lock washers from bolts attaching propeller shaft U-joint flange and brake drum to transm ission output shaft flange. T eles cope propeller shaft at slip joint and lower end of propeller shaft to floor. Remove if necessary, nuts,

G M C S E R V I C E M A N U A L

Sec. 5C

Page 254A

PARKING BRAKES

lock washers, and bolts attaching propeller shaft center bearing hanger bracket to crossm em ber.

3. On some vehicles, brake drum is mounted on forward side of transm ission mainshaft com panion flange, and on other vehicles it is mounted on rear side of flange. If mounted on rear side of flange, drum may be removed without removing flange; if mounted on forward side of flange, r e move retaining nut and flange from output shaft.

Press serrated bolts from flange to remove drum.

BRAKE DRUM INSTALLATION

1. Wipe mating surfaces of brake drum and output shaft flange clean. Position brake drum on flange and p ress serrated bolts into place. Replace drum assembly and retaining nut on output shaft.

Refer to "TRANSMISSION ON-VEHICLE SERVICE

OPERATIONS" for nut torque on various transm is sion models.

2. Position propeller shaft flange against brake drum (or output shaft flange). If removed, attach propeller shaft center bearing hanger bracket to crossm em ber. Replace all lock washers and nuts and tighten securely.

3. Install brake band and lining assembly and adjust brake.

TWO-SHOE (DUO-GRIP) PARKING BRAKE

The two-shoe duo-grip type brake con sists of two brake shoes operating on a brake drum attach ed to transm ission mainshaft flange in conjunction with the propelller shaft (fig.

Linkage connecting parking brake lever to operating lever at brake varies on different models, however, adjustment is made at brake assembly on all models in same manner.

BRAKE ADJUSTMENT (Fig. 2)

1. Place parking brake lever in fully released position.

2. Loosen lock nut (12) and adjust bolt (13) as n ecessary to obtain 0.010" to 0.015" clearance be tween outer shoe lining and brake drum at a point directly above adjusting bolt (13). Hold bolt and tighten lock nut securely.

3. Loosen lock nut (

) and adjust nut (11) as necessary to obtain 0.010" to 0.015" clearance be tween inner shoe lining and drum. Hold nut (11) and tighten lock nut (

4. Recheck lining to drum clearance. Final clearance between both linings and drum must be

0.010" to 0.015".

BRAKE SHOE REMOVAL (Fig. 2)

1. Remove adjusting nut (11) and disengage link from operating lever.

2. Loosen adjusting bolt lock nut (12) and back off adjusting bolt (13) until it clears the brake shoe web. Unhook return spring from outer shoe.

3. Remove lock from outer shoe upper pivot pin and slide shoe and operating lever assembly off pivot pin and brake drum.

4. Place shoe and operating lever assembly on bench. Remove lock rings securing brake shoes on operating lever pins and remove shoes from pins.

LINING REPLACEMENT

1. Remove linings from shoes, using deliner punch in a brake relining machine.

. Clean all dirt and corrosion from shoes, using a wire brush if necessary.

3. Install new linings on shoes, installing rivets in center holes first. A 0.010" feeler must not enter between lining and shoe at any point.

BRAKE SHOE INSTALLATION (Fig. 2)

1. Install brake shoes on operating lever pins and secure with lock rings.

2. Install shoe and operating lever assembly on brake drum, with upper end of outer lever in place on pivot pin. Install lock on pivot pin.

3. Insert link through operating lever, with washer and spring in place on top of lever. Install adjusting nut (11) on link. Connect return spring to outer shoe.

Sec. 5C

Page 254B

PARKING BRAKES

G M C S E R V I C E M A N U A L

4. Adjust lining to drum clearance as previ ously directed under "Brake Adjustment.”

BRAKE DRUM REMOVAL

1. Remove brake shoes as previously directed under "Brake Shoe Removal.”

2. Disconnect propeller shaft at transm ission.

Remove bolts attaching center bearing bracket to crossm em ber, then lower center bearing and front propeller shaft to floor.

3. Remove brake drum from bolts in trans m ission mainshaft flange. Remove four nuts, lock washers, and bolts attaching oil deflector to inner side of brake drum.

BRAKE DRUM INSTALLATION

1. Position oil deflector in brake drum and attach with four bolts, lock w ashers, and nuts.

Tighten nuts to 5-8 foot-pounds torque.

2. Install brake drum on bolts in transm ission mainshaft flange. Connect propeller shaft at trans m ission and attach center bearing bracket to frame crossm em ber. Refer to "PROPELLER SHAFTS"

(SEC. 4D) of this manual for universal joint con struction.

3. Install brake shoes as previously directed under "Brake Shoe Installation."

IMPORTANT

Any tim e that brake shoes have been removed or disturbed for any service operation it is ad visable to adjust the brake as directed under "Brake

Adjustment."

1 Brake Cable

2 Adjustable C levis

3 Connecting Lever

4 Return Spring

5 Link

Lock Nut

7 Operating Lever

Inner Shoe

9 Outer Shoe

10 Brake Drum

11 Adjusting Nut

12 Lock Nut

13 Adjusting Bolt

14 Return Spring

15 Adjuster Bracket

T P M - 9 8 2 9

Figure 2— Two Sh o e (D uo-G rip) Parking Brake

INTERNAL-EXPANDING TYPE BRAKE

Figure 3 illustrates the internal-expanding type parking brake used on the PS-4500 Models.

In order to remove components of this brake, it is necessary to disconnect the propeller shaft from the transm ission at the front universal joint. This can be done as instructed in "PROPELLER SHAFTS"

(SEC. 4D) in this Manual. Then remove four nuts from transm ission output flange and remove pro peller shaft yoke and brake drum from flange.

NOTE: It may be necessary to back off the shoe adjustment before removing drum.

Brake components are now ejqposed.

REMOVAL

1. Remove two pull-back springs.

2. Remove guide plate from anchor pin.

3. Remove shoe holddown cups, springs, and washers from hold-down pins. Remove pins from backing plate.

4. Pull brake shoe and lining assem blies away from anchor pin and remove lever strut and strut spring.

5. Lift brake shoe and lining assem blies with adjusting nut and bolt and connecting spring off backing plate.

. Move tops of shoes toward one another until adjusting nut and bolt assem bly and connecting spring drop off.

7. Remove clip from pin and remove pin, lever, and washer from primary shoe and lining assembly (the primary shoe is the shoe with the short lining).

. Compress spring on cable and remove cable from lever.

9. If necessary to remove anchor pin, straight en bent over tangs of washer from pin hex and

1 Plate Locating Pin

2 Primary Shoe and Lining

3 Brake Lever

4 Return Spring

5 Lever Strut

Pin

7 Clip

Backing Plate

9 Guide Plate

10 Reinforcement

11 Anchor Pin

12 Lock Washer

13 Anchor Pin Nut

14 Secondary Shoe and Lining

15 Strut Spring

16 Backing Plate Bolts

17 Cable Bracket

18 Cable Assembly

19 Socket

20 Adjusting Screw

21 Nut

22 Connecting Spring

23 Washer

24 Spring

25 Cup

26 Hold-Down Pin T

Figure 3 — Internal-Expanding Parking Brake

from reinforcement. Remove pin from backing plate by threading it from nut. Remove reinforce ment and washer with anchor pin.

10. If necessary to remove cable, com press tangs on cable lock and pull assem bly out of hole in backing plate.

11. If necessary to remove backing plate, re move transm ission flange nut and transm ission output flange. Remove bolts which fasten backing plate to bearing retainer and remove backing plate.

INSTALLATION

1. Place backing plate in position on rear bearing retainer and fasten with four bolts. Torque bolts to 20-26 foot-pounds.

2. Install transm ission output flange on spline of mainshaft and fasten with flange nut. Torque nut to 80-120 foot-pounds.

G M C S E R V I C E M A N U A L

Sec. 5C

Page 254C

PARKING BRAKES

3. Install cable assem bly from back of back ing plate. Push retainer through hole in backing plate until tangs securely grip inner side of plate.

4. Place washer and reinforcement over the threaded end of anchor pin. Hold anchor pin nut

(flat side against flange on backing plate) in p o si tion behind backing plate and insert threaded end of anchor pin from front side. Thread anchor pin into nut and tighten securely. Bend tang of washer over reinforcement and side of washer over hex of anchor pin.

5. Install lever on cable by compressing spring and inserting cable in channel of lever. R elease spring.

. Install primary shoe (the one with the short lining) to lever as follows: Place pin in lever with head of pin toward backing plate. Place washer on pin and push pin through hole provided in primary shoe. Fasten parts together by installing clip in groove of pin.

7. Fasten two brake shoe and lining assem b lies together by installing adjusting screw and nut assem bly and connecting spring. Lubricate adjusting screw sparingly before assembly with

S-17 Special Lubricant.

. Lubricate the six bearing surfaces on the backing plate with a heavy grade of S-17 Special

Lubricant.

9. Place brake shoe and lining assem blies in position on backing plate.

NOTE: When facing the brake assembly the shoe with the short lining (primary) should be to the left with the lever assem bled to it.

10. Pull brake shoes apart and install lever strut and strut spring between the secondary shoe and the lever. The loop on the strut spring should be in the "up" position.

11. Hold shoe and lining assem blies in p o si tion and fasten to backing plate by inserting pin through back side of plate. Then, install washer, hold-down spring, and cup (in that order) on holddown pin.

12. Place guide plate on anchor pin.

13. Install the two pull-back springs.

14. Before installing brake drum, remove the two "knock-out” plugs and replace with rubber plugs as used on standard service brakes with screw-type adjustment. This will provide holes for adjustment without the necessity of removing drum.

Install brake drum and propeller shaft yoke.

15. Connect propeller shaft as instructed in

"PROPELLER SHAFTS" (SEC. 4D) in this Manual.

Sec. 5C

Page 254D

PARKING BRAKES

G M C S E R V I C E M A N U A L

OPTIONAL AIR-OPERATED PARKING BRAKES

Models in this manual using air brake system s may have installed, as optional equipment, one of the following three parking-emergency brake s y s tems: "DD-3," "Anchorlok," or Stopmaster "Fail-

Safe." For information concerning these features refer to "AIR BRAKES" (SEC. 5B) of this manual under appropriate heading.

SPECIFICATIONS

B R A K E T Y P E

Brake S iz e .............................

Brake Drum Diameter

O utside...............................

In sid e .................................

Lining Length (a p p r o x .)....

Internal..............................

Exte rn al.............................

Lining W idth.........................

Lining T h ickn e ss..................

Total Lining Area (Sq . In .).

BAN D

21/2

—

27% "

—

IVz"

5/l6"

67.5

D U O -G R IP

T W O -S H O E

10"

—

729/64"

83/g"

21/4"

V\"

35.6

IN T E R N A L

E X P A N D IN G

11 x 2

—

11"

—

!4"

41.75

G M C S E R V I C E M A N U A L

Sec. 6A

Page 255

SECTION 6A

Q a f a l i n e

TRUCK SERIES

LA, LV4000

EM4500

ES4500

PS4500

EM5500

Contents of this section are listed in Index below:

Subject Page No.

General Information ........................................................................... 255

Engine L u b r ic a tio n ..............................................................................

Engine Maintenance and Tune-up ..................................................

255

256

Tune-up, Checks, and Adjustments ..............................................

In-Line Engine R e p la c e m e n t.............................................................

V6 Engine Replacement ....................................................................

In-Vehicle Service Operations (In-Line Engine) ......................

In-Vehicle Service Operations (V6 Engines) .............................

258

265

266

267

274

Trouble Diagnosis Chart ................................................................

Torque Wrench Specifications .........................................................

283

282

ENGINE APPLICATION CHART

GMC ENGINE

STANDARD

305C

305E

OPT.

351C

—

250

305C

292

351C

TRUCK SERIES

SM5500

ES5500

SS5500

EM6500

SM6500

GMC ENGINE

STANDARD OPT.

351C

305C

292

- -

305C

351M

351C

—

GENERAL INFORM ATION

A definite, system atic maintenance program is required to assure satisfactory economical p er formance of engine. Included in maintenance pro gram must be the servicing of related units and system s as well as regular tune-up of engine.

Frequency of tune-up is dependent upon the type of service in which the vehicle is used.

This section of manual provides instructions for servicing the various item s and tuning the en gine. Unless otherwise stated, the procedures are applicable to all gasoline engines used in vehicles covered by this manual. To adequately accomplish a satisfactory tune-up, reliable test equipment in the hands of trained personnel is necessary.

ENGINE LUBRICATION

IN-LINE ENGINES

Lubrication system for In-line engines is shown in figure 1. After passing through full-flow oil filter, oil is supplied under p ressure to main oil gallery where it is distributed to main bearings, and crankshaft drillings. Hydraulic valve lifters receive oil from main gallery. Oil metered from valve lifters p a sses through hollow push rods to lubricate individually-mounted rocker arm s.

V6 ENGINES

Lubrication of V6 engines is typically illu s trated in diagram shown in figure 2.

High capacity type oil pump (9, fig. 2) delivers o il to main oil gallery in cylinder block after oil

Sec. 6A

Page 256

GASOLINE ENGINES

G M C S E R V I C E M A N U A L

1 To Timing Chain and Sprocket

2 Oil From Camshaft

Front Bearing

3 Rocker Arm Shaft

Bracket

4 Rocker Arms

5 Oil From Camshaft

Rear Bearing

6 Oil Galleries

7 Oil Drain-Back Holes

8 Oil Filter

9 Engine Oil Pump

T-3319

Figure 2 — Engine Lubrication D iagram for V6 Engine

p a sses through oil filter. Oil passages carry oil under p ressure to all crankshaft, camshaft, and connecting rod bearings. Oil for lubrication of valve rocker arm s is supplied through passages

Figure 3 — O il Filter with T hrow -Aw ay Type Element

drilled in block, cylinder heads, and one rocker arm shaft bracket on each head. From the bracket, the oil p asses into hollow rocker arm shaft and out through an oil hole to each rocker arm.

C'Moine M aintenance, an d <1u m -rU‘p.

ENGINE M AINTENANCE

SERVICING AIR CLEANERS

Carburetor air cleaners on all vehicles re quire occasional servicing. For type and location of air cleaners, recommended element servicing intervals, and servicing procedures, refer to LU

BRICATION (SEC. 0) of this manual.

CHECKING AND MAINTAINING

CRANKCASE OIL LEVEL

Daily, or oftener if necessary, check oil level.

Check when at operating temperature, and after engine has been stopped for at least five minutes.

Remove dipstick, wipe clean, reinsert and remove