5.2.9 SLACK ADJUSTERS (cont'd)

5.2.9.2 AUTOMATIC SLACK ADJUSTER MAINTENANCE

In an S-cam type foundation brake, the final link between the pneumatic system and the foundation brake is the slack adjuster. The arm of the slack adjuster is fastened to the push rod of the chamber with a clevis and the spline end is installed on the brake camshaft.

Primarily, the slack adjuster is a lever that converts the linear force of the air chamber push rod into a torque which turns the brake camshaft and applies the brakes.

IMPORTANT

Automatic slack adjusters are for brake adjustment and will not compensate for faulty foundation brakes.

Routine Visual/Operational Checks

- Haldex strongly recommends that routine visual/ operational checks, including brackets and control arms, be performed at each Preventative

Maintenance Service Interval.

- Adjusters or anchor brackets that have visual damage, or which fail the operational checks, MUST be replaced immediately.

- Automatic adjusters should not be operated as manual adjusters except as may be necessary to get the vehicle off the road for service.

Service and Lubrication Intervals for

Standard Haldex AA1 and S-ABA Brake Adjusters

71

AUTOMATIC SLACK ADJUSTERS

While automatic slack adjuster designs vary in the manner in which they are installed and operate, all are designed to automatically maintain a predetermined shoe-to-drum clearance or brake chamber stroke.

Some automatic slack adjusters adjust upon the brake application stroke, others adjust upon release.

Automatic slack adjusters can greatly reduce manual adjustments. Automatic slack adjusters do not reduce the need for periodic maintenance.

Automatic Brake Adjuster Checking Procedures

If the brake adjuster is not maintaining the proper applied stroke, before removing the brake adjuster , check the condition of the foundation brake. If after inspecting the foundation brake no apparent problems are found, inspect the automatic brake adjuster to determine if it is operating properly. The inspection can be performed on or off the vehicle using the following procedures.

Note:

- Block wheels to prevent vehicle from rolling.

- Ensure system reservoir pressure is at

90-100 PSI.

- Check that push rod is fully retracted; apply

air to release spring brake.

- If air is not available, spring brake must be

manually caged back.

- Do not use air tools on brake adjuster!

Automatic Brake Adjuster Operational Check

Functional operation of the brake adjuster can be performed on the vehicle by using the following procedure:

- Block wheels to prevent vehicle

from rolling.

- Ensure reservoir pressure is at

90-100 psi.

- Check that the push rod is fully retracted; apply air to release spring brake. If air is not available, spring brake must be manually caged back.

Manually de-adjust brakes (turn adjustment hex counterclockwise one full turn) to create an excessive lining to drum clearance condition. (A ratcheting sound should occur.)

Make a full service brake application. On release, allow sufficient time for air chamber to fully retract.

During the brake release, observe rotation of the adjustment hex (attaching a wrench on the hex or scribing the hex will make this rotation easier to see).

This rotation indicates that an excessive clearance condition has been determined by the brake adjuster, and it is making an adjustment to compensate. On each subsequent brake release , the amount of adjustment and push rod travel will be reduced until the desired lining to drum clearance is achieved.

If rotation of the adjustment hex is not observed, refer to Foundation Brake Operational Check and

Troubleshooting Procedures at www.haldex.com.

If foundation brake assembly checks out okay and hex still does not turn, check control arm and mounting bracket for possible worn, bent or broken components. If the control arm and mounting bracket check out okay, replace the adjuster and hardware per Installation Instructions at www.haldex.com.

On Vehicle Inspection

72

5.2.9 SLACK ADJUSTERS (cont'd)

5.2.9.2 AUTOMATIC SLACK ADJUSTER MAINTENANCE (cont'd)

BRAKE ADJUSTMENT PROCEDURE

NOTE

All adjustments should be made with cold brake drums and the brakes fully released.

WARNING

To avoid possible injury, proper precautions must be taken to prevent automatic actuation of the brake chambers while adjusting slack adjusters. Always block the wheels or mechanically secure the vehicle. Spring brakes must be mechanically caged or released with air. All brakes should be released.

Foundation Brake Operational Check and Troubleshooting

Note:

- Block wheels to prevent vehicle from g rolling.

- Ensure system reservoir pressure is at g 90-100psi.

- Check that push rod is fully retracted; apply

air to release spring brake.

North American Commercial Vehicle Safety Alliance (CVSA) Uniform Vehicle Inspection Criteria

The applied stroke of the brake should be checked per CVSA guidelines at 90-100 PSI reservoir pressure.

Applied stroke should be at or less than the specified re-adjustment limits as follows:

73

Free Stroke

Measuring the Free Stroke

Free stroke is the amount of movement of the adjuster arm required to move the brake shoes against the drum.

With brakes released, measure from the face of the chamber to the center of the clevis pin “A” (fig. 13). Use a lever to move the brake adjuster until the brake shoes contact the drum “B” (fig. 13). The difference between the fully retracted and drum contact measurement “B”–“A” (fig. 13), is the free stroke. The free stroke range should fall between 3/8"–3/4".

Free Stroke Within Range

If the free stroke is good, but the applied stroke is too long, there is probably a problem with the foundation brake. Check the following and reference CVSA out-of-service criteria:

74

Free Stroke Above the Range

If the free stroke is above the range and the applied stroke is too long, there is a problem with the foundation

Component Cause Action

Camshaft

Camshaft bushings

Camshaft bushings Binding shaft

Air chamber return springs Broken, weak, missing

Air chamber push rod

Binding

Excessive movement

Remove, replace, lubricate camshaft

Remove and replace cam bushings per OEM specs

Lubricate camshaft bushings or replace

Replace chamber

Binding on chamber housing Check adjuster for proper shimming and air chamber position for proper adjuster arm length

Air system

Shoe return springs

Automatic brake adjuster

Automatic brake adjuster

Not exhausting completely

Broken, weak, missing

Unknown

Unknown

Check for cause of air problem and repair

Replace springs

Check automatic brake adjuster for proper installation. Refer to Installation Instructions at www.haldex.com.

Refer to Automatic Brake Adjuster Checking

Procedures and Operational Check at www.haldex.com.

Free Stroke Below the Range

If the free stroke is less than 3/8”, a dragging brake can occur. Check the following:

Component

Wheel bearing

Automatic brake adjuster

Automatic brake adjuster

Cause

Out of adjustment

Unknown

Unknown

Action

Readjust per OEM specs

Check automatic brake adjuster for proper control arm position. Refer to Installation Instructions at www.haldex.com.

Refer to Automatic Brake Adjuster Checking

Procedures and Operational Check at www.haldex.com

.

Free Stroke = B minus A

Applied Stroke = C minus A

A

(Fully Retracted)

C

(Brake Application at 90-100 PSI reservoir pressure.)

Figure13

Stroke Measurements

(taken from face of air chamber to center of clevis pin)

8

75

FAILURE ANALYSIS

Automatic Slack Adjuster Failure Analysis

If the power stroke is at or more than the maximum stroke, measure free stroke to determine if the slack adjuster is operational.

FREE STROKE MEASUREMENT

Free stroke is the amount of slack arm movement required to move the brake shoes against the drum.

To measure free stroke, perform the following:

1. With brakes released, measure from the brake chamber face to the center of the clevis pin.

2. With a lever, pry the slack adjuster arm untilthe brake shoes contact the drum and measure the slack adjuster movement (see Fig. 72).

3. The difference between the brake released and applied measurements is the free stroke. The free stroke should be 3/8" - 5/8". If the free stroke is in the correct range, the out of spec stroke is due to a foundation brake problem.

Check for missing or worn components, cracked brake drums, or improper lining-to-drum contact.

If the free stroke is greater than recommended, an automatic slack adjuster function test should be performed.

Fig. 72 FREE STROKE

76