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SUBJECT
DATE
Belt Drive Noise
February 2014
Additions, Revisions, or Updates
Publication Number / Title
Platform
Section Title
Change
DDC-SVC-MAN-0084
DD Platform
Belt Drive Noise
Altered instructions, moved into own section.
All information subject to change without notice.
2 31-14 Copyright © 2014 DETROIT DIESEL CORPORATION
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2 Belt Drive Noise
2
Belt Drive Noise
Excessive belt noise can be caused by a damaged belt, misaligned pulley, inadequate belt tension, or excessive belt wear.
Inspect the belt drive assembly as follows.
1. With the engine running at idle, monitor the belt tensioner movement. Does the belt tensioner move excessively at
certain engine RPMs?
a. Yes; inspect the belt tensioner damper for signs of leakage – replace tensioner and belt as necessary.
b. No, Go to step 2.
2. Inspect the belt; Refer to section "Inspection of the Poly-V-Belts".
WARNING: ENGINE EXHAUST
To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area.
Engine exhaust is toxic.
WARNING: PERSONAL INJURY
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level
surface, parking brake is set, and the wheels are blocked.
3. Start the engine. Using a spray bottle filled with water, spray water on the underside (ribbed side) of the belt, noting the
characteristic of the belt squeal.
a. If squeal subsided temporarily, inspect for misalignment; Go to step 4.
b. If squeal became audibly louder, inspect the tensioner; Go to step 4.
4. Shut off engine and remove the accessory drive belt.
NOTE: Belt tracking toward the forward side of the pulley may be evidence of worn bushings.
5. Inspect the tensioner assembly. Is the spring damper damaged/leaking or is there wear on the bushing of the alternator
side arm?
a. Yes; change the tensioner assembly and accessory drive belt.
b. No; Go to step 6.
6. Using the appropriate tool, rotate the tensioner through its travel. Does the tensioner move with smooth resistance
without binding or sticking?
a. Yes; Go to step 7.
b. No; replace tensioner assembly and accessory drive belt.
NOTE: A mechanic's stethoscope is useful when inspecting the bearings in the pulleys.
7. Inspect the idler pulley bearings by rotating the pulleys to look for bearing slop or choppy feeling bearings. Does each
of the idler pulleys rotate freely?
a. Yes; Go to step 8.
b. No; replace the worn pulley(s) and accessory drive belt as necessary.
8. Inspect the accessory pulleys for free rotation, damage, and excessive wear. Do any of the pulleys or the belt show
signs of damage?
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All information subject to change without notice.
Copyright © 2014 DETROIT DIESEL CORPORATION 2 31-14
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a. Yes; replace the damaged pulley and the accessory drive belt.
b. No; Go to step 9.
9. Check the belt wear pattern on all idler pulleys. The wear pattern should be centered across each pulley surface.
a. If the belt wear pattern is incorrect, inspect components for misalignment (parallel and angular)(A). Replace
components and accessory drive belt as necessary.
b. If the belt wear pattern is correct, the components are in proper alignment (B).
All information subject to change without notice.
2 31-14 Copyright © 2014 DETROIT DIESEL CORPORATION
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