Chevrolet Silverado / GMC Sierra. Service manual - part 410

DRIVE BELT FALLS OFF AND EXCESSIVE WEAR DIAGNOSIS

Diagnostic Aids

If the drive belt repeatedly falls off the drive belt pulleys, this is because of pulley misalignment.

An extra load that is quickly applied on released by an accessory drive component may cause the
drive belt to fall off the pulleys. Verify the accessory drive components operate properly.

If the drive belt is the incorrect length, the drive belt tensioner may not keep the proper tension
on the drive belt.

Excessive wear on a drive belt is usually caused by an incorrect installation or the wrong drive
belt for the application.

Minor misalignment of the drive belt pulleys will not cause excessive wear, but will probably
cause the drive belt to make a noise or to fall off.

Excessive misalignment of the drive belt pulleys will cause excessive wear but may also make the
drive belt fall off.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Tighten any loose fasteners. Refer to

Fastener Tightening Specifications.

2. Replace improper or missing fasteners.

Did you complete the repair?

Go to Step 13

Go to Step 11

Inspect for a bent water pump shaft. Refer to
Water Pump Replacement (LU3) or Water
Pump Replacement (LY6, L76 and L92) or
Water Pump Replacement (LH6, LY2,
LY5, and LMG) or Water Pump
Replacement (LMM) .
Did you find and correct the condition?

Go to Step 13

Go to Step 12

Inspect for bent or cracked brackets.
Did you find and correct the condition?

Go to Step 13

Go to Diagnostic
Aids

Operate the system in order to verify the repair.
Did you correct the condition?

System OK

Go to Step 3

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

2: This inspection is to verify the condition of the drive belt. Damage may of occurred to
the drive belt when the drive belt fell off. The drive belt may of been damaged, which
caused the drive belt to fall off. Inspect the belt for cuts, tears, sections of ribs missing, or
damaged belt plys.

4: Misalignment of the pulleys may be caused from improper mounting of the accessory
drive component, incorrect installation of the accessory drive component pulley, or the
pulley bent inward or outward from a previous repair. Test for a misaligned pulley using a
straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is
found refer to that accessory drive component for the proper installation procedure of that
pulley.

5: Inspecting the pulleys for being bent should include inspecting for a dent or other damage
to the pulleys that would prevent the drive belt from not seating properly in all of the pulley
grooves or on the smooth surface of a pulley when the back side of the belt is used to drive
the pulley.

6: Accessory drive component brackets that are bent or cracked will let the drive belt fall
off.

7: Inspection of the fasteners can eliminate the possibility that a wrong bolt, nut, spacer, or
washer was installed. Missing, loose, or the wrong fasteners may cause pulley misalignment
from the bracket moving under load. Over tightening of the fasteners may cause
misalignment of the accessory component bracket.

13: The inspection is to verify the drive belt is correctly installed on all of the drive belt
pulleys. Wear on the drive belt may be caused by mis-positioning the drive belt by one
groove on a pulley.

14: The installation of a drive belt that is too wide or too narrow will cause wear on the
drive belt. The drive belt ribs should match all of the grooves on all of the pulleys.

15: This inspection is to verify the drive belt is not contacting any parts of the engine or
body while the engine is operating. There should be sufficient clearance when the drive belt
accessory drive components load varies. The drive belt should not come in contact with an
engine or a body component when snapping the throttle.

Step

Action

Yes

DEFINITION: The drive belt falls off the pulleys or may not ride correctly on the
pulleys.DEFINITION: Wear at the outside ribs of the drive belt due to an incorrectly
installed drive belt.

NOTE:

Refer to Belt Dressing Notice .

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Did you review the drive belt symptom
operation and perform the necessary
inspections?

Go to Step 2

Go to Symptoms
- Engine
Mechanical

If diagnosing excessive wear, proceed to
step 13.

If diagnosing a drive belt that falls off,
inspect for a damaged drive belt.

Did you find the condition?

Go to Step 3

Go to Step 4

Install a new drive belt. Refer to Drive Belt
Replacement .
Does the drive belt continue to fall off?

Go to Step 4

System OK

Inspect for misalignment of the pulleys.
Did you find and repair the condition?

Go to Step 12

Go to Step 5

Inspect for a bent or dented pulley.
Did you find and repair the condition?

Go to Step 12

Go to Step 6

Inspect for a bent or a cracked bracket.
Did you find and repair the condition?

Go to Step 12

Go to Step 7

Inspect for improper, loose or missing fasteners.
Did you find loose or missing fasteners?

Go to Step 8

Go to Step 9

1. Tighten any loose fasteners. Refer to

Fastener Tightening Specifications.

2. Replace improper or missing fasteners.

Does the drive belt continue to fall off?

NOTE:

Refer to Fastener Notice .

Go to Step 9

System OK

Test the drive belt tensioner for operating
correctly. Refer to Drive Belt Tensioner
Diagnosis.
Does the drive belt tensioner operate correctly?

Go to Step 11

Go to Step 10

Replace the drive belt tensioner. Refer to Drive
Belt Tensioner Replacement .
Does the drive belt continue to fall off?

Go to Step 11

System OK

Inspect for failed drive belt idler and drive belt
tensioner pulley bearings.
Did you find and repair the condition?

Go to Step 12

Go to Diagnostic
Aids

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

DRIVE BELT TENSIONER DIAGNOSIS

Operate the system in order to verify the repair.
Did you correct the condition?

System OK

Go to Step 2

Inspect the drive belt for the proper installation.
Refer to Drive Belt Replacement .
Did you find this condition?

Go to Step 16

Go to Step 14

Inspect for the proper drive belt.
Did you find this condition?

Go to Step 16

Go to Step 15

Inspect for the drive belt rubbing against a
bracket, hose, or wiring harness.
Did you find and repair the condition?

Go to Step 17

Go to Diagnostic
Aids

Replace the drive belt. Refer to Drive Belt
Replacement .
Did you complete the replacement?

Go to Step 17

Operate the system in order to verify the repair.
Did you correct the condition?

System OK

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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