Chevrolet Silverado / GMC Sierra. Manual

DRIVE BELT RUMBLING AND VIBRATION DIAGNOSIS

Diagnostic Aids

The accessory drive components can have an affect on engine vibration. Vibration from the
engine operating may cause a body component or another part of the vehicle to make rumbling
noise. Vibration can be caused by, but not limited to the air conditioning (A/C) system over
charged, the power steering system restricted or the incorrect fluid, or an extra load on the
generator. To help identify an intermittent or an improper condition, vary the loads on the
accessory drive components.

The drive belt may have a rumbling condition that can not be seen or felt. Sometimes replacing
the drive belt may be the only repair for the symptom.

If replacing the drive belt, completing the diagnostic table, and the noise is only heard when the
drive belts are installed, there might be an accessory drive component with a failure. Varying the
load on the different accessory drive components may aid in identifying which component is
causing the rumbling noise.

Test Description

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

2: This test is to verify that the symptom is present during diagnosing. Other vehicle
components may cause a similar symptom.

3: This test is to verify that one of the drive belts is causing the rumbling noise or vibration.
Rumbling noise may be confused with an internal engine noise due to the similarity in the
description. Remove only one drive belt at a time if the vehicle has multiple drive belts.

Inspect for the correct pulley size.
Did you find and correct the condition?

Go to Step 20

Go to Diagnostic
Aids

Replace the bent pulley.
Did you complete the repair?

Go to Step 20

Go to Step 19

Replace the drive belt. Refer to Drive Belt
Replacement - Accessory or Air
Conditioning Compressor Belt
Replacement .
Did you complete the repair?

Go to Step 20

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 - 4.3L - Sierra & Silverado

When removing the drive belts the water pump may not be operating and the engine may
overheat. Also DTCs may set when the engine is operating with the drive belts removed.

4: Inspecting the drive belts is to ensure that they are not causing the noise. Small cracks
across the ribs of the drive belt will not cause the noise. Belt separation is identified by the
plys of the belt separating and may be seen at the edge of the belt or felt as a lump in the
belt.

5: Small amounts of pilling is normal condition and acceptable. When the pilling is severe
the drive belt does not have a smooth surface for proper operation.

9: Inspecting of the fasteners can eliminate the possibility that the wrong bolt, nut, spacer,
or washer was installed.

11: This step should only be performed if the water pump is driven by the drive belt. Inspect
the water pump shaft for being bent. Also inspect the water pump bearings for smooth
operation and excessive play. Compare the water pump with a known good water pump.

12: Accessory drive component brackets that are bent, cracked, or loose may put extra
strain on that accessory component causing it to vibrate.

Step

Action

Yes

DEFINITION: The following items are indications of drive belt rumbling:

A low pitch tapping, knocking, or thumping noise heard at or just above idle.

Heard once per revolution of the drive belt or a pulley.

Rumbling may be caused from:

Pilling, the accumulation of rubber dust that forms small balls (pills) or strings in
the drive belt pulley groove

The separation of the drive belt

A damaged drive belt

DEFINITION: The following items are indications of drive belt vibration:

The vibration is engine-speed related.

The vibration may be sensitive to accessory load.

NOTE:

Refer to Belt Dressing Notice .

Did you review the Drive Belt Symptom
operation and perform the necessary
inspections?

Go to Step 2

Go to Symptoms
- Engine
Mechanical

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

Verify that there is a rumbling noise or that the
vibration is engine related.
Does the engine make the rumbling noise or
vibration?

Go to Step 3

Go to Diagnostic
Aids

1. Remove the drive belt.

2. Operate the engine for no longer than 30-

40 seconds.

3. Repeat this test if necessary by removing

the remaining belt(s).

Does the rumbling or vibration still exist?

IMPORTANT:

If the engine has multiple drive belts, remove
the belts one at a time and perform the test
below each time a belt is removed.

Go to Symptoms
- Engine
Mechanical or
Vibration
Analysis -
Engine

Go to Step 4

Inspect the drive belts for wear, damage,
separation, sections of missing ribs, and debris
build-up.
Did you find any of these conditions?

Go to Step 7

Go to Step 5

Inspect for severe pilling of more than 1/3 of
the drive belt pulley grooves.
Did you find severe pilling?

Go to Step 6

Go to Step 7

1. Clean the drive belt pulleys using a

suitable wire brush.

2. Reinstall the drive belts. Refer to Drive

Belt Replacement - Accessory or Air
Conditioning Compressor Belt
Replacement .

Did you correct the condition?

Go to Step 8

Go to Step 7

Install a new drive belt. Refer to Drive Belt
Replacement - Accessory or Air
Conditioning Compressor Belt
Replacement .
Did you complete the replacement?

Go to Step 8

Go to Step 9

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

System OK

Go to Step 9

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

DRIVE BELT FALLS OFF AND EXCESSIVE WEAR DIAGNOSIS

Diagnostic Aids

The drive belt may have a rumbling condition that can not be seen or felt. Sometimes replacing
the drive belt may be the only repair for the symptom.

Test Description

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

Inspect for improper, loose or missing fasteners.
Did you find any of these conditions?

Go to Step 10

Go to Step 11

1. Tighten any loose fasteners. Refer to

Fastener Tightening Specifications .

2. Replace improper or missing fasteners.

Did you complete the repair?

NOTE:

Refer to Fastener Notice .

Go to Step 13

Go to Step 11

Inspect for a bent water pump shaft. Refer to
Water Pump Replacement (LU3) .
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 - 4.3L - Sierra & Silverado

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Chevrolet Silverado / GMC Sierra. Manual - part 14