GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Engine 🢒 Engine Mechanical - 7.8L 🢒 Drive Belt Vibration Diagnosis

Diagnostic Aids

The accessory drive components can have an affect on engine vibration. Such as but not limited to the A/C system over charged or an extra load on the generator. To help identify an intermittent or an improper condition, vary the loads on the accessory drive components.

Test Description

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

  1. This test is to verify that the symptom is present during diagnosing. Other vehicle components may cause a similar symptom such as the exhaust system, or the drivetrain.

    2.

  2. This test is to verify that the drive belt or accessory drive components may be causing the vibration. When removing the drive belt the water pump will not be operating and the engine may overheat. Also DTCs may set when the engine is operating with the drive belt removed.

    3.

  3. The drive belt may cause a vibration. While the drive belt is removed this is the best time to inspect the condition of the belt.

    4.

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

    5.

  5. Inspect the engine cooling fan for bent, twisted, loose, or cracked blades. Inspect the fan clutch for smoothness, ease of turning. Inspect for a bent fan shaft or bent mounting flange.

    6.

  6. Inspect the water pump shaft for being bent. Also inspect the water pump bearings for smoothness and excessive play. Compare the water pump with a known good water pump.

    7.

  7. 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

No

Notice: Refer to Belt Dressing Notice in the Preface section.

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

    • The vibration is engine-speed related.
    • The vibration may be sensitive to accessory load.

1

Verify that the vibration is engine related.

Does the engine make the vibration?

Go to Step 2

System OK

2

  1. Remove the drive belt. Refer to Drive Belt Replacement .
  2. Operate the engine for no longer than 30 to 40 seconds.

Does the engine still make the vibration?

Go to Vibration Analysis - Engine in Vibration Diagnosis and Correction

Go to Step 3

3

Inspect the drive belt for wear, damage, debris build-up and missing drive belt ribs.

Did you find any of these conditions?

Go to Step 4

Go to Step 5

4

Install a new drive belt. Refer to Drive Belt Replacement .

Did you complete the replacement?

Go to Step 10

--

5

Inspect for improper, loose or missing fasteners.

Did you find any of these conditions?

Go to Step 6

Go to Step 7

6
    • Tighten any loose fasteners.
    • Replace improper or missing fasteners. Refer to Fastener Tightening Specifications .

Did you complete the repair?

Go to Step 10

--

7

Inspect for damaged fan blades or bent fan clutch shaft, if the fan is belt driven. Refer to Fan Clutch Replacement in Engine Cooling.

Did you find and correct the condition?

Go to Step 10

Go to Step 8

8

Inspect for a bent water pump shaft. Refer to Water Pump Replacement in Engine Cooling.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

9

Inspect for bent or cracked brackets.

Did you find and correct the condition?

Go to Step 10

Go to Step 2

10

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2