GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Engine 🢒 Engine Electrical 🢒 Drive Belt Vibration Diagnosis

Diagnostic Aids

The accessory drive components can have an affect on engine vibration. An overcharged air conditioning (A/C) system, a power steering system restriction, or the incorrect fluid, or an extra load placed on the generator. To help identify an intermittent or an improper condition, vary the loads on the accessory drive components.

Test Description

The number(s) below refer to the step(s) on the diagnostic table.

  1. This test is to verify that the vibration 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. Remove the drive belt and operate the engine for a few seconds, this will verify if the vibration is engine related. With the drive belt removed the water pump will not operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated 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. Inspection of the fasteners can eliminate the possibility that a incorrect bolt, nut, spacer, or washer was installed.

    5.

  5. This step should only be performed if the fan is driven by the drive belt. Inspect the engine cooling fan for bent, twisted, loose, or cracked blades. Inspect the fan clutch for smooth operation. Inspect for a bent fan shaft or bent mounting flange.

    6.

  6. Inspect the water pump drive 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.

    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

Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Engine Mechanical

2

Verify that the vibration is engine related.

Does the engine make the vibration?

Go to Step 3

Go to Diagnostic Aids

3

  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 Diagnostic Starting Point - Vibration Diagnosis and Correction in Vibration Diagnosis and Correction

Go to Step 4

4

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

Were any of these conditions?

Go to Step 5

Go to Step 6

5

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

Did you complete the replacement?

Go to Step 11

--

6

Inspect for incorrect, loose, or missing fasteners.

Were any of these conditions?

Go to Step 7

Go to Step 8

7
  1. Replace the incorrect or missing fastener(s).
  2. Tighten any loose fasteners. Refer to Fastener Tightening Specifications .

Were the fasteners replaced and/or tightened?

Go to Step 11

--

8

Inspect for damaged fan blades or a bent fan clutch shaft.

Did you find and correct the condition?

Go to Step 11

Go to Step 9

9

Inspect for a bent water pump shaft.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

10

Inspect for bent or cracked accessory drive bracket(s).

Did you find and correct the condition?

Go to Step 11

--

11
  1. Clear any codes.
  2. Run the engine in order to verify the repair.

Does the vibration still exist?

--

System OK