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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 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 cannot 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.

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

    2.

  2. 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. 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.

    3.

  3. 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 our felt as a lump in the belt.

    4.

  4. 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.

    5.

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

    6.

  6. 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.

    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

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

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.

1

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

Go to Step 2

Go to Symptoms - Engine Mechanical : LE5 or LE9

2

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

3

  1. Remove the drive belt.

    2. 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.

  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?

Go to Symptoms - Engine Mechanical : LE5 or LE9

or

Vibration Analysis - Engine

Go to Step 4

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

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

6
  1. Clean the drive belt pulleys using a suitable wire brush.
  2. Reinstall the drive belts. Refer to Drive Belt Replacement : LE5 or LE9 .

Did you correct the condition?

Go to Step 8

Go to Step 7

7

Install a new drive belt. Refer to Drive Belt Replacement : LE5 or LE9 .

Did you complete the replacement?

Go to Step 8

Go to Step 9

8

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 9

9

Inspect for improper, loose or missing fasteners.

Did you find any of these conditions?

Go to Step 10

Go to Step 11

10

    Caution: Refer to Fastener Caution in the Preface section.

  1. Tighten any loose fasteners. Refer to Fastener Tightening Specifications : LE5 or LE9 .
  2. Replace improper or missing fasteners.

Did you complete the repair?

Go to Step 13

Go to Step 11

11

Inspect for a bent water pump shaft. Refer to Water Pump Replacement : L4  → LNQ  → LF1 .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

12

Inspect for bent or cracked brackets.

Did you find and correct the condition?

Go to Step 13

Go to Diagnostic Aids

13

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3

   


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