GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 GMC C Sierra - 2WD 🢒 Transmission/Transaxle 🢒 Manual Transmission - ZF S6-650 🢒 Transmission Clunk on Acceleration or Deceleration

Diagnostic Aids

All manual transmissions have gear play that might cause a clunk. If the transmission is suspected of causing the clunk, compare it with a similar vehicle. An internal clunk in the transmission is usually caused by wear between 2 components, or from improper assembly, which would also cause other symptoms.

Test Description

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

  1. This step inspects for the transfer case causing the clunk. Shift the transfer case into another mode. If the transmission is causing the clunk, there is not be a change.

    2.

  2. This step inspects for the dual mass flywheel causing the clunk. A clunk from the dual mass flywheel would also be present in neutral.

Step

Action

Yes

No

DEFINITION: A clunk is heard and/or felt on acceleration or deceleration.

1

Did you review the Symptoms - Manual Transmission and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Manual Transmission

2

Inspect the engine mounts for being loose or damaged. Refer to Engine Mount Inspection in Engine Mechanical - 6.6L or Engine Mount Inspection in Engine Mechanical - 8.1L.

Did you find and repair the condition?

Go to Step 13

Go to Step 3

3

Inspect the transmission mounts for being loose or damaged. Refer to Transmission Rear Mount Replacement .

Did you find and repair the condition?

Go to Step 13

Go to Step 4

4

Inspect the transmission to engine fasteners for being loose or missing. Refer to Fastener Tightening Specifications .

Did you find and repair the condition?

Go to Step 13

Go to Step 5

5

Inspect the exhaust hanger mounting bracket on the transmission for being loose or for missing fasteners. Refer to Exhaust Hanger Mounting Bracket Replacement in Engine Exhaust.

Did you find and repair the condition?

Go to Step 13

Go to Step 6

6

Inspect the driveline for causing the clunk. Refer to Diagnostic Starting Point - Propeller Shaft in Propeller Shaft.

Did you find and repair the condition?

Go to Step 13

Go to Step 7

7

Is the vehicle equipped with a transfer case?

Go to Step 8

Go to Step 10

8

Shift the transfer case into 4HI.

Is the clunk still present?

Go to Step 10

Go to Step 9

9

Inspect the transfer case for causing the clunk. Refer to Diagnostic Starting Point - Transfer Case in Transfer Case - NVG 246-NP8 or Diagnostic Starting Point - Transfer Case in Transfer Case - NVG 261-NP2.

Did you find and repair the condition?

Go to Step 13

Go to Step 10

10

Is the vehicle equipped with the 6.6L diesel engine?

Go to Step 11

Go to Step 12

11

Inspect the dual mass flywheel. Refer to Engine Flywheel Replacement in Engine Mechanical - 6.6L.

Did you find and repair the condition?

Go to Step 13

Go to Step 12

12
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Disassemble the transmission. Refer to Transmission Disassemble in Manual Transmission - ZF S6-650 Unit Repair.
  3. Inspect the following transmission components that could be causing the clunk:
    4. • The mainshaft bearing preload
    • The countershaft bearing preload
    • Worn speed gear teeth
    • Worn countershaft gear teeth
    • Worn synchronizer sleeve to hub
    • Worn thrust washers and thrust surfaces on the speed gears or mainshaft

Did you find and repair 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 1