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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 Transmission/Transaxle 🢒 Manual Transmission - ZF S6-650 🢒 Transmission Fluid Leak Diagnosis

Diagnostic Aids

Using the incorrect type of transmission fluid may affect the sealing ability of the seals. Ensure the use of the correct type of transmission fluid. The incorrect type of sealer may not be compatible with the transmission fluid or may not have the correct characteristics for sealing the affected components. Ensure the use of the correct type of sealers. Refer to Sealers, Adhesives, and Lubricants in Manual Transmission - ZF S6-650 Unit Repair.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Use an approved method to clean the transmission to ensure the leak location is correctly identified. If using a powder method or dye method ensure the products are compatible with the transmission fluid.

Step

Action

Yes

No

DEFINITION: Visible sign of the transmission fluid leaking from the transmission.

1

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

Go to Step 2

Go to Symptoms - Manual Transmission

2
  1. Inspect for the transmission fluid level higher than the recommended level. Refer to Transmission Fluid Replacement .
  2. Adjust the transmission level if incorrect.

Was the transmission fluid level too high?

Go to Step 26

Go to Step 3

3

Inspect the transmission vent for a blockage.

Is the transmission vent blocked?

Go to Step 4

Go to Step 5

4

Repair or replace the transmission vent. Refer to Transmission Front Case Disassemble and Transmission Front Case Assemble in Manual Transmission - ZF S6-650 Unit Repair.

Did you find and repair the condition?

Go to Step 26

Go to Step 5

5

Verify the location of the leak.

  1. Clean the transmission assembly.
  2. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.
  3. Visual inspect or use the powder method or dye and black light method to locate the leak.

Is the leak occurring at the drain or fill plug?

Go to Step 6

Go to Step 7

6

Replace the drain or fill plug. Refer to Transmission Fluid Replacement .

Did you find and repair the condition?

Go to Step 26

Go to Diagnostic Aids

7

Is the leak at the transmission output shaft seal?

Go to Step 8

Go to Step 9

8

Remove the output shaft seal and inspect for the following conditions:

    • Damaged or worn seal
    • Damaged seal bore
    • Improper installation
    • Cracks in the component
    • Propeller shaft yoke sealing surface for being scratched, nicked, damaged, or worn
    • Loose or worn bearing causing excessive seal wear
    • Yoke flange nut loose

Refer to Transmission Output Shaft Seal Replacement .

Did you find and repair the condition?

Go to Step 26

Go to Diagnostic Aids

9

Is the leak at the shift lever area?

Go to Step 10

Go to Step 11

10
  1. Inspect the shift control lever lower boot for damage.
  2. Inspect for loose shift control lever mounting bolts.
  3. Remove the shift control lever. Refer to Shift Lever Assembly Replacement .
  4. Replace the shift control lever lower boot, if damaged.
  5. Inspect the shift control lever sealing surfaces for being scratched, nicked or damaged.

Did you find and repair the condition?

Go to Step 26

Go to Diagnostic Aids

11

Is the leak at the front of the transmission?

Go to Step 12

Go to Step 14

12
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Remove the clutch actuator cylinder.
  3. Inspect for the leak at the input shaft seal.
  4. Inspect for the following if the input shaft seal is leaking:
    5. • Damaged or worn seal
    • Damaged seal bore
    • Improper installation
    • Cracks in the component
    • Input shaft sealing surface for being scratched, nicked, damaged, or worn
    • Loose or worn bearing causing excessive seal wear
  5. Replace the input shaft seal if leaking. Refer to Transmission Input Shaft Seal Replacement .

Did you find and repair the condition?

Go to Step 26

Go to Step 13

13
  1. Inspect the case for cracks or porosity.
  2. Replace the transmission front case half if it is faulty. Refer to Transmission Disassemble in Manual Transmission - ZF S6-650 Unit Repair.

Did you find and repair the condition?

Go to Step 26

Go to Diagnostic Aids

14

Is the leak at the vehicle speed sensor (VSS)?

Go to Step 15

Go to Step 16

15
  1. Remove the VSS. Refer to Vehicle Speed Sensor Replacement .
  2. Inspect for the following:
    3. • Cut or damaged O-ring seal
    • VSS over tightened causing deformation in the VSS
    • VSS bore scratched or damaged

Did you find and repair the condition?

Go to Step 26

Go to Step 1

16

Is the leak at the backup lamp switch?

Go to Step 17

Go to Step 18

17
  1. Remove the backup light switch. Refer to Backup Lamp Switch Replacement .
  2. Inspect for the following:
    3. • Cross threaded or damaged threads
    • Insufficient sealant
    • Leaking switch
    • Improper installation

Did you find and repair the condition?

Go to Step 26

Go to Step 1

18

Is the leak at the shift shaft detent sleeve?

Go to Step 19

Go to Step 20

19
  1. Remove the shift shaft detent sleeve. Refer to Transmission Disassemble and Transmission Assemble in Manual Transmission - ZF S6-650 Unit Repair.
  2. Inspect for the following:
    3. • Cross threaded or damaged threads
    • Insufficient sealant
    • Cracked sleeve or case
    • Improper installation

Did you find and repair the condition?

Go to Step 26

Go to Step 1

20

Is the leak at the power take off (PTO) or PTO access cover?

Go to Step 21

Go to Step 22

21
  1. Remove the PTO, if equipped, following the PTO manufacturers instruction.
  2. Remove the PTO access cover.
  3. Inspect for the following:
    4. • Loose fasteners
    • Damaged or missing gasket
    • Insufficient sealant on the bolts
    • Damaged mounting threads
    • Sealing surface for being scratched, nicked, damaged, or worn

Did you find and repair the condition?

Go to Step 26

Go to Step 1

22

Is the leak at the sealing flanges of the transmission cases?

Go to Step 23

Go to Step 24

23
  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 sealing surfaces. Refer to Transmission Case Cleaning and Inspection in Manual Transmission - ZF S6-650 Unit Repair.

Did you find and repair the condition?

Go to Step 26

Go to Step 24

24

Is the leak coming from a crack or porosity in the transmission case ?

Go to Step 25

Go to Diagnostic Aids

25
  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. Replace the faulty case. Refer to Transmission Front Case Assemble or Transmission Intermediate Case Assemble or Transmission Rear Case Assemble in Manual Transmission - ZF S6-650 Unit Repair.

Did you find and repair the condition?

Go to Step 26

Go to Diagnostic Aids

26

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 1