GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Kodiak C-Series (Conventional) C6/C7/C8 🢒 Transmission/Transaxle 🢒 Manual Transmission - Medium Duty 🢒 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 .

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 manual transmission symptoms 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 Check .
  2. Adjust the transmission level if incorrect.

Was the transmission fluid level too high?

Go to Step 25

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 the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

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 Oil Changing .

Did you find and repair the condition?

Go to Step 25

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. Refer to Rear Oil Seal Replacement .

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

Did you find and repair the condition?

Go to Step 25

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 the transmission manufacturer service manual.
  4. Replace the shift control lever lower boot if damaged.
  5. Inspect the shift control lever sealing surfaces for scratched, nicked or damaged.

Did you find and repair the condition?

Go to Step 25

Go to Diagnostic Aids

11

Is the leak at the front of the transmission?

Go to Step 12

Go to Step 15

12
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Inspect the front bearing retainer for leaking.
  3. Remove the bearing retainer. Refer to the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

Go to Step 13

13
  1. Inspect for the leak at the input shaft seal.
  2. Inspect for the following if the input shaft seal is leaking:
    3. • Damaged or worn seal
    • Damaged seal bore
    • Improper installation
    • Cracks in the component
    • Input shaft sealing surface is scratched, nicked, damaged, or worn
    • Loose or worn bearing causing excessive seal wear
  3. Replace the input shaft seal if leaking. Refer to the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

Go to Step 14

14
  1. Inspect the case for cracks or porosity.
  2. Replace the transmission case if it is faulty. Refer to the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

Go to Diagnostic Aids

15

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

Go to Step 16

Go to Step 17

16
  1. Remove the VSS. Refer to the transmission manufacturer service manual.
  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 25

Go to Step 1

17

Is the leak at the backup light switch?

Go to Step 18

Go to Step 19

18
  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 25

Go to Step 1

19

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

Go to Step 20

Go to Step 21

20
  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 is scratched, nicked, damaged, or worn

Did you find and repair the condition?

Go to Step 25

Go to Step 1

21

Is the leak at the sealing flanges of transmission cases?

Go to Step 22

Go to Step 23

22
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Disassemble the transmission. Refer to the transmission manufacturer service manual.
  3. Inspect the sealing surfaces. Refer to the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

Go to Step 23

23

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

Go to Step 24

Go to Diagnostic Aids

24
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Disassemble the transmission. Refer to the transmission manufacturer service manual.
  3. Replace the faulty case. Refer to the transmission manufacturer service manual.

Did you find and repair the condition?

Go to Step 25

Go to Diagnostic Aids

25

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 1