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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 19 (Manual Transmission - NV 3500 - Service) >> Diagnostic Information and Procedures >> Transmission Fluid Leak Diagnosis >> Test Description

Test Description

WARNING: This page is about a different variant/trim than selected.

The number below refers to step number on diagnostic table.

  1. 5:  Use an approved method to clean transmission to ensure leak location is correctly identified. If using a powder method or dye method ensure products are compatible with transmission fluid.
Transmission Fluid Leak Diagnosis

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 24  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 FRONT HOUSING DISASSEMBLE and FRONT HOUSING ASSEMBLE .
Did you find and repair the condition?		 Go to Step 24  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 24  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 is scratched, nicked, damaged, or worn
  • Loose or worn bearing causing excessive seal wear
  • Yoke flange nut loose

Refer to Transmission Housing Oil Seal Replacement - Rear (2WD)  or Transmission Housing Oil Seal Replacement - Rear (4WD) .
Did you find and repair the condition?		 Go to Step 24  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 scratched, nicked or damaged.
Did you find and repair the condition?		 Go to Step 24  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. Refer to Transmission Housing Oil Seal Replacement - Front .
  3. Inspect for the leak at the input shaft seal.
  4. Inspect for the following if the input shaft seal is leaking:
    • 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 Housing Oil Seal Replacement - Front .
Did you find and repair the condition?		 Go to Step 24  Go to Step 13 
13
  1. Inspect for a leak at the countershaft front bearing.
  2. Repair the leak at the countershaft front bearing. Refer to TRANSMISSION DISASSEMBLE and TRANSMISSION ASSEMBLE .
Did you find and repair the condition?		 Go to Step 24  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 (VSS) Replacement .
  2. Inspect for the following:
    • 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 24  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 lamp switch. Refer to Backup Lamp Switch Replacement .
  2. Inspect for the following:
    • Cross threaded or damaged threads
    • Insufficient sealant
    • Leaking switch
    • Improper installation
Did you find and repair the condition?		 Go to Step 24  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 .
  2. Inspect for the following:
    • Cross threaded or damaged threads
    • Insufficient sealant
    • Cracked sleeve or case
    • Improper installation
Did you find and repair the condition?		 Go to Step 24  Go to Step 1 
20 Is the leak at the sealing flanges of the transmission cases? Go to Step 21  Go to Step 22 
21
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Disassemble the transmission. Refer to TRANSMISSION DISASSEMBLE .
  3. Inspect the sealing surfaces. Refer to FRONT AND REAR HOUSINGS CLEANING AND INSPECTION .
Did you find and repair the condition?		 Go to Step 24  Go to Step 22 
22 Is the leak coming from a crack or porosity in the transmission case ? Go to Step 23  Go to Diagnostic Aids 
23
  1. Remove the transmission. Refer to Transmission Replacement .
  2. Disassemble the transmission. Refer to TRANSMISSION DISASSEMBLE .
  3. Replace the faulty case. Refer to FRONT HOUSING ASSEMBLE or REAR HOUSING ASSEMBLE .
Did you find and repair the condition?		 Go to Step 24  Go to Diagnostic Aids 
24 Operate the system in order to verify the repair.
Did you correct the condition?		 System OK Go to Step 1 
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