Transfer Case Leak Diagnosis

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Cause	Correction
DEFINITION: A visible indication of an external fluid leak from the transfer case. Review the Symptoms - Transfer Case and perform the necessary inspections.
Drain plug or fill plug leak	Inspect for the correct sealer and the correct amount of sealer on the plugs. Install the plugs correctly. Refer to Transfer Case Fluid Replacement .
Access hole plug leaking	Replace the access hole plug or seal with RTV sealer.
Vehicle speed sensor leaking	Remove the vehicle speed sensor (VSS). Inspect for the following conditions: Cross threaded Cut or damaged O-ring seal VSS over tightened causing deformation in the VSS Refer toTransfer Case Speed Sensor Replacement . Replace the VSS O-ring seal if faulty. Refer to Transfer Case Speed Sensor Replacement . Replace the VSS if faulty. Refer to Transfer Case Speed Sensor Replacement .
Rear output shaft seal leaking	Inspect for the following conditions: Overfilled or improper transfer case fluid Blocked vent Seal improperly installed, worn or damaged Seal bore damaged or cracked Rear output shaft bushing for excessive wear Slip yoke seal surface for wear or pitting Repair or replace the following components if found faulty: Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement . Clean or properly route the vent hose. Replace the slip yoke if the surface could cause leakage. Refer to Propeller Shaft Replacement - One Piece or Propeller Shaft Replacement - Two Piece in Propeller Shaft. Replace the rear bushing if worn. Refer to Transfer Case Output Shaft Seal Replacement - Rear . Replace the rear case half if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair. Replace the rear output shaft seal. Refer to Transfer Case Output Shaft Seal Replacement - Rear .
Front output shaft seal leaking	Inspect for the following conditions: Overfilled or improper transfer case fluid Blocked vent Seal improperly installed, worn or damaged Seal bore damaged or cracked Leaking cup plug in the front output shaft Repair or replace the following components if found faulty: Adjust or replace the transfer case fluid. Refer to Transfer Case Fluid Replacement . Clean or properly route the vent hose. Replace the front case half if the seal bore is damaged. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair. Replace the front output shaft seal. Refer to Transfer Case Output Shaft Seal Replacement - Front . Replace the cup plug in the front output shaft if it is leaking. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair.
Shift shaft detent lever seal leaking	Replace the shift shaft detent lever seal. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair.
Leaking at the vent tube	Transfer case overfilled Inspect for the correct transfer case fluid level. Refer to Transfer Case Fluid Replacement . Inspect the transmission fluid level. Refer to Transmission Fluid Checking Procedure in Automatic Transmission - 4L80-E or Transmission Fluid Checking Procedure in Automatic Transmission - Allison. If the transmission fluid level is low and the transfer case fluid level is too high, replace the transfer case input shaft seal. Refer to Transfer Case Input Shaft Seal Replacement . Inspect for the following conditions: Seal improperly installed, worn or damaged Seal bore damaged or cracked Input shaft seal surface worn, grooved or damaged Replace a damaged or broken vent and seal the vent tube with the correct sealer. Refer to Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair.
Transfer case to adapter leak	Inspect for the following conditions: Loose mounting fasteners Gasket faulty The transfer case input shaft seal leaking The cup bearing in the input shaft leaking Repair or replace the following components if found faulty: Replace the transfer case input shaft seal. Refer to Transfer Case Input Shaft Seal Replacement . Inspect for the following conditions: Seal improperly installed, worn or damaged Seal bore damaged or cracked Input shaft seal surface worn, grooved or damaged Replace the cup bearing in the input shaft if it is leaking. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair. Repair or replace the loose fasteners. Refer to Transfer Case Adapter Replacement . Replace the transfer adapter case gasket. Refer to Transfer Case Adapter Replacement .
Case leaking	Inspect for a cracked case or case porosity. Inspect for the oil pump wear sleeve missing and the oil pump wearing a hole in the case. Refer to Transfer Case Disassemble in Transfer Case - NVG 263-NP1 Unit Repair. Replace the faulty case half. Refer to Transfer Case Disassemble and Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair.
Front case half to rear case half seam leak	Disassemble and seal the case halves. Refer to Transfer Case Assemble in Transfer Case - NVG 263-NP1 Unit Repair.