Transfer Case

[LeftyDB58]

I have a 2000 LT Z71 Extended Cab with 77,000 miles. Noticed when turning that the transmission felt like it slipped and didn't catch. When I took it to the dealer they said my Auto4WD was engaged - news to me. I rarely use this feature or standard 4 Wheel Drive HI or LO. Dealer checked the transfer case and said it needed to be rebuilt. Anyone else experience this problem at 77K or 4 years?

[budhayes3]

I never experienced this problem but read a tsb that might help:

4X4 System - Front Wheels Slip in Four Wheel Drive

 

Bulletin No.: 99-04-21-003C

 

Date: August 20, 2003

 

TECHNICAL

 

Subject:

Front Wheels Slipping with Vehicle in Four Wheel Drive (Replace Transfer Case Clutch Plates and Front Drive Axle Lubricant)

 

Models:

1999-2001 Chevrolet Blazer, Silverado

1999-2001 GMC Envoy, Jimmy, Sierra

with NV2361246 Transfer Case (RPO NP8)

 

Supercede:

 

This bulletin is being revised to correct two part numbers in the Parts Information section. Please discard Corporate Bulletin Number 99-04-21-003B (Section 04 - Driveline/Axle).

 

Condition

 

Some owners may comment on a slipping type condition at the front wheels while the vehicle is in four wheel drive (4WD).

 

Cause

 

When the vehicle is driven extensively in low temperatures (-12°C (10°F) or below), slipping may occur when the vehicle is in the 2 HI mode. This occurs because the transfer case clutch pack does not have enough torque capacity to overcome the viscosity of the front axle lubricant. The friction generated by the slipping clutch discs may cause premature wear of the clutch pack assembly.

 

Correction

 

Overhaul the transfer case and replace the clutch plates on affected vehicles. Replace the lubricant in the front drive axle with synthetic axle lubricant, P/N 12378261 (Canadian P/N 10953455). Use the following procedure and the part numbers listed below.

 

1. Remove the transfer case drain plug. If the plug is difficult to remove or stripped, refer to Corporate Bulletin Number 99-04-21-001.

 

2. Drain the fluid from the transfer case. Refer to the Transfer Case sub-section of the applicable Service Manual.

 

3. Remove the transfer case assembly from the vehicle. Refer to the Transfer Case sub-section of the applicable Service Manual.

 

Important: The NV236 transfer case (T Models) uses 8 friction and 7 steel plates. The NV246 transfer case (K Models) uses 10 friction and 9 steel plates.

 

4. Overhaul the transfer case and replace the clutch plates. Refer to the applicable Transmission/Transaxle and Transfer Case Unit Repair Manual.

 

5. Install the transfer case assembly into the vehicle. Refer to the Transfer Case sub-section of the applicable Service Manual.

 

6. Install the transfer case drain plug.

 

Tighten

 

Tighten the drain plug to 20 N.m (15 lb ft).

 

Important: Do not use standard DEXRON®III fluid. Performance of the transfer case may be impaired.

 

7. Remove the transfer case fill plug. If the plug is difficult to remove or stripped, refer to Corporate Bulletin Number 99-04-21-001.

 

8. Fill the transfer case with 1.9 L (2 qts) of Automatic (AUTO-TRAK II) Transfer Case fluid, P/N 12378508 (Canadian P/N 10953626).

 

9. Install the transfer case fill plug.

 

Tighten

 

Tighten the fill plug to 20 N.m (15 lb ft).

 

10. Change the front drive axle lubricant to synthetic axle lubricant, P/N 12378261 (Canadian P/N 10953455). Fill the drive axle with 1.66 L (1.76 qts) for K Truck or 1.20 L (1.27 qts) for T Truck. Refer to the Front Drive Axle sub-section of the applicable Service Manual.

 

Here's another one:

 

Drivetrain - Noise/Vibration/Leaks/Slipping in 4WD

 

File In Section: 04 - Driveline Axle

 

Bulletin No.: 02-04-21-005A

 

Date: February, 2003

 

TECHNICAL

 

Subject:

Slips in 4-Wheel Drive, Noise, Vibration, Leaks, Hot Odor (Diagnose and Repair Front Differential and/or Transfer Case)

 

Models:

1999-2000 Cadillac Escalade

1998-2002 Chevrolet S-10, Silverado, Blazer, Suburban, Tahoe

2002 Chevrolet Avalanche

1998-2002 GMC Sierra, Sonoma, Jimmy, Suburban, Yukon, Yukon XL

with Autotrak Transfer Case (RPO NP8) (Selector Pad on Instrument Panel Must Have Auto 4WD, 4HI, 4L0, and 2HI Selections)

 

This bulletin is being revised to incorporate changes to the diagnostic procedure. Please discard Corporate Bulletin Number 02-04-21-005 (Section 04 - Driveline Axle).

 

Condition

 

Some customers may comment on any of the following conditions:

 

^ Slips in 4WD

^ Noise

^ Vibration

^ Leaks

^ Hot odor

 

 

Cause

 

The front axle may have excessive preload in the pinion or carrier bearings or may be locked up not allowing the pinion to rotate freely. Vehicles with a NVG 236 or 246 transfer case (RPO NP8) have a preload in the clutch pack of the transfer case that supplies torque to the front driveshaft at all times. The front and rear driveshafts should be rotating at approximately the same speed (the front driveshaft display on the Tech 2® may be slightly higher but never less than the rear).

 

Diagnostic Tips

 

1. Position the vehicle on the hoist and raise the hoist until all four wheels are off the ground.

 

2. Connect the Tech 2® to the vehicle.

 

3. Start the engine.

 

4. Select the following screens on the Tech 2®:

 

^ F0; Diagnostics

 

^ Vehicle model year

 

^ LD truck; MPV; Incomplete

 

^ F0; Powertrain

 

^ Vehicle engine

 

^ 4-speed automatic

 

^ 2 speed Active

 

^ F1; Data Display

 

^ F2; ATC Data Display

 

^ F0; Transfer Case Data

 

 

5. Select 2 HI with the transfer case selector switch.

 

6. Apply the service brake and move the transmission selector lever in any forward gear.

 

7. Release the service brake.

 

8. Observe the front and rear propeller shaft speeds displayed on the Tech 2®. The front and rear driveshafts should be rotating at approximately the same speed (the front driveshaft display on the Tech 2® may be slightly higher but never less than the rear). If they are not, skip to the Correction section below. If the driveshaft speeds are approximately the same, diagnose for other conditions that may be causing the concern. If the vehicle is stationary, the front propeller shaft should not rotate freely. It may take up to 54 N.m (40 lb ft) of torque to turn the front output shaft of the transfer case. If the front axle for any reason does not allow the front propeller shaft to spin while in the 2WD setting, the clutch pack in the transfer case will overheat because of the speed difference (slip) across the clutch pack between the stationary front driveshaft and the rotating rear driveshaft.

 

 

Correction

 

For vehicles with the NPB transfer case option (Autotrak with push-button selections for 2HI, Auto 4WD, 4HI, 4L0 and Neutral) only, when a vehicle comes in for issues with the front axle, the transfer case should also be inspected for overheating by inspecting for burned fluid or a free rotating front driveshaft. In addition to correcting front axle concerns, necessary repairs should be made to the transfer case.

 

Hope this helps

[Blue-2001-Z71]

Sounds like that's what they want to do. Sucks that it happened at such low mileage.

[LeftyDB58]

Thanks for the information, it's more than I received from the local dealer or Chevrolet.

[concours]

Thank you kindly... This is exactly what I've been looking for. My front diff gets too hot to touch after highway running, (Mobil 1 lube inside) and the t-case is hot as well. This all started after I exchanged the Autotrak fluid in the case as part of routine preventative maintenance. I am planning on exploratory surgery on my front diff. next week. It's reassuring to hear I'm on the right path anyway. My symptoms are noise/vibration from the front driveline and the super hot front diff. , it's pushing the fluid out the overflow tube. Anyone else have experiences with this they'd like to share?