Posted by PeteL on July 02, 01 at 10:32:38:
In Reply to: K2500 99 problems and TSB info posted by Sean on July 02, 01 at 09:55:55:
Front Wheels Slipping with Vehicle in Four WHeel
Drive (Replace Transfer Case Clutch Plates and Front
Drive Axle Lubricant) #99-04-21-003B
Front Wheels Slipping with Vehicle in Four Wheel Drive (Replace Transfer Case Clutch Plates and Front Drive Axle
Lubricant)
1999-2001 Chevrolet and GMC K and T Models (Silverado, Sierra, Blazer, Envoy, Jimmy)
with NV236/246 Transfer Case (RPO NP8)
This bulletin is being revised to correct a part number in the Parts Information section. Please discard Corporate Bulletin
Number 99-04-21-003A (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 (in Canada, use 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® lll 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 ll) Transfer Case fluid, P/N 12378508 (in Canada,
use P/N 10953626).
9.Install the transfer case fill plug. Tighten
Tighten the fill plug to 20 N·m (15N·mlbN·mft).
10.Change the front drive axle lubricant to synthetic axle lubricant, P/N 12378261 (in Canada, use 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.
Parts Information
P/N
Description
Qty
12378261 (In Canada use 10953455)
SAE 75W-90 Synthetic Axle Lubricant (K, T Models)
2
12378508 (In Canada use 10953626)
Automatic (Auto Trac) Transfer Case Fluid (K, T Models)
2
12472603
Bolt, Transfer Case (K Models)
17
12472603
Bolt, Transfer Case (T Models)
13
12473054
Plate, Transfer Case Pressure - Friction (K Models)
10
12473054
Plate, Transfer Case Pressure - Friction (T Models)
8
12547608
Plate, Transfer Case Pressure - Steel (K Models)
9
12547608
Plate, Transfer Case Pressure - Steel (T Models)
7
12547466
Seal, Frt. Input Gear Oil (K, T Models)
1
12547656
Seal, Frt. Output Shaft Oil (K, T Models)
1
12547638
Seal, Rear Output Shaft (K, T Models)
1
12474121
Shim Kit, Transfer Case (K, T Models)
1
12473057
Stud, Transfer Case (T Models)
4
Parts are currently available from GMSPO.
Warranty Information
For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
K4400
Transfer Case Assembly - Recondition (Incl. R&R)
4.0 hrs
Add
w/Transfer Case Skid Plate
0.2 hr
Add
w/Front Differential Skid Plate
0.2 hr
In Other Labor Hours, add 0.2 hr for Draining and Refilling Front drive axle lubricant. Authorization is required.