Synthetic in front diff

[tryn2lrn]

I thought I read that GM was putting synthetic oil in the front diffs in cold climate areas, but to do so required changing, I believe, the vent tube due to material incompatability. Has anyone changed the fluid to synth and had issues due to not changing the vent tube? Thanks

 

Is changing the venting difficult?

[budhayes3]

I read the 2 different TSB's also...first one said to switch to synth in the front diff to help prevent damage to the autotrak transfer case in colder climates. (viscous clutch can't overcome the dino gear oil and burns out). Second TSB said that using synthetic gear oil with RTV will cause leaks from the syn oil attacking the RTV.

 

I weighed it out and decided that I'd rather repair a leak than buy/rebuild my transfer case. I've been running the synthetic stuff in my front diff now for 2 years with no problems (knock on wood).

 

I'll locate the TSB's and post em up

 

P.S. I didn't change my vent tube...haven't heard of that...maybe I'll look for a TSB about that too.

[budhayes3]

Here we go:

 

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 that other one:

 

Drivetrain - Rear Axle Lubricant Compatibility & Usage

 

File in Section: 04 - Driveline Axle

 

Bulletin No.: 99-04-20-001

 

Date: June, 1999

 

INFORMATION

 

Subject:

Rear Axle Lubricant Compatibility and Usage

 

 

 

 

 

Models:

1999 Cadillac Escalade

1988-99 Chevrolet and GMC C/K, G Van and P1-3 Series Models

Built after the VIN Breakpoints (C/K) listed.

 

This bulletin is being revised to add the 1999 Model Year, VIN Breakpoint information, and additional text Please discard Corporate Bulletin Number 86-42-04 (Section 4 - Driveline/Axle).

 

 

 

 

 

This bulletin is being issued to inform dealers about the compatibility and usage of the new Fuel Efficient SAE 75W-90 Synthetic Axle Lubricant, GM P/N 12378261 (In Canada use P/N 10953455), with current axles, and with the non-synthetic axle lubricant, GM P/N 1052271 (In Canada use P/N 10950849), for the rear axles on the above light-duty trucks.

 

Testing has shown that the new synthetic lubricant will chemically attack the Room Temperature Vulcanizing (RTV) sealant. Use only the non-synthetic lubricant, P/N 1052271, in axles using RTV sealant (See 9.5 and 10.5 information below).

 

American Axle and Manufacturing (A.A.M.) has approved the use of the new Fuel Efficient SAE 75W-90 synthetic axle lubricant for rear axles with the following restrictions:

 

^ All 8.6 inch axles are compatible as originally built.

 

^ 9.5 inch axles on vehicles built prior to mid-February 1998 are NOT compatible because RTV sealant is used on the cover pans.

 

On vehicles built after mid-February 1998 and equipped with 9.5 inch rear axles, synthetic lubricant, P/N 12378261, can be used because the RTV was replaced with a gasket. Other mid-February changes to the 9.5 inch rear axles include a new cover pan and cover pan fasteners common to other axles.

 

Important : The new cover pan is not retrofittable to the housing of 9.5 inch axles on vehicles built prior to mid-February 1998. A new retrofit kit is available that will enable the use of synthetic lubricant for vehicles built after mid-February, 1998.

 

^ All 10.5 inch axles prior to March 3, 1999 are compatible if the axle shaft hub seal (RTV) is replaced with P/N 327739 gasket when changing to synthetic lubricant.

 

 

As a product improvement, this new lubricant has been released into 1999 current production C/K vehicles built after the above VIN breakpoints (Except HD3SOO models which use 75W-140 synthetic lubricant, P/N 12346140).

 

It is recommended that synthetic lubricant be used when changing rear axle lubricant for the following reasons:

 

^ Potential fuel economy

 

^ Lower operating temperature under severe usage conditions

 

Important :^ You do not need to wash/rinse any non-synthetic lubricant from the axle cavity when changing over to a synthetic lubricant. However, you should remove debris from the magnet and the bottom of the axle cavity whenever the axle fluid is changed.

 

^ On light-duty trucks equipped with locking differentials, do NOT use a limited-slip additive.

 

 

Parts Information

 

Parts are currently available from GMSPO.

 

................................................................................

.......................................

 

I'd like to see the info on the revised vent tube if anyone has it...part #'s ?

[Bish]

I thought I read that GM was putting synthetic oil in the front diffs in cold climate areas, but to do so required changing, I believe, the vent tube due to material incompatability.  Has anyone changed the fluid to synth and had issues due to not changing the vent tube?  Thanks

 

Is changing the venting difficult?

 

<{POST_SNAPBACK}>

 

 

 

I've been runing Mobil 1 in the front since 10K. I've got 140K now and never had a leak. Change it every 25K.

[tryn2lrn]

Thanks guys maybe I will take the leakage risk and switch.

[bigdogs]

Mine already had the white vent when the dealer did the fluid swap per the TSB, but I think even if you had to buy it, it is only $18 at GMDieselTech.com