AWD Astro

I recently bought a used 2003 Asto van still under warranty. When I turn sharply at slow speeds I get a grinding/bumping noise form the wheels as they seem to be slipping on the concrete. If I go up a steep hill 10-15 mph I get a wump-wump noise like there are evenly spaced bumps in the road. If I go 35-40 it goes away. Should I be concerned?
Thank you for any advice in advance you may be able to provide.

we have a similar problem with our 2001 safari awd... the fluid in the transfer case is bad. We have had it replaced, only for it to go bad again. There is a known defect in the transfer case, and GM wont do anything about it.

I have the same problem with a 2000 I just recently bought. I was getting ready to replace the fluids. I had a different vehicle that I bought and the problem was the wrong gear oil in the differential. Does anyone no if these vehicles require a special gear oil or limited slip addative in the differentials.

I have a 2000 AWD Astro with the same problem I am getting ready to replace transfer case oil and was wondering if the differentials could be the culprit. Does anyone know if they require any addatives or special oils.

Hello,
I have a 2003 AWD and the rear end was slipping/clunking/dragging etc. the dealer informed me that the rear end and transfer case had to have the oil changed. The mechanic told me there was an internal service bulletin to change and flush the posi-rear diff and the transfer case from the factory regular gear lube to a new synthetic with a moly type booster.

It did solve the problem. maybe they should've put synthetic in from the factory?? Who woulda thought!

paul

Here is a service bulletin related to your problems. I tried it...so far so good (after about 3000 miles with the new fluid). The transfer case is easy to get to. Both plugs are easily accessable on the side of the case...just need a way to get the new oil in the side hole...bought a special gadget at Walmart for that.

Hope it helps....

Bulletin No.: 99-04-21-005B

Date: September, 2002

TECHNICAL

Subject:
Transfer Case Shudder
(Flush and Replace Transfer Case Fluid)

Models:
1999-2003 Chevrolet Astro (AWD)
1999-2003 GMC Safari (AWD)
1999-2001 Oldsmobile Bravada
with All-Wheel Drive (NV136) Transfer Case (RPO NP4)

This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 99-04-21-005A (Section 04 - Driveline Axle).

Condition

Some customers may comment about a vibration (shudder) during tight turning maneuvers on dry pavement at vehicle speeds less than 8 km/h (5 mph).

Cause

This condition may be caused by a slip-stick of the clutch plates in the transfer case clutch pack. On 1999 and newer models, the preload that is designed into the clutch pack may contribute to the condition. In addition, contamination of the fluid may interfere with the friction modifiers.

Correction

Flush and replace the transfer case fluid on affected vehicles using the following procedure and the part number listed below.

Perform the following diagnosis prior to flushing and replacing the transfer case fluid in order to properly identify the shudder.

Diagnosis

1. Verify the shudder in the vehicle. The vehicle needs to be at operating temperature (driven at least 5 miles) for proper diagnosis. After the vehicle is at operating temperature, drive in a tight circle just short of steering wheel lock, at a speed less than 8 km/h (5 mph) in order to identify the shudder.

2. Identify what rear axle type the vehicle has.

^ If the vehicle has a standard rear axle, then proceed to step 3.

^ If the vehicle has a locking rear axle, remove the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual. Drive the vehicle as outlined in step 1.

^ If the shudder goes away, install the front propeller shaft and proceed to step 3. Refer to the Propeller Shaft subsection in the Service Manual.

^ If the shudder does not go away, the locking rear axle may be the cause. Review the owner's records and determine if the rear axle was serviced at the first scheduled oil change. If records indicate that the axle service was done, then revaluate the condition using diagnostic information in the appropriate Service Manual. If the rear axle was not serviced, service the rear axle.
INFORM THE CUSTOMER THAT THE AXLE SERVICE IS AN OWNER'S MAINTENANCE ITEM NOT COVERED UNDER THE VEHICLE'S WARRANTY.

^ Install the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual.


3. Flush the transfer case with the blue colored fluid (AUTO-TRAK II) using the procedure and part number listed below. Perform the flush procedure even if the transfer case contains the blue colored AUTO-TRAK II fluid in order to remove any possible contaminants. The AUTO-TRAK II fluid contains an improved friction modifier that should correct the slip-stick condition. Refer to the Transfer Case subsection in the Service Manual for information on draining and filling the transfer case.


Flush Procedure

Important :Refer to Corporate Bulletin Number 99-04-21-001, dated April 1999, for important information on removing the transfer case drain and fill plugs.

1. Drain the transfer case fluid.

2. Refill the transfer case with 2 L (2 qts) of new fluid, P/N 12378508 (Canadian P/N 10953626).

3. After refilling the transfer case, drive the vehicle a minimum of 8 km (5 mi).

4. With the transfer case at operating temperature, drain the transfer case fluid again.

5. Refill the transfer case with new fluid.

Important :The vehicle may require approximately 160 km (100 miles) of driving before the condition is completely corrected.

Hi All, as Finewine stated. I changed all three rear, front, and tranfer case with 75/90 synthetic and all is well.

Hi, I have this problem also on my 1999, at times when I am take off from a light, it "slams" into gear, I can feel that something is tight, or dragging, I am very gentle on the gas untill, It "breaks" , then it drives fine. I guess you could describe the feeling as a doing a "nuetral drop" with bad u joints.
I bought the truck used used w 80 k it has always done this, I took it to a dealer with a differnt problem, and pointed out this problem also. they took me for a $1200 TUNE UP AND SERVICE WHAT A RIP OFF !! Never said nothing about this change or bulliten, the thing is I would have paid for it!
Anyway I will be doing this service and checking the rear end in a couple of weeks.

This is a great board I just found, I am also going to post another incident I had as "ignition switch" hope it will help someone

Rick

Hi, I have this problem also on my 1999, at times when I am take off from a light, it "slams" into gear, I can feel that something is tight, or dragging, I am very gentle on the gas untill, It "breaks" , then it drives fine.Rick

Have you checked the throttle body? It seems common that it or its cables will stick and make it hard to initially press the gas pedal.

Are you sure that the tranfer case uses the same fluid as the diffs? I know with 4wd trucks some use tranny fluid in their diffs.

Have you checked the throttle body? It seems common that it or its cables will stick and make it hard to initially press the gas pedal...
Thanks, that'll be on the "to do" list for next week, probably wouldn't of thought of lubing the cable, but it's not a problem I'm having.
I guess when I say "feel" I mean I can hear and feel the engine power. I guess I'll know more when I change the fluids, and see what happens...

I can't thank you guys enough. My son and I both have '03 Astros with shuddering when tourning corner problems. Both have been serviced by GM. One of our Astros could hardly negotiate a turn. We were thinking it needed a new differential and/or a transfer case. I took it into Mr. Goodwrench after reading your threads and at first they feigned interest. After I threatened to call the owner they finally agreed they knew about the recall and fixed both vans at no charge by changing to synthetic fluid.They knew all about it all they time but weren't going to do a thing until I showed them your threads. Thanks again...I'm now a happy camper!

I also have had issues on my 2002 Astro AWD, after trying many transfer case oil changes I found out from Mercury Marine ( I am a boat mechanic) that many race car drivers use the Mercury Marine hi Perf gear lube in their differentials. That is the blue-ish gear lube. I put that in my front and rear diffs and transfercase and have not had an issue since.

Okay, all of this happened in 2003 - did GM fix it? I don't think so, my 2005 started acting like this at about 93K. Has there been any further maintenance bulletins?

The transfer case oil needs to be changed routinely, just like any other lubricant. Get 4L of Auto-Trak II and follow the procedure outlined above. My 2000 has has four such changes in its 200K miles.

I guess that's a yes. Thanks!

Finewine, Many many thanks!

I purchased a 2004 GMC Safari AWD 4 days ago. It has 180,000 km and shuddered real bad on low speed slow turns, but I only noticed AFTER buying it (oversight ... no slow speed tight turns during the test drive by me or my mechanic!). I thought I had been bamboozled by the used car dealer.

Your advice fixed the slow-speed-turn-shudder sound immediately. I proceeded with new Synthetic 75-90 in the front and rear differentials then flushed (2 litres), drove and replaced (another 2 litres) the transfer case with AutoTrak II. Cost: $60 worth of oil. The shuddering sound went from downright annoying to non-existent. Thank you, thank you, thank you!!

Happy Camper

Hi All, as Finewine stated. I changed all three rear, front, and tranfer case with 75/90 synthetic and all is well.

Confusion is setting in (on my part?) with all the recent posts
- is the same fluid used for the front and rear differentials as the transfer case?
- I went to NAPA for the ACDelco Auto-Trak II fluid - their docs recommend 2 1/2 quarts and, after all these years, the fluid has a different stock number.
- the minimum of five miles driving during the flush - is it better with more to a maximum of say between ten to fifty miles?
- any advantage to raising the front end to drain more, possibly, from the transfer case?

Also, as I read about the AWD on this site, I see there is a swap to a different, older S-10/S-15 TC that allows for selection and engagement between 2 HI, 4Lo and 4Hi. Is this recommended or just an option that leads to more maintenance or problems along the way? It would be nice to be able to select and stay in 4WD in some winter situations around here.

HarryEvan,

My trusted mechanic insisted I use AutoTrak II in the transfer case and the Synthetic 75-90 in the front and rear differentials. I drove 10 miles between the flushes of the transfer case. The transfer case was drained with the van level. The shudder went away immediately and after 300 miles is still running smoothly.

Happy Camper

Well I did the flush after an oil change, what came out had the color of dark engine oil with a slight red tinge to it. Put 2 Liters in, drove it for 10 miles, during which it ran smooth from the get go. Drained it and put 2.5 liters back in (as per NAPA's listing). Just amazing. My first Astro had the blue fluid in it when I checked it out, but I couldn't depend on the AWD to work. Thanks again, folks.