AWD Question

[mjb0715]

Hi,
I have a 99 gmc safari AWD 4.3. Ever since we bought it we thought something was not right with the AWD, but we never had an AWD van before and thought maybe it was "normal". Anyways the question I have is when we are turning sharply, like in a parking spot, the front tires are jumping/skidding. It is very hard to explain, but it is like the AWD is not disengaging. It is even supposed to? Is this the way this van is? I just want to make sure this is not a problem, if it is, I want to get it fixed before it causes damage to other things.

[dewaynep]

This could be caused by the abs problems you are having. Get that fixed first, then see what happens to the AWD. I believe the AWD is activated by the difference in wheel speed as measured by the wheel speed sensors (abs sensors).

[tbruno]

There is a TSB on this problem. I had the same problem on my 2000 Astro. You will need to warm up the transfer case oil(I believe TSB says a minimum of 5 miles but I drove it further),drain the transfer case,refill,warm it up again, drain and refill a final time. This eliminated the problem for me the first time(about 6 years ago) but it is starting to do it again and I will be changing it soon. Takes about 2.5 quarts of GM Transfer Case Fluid

[Steve47]

I just experienced a similar problem this morning. I was taking a left hand turn into a parking space and a lot of banging noise was coming from (sounds like the rear of the van.) It sounds like one of the tires is not turning as if locked up. Is this the same problem as described in the above posts? Should I go with the instruction from the TSB as posted above?

One other thing. The anti-locking light is lit up on the dash. It has been for some time now but I just started encounteing this wheel/turning problem. Could this be part of the problem?

Does this bulletin cover the 97 AWD as well? Same symptoms.

[Steve47]

Does thi bulletin cover the 97 AWD as well? I haven't seen the bulletin.

[old_master]

The TSB covers all AWD Astro/Safari vans. It's a special fluid, blue in color, and to my knowledge, is only available through a GM dealer. As mentioned, the procedure may need to be performed more than once to correct the problem.

[Steve47]

Thanks. I'm going to have the fluids changed. I drove the van this morning and it was banging quite a bit, the close quarter turn bang wasn't there but as the van shifted on a straight away there was a bang that came from the tranny, it would bang at the tranny and be followed by a bang in the rear end, was doing this as it shifted through each gear. I spoke to my mechanic yesterday and explained the TSB to him, he kind of rolled his eyes but he'll do what I asked. I hope this takes care of the problem.

Is this what I should use?

P/N 12378508 ,,
blue colored fluid (AUTO-TRAK II)

What should I use for new rear end fluid?

[old_master]

That's the correct part number for the transfer case fluid. However, if your vehicle is making noise when shifting without turning, it's probably NOT the transfer case.

[Steve47]

Well let's put it this way. The other morning it displayed those symptoms while making a left hand turn into a parking space. Less than 5 mph for sure. As for the other noise, sometimes the bang comes from only the rear end and at other times it bangs right below me up front followed by a bang in the rear. So what do I have to lose? I've picked up the fluid for both the transfer case and the rear end for $84.00 ,,, The van now has 197,000+ miles on it and I doubt the fluids were ever changed in those two places. I bought it used and had the tranny fluid and filter changed when I got it, they told me everything looked good. As for the speed sensor at the transfer case, brand new, BUT, it keeps working itself loose. I wrapped it in electrical tape the other day and since then I have no speedometer jumping around issues. If this fluid change doesn't do the trick I'm going to junk it and find a different van.

I'm open to all suggestions here and possibilities of what people think might be the problem.

Major sympton of concern: Banging noise from below up front followed by banging noise in rear.

[Steve47]

Any help appreciated.

[Steve47]

The fluids fore and aft have been changed. I drove the van and have experienced zero noise from the transmission or rear end. My son drove it and reported the same. I just drove it again and still zero problems. Hopefully the issue is resolved.

[Steve47]

Day two since fluids changed. No banging or unusual noises from front or rear of van. The van did shudder once on a tight low speed left hand turn. If all is correct in the TSB, I will expect this to cease.

Had 4 new tires installed on it today as well. Currently driving and handling like a dream.

[Blue Bowtie]

You may experience a recurrence of the problem within a few months. If so, change the AutoTrak oil again. The synthetic (new) oil may get contaminated by the remnants of the old oil and by cleaning up any accumulated deposits. There are some vehicles which require two changes, but most do not. In any case (no pun intended) the transfer case oil needs to be changed every 30-50,000 miles depending upon vehicle use (towing, hauling, etcetera). Since the transmission oil should be changed every 30,000 miles, it's a good time to do both, or at least, at every other trans oil change.