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2001 Astro Van all wheel drive - Bad Vibrations


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02-11-05, 05:04 AM   #1  
jetex
2001 Astro Van all wheel drive - Bad Vibrations

I'll be driving along a straight smooth road in drive gear, at about 40-50mph, I'll start to feel a front end vibration similar to driving over a mild washboard road surface. As I take my foot off the gas and apply the brakes the vibration becomes stronger causing the whole van to shudder. I'll stop the van and then continue to drive and the van feels normal. This occurance may happen again 20 miles latter, or may not happen again in a day of normal driving. Always happens on a smooth straight road. My Cheve dealer mechanic has driven the van, but the problem did not show up at the time. The machanic was unable to provide a cause based on my discription.

Mileage: 64,000.00 / Front end has been checked on a lift and is ok, including idler arms / All tires are inflated to 35lbs., the correct size, good tread, balanced, not damaged / Shocks are original, but seem to work fine / All fluid levels are full and smell ok / Brakes are relatively new and do not pull / Alignment is ok.

This problem has just started and the dealer feels I'll just have to let it get worse before they can provide a solution. I've never had an all wheel drive before, but I'm wondering if this is a transfer case problem.

Any ideas would be appreciated.

Thank you


Last edited by jetex; 02-11-05 at 05:18 AM.
 
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02-11-05, 03:39 PM   #2  
Buy 4 quarts of transfer case fluid from the dealer.Drive the van for about 10 miles and drain the fluid and refill with 2 quarts.Drive the van about 10 miles and drain again and refill with 2 quarts of fluid.This may or may not help but it is a hunch I have about your van.You will need a suction gun to refill the transfer case most are about 12 bucks.Yes I think the transfer case is causing the vibration but I haven't driven it.

 
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02-12-05, 07:36 AM   #3  
jetex
Transfer Case

davo:

I am past due for Transfer Case fluid change. I asked the dealer mechanic about this and what is done. He said, the case is flushed and refilled. I also asked him what's inside? He said, some clutches that may have varnish build up.

Is this what I'd be doing, flushing, when following your proceedure?

Can you tell me what is happening in the Transfer Case to cause this problem?

Can you explain your "HUNCH"?

I need a proper maintenance manual as the owners manual gives a fluid type, but not a capacity.

I have a suction gun.

Appreciate your reply and interest.

 
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02-13-05, 04:18 AM   #4  
Yes if you do what I said you will be flushing the transfer case.My hunch is that under certain load conditions the clutches in the transfer case are chattering causing the vibration.I can't say for sure though but it needs changed any way so do your flush and see what happens.If your transfer case is overdue so are the front and rear differentials.You could remove the front driveshaft and drive it for awhile to see if the problem goes away if it does it's in the transfer case and you would need to flush it any way.If it doesn't it's something else.Transfer case holds 2 quarts of Auto-Track II fluid (GM part #12378508).Front diff holds 2.6 pints of 80w-90 gear oil (GM part # 1052271).Rear diff holds 3.5 pints of synthetic gear oil 75w-90 (GM part # 12378261).I suggest using synthetic gear oil in the front also if you live in a cold climate.The part #s may have been superceded but they will know the replacement # at the dealer.I don't know if there are aftermarket equivilents for the Auto-Track II fluid but aftermarket synthetic gear oil should be fine.

 
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02-13-05, 08:53 AM   #5  
jetex
What a great reply!

davo; Can't thank you enough. Picked up 5 litters of the magic stuff only available from the dealer.

About to start the transfusion, so your response was timely. Will post results by end of this week.

Appreciate your details and time to reply.

 
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02-17-05, 12:55 PM   #6  
jetex
Still have the problem...........

The fluid was drained from the Transfer Case. The original fluid came out looking clean, a greenish color and no burned smell. Refilled with new fluid (transparent bluish color) and drove for approx 30 miles during which time the problem didn't occur. Drained (looked clean) and refilled with new fluid. After driving apprx. 20 miles, the problem occured again under the same previous conditions: Stopping and then continuing, the problem is gone. The next trip was approx. 50 miles, with some freeway miles and no problem.
Today, on a 5 mile trip, the problem started again just once.

I would add that the Van makes no unusual noises before or during this problem other than feeling vibrations.

Could the Transfer Case Sensors have anything to do with this problem?

I don't relish the idea of removing the front wheel driveshaft, but then........

While the problem only occures in the 40 mph range, I'm wondering what it would be like in the 70 mph range. Any thoughts on that?

The only reference I have for the Transfer Case is my old 1990 GM service and unit repair manual and the diagnosis guide makes no mention of my problem. Perhaps it just needs a new clutch assembly, but I would be disappointed in the service life of the present one.

Rear axel has new 80w90. The front axel has new 75w90 synthetic.

 
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02-17-05, 01:45 PM   #7  
Do you have a manual transmission?
Billy

 
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02-17-05, 02:01 PM   #8  
I hope you mean the rear axle got the synthetic oil putting it in the front was a suggestion.Maybe what you need to do is start checking u-joints and start with the rear driveshaft.Sometimes changing the transfer case fluid takes a couple hundred miles of driving to work if it is the cause.

 
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02-18-05, 05:38 AM   #9  
jetex
billys68ss: I have automatic transmission.

davo: The owners manual says 80w90 for front and rear axels. I followed your suggestion and refilled the front axel with 75w90 synthetic.

Dealer mechanic looked at both drive shafts and joints and felt them to be ok.

Plan to continue driving it for awile and see what happens.

Other options are rotating tires front to back and perhaps new shocks.

 
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02-18-05, 06:09 AM   #10  
Unless it needs it, shocks arent going to cause the shutter that you are describing, so save your money. I think Davo has some good suggestions for you. He is, after all, a GM Tech, so I think he knows what hes talking about.
Take his advice and see where it leads you.
Good Luck.
Billy

 
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02-19-05, 06:33 AM   #11  
jetex
billys68ss:

I have a good feeling about the advice, suggestions and details posted by davo. I wish he was a neighbor!

This problem I have is very subtle and intermittent, but always occuring under the same conditions and speed range. I can always verify the condition with the application of light braking.

If the "hands on" dealer mechanic has a difficult time in diagnosing the cause of this problem, it's not going to be any easier for you and davo to accomplish unless something I tell you rings a bell of a past situation.

Yesterday I drove approx. 80 miles, 40 freeway miles @ 65-75mph and 40 local miles @ 35-45mph with stop and go. The problem didn't happen.

davo: I would like to know if I misunderstood about refilling the front diff. with 75w90 synthetic gear oil.

I have to say this too: I posted changing the the front and rear diff. before actually doing it. As the rear diff. has no drain plug and I didn't have a replacement gasket, just in case, I only topped off the rear with the recommended 80w90 oil. The owners manual said nothing about 75w90 synthetic oil.

As you suggest davo, continued driving might help the situation, I will continue and see if things improve. I'm mostly concerned I don't make things worse. If I can get a couple of weeks free of the problem, I'll change the transfer Case oil again.

Thanks for the hand holding.

 
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02-19-05, 06:03 PM   #12  
Something you might want to consider. If you take it in to the dealer and they have been unsuccessful at duplicating the concern, you should suggest, since you know how to "make it happen", that the tech go for a ride with you while you drive. This way you can "make it happen" and he can be there to experience it. Just be considerate of his time. Dont take him on a 2 hour drive. Remember he gets paid for what he does and does not get paid for joy riding.
Billy

 
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02-20-05, 05:49 AM   #13  
jetex
billy

I'm afraid that with the inconsistant occurance of this problem, I might have to have the dealer mechanic move in with me. That might be worth a new van. Both the service manager and the mechanic know that I'm monitoring the problem and will let them know how it goes even if the problem heals itself.

The dealer has been extreemly fair with me on this. The mechanic test drove the van, checked the suspension, the drive train, removed the front tires and checked their balance, checked the transfer case, front and rear diff fluid levels and chalk marked the 4 tires to confirm tire sizes. The charge for this was $18.95.

My thanks to you and davo for taking the time to consider my problem.

Will post my results.

When this problem is solved, I'm gonna ask you guys how to kill the little GM gremlin who has taken over the control of my headlights. Hey, if I can use toilet paper, I can turn my headlights on by myself thank you!

David

 
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02-20-05, 07:32 AM   #14  
The rear diff takes synthetic gear oil and it would be a good idea to also use it in the front diff if you live in a cold climate.That's what I meant by my previous post.If the problem doesn't happen again you don't need to change the transfer case fluid again until it's due to be changed.

 
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02-20-05, 08:46 AM   #15  
jetex
Do I have a "locking" rear axel

The Owners manual says 80W90 for front and rear "standard Diff" and GM PN 1052271 (which I assume) is synthetic for rear "locking" diff.

As you're pressing the use of synthetic in the rear diff., do you feel I have a locking diff.? How would I know this or find out. Is there a tag on the rear diff I haven't noticed. I do have the tow-haul option if that's an indication.

Good to know I don't have to change the transfer case oil again, but if the problem clears up I will consider an earlier interval. I was 13000 miles overdue for this one.

I realize you must respond to a great many posts, so I do appreciate your attention.

David

 
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02-21-05, 01:55 PM   #16  
The service manual for your van is what I'm going by and it states synthetic gear oil for a standard or locking differential.If I had your vin# I could tell you if it is a standard or locking differential.

 
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02-22-05, 06:24 AM   #17  
jetex
Vin Number......

That's very kind of you.

Vin No. xxxxxxxxxxxxxxxxxxxxxx

Now this might not be the thing to do, as not up to date, but in looking at the RPO listing in my 1990 Service Manual I see G80 as locking diff. On my 2001 passenger door RPO list, the only G number is; GU6, which might be rear axel: 3.42 Ratio for this van. Can you confirm this based on my VIN?

I think my 2001 owner's manual is different from yours, as on page 7-51, (manual part no. C2110 B First Edition) there is a distinction between front and rear standard and locking rear diffs., BUT for each, it says the GM Part No. 1052271 is the gear oil to use. Only for front and rear standard diff. does it say SAE 80w90 Axel Lubricant along with GM part no. 1052271. On the rear locking diff. it says; Use only GM part no. 1052271 and Do not add friction modifier.

I can scan this page if you like as it seems to be a source of confusion.

In any case, I'll yield to your better judgement. Does GM do recalls on owner's manuals?

Thanks, David


Last edited by davo; 02-22-05 at 01:43 PM. Reason: Vehicle Owner's Manual verification/Removal of vin
 
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02-22-05, 11:50 AM   #18  
Hi guys;
I know nothing about your auto problem, but please take a friendly piece of advice from someone who spent 30 years chasing auto thieves. NEVER EVER(!!!!!!!!) post a auto VIN on a open internet forum site. No matter how trusted the site is. That number can be copied and used in some states to obtain fraudulant loans, liens, and all sorts of nefarious things with YOUR auto as collateral. It is a BIG business in the United States with certain Soprano and Good-Fellas involved.
You should use the e-mail option to send the VIN to that person alone.
Just a friendly word of advice.

Submitted for your information.

 
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02-22-05, 01:59 PM   #19  
You don't have a rear locking diff according to the build sheet and yes you do have a 3:42 ratio.I removed the vin from your previous post.

 
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02-23-05, 04:04 AM   #20  
jetex
Bob M; Thanks for the advice. Wasn't aware of email option at the time. I wasn't comfortable about posting the number.

davo; Thank you for the confirmation and vin removal.

The vibrations have occured a couple of times during the last 200 miles, but seem to be less obvious. will post further results.

Thank you. David

 
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03-05-05, 09:53 AM   #21  
jetex
Vibration problem is no longer apparent

During the last 600 miles, in conditions where the vibration problem occured, I have not felt the vibrations again. I'm hopeful the cause has cleared up in the Transfer Case.

Davo, Thanks for your attention and suggestions.

David

 
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