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Discussion Starter · #22 ·
going to check gear ratios this weekend. i fear the rear diff is different from the front and causing the binding. will aslo flush and fill t-case again. believe it's two issues - 1 awd and 1 abs...
 

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1998 LS AWD Forest Green metallic
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If you had two different gear ratios, you would not be complaining about 'a
little vibration or shudder' .
It would be, essentially, not driveable. You would have a lot of noise and binding all the time!
I do not think it is even possible to drive it that way. The transfer case, or whatever is the weakest link, would destroy itself when the front and back wheels try to rotate at those different speeds.
It probably would feel a lot like having a solid axle rear diff, while cornering continuously, if it would even move more than a few feet.
The difference in ratios means with a 3.73 ratio diff( and a ~30" tire) will travel a little less than 7 feet ( about 6.7 feet) for every 10 revolutions of the drive shaft. With a 3.43 ratio diff the same tire should travel about 7.25 feet. So if my quick calc's are accurate, the 3.73 wheel will have to rotate almost another 1/3 of a rotation to keep up with one of the 3.43 axle rotations That sounds like a lot, so maybe my calc's are off. ( C = 3.14 x D) 3.14 x 30" /12 = ~7.85 feet per tire revolution

Rod J
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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My speculation... I suspect mismatched gears might give some initial bind off the line (assuming AWD is working).. but would then cause clutches to severely slip, grind, and burn up rather quickly once you started rolling. Pulling the fuse would likely prevent the engagement bind, but would not prevent the eminent catastrophic clutch damage.

Same happens if vehicle is towed with 2 on the ground (maybe this happened too)
Mismatched tires simply cause the damage to happen more slowly over a longer period of time.

Obviously pulling the driveshaft would be one work-around solution.
If everything is matched correctly, then this accomplishes nothing.
 

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Discussion Starter · #25 ·
My speculation... I suspect mismatched gears might give some initial bind off the line (assuming AWD is working).. but would then cause clutches to severely slip, grind, and burn up rather quickly once you started rolling. Pulling the fuse would likely prevent the engagement bind, but would not prevent the eminent catastrophic clutch damage.

Same happens if vehicle is towed with 2 on the ground (maybe this happened too)
Mismatched tires simply cause the damage to happen more slowly over a longer period of time.

Obviously pulling the driveshaft would be one work-around solution.
If everything is matched correctly, then this accomplishes nothing.
yes, awd is now working, as i'm getting the dash light upon starting up. was not illuminating previously.
 

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Discussion Starter · #26 ·
yes, awd is now working, as i'm getting the dash light upon starting up. was not illuminating previously.
also now getting air bag light to illuminate at start up, was not previously
 

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Discussion Starter · #27 ·
getting going on some work and troubleshooting. will first check t-case fluid with a flush and fill. once i confirm auto-trak ii was indeed used, will reinstall front drive shaft. i would like to experience the binding for myself, as i have yet to feel. i have a feeling that the shop did not follow completely the gm service notice (drive the van 100 miles, flush and fill, and figure 8s). yes, interesting that they tried two refurbished t-cases and experienced the issue with both. but, if they were using wrong fluid, and/or didn't flush through multiple times, maybe this could point towards the awd issue they felt. the shop mentioned that once up to driving speed, the issue stopped. the shutter/binding was under 10mph, and maybe they felt a combo of the awd and abs malfunctioning, i understand the systems are separate. i have not opened the diffs, but i did go back into my service receipts and found that the driveline shop i used to rebuild the rear used the oem specs. i am confident the front diff was never rebuilt. will report back, thanks to all.

 

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Discussion Starter · #28 ·
wow. alright.

brakes are gone, toast. whatever the transmission/t-case shop did to the brakes while messing with the abs system, which included relining to some of the brakes, has failed. fluid on the ground, brake pedal to the floor. this was when i left the house, before i touched anything underneath.

went to napa up the street, found some ac delco auto trak 2, flushed and filled the t-case. blue on the way out, blue on the way in. installed front drive shaft. drove around the parking lot, all felt fine (besides the brakes), no binding or sounds. tight turns, some figure 8's, felt ok! left the parking lot and got up to about 30 mph before a real shutter and binding, pulling the car to the left with a solid shake. went back to parking lot, drove fine again under 10-15 mph. went back onto street and 30 mph again, same thing. removed drive shaft. drove home with my tail between my legs.

super bummed. i am nearing the end of being able to toss money into the van. will get her towed to the dealership and have them rework the brakes. then figure out next step.

whelp.
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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Unfortunately, your story is why people are often advised to stay away from AWD if you don't need it. It's a complex system with common issues, and not easily diagnosed or cost effectively repaired.

Couple things:
As you've stated you understand ABS has NOTHING to do with AWD.
Two completely DIFFERENT problems!
As such, it might be more productive to not confuse or mix discussion of both.

ABS: Pedal to the floor.. huge problem! I've had it happen to me, only in my case I believe the ABS was reacting to poor hydraulic pressure from a bad pressure valve in my power-steering pump. New PS pump and my brakes worked great again. This is assuming the ABS unit is working properly... brake lines are bled properly and free of air.

Fluid on the ground: that's ANOTHER SEPERATE ISSUE ALTOGETHER.
What kind of fluid? Are we talking about brake fluid?
If you have brake fluid on the ground, then you likely have AIR in the ABS system... HUGE problem.

AWD: The symptoms your are describing are NOT the typical AWD shutter/bind most people have. What typically happens is simply the AWD system "engages" while making sharp turns (due to mismatch in front to rear drive-shaft speeds).. and when AWD is locked in 4-wheel drive you literally are LOCKED in place... and can't move. The AutoTrac II fluid is supposed to allow the clutches to slip in this condition. The "shudder" you would typically feel is the binding/unbinding of clutches, again which happens at slow speed or no speed. Again, this is typically at slow speed or from a standing stop... NOT at 30mph!

What you describe is something different! It can't be binding.. you are already moving at 30mph. It sounds like you are describing a violent shaking or vibration. Many things can cause this.. and it likely will have nothing to do with the transfer case (unless it's seriously defective). Maybe your front differential has a serious issue with the drive-shaft engagement? (pinion bearing or similar) Note however, the differential is always spinning whether drive-shaft is in place or not. If not faulty front differential (or t-case), then possibly bad front drive-shaft itself, or u-joints?

But then you say it pulls to the left. This is likely something DIFFERENT altogether! The transfer-case could not cause a pull to the left, and neither could an open front differential. Normally a pull to the left indicates a right-brake caliper sticking. This could ALSO cause a violent shaking, as the brakes and rotor react badly with each other while seriously being over-heated.

But ALL the problems go away when you pull the front drive-shaft?
That doesn't seem correct, especially the pull to the left.
And how are you driving this van if the brake pedal goes to the floor?

I suspect you may have more than one issue.. and might possibly be getting them confused with each other.
 

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Discussion Starter · #30 ·
Unfortunately, your story is why people are often advised to stay away from AWD if you don't need it. It's a complex system with common issues, and not easily diagnosed or cost effectively repaired.

Couple things:
As you've stated you understand ABS has NOTHING to do with AWD.
Two completely DIFFERENT problems!
As such, it might be more productive to not confuse or mix discussion of both.

ABS: Pedal to the floor.. huge problem! I've had it happen to me, only in my case I believe the ABS was reacting to poor hydraulic pressure from a bad pressure valve in my power-steering pump. New PS pump and my brakes worked great again. This is assuming the ABS unit is working properly... brake lines are bled properly and free of air.

Fluid on the ground: that's ANOTHER SEPERATE ISSUE ALTOGETHER.
What kind of fluid? Are we talking about brake fluid?
If you have brake fluid on the ground, then you likely have AIR in the ABS system... HUGE problem.

AWD: The symptoms your are describing are NOT the typical AWD shutter/bind most people have. What typically happens is simply the AWD system "engages" while making sharp turns (due to mismatch in front to rear drive-shaft speeds).. and when AWD is locked in 4-wheel drive you literally are LOCKED in place... and can't move. The AutoTrac II fluid is supposed to allow the clutches to slip in this condition. The "shudder" you would typically feel is the binding/unbinding of clutches, again which happens at slow speed or no speed. Again, this is typically at slow speed or from a standing stop... NOT at 30mph!

What you describe is something different! It can't be binding.. you are already moving at 30mph. It sounds like you are describing a violent shaking or vibration. Many things can cause this.. and it likely will have nothing to do with the transfer case (unless it's seriously defective). Maybe your front differential has a serious issue with the drive-shaft engagement? (pinion bearing or similar) Note however, the differential is always spinning whether drive-shaft is in place or not. If not faulty front differential (or t-case), then possibly bad front drive-shaft itself, or u-joints?

But then you say it pulls to the left. This is likely something DIFFERENT altogether! The transfer-case could not cause a pull to the left, and neither could an open front differential. Normally a pull to the left indicates a right-brake caliper sticking. This could ALSO cause a violent shaking, as the brakes and rotor react badly with each other while seriously being over-heated.

But ALL the problems go away when you pull the front drive-shaft?
That doesn't seem correct, especially the pull to the left.
And how are you driving this van if the brake pedal goes to the floor?

I suspect you may have more than one issue.. and might possibly be getting them confused with each other.
yup, woof. step 1 is to get the brakes inspected and reworked. without the front drive shaft in, the car runs totally fine. i live near the mountains now and will need awd, eventually at least. musicman, i drove 3,000 miles out here with both drive shafts in. my awd system clearly was not working at that point, but everything felt totally fine. as soon as the transfer case and awd electronic components were reworked, issues have arose. u joint or front shaft or front diff maybe.

drove without great brake pressure very slowly, using the engine to slow me down. it felt as if one or two brakes were working if that makes any sense, though the pedal would touch the floor. yes break fluid on the ground under front right and left wheel wells.

i know i have a front diff leak and a power steering line leak.

super bummed. will let you know how it goes on the brakes. will ask for advice on awd/front shaft/front diff while it's in the shop.
 
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