97 Bravada with Trnasfer Case Gear problem!

[HeyRobi]

I see there are others with the same problems. We are out of town so when we get home I am going to check the motor mount. On my vehicle I had it checked out by a mechanic friend who attatched microphones to the transfer case and other various drivetrain parts and we isoladed it down to the transfer case to be the suspect of the clunking noise when accelerating. It sounds like a the gears are not meshing well! I took the advice of a friend to change the oil in the transfer case and that seemed to help alot in fact it will not do it unless hard acceleration. I was thinking about changing it again, sorda like a flush! Could the motor mount cause that sound from the gearbox itself or does it sound like a more in-depth problem? If it is in the transfercase what is the best way to fix it? I am mechanically inclined and can tear one apart, I think!!! Or just replace the whole thing. I had a junkyard qoute me 800 bucks that seemed high!! Thanks for reading and thanks for any input!!

Phillip

[Chris Stewart]

Ya got a chain and sprockets inside the case.

[HeyRobi]

So what do I need to do? Can you tighten the chain??

Phillip

[Chris Stewart]

The book shows no chain adjustment, just chain....like a wide timing chain, wide sprockets and gears. The manual mentions bearings and driveshaft joints making noise...have you checked the u-joints on the rear shaft or the CV joints on the front shaft? They should move freely in all directions with no binding.

[herbravada]

I have had two Chevy Astro/ Gmc Safari vans with the AWD. The 2000 safari started making noise from the AWD unit shortly after my (now ex) wife had ruined a tire and had it (just the one) replaced. She hid it from me until I heard the noise - it was like the AWD was sticking in 4wd and then releasing - a thunk sort of.

After replacing the other three tires the noise was less but still there - then it seemed to get worse as time went by. Found out that the fluid in the AWD got burned from the abuse of the mismatched tires. Changing fluid (it uses the blue synthetic ATF) the noise was gone and all was fine.

The 91 Chevy went 250k without any problems w/awd. The 2000 GMC eventually had terminal problems with the AWD at about 180k (30k after the tire problem). The AWD unit simply quit working - the van was not worth the effort at that point so I never tore the unit down - might just have been a bloken chain - it went out on a tight corner, the unit seemed to bind up - fighting like a 4wd on dry pavement and then bang. After that there was no drive from the front but no warning light - no oil leaks no external signs of damage.

I suspect that the tire mismatch was the cause of the eventual failure. But then she is my ex the van is gone to a new owner and I live where AWD is not a big selling point (unless you drive on the beach).

[Chris Stewart]

The '91 had a Viscous Clutch which is engaged at at times and is designed to slip enough to keep the parts from binding up due to minor differences the tire diameters & turns.
The 2000 had an electro-mechanical clutch engaged and disengaged by computer commands. Sometimes the clutch pack sticks which allows the parts to bind up due to minor differences the tire diameters & turns hence the need for the transfer case fluid change.
Who knows, maybe with a transfer case fluid change every 20k, they wouldn't give so much trouble.

I found out there's no clutch, just a gear engaging & disengaging by the encoder motor but the blue TracII transfer case fluid change appears to be helping folks.