Chevy & GMC Vans

Ok this thread is kind of all over the place so let me organize everything nicely.

Upon picking up my car I blew my rear diff 200 miles from home and had the mechanic replace it with the stock 4:32 ratio.

A few days later the mechanic calls me that it's done so I go pick up my truck

At that time I did not know that the rear right tire was a 205 not a 215. Also at the same time when I picked up my truck from the mechanic he said I should replace the front differential when I get home because it was making a thump and weird jerk at low speeds but was fine at higher speeds so the guy told me that if i drive it constant 60mph I should be fine, so i drove the car home 200 miles with out any weird noises or problems.

Once I got home I took out my front diff, and in fact the right shaft completely came out and it was ruined at the end. So I picked up a front diff from a junk yard from a 1993 which later today I did confirm that it is a 4:32.

Upon replacing my front diff I took the car for a test drive, this is where the 15 miles come in. About half of it was in straight away 0-40 but not hard acceleration and the other rest driving in circle slowly and figure 8s.

Note:I also fixed the spring mount by this point it was only a 10 minute job hehe. Continuing on.

When driving the car I noticed my car would become kinda unstable as getting to 40mph and when making tight slow turns it would jerk. That's when i went online and found out from my research that a seized viscous coupling in the T-Case is what causes these problems.

The tire I difference I noticed after all of these has been determined.

So my plan of Attack is to:

Stick on the correct tire size on there, and take it for a test drive. If my problems persist I will replace the transfer case.

Also looking back at all of my facts everything would make sense. As I blew the rear end and still driving for a couple miles until I realized what happen, I probably screwed up the transfer case which in turned screwed up the front diff.

Upon the mechanic fixing my rear end, the viscous coupling in the transfer case was already sized up but since my front diff was blown by that point it allowed me to drive home with out causing much problems.

now when I got home replaced the front diff the problem with the transfer case comes up.

Make sure ALL 4 tires are the same brand, model and size and test drive. If it still is jerky, pull the front driveshaft and test drive again. If it drives smoothly, replace the transfer case.

sxfx, Thanks for the clarification. It sounds like you are on the right track. Good Luck and please keep us posted. Jim

Yes upon completing everything and I get the van in running condition I plan on creating a new thread and documenting everything for future user use.

I have definitely learned a ton about awd I never knew before.

Don't make a new thread. I will just merge it. Add to this one and there will be a single location with all the problems, trials, and fixes.

Just a quick question to double check.

Is Dexron VI ok to use in all 90 to 96 viscous coupling t-cases? Just wanted to make sure before I swap out my t-cases Tomorrow hehe.


P.S. I put in all the same wheels from my 88 Astro to make them all the same size and everything the problem is still there. I didn't run the test with out the front drive shaft disconnected. But Im literally 100% sure it is the T-Case.

I have only run Dexron 3. As long as it is compatible you will be ok.

LiftedAWDAstro wrote:I have only run Dexron 3. As long as it is compatible you will be ok.

Cool awesome don't wanna be breaking more shit hehe. But I guess since your running Dex 3 I think Il run the same thing unless someone else chimes in saying they run Dex 6 succesfully.

The bottle does state that its an improvement for cars that require Dex 3, but from my recent activities with the car and how picky it is on what you put in, I think I rather go with the tested methods ..

it's not really picky i think you're just jumpin' the gun a weee-bit. i wanted to get the dex 6 when i did my transmission but i ended up getting the mobil1 ATF since their dex 6 is not available in Canada

Well guys you are all going to laugh at me.

It was the gear ratios being wrong all this time. But the viscous cup was siezed from the previous problems so at least I didn't waste my time. Now when I drove it my wheels didn't bind any more, just once everything warms up I get the whirring noise.

The second my friend mechanic heard it his like dude its gear ratios. But not too fear Im going to the junkyard tomorrow and pick up the rear end from the same vehicle i got my front end and t-case from hehe. The dude there is just swapping me them one for one since mine is still good.

But yeah let me tell you has this all been a learning experience about differ tires sizes, and awd al together hehe.

Did you pull the rear cover and verify the ratio?

sxfx wrote:Well guys you are all going to laugh at me.

It was the gear ratios being wrong all this time. But the viscous cup was siezed from the previous problems so at least I didn't waste my time. Now when I drove it my wheels didn't bind any more, just once everything warms up I get the whirring noise.

The second my friend mechanic heard it his like dude its gear ratios. But not too fear Im going to the junkyard tomorrow and pick up the rear end from the same vehicle i got my front end and t-case from hehe. The dude there is just swapping me them one for one since mine is still good.

But yeah let me tell you has this all been a learning experience about differ tires sizes, and awd al together hehe.

sxfx, What was your old ratio? What is your new ratio going to be? Thanks, Jim

LiftedAWDAstro wrote:Did you pull the rear cover and verify the ratio?

Yes the mechanic that put my rear diff in verified that it's a 3:42, my door sticker says stock is suppose to be the GT4 Which is the 3.73

And the 93 I got my front diff from was a 3.73.

I like this guy. Kind of reminds me of myself, lol.

My T-case in my 94 works great. I can hold the brakes (on gravel) and get about a turn or two from the rears before the t-case gets a hold and stops them or turns the fronts, slipping the brakes.

I just love the BW4472. It is a marvel of engineering, in my opinion.

There should be one of those stickers on the visors (like the ones that say SUVs roll over) that say to run exact matched tires on the AWDs. I've heard of several ruined by mismatched tires.

OK quick change of plans.

The junk yard didn't have the rear end for the 93 that I got my front diff from and t-case.

So new plan of attack. I confirmed that I have a 3:42 in the back by pulling the rear cover from the diff.

Now the junk yard does have a 96 safari with a GU6 which is the 3:42 that I need. Unfortunately I cant confirm what ratio was the front diff from the 93 since they already scrapped it.

So my question is there another way to find the ratio of the front diff by just looking for a number on the out side or inside? I am going to get the 3:42 from the junk yard to match what I have in the rear. But just out of curiosity I would like to see what the front is too.