Chevy & GMC Vans

Hello to all you astro/safari owners!! This seems to be a great site for all things astro. I'm rather new to the world of astros but really like this truck and this site. Hope someone can help me out?
Recently purchased 91 awd astro ,4.3. Truck is in great shape except for the drive train. So far I replaced one front cv axle that had a torn boot. The truck binds up when turning sharply right or left, forwards or backwards. Feels like the wheels want to stop turning. A visit to well respected trans shop determined the transfer case to be the culprit. A used unit with 130k is going to run me $400. I can get one for as low as $55 but with no idea of how many miles is on it. It would have a 30 day return policy if it doesn't work. May or may not be worth the effort.
So my quandry is wether to go low ball and see if I can buy enough time to gather all the data to do a swap to manual 4x4 setup. I see it can be done but need more info on the process and costs involved. A rebuild of the current TC is $700!!!. So I figure why not bite the bullet and go for the swap instead. Like I mentioned the truck is in very good condition except for this. I have found some good info so far but need more specifics as to the easiest swap method and the necessary doner vehicles.
Also wondering about the side effects of just dis-connecting the TC all-together and going with 2wheel drive for a while. How is this done and are there any potentials for more harm than good? I did read about the truck needing to use the emergency brake when parked. Other than that are there any other concerns?

Anyway hope you guys can point me in the right direction to threads on the archived forums as well as the current forums to find the info needed. I appreciate any and all help.

Your van should have a Borg Warner 4472 t-case.If you can do the job yourself and can get a 30 day warranty, I'd try the cheaper route. I changed mine this past summer.I drove mine without the front driveshaft for 6 months.I figured it was already toast so it wouldnt hurt much.Checkout the "Which AWD system and why?" post here.Sorry,not sure how to link it .
Anyways,If you go this route,be sure to count the splines.Preferably before your lieing under your van trying to hook it up! #-o Keep us posted.I'm still debating a rebuild on my old case.At the very least open it up,and give a lookover.
Later, Bill

Bill is right on the money. Go the cheaper route and if it doesn't work, you have 30 days to return it. Check the rear output spline count. GM used either 27 or 32 spline versions. To check what you have now, you will need to remove the rear drive shaft from the t-case. Once you know this, get a replacement t-case with the same spline count. If you end up getting the other one, you can still use it. You will need to swap the slip yoke to the correct spline count. The u-joints will install into either one as they are the same.

Thanks for the reply's all,

A couple other questions.

1. I'm going to change the fluids in both differentials. Is there a way to drain the front by removing a cover or whatever just like removing the rear cover instead of using the drain plug? The rear cover is straignt forward, will be replacing the seal after cleaning the pumpkin insides etc. Would like to do the same to the front if I dont have to remove anyting major. Also would like to try the t-case as well if there is a good way to get all the old fluid out before replacing with new.

2. I'm having a heck of a time finding a good manual with info specific to awd. Any recommendations?

3. Are there any posts dealing with procedure for removing the t-case and changing the u-joints? Could the u-joint/joints possibly be the culprit?

Thanks again.

viewtopic.php?f=21&t=1344&start=0&st=0&sk=t&sd=a

Read this, it explains a lot. If your case is "locked" solid, and you continue to drive it, you will be replacing the front differential, driveshaft, etc. That's what happened to my '91, according to the previous owner Mic, aka V8 Astro Captain. If you plan to drive it as is, pull the front shaft.
From what I've read, mismatched tires are the biggest killers of BW 4472s. Even the same "size" can be very different from brand to brand. Replacing just 2 tires is also a mistake, IMHO.

My van has a 2 speed T-case in it now, hint, hint.

There is no drain plug on the 1990 to 1996 front diff's. To get the old oil out you will either need to drop the diff out and split it or you will need to suck the oil out.

The transfer case will have a drain and fill plug about 2-3" apart. They will be on the rear towards the driver side of the van.



The only manual you need is the Factory Service Manual. The FSM has the complete van in it including differential rebuilding and a full line of troubleshooting guides.

thanks for all the help folks. The t-case is not completely out yet. It still drives well as long as I'm not making tight turns. I think I'll go the junkyard route and see if I can dodge a bullet for now. I will remove the front driveshaft just to see if it helps. At least this way I'll learn how to remove the t-case and if neither is good I can take the one to be rebuilt and save the install labor cost,about $150-200 i figure. I'll have to remember to grab the drive shafts as well when I do the pull. I guess I really only need the rear shaft if I understand it all.
Thanks again =;

Hey lifted/risllc!!
Really appreciate your help. Can you point me to a post regarding the best/easiest 2speed t-case swap. I going to be at the wrecking yard and they possible have many of the parts. I've read the np231c is the best choice from 1996 or newer s10 or blazer. What all will I need from the donor? I'm going to post all this info in this thread I've started or place it in another forum for easy searches for others. I imagine I need the :
1. t-case
2. front axle and diff
3. drivelines
4.pedals/shifters
I figure to just get it going with the same t-case and front diff if the junkyard stuff works and start collecting the 2spd stuff as I find it. Really sounds like the way to go. Anyway trying to time my j-yard visits between the rain showers here in Washington.
Thanks again for your help.
p.s- Is there any means of making a $$ contribution to those that host and maintain this site? It really does save folks a lot of money.
=;

snowy23 wrote:Hey lifted/risllc!!
Really appreciate your help. Can you point me to a post regarding the best/easiest 2speed t-case swap. I going to be at the wrecking yard and they possible have many of the parts. I've read the np231c is the best choice from 1996 or newer s10 or blazer. What all will I need from the donor? I'm going to post all this info in this thread I've started or place it in another forum for easy searches for others. I imagine I need the :
1. t-case
2. front axle and diff
3. drivelines
4.pedals/shifters
I figure to just get it going with the same t-case and front diff if the junkyard stuff works and start collecting the 2spd stuff as I find it. Really sounds like the way to go. Anyway trying to time my j-yard visits between the rain showers here in Washington.
Thanks again for your help.

The thread you want is in the AWD/4x4 section. It is labeled Transfer case swap to a 2 speed - manual shift. Look this over and you will see the info you need. Basically you need a front diff from a late 80's to 1996 S-10 Blazer or truck. You will need a NP231C transfer case from any S-10. The only difference is the way the transfer case bolts to the tranny. There are 6 bolt round patterns as well as 4 bolt square patterns. Yours will be the 4 bolt pattern. I am talking about the adapter mounting to the tranny.

snowy23 wrote:p.s- Is there any means of making a $$ contribution to those that host and maintain this site? It really does save folks a lot of money.
=;

Donations can be made through Paypal to: astrosafari@animegrafx.com

I'm surprised it hasn't been brought up yet but if you remove the front driveshaft the van WILL creep (as in roll away) if you park on any kind of incline. Regardless if you are in Park or not. If your tcase is totally toasted this may not happen but in general, this is the rule. So make sure your ebrake works and use it.

Yes, one of the posts mentions the drift issue. I found a np231c t-case from a 1991 GMC S-15 Jimmy with very light use. Will be getting it for my eventual conversion.
One problem guys. Removing the front d-shaft has become a pita. The bolts at the front diff are these crazy start shaped bolts. One has become worn, the other seems to be almost welded to the flange I imagine it's due to the exhaust heat. I've seen a good bolt extracter somewhere on this site. Don't need it yet but open to advice on which one works best with rounded bolts etc. Trying vise grips, heat and penetrating oil.
Also what's the sequence for removing the t-case/transmission support in order to get to the one bolt, (1 of 5), holding the t-case to the transmissions back in? I got the bolt out at the j-yard but I can see getting it back in will be a pain unless there's a way to lower the support while supporting the transmission/t-case as it goes back together. The bolt I'm referring to is at the bottom of the t-case, right above and somewhat hidden by the support cross-member. Seems like I'll have to remove the mounts on top of the support to get to that one bolt for re-assembly.
Also the torsion bars go through the support so I'm not sure how to deal with all the various parts involved with removing the t-case to try the one I got from the j-yard. Sorry for the long post just trying to be clear and concise.

thanks all

I mentioned the "creep" problem in a PM. As long as you set the brake, you should be OK.

I would like to add that the front end disconnect (and swapping to the S10 front axle) is a really good idea, but completely unnecessary. It saves wear and gas, but that's all. A couple new vehicles (Jeep TJs, for one) don't even use them anymore.

I'm glad mine has the Blazer front end with the disconnect, since my driveshaft isn't perfectly balanced, and is annoying at highway speed. My original front end was toast, so when Mic replaced it, he upgraded and installed the 4x4 Posi-Lock.

If I recall correctly, one member swapped in a T-case from a 1995 Blazer that had a 5-speed, and used the stock drive shafts from a '99 up AWD astro. Just something to think about, Mic paid $400 something for the shafts in my van to be built.

Oh, yeah, On the drive shaft bolts, you will need the right socket, I think it's a 12 point, but it could be a inverted torks. Can't remember. ](*,) Mine were tight, but once cracked loose, they came right out.

I'm not sure on the T-case bolts, I hate to admit that I haven't had mine out.

rlsllc wrote:Oh, yeah, On the drive shaft bolts, you will need the right socket, I think it's a 12 point, but it could be a inverted torks. Can't remember. ](*,) Mine were tight, but once cracked loose, they came right out.

I'm not sure on the T-case bolts, I hate to admit that I haven't had mine out.

Yes, They are e-torx. They were pretty tight,also 2 different sizes on each end of the shaft.
Sorry,definitely should have mentioned ,I was using my e-brake all the time! #-o
When you jack up the tranny to remove the mount,you should have enough room to get the t-case bolts in,its tight.But you shouldnt need to lower the crossmember.However I was putting another BW4472 t-case back in.Good luck with your swap!

snapple wrote:

rlsllc wrote:Oh, yeah, On the drive shaft bolts, you will need the right socket, I think it's a 12 point, but it could be a inverted torks. Can't remember. ](*,) Mine were tight, but once cracked loose, they came right out.

I'm not sure on the T-case bolts, I hate to admit that I haven't had mine out.

Yes, They are e-torx. They were pretty tight,also 2 different sizes on each end of the shaft.
Sorry,definitely should have mentioned ,I was using my e-brake all the time! #-o
When you jack up the tranny to remove the mount,you should have enough room to get the t-case bolts in,its tight.But you shouldnt need to lower the crossmember.However I was putting another BW4472 t-case back in.Good luck with your swap!

You guys are great. I'm really starting to feel this swap thing.
I did finally get the proper socket for the e-torx bolts. Had to use a bolt remover from Sears to get the stripped one off, but it worked like a charm. I now have the np231c and will be rounding up the other parts soon. Traded a old laptop with a guy on craigslist. Still not sure about the front diff. If I get one from a s-10, then need to change the rear diff gears to match, is there a way to determine what gears the s-10 has before I buy it? Would like to not change the rear if I don't have to.
If I do need to swap out some gears, what is the ideal ratio for highway driving up to 70 mph yet be able to tow a 17' boat easily? I've read where some go to 4.10's but not sure if that would be ideas for my situation. Is this something I can do myself or is it best left to a mechanic? I do know a few who could work for less that shop rates and still do a good job. Also guys there seems to be a leak where the t-case and rear d-shaft connect. right around the vent tube area and it's quite wet on the floor of the van (underside). I see there's a seal where the d-shaft slips into the t-case. Can that be changed easily? The one I got from the j-yard seems to be in good shape.
Thanks again for all the help and inspiration.