Can a '93 GT4/G80 replace an open GT4 on a '98 ??

ANYTHING TO DO WITH MAKING YOUR VAN MOVE EXCEPT FOR THE ENGINE ITSELF.
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WE7X
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Can a '93 GT4/G80 replace an open GT4 on a '98 ??

Post by WE7X »

I am still looking for a donor chassis with a GT4/G80 rear diff, to replace my '98 open GT4 ( 3.73) diff. Have cash in hand, but nothing yet to purchase. Two more Pick'n'Pulls to look at, within a 100 mile radius.
Any 4WD S-10's or S-15's that might have the same type of rear end? Where are the RPO codes located on those P/U's and are they the same codes as for our A/S vans? I have looked some but don't see any label with RPO codes, except very old ones with the label in the glove box. Others do not seem to have any signs of a label.
Will an entire '93 Astro GT4/G80 rear axle assembly be a suitable replacement for the open diff GT4 (3.73) on my '98?
Axle spline count should not matter if swapping the whole assembly. Are there issues with dimensions or spring mounts or other difficulties I might run into. I think the '93 rear end I found was on composite springs. Is that a problem, and can I use my original springs and hangers, or do I need something else off the '93 donor?
I would just like to know what I am getting into before I spend an afternoon on large crushed gravel under the rear of a muddy rusty donor chassis. I will want pull the cover to be sure the unit looks serviceable.

Thanks in advance
Rod J
Issaquah, WA
WE7X aka Rod Johnson
Forest Green Metallic '98 LS AWD
Issaquah, WA

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Re: Can a '93 GT4/G80 replace an open GT4 on a '98 ??

Post by Captn. Crunch »

I don’t think that is a straight up swap as the width of the fiberglass springs is different than the steel springs. I’ve never messed with the glass springs but I seem to remember reading I’m sure if you search here you might find what you’re looking for.
This is no place to skimp. If your rear end fails you are done! Don’t step over dollars to pick up dimes, spend the money once and never worry again. Used G80’s are a crap shoot. Thy weren’t that good when they were new. Google limited slip GM 7.625”. You will find new and used options. Some of the used ones will be rebuilt. Most will be from camaro/firebird. Ive never liked the G80. I wouldn’t go looking for one when there are much better options for same money.
The G80 only locks up to 25 mph and not until it senses 100 rpm wheel speed difference. A clutched limited slip or a Torsen style carrier will operate invisibly and at all speeds
Captn. Crunch
"I don't beat my rig-I use it to it's maximum potential"
1994 Safari conversion (sold) and miss'n it!
1999 Safari SLE AWD junked
2003 GMC Safari AWD SLT
cast iron Torsen equipped front diff
S-10 leafs-G80 rear w/3.73’s
2” body lift w/Falken Wildpeak AT’s

Topic author
WE7X
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Joined: Mon Jan 01, 2018 6:11 pm

Re: Can a '93 GT4/G80 replace an open GT4 on a '98 ??

Post by WE7X »

I do agree that the G80 is a bit of a ticking bomb, but I am not yet ready to spend more on a rear end than I paid for the whole rig.....until I have a bit more experience in it (only about 350 miles so far, and just about ready for my second tank of fuel).
If I find a suitable used GU4/G80 in a Pick'n'Pull' after inspectiion, I would install new lubricant, and install it under my van. I would be into it less than $200, and for that I would hope to get a summer of moderate use, and some experience with the rig. I would also have a 'spare' rear end of the correct ratio...just in case the fuse was a bit shorter than anticipated
I am not afraid of spending the money, when I decide this is going to be the correct rig for my use.
I have been talking to some of the local off-road crowd, and got recommendation for three shops in the area who do some serious rear end work. One shop was the unanimous leader by reputation. When I called that shop, I was given a labor estimate right off the top of the fellows head, and then he told me I could bring in my own Posi unit to be installed, if it was a Torsen, Eaton, or a Yukon. He was also the cheapest labor at $400 -$600, depending upon condition of the existing parts.
I guess another option would to look for another open GU4 diff, have the new Posi unit installed in that. I can do the work putting the LS rear end back in the van.
For now... I am still looking.

Rod J
WE7X aka Rod Johnson
Forest Green Metallic '98 LS AWD
Issaquah, WA
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