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4th Gen Rear End?

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Old Feb 16, 2016 | 12:10 PM
  #1  
mattbhm's Avatar
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
4th Gen Rear End?

Well, I have yet another question.

So a little over a week ago, I bought these seats and while I was down there, he said he had a 3.42 low mile 4th gen posi with all of the disc brakes. He wants $350, it supposedly has somewhere between 50-100k miles.

I was already looking at getting the rear disc brake conversion kit, and the rear end that's on it has many thousands of miles on it. If I'm not mistaken, I mean 250k+.


He said he'd hold onto it for me, will it work? First question, will it definitely work on a 3rd gen Trans am? I know it'll work on a 3rd gen camaro, and that they're almost identical in most ways, but I want to be sure. How are the stock 3.42 for street driving? It's probably exaggerating but I'm hoping to have 300-350ish HP when it's all said and done. Can they handle that?

It's not going to be a daily driver, but it will be driven enough and occasionally back and forth to college/work.

I read that they're quite a bit bigger, does that make the 3rd gen wheels look stupid on them? I'm not really a fan of the 4th gen wheels..



Thanks!!

Last edited by mattbhm; Feb 16, 2016 at 12:15 PM.
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Old Feb 16, 2016 | 12:36 PM
  #2  
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Car: 92 RS
Engine: Sbc With h/c/i/e holly4150
Transmission: 700r
Re: 4th Gen Rear End?

yes will fit in TA, 3.42 is good gear, will be fine with 300hp and yes will look stupid with 3rd gen wheels they will stick out
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Old Feb 16, 2016 | 12:45 PM
  #3  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by Amillionoh7
yes will fit in TA, 3.42 is good gear, will be fine with 300hp and yes will look stupid with 3rd gen wheels they will stick out
Thanks! Sounds alright so far.

If it ends up looking really stupid, I'll probably end up with aftermarket or Corvette.. Or maybe I'll rethink the 4th gen wheels..


More opinions please!
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Old Feb 16, 2016 | 05:16 PM
  #4  
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Re: 4th Gen Rear End?

4th gen rear ends came with 2 limited slip differentials. The '93 to '97 used the Auburn, which sits at the bottom of my list of good differentials (junk). The other is the Torsen, which was used from '98 to '02. This is a much better differential.
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Old Feb 16, 2016 | 05:38 PM
  #5  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by big gear head
4th gen rear ends came with 2 limited slip differentials. The '93 to '97 used the Auburn, which sits at the bottom of my list of good differentials (junk). The other is the Torsen, which was used from '98 to '02. This is a much better differential.

I will be sure to ask him! I'd like to know if it's good and worth the $350 tonight, so that's great info!
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Old Feb 17, 2016 | 07:47 AM
  #6  
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From: South TX
Car: 92 RS
Engine: Sbc With h/c/i/e holly4150
Transmission: 700r
Re: 4th Gen Rear End?

I ended up using corvette c5 z06

https://www.thirdgen.org/forums/tran...rear-swap.html
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Old Feb 18, 2016 | 08:58 AM
  #7  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Alright, he said it's 98-02, so that's a plus. He also says it's under 100k, but is thinking closer to 50-60k. How long do these things last?

How does $350 sound for one with very low miles, disc brakes inc?
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Old Feb 18, 2016 | 10:04 AM
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Re: 4th Gen Rear End?

If it has the Torsen differential then it's probably fine. Lately I have heard of a later 4th gen that had a Auburn in it. Pull the cover and check it before putting your money down.
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Old Feb 18, 2016 | 10:22 AM
  #9  
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Car: 1984 z28
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Transmission: T56
Axle/Gears: 7.625" 28 spline 3.23
Re: 4th Gen Rear End?

Originally Posted by big gear head
4th gen rear ends came with 2 limited slip differentials. The '93 to '97 used the Auburn, which sits at the bottom of my list of good differentials (junk). The other is the Torsen, which was used from '98 to '02. This is a much better differential.
I thought the torsens started in 99?
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Old Feb 18, 2016 | 10:57 AM
  #10  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by big gear head
If it has the Torsen differential then it's probably fine. Lately I have heard of a later 4th gen that had a Auburn in it. Pull the cover and check it before putting your money down.
My father will give him a call and at least ask what year it is. And see if he can pop the cover and see.

Would you say if it's 2000+ it's definitely good, or still pull the cover? It's just that he said he'd hold it for us, and I'd hate to go there pull the cover and say we don't want it..
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Old Feb 19, 2016 | 08:07 AM
  #11  
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From: South TX
Car: 92 RS
Engine: Sbc With h/c/i/e holly4150
Transmission: 700r
Re: 4th Gen Rear End?

I have a auburn in my 93 and swapped 92 and never had a problem with either one. but only payed 200 for the 96 rear I put in the 92
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Old Feb 19, 2016 | 09:19 AM
  #12  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by Amillionoh7
I have a auburn in my 93 and swapped 92 and never had a problem with either one. but only payed 200 for the 96 rear I put in the 92
Well, we're going to call him Sunday and see what he says.

Was that $200 for the whole rear end with the brakes? $350 still sounds good to me, especially because of the low miles.
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Old Feb 21, 2016 | 04:08 AM
  #13  
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From: Howard Lake, MN
Car: 86 Camaro
Engine: 355- hopefully a 5.3 this summer
Transmission: 700r4
Axle/Gears: 3.42
Re: 4th Gen Rear End?

it might also have the factory locker differential in it like the one i bought last spring.. paid the guy $300 for a 3.42/locker/non traction control/disc brake rear end out of a 70,000 mile '02 Z28 convertible that got hit hard in the right front corner.. it bolted right into my 86 Camaro and the brake line hooked right up. parking brake cables are different, but i just zip tied them to the torque arm for the time being. i will make some brackets to mount them in the car in the next couple of weeks when i have the car apart to swap a proper manual trans in place of the boring auto..

regarding wheels, i'm running GTA wheels and they look simply badass sticking out 1.75" farther on each side than they did with the stock rear end. the outer sidewall is about 1/2" inside the edge of the wheelwell.. perfect..
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Old Feb 21, 2016 | 09:01 AM
  #14  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by novaderrik
it might also have the factory locker differential in it like the one i bought last spring.. paid the guy $300 for a 3.42/locker/non traction control/disc brake rear end out of a 70,000 mile '02 Z28 convertible that got hit hard in the right front corner.. it bolted right into my 86 Camaro and the brake line hooked right up. parking brake cables are different, but i just zip tied them to the torque arm for the time being. i will make some brackets to mount them in the car in the next couple of weeks when i have the car apart to swap a proper manual trans in place of the boring auto..

regarding wheels, i'm running GTA wheels and they look simply badass sticking out 1.75" farther on each side than they did with the stock rear end. the outer sidewall is about 1/2" inside the edge of the wheelwell.. perfect..
Awesome! Is that using the original master cylinder? Chances are I'll end up replacing mine.. It's all dried up and nasty. Actually, before everything is said and done I'll probably have replaced 90% of everything brake related.

I assume your talking about the 3rd Gen GTA Mesh wheels?

No rush, but would you happen to have a picture?
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Old Mar 1, 2016 | 07:09 PM
  #15  
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Re: 4th Gen Rear End?

Any body know how to aling the wheels. I just swap mine to a 2002 ss rear en but when I bolt everything back up my right tire is toe in. I'll appreciate any help on how to fix this
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Old Mar 1, 2016 | 07:30 PM
  #16  
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From: El Sobrante, California
Car: 1984 z28
Engine: Crate replacement L31R 350
Transmission: T56
Axle/Gears: 7.625" 28 spline 3.23
Re: 4th Gen Rear End?

The diff is bent if you have toe problems. A differential shop or some collision shops can straighten it out for you.
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Old Mar 1, 2016 | 07:43 PM
  #17  
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Re: 4th Gen Rear End?

Yea, the only way you can have toe in is if the housing is bent, and pretty bad. I'd scrap it and find another one.
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Old Mar 1, 2016 | 08:02 PM
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Re: 4th Gen Rear End?

Ok thanks guys really appreciate it
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Old Mar 19, 2016 | 09:11 AM
  #19  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Just as an update, we're picking it up today! Will get pics, even if it's just going to bad pictures of a rusty rear end.

We did call him last week, he said he can guarantee it came from a 2002 z28 SS. Possibly the same car that my seats came out of.
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Old Mar 23, 2016 | 10:58 AM
  #20  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Well, we got it, it looks like a big, rusty, oil covered, rear end.

I've been doing more and more research, and people seem to say these rear ends could barely(and sometimes couldn't) even handle stock power? And they last longer with an auto(like I have) but still can't handle much more than stock at all. Are they really that bad? I mean like I said, this is going to be a daily/weekend driver, but I want a nice amount of power. And for when I need it, I can't have the rear end blow when I take off from a red light. My budget is pretty low(Just graduating high school so I don't have much haha) so obviously I wasn't going to get a new moser 12 bolt or anything, but I wish I had looked some more before I bought this.

Or I could be wrong.
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Old Mar 23, 2016 | 11:24 AM
  #21  
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Re: 4th Gen Rear End?

Originally Posted by mattbhm
Well, we got it, it looks like a big, rusty, oil covered, rear end.

I've been doing more and more research, and people seem to say these rear ends could barely(and sometimes couldn't) even handle stock power? And they last longer with an auto(like I have) but still can't handle much more than stock at all. Are they really that bad? I mean like I said, this is going to be a daily/weekend driver, but I want a nice amount of power. And for when I need it, I can't have the rear end blow when I take off from a red light. My budget is pretty low(Just graduating high school so I don't have much haha) so obviously I wasn't going to get a new moser 12 bolt or anything, but I wish I had looked some more before I bought this.

Or I could be wrong.
Sounds like you bought a rear end. Most are going to have rust. Take off the cover, make sure it's good, seal it back up. If the rust is bothering you, clean it up and paint it. It's the perfect time with it out of the car. A little more than stock power for a 02 SS is a fair difference from little more than stock for a third gen. If it's good, clean it up, hook it up, fill it up with proper fluids and have fun with it.
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Old Mar 23, 2016 | 11:31 AM
  #22  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by brettr81
Sounds like you bought a rear end. Most are going to have rust. Take off the cover, make sure it's good, seal it back up. If the rust is bothering you, clean it up and paint it. It's the perfect time with it out of the car. A little more than stock power for a 02 SS is a fair difference from little more than stock for a third gen. If it's good, clean it up, hook it up, fill it up with proper fluids and have fun with it.
Yeah, I'm not really worried about the rust. We popped the cap, made sure it was 3.42, dumped the fluids and will refill before installing.

It'll get painted. My budget may be low, but I have time, and this car will be SHARP when it's done.

And I'm feeling a little better. I never thought about the stock power that they're talking about is an LS1 with 330HP. I'm planning on grabbing an old Yukon or something 350, changing the cam out, adding headers and a new dual exhaust. Not 400HP, so I feel like I should be good. Bigger problem is going to be the stock tranny, but I've heard that for 600-700 you can rebuild the 700r4 to easily handle 350-450HP. And as much as some people might say otherwise, I want an auto. Not just to save the rear end, but for convenience.. No need to be shifting all the time when I'm city driving..
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Old Mar 23, 2016 | 12:34 PM
  #23  
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Re: 4th Gen Rear End?

As long as you use regular street tires it should be fine. If you put something sticky on it then you might have problems. I don't know how much trouble 3rd gens have with wheel hop, but as long as you keep it under control you shouldn't have any problems.
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Old Mar 24, 2016 | 04:23 AM
  #24  
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Car: 91 Firebird
Re: 4th Gen Rear End?

Since you have it off, might as well go with tubular LCA's and panhard bar. Put in a poly torque arm bushing as well, and check the trans mount as well. IDK what condition the rear shocks are, but if you have to connect everything, may as well connect them all with new and better parts.
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Old Mar 24, 2016 | 09:05 AM
  #25  
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From: Birmingham, AL
Car: 1985 Trans am
Engine: LG4
Transmission: 700R4
Axle/Gears: Will be 3.42
Re: 4th Gen Rear End?

Originally Posted by brettr81
Since you have it off, might as well go with tubular LCA's and panhard bar. Put in a poly torque arm bushing as well, and check the trans mount as well. IDK what condition the rear shocks are, but if you have to connect everything, may as well connect them all with new and better parts.
Yeah.. We're gonna end up replacing a lot.. This car has had 250k+ miles put on it with no care at all.(Not by me. ) I'm glad she looks as good as she does.

But for right now, there's gonna be a major halt in the build. I'm going to help my sister build her 68' VW Bug for college before going anywhere on mine. When I get back to it, I'll have the money I collected up while helping my sister, and we can just start the build right up.
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Old Mar 29, 2016 | 06:18 PM
  #26  
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From: Mersea island UK
Car: 1989 Trans Am GTA
Engine: Procharged 350tpi
Transmission: uprated 700R4
Re: 4th Gen Rear End?

Originally Posted by novaderrik
it might also have the factory locker differential in it like the one i bought last spring.. paid the guy $300 for a 3.42/locker/non traction control/disc brake rear end out of a 70,000 mile '02 Z28 convertible that got hit hard in the right front corner.. it bolted right into my 86 Camaro and the brake line hooked right up. parking brake cables are different, but i just zip tied them to the torque arm for the time being. i will make some brackets to mount them in the car in the next couple of weeks when i have the car apart to swap a proper manual trans in place of the boring auto..

regarding wheels, i'm running GTA wheels and they look simply badass sticking out 1.75" farther on each side than they did with the stock rear end. the outer sidewall is about 1/2" inside the edge of the wheelwell.. perfect..

same here, got a STRANGE rear axle (4th gen width) with GTA wheels and looks way cooler. makes standard GTA look narrow/tucked in
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