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Bear with me here folks. I'm new to the third gen world here. I've done searches trying to find out why the 4th gen swap is so common.
I would presume it's for its ability to withstand more power, but I'm just guess isn't.
LOTS of info in searches for HOW, but nothing about WHY.
I think a lot of the 4th gen rear swaps is just because a 4th gen rear is easier to obtain in many cases.4th gen rear is the same strength as a 1990 up 28 spline 3rd gen rear-gears are the same as in a 1985 up 3rd gen rear.1998 up posi 4th gen axles have a Zexel torsen posi-the torsen carrier can be installed in a 3rd gen rear end-pre 1990 will need 28 spline axle retrofit.
Comes with a better disk brake system.
Has 28 spline axles but a third gen diff can be upgraded to 28 spline but the posi also needs to be replaced for 28 splines.
Diff is wider so using fourth gen rims makes them fit better.
There is no strength difference between a fourth gen diff and a 90-92 third gen diff which comes with 28 spline axles.
Third gen ring gear size increased from 7.5" to 7/5/8" in 1986 which is the same tiny size the fourth gen diff uses.
So other than a better disk brake system, there is no great advantage to upgrade to a fourth gen diff. The larger 28 spline axles are still weaker than aftermarket 28 spline axles in a third gen. Without changing the rims with a different backspace, you'll have a bit of clearance issues depending what size tires you use.
You can upgrade your third gen diff with better brakes, 28 spline axles and a better posi and it will be better than a stock fourth gen diff plus you get to keep using the rims/tires you currently have on the car.
If you're spending all that money to try and make a 10 bolt better, spend a little more on a better upgrade like a 12 bolt or 9".
Lot of 4th gens have a 3:23 rear ratio, much better than the 2:77 in most IROCs. What the others have posted is also true, not hard to find a 4th gen rear too these days.
The main reason I see some going to a 4th gen rear is a blown differential in the car they have now. Its much cheaper to put in a 4th Gen rear than spend $1,500.00 for a rebuilt 10 Bolt with quality parts or the 9" or 12 Bolt replacement. I think if you shop around you can build a 9" for just over $2,000.00 and up from there.
they are wider- makes the car look meaner with stock wheels and maybe stick a little better in the corners.
better brakes.
the '02 Z28 rear that i have in my car has a factory locking differential in it- you won't put the better brakes and that locker into a third gen housing for less than the $300 i gave for the whole rearend...
Everyone has pretty much said why, and I agree. I'll add my $.02.
I spent $350 + shipping for an '02 SS rear diff I found on ebay. 3.23 gears had a noticeable affect on acceleration in my '86 IROC , not too much difference in fuel consumption.
Be prepared for modifying/changing the master cylinder and/or proportioning valve if you currently have a 3rd gen drum brake setup. Although, I haven't changed/mod'd my MC/prop valve yet and the car seems to brake OK. You can read more in the BRAKE Section of TGO.
I plan on replacing the axles (pitted) and the auburn carrier housing because although the posi still works, the pinion shaft hole in the carrier is wallowed out, allowing for excessive axle endplay.
Point being, unless you're extremely lucky, plan on spending a few more bucks to get the rearend back to 'like new' condition.
Due to the ease of the swap and the many benefits, I highly recommend it.
Its cheap upgrade for a posi rear if your car came with a peg leg like my 91 z.
Good rear brakes discs to replace my drum brakes. So nice upgrade there
Quite common to find 3.23-3.42 gears so nice upgrade over most thirdgens 2.77,2.73 combos.
And i am a big fan of the torsen diff. Better than clutch types and doesnt wear out like those do.
And 4th gen spec and latemodel c5-c6 vette wheels fit better on these rears.
I just put one in, so here is everything I know is an advantage
It is way cheaper than a Ford 9 inch, moser, or strange rear end
I picked up mine for $300, with a new posi unit and 4k miles on the rebuild, which is probably $1000 less than an ftermarket one
Rear Disc Brakes
If you get it out of a Z28/SS, AFAIK they came standard with Posi
They come with higher numerically gear ratios
And you can use Corvette wheels without spacers
Everyone already mentioned this all
However, it is not entirely drop in and go
You will need a new proportioning valve if you don't have a disk brake car
And you will need to mess with the E brake cables, or at least I did because I had rear Drum brakes
Besides that everything does bolt in, you will just need to sort out the things I mentioned above
Well that settles it.
I'll be searching for a 4th gen rear.
-wider to fit vette wheels better.
-better gear ratios.
-disk brakes.
All are options I would like to utilize.
In searching for the best rear end in the junk yards, what's the best way to find rear end ratios? I know on my truck, the equipment idea fixation sticker in the glove box shows the ratios. Is there a similar sticker on the third gens somewhere?
Thanks for everyone's valuable input!
Last edited by Jmlcolorado; 07-10-2015 at 05:04 PM.
Hard to say on gear ratios. If its an ss or ws6 car chances are its 3.42 for 6spd car and 3.23 for auto. Else it could be 2.73 for auto non ss or ws6 like my old ta was.
V6 cars could have 3.08's but also peg legs, not ideal swap there.
If rear is still in the junk or donor car, rpo codes can give you an idea.
...And i am a big fan of the torsen diff. Better than clutch types and doesnt wear out like those do...
When I was doing the research for the posi type I wanted, I read Torsen is stronger, but it has so many small parts and is a pain to rebuild compared to an Auburn unit. When the Auburn unit does need a rebuild, it's not so bad when you do the repairs yourself. Auburn carriers are about $450 new. I've not seen the Torsen on sites like SummitRacing...
Also, I'm curious, are you running a Torsen diff in your twin turbo Orr?
so LCA's and shocks, and torque arm are all the same locations on a 4th gen to bolt in?
thank you
Yes, yes, and yes. Other than the ebrake cables(if you currently have drums) it is a true bolt-in swap.
I picked up a rear from a 97 trans am at my local u-pull back during the Cash-for-Clunkers BS. $110 complete end-to-end, minus the wheels. Added a set of 3.73 gears from an 80's S10 for another $75, new shims and seals for $100, caliper rebuild kits for $16 or so, and new ebrake cables for another $32. Swapped the gears myself so I got to learn something new(priceless), and now have a basically brand-new rear with posi and disc brakes for less than the cost of adding a new posi carrier and a disc brake swap kit to my old rear. And the car is a lot more fun to drive with the posi and new gears.
I have a guy that will sell me a complete 4th gen rear end with 4.10 gears and disc brakes, I've been trying to search up on putting 4th gen gears into my 3rd gens rear end housing, is there in problems that I might come across?
I see everyone saying just do the whole rear end swap, but I do not like the look of the tires sticking out like that...
I have a guy that will sell me a complete 4th gen rear end with 4.10 gears and disc brakes, I've been trying to search up on putting 4th gen gears into my 3rd gens rear end housing, is there in problems that I might come across?
I see everyone saying just do the whole rear end swap, but I do not like the look of the tires sticking out like that...
They will fit, assuming your 3rdgen rear has 28 spline axles. Just swap the entire carrier assembly and pinion over, along with the disc brake parts. Check the backlash first before pulling the gears from the 4thgen rear and set them for the same backlash in your 3rdgen rear.
The Torsen basically DOESN'T EVER need a "rebuild". It has no clutches. Nothing there TO "rebuild".
You "rebuild" an Auburn by throwing it in the trash and installing a new something else. It can't be "rebuilt". Call em yourself and ask, try to get parts out of em yourself, if you don't believe me. That company and its products are a total steaming bucket of spit. Don't put that garbage in your car.
Tahoe, all ya gotta do, is use wheels with the 4th gen, or C5 or later, backspacing. Just put it in. Doesn't make sense to tear it down and put all that into your existing drum-brake rear.
They will fit, assuming your 3rdgen rear has 28 spline axles. Just swap the entire carrier assembly and pinion over, along with the disc brake parts. Check the backlash first before pulling the gears from the 4thgen rear and set them for the same backlash in your 3rdgen rear.
Thanks I will for getting back to me... I will check it out when I take the rear apart...
We purchased our 82 Indy pace car about 3 years ago & only recently replaced the Boyd Coddingtons it came with back to factory rims. The interesting thing is our rear wheels seem to have a much wider track with the tires lining up with the guard flare rather than inside the guards. Could this have a 4th gen diff fitted?
Thank you! Our plan is to remove the black wrap from the roof & give her a paint freshen up & fit new decals along with the factory glass flappy hood we sourced a while ago
I suppose you'd either have a late 3rd gen Aussie rear with the rubber fill plug in the cover, or the fourth gen. Either way you'd have that offset.
She’s never been in Aussie. She came to New Zealand via Hawaii but maybe fitted later. I’m going to measure the overall length on our diff & measure another 3rd Gen diff to try & identify
Last edited by Highlandlad; 01-20-2024 at 11:47 PM.
The "Aussie" would be a borg warner unit, 9 bolt cover. At least im guessing that what tom meant. 82 third gen would be 10 bolt.
4th gen is also 10 bolt cover, but the calipers would be aluminum vs cast iron on a 82.
4th gen has more material around the long bolts that hold the torque arm, 3rd gens are open in that area (you can see the bolts the entire length).
There are other minor differences from 3rd to 4th gen 10 bolts, but id check if those bolts are visible.
The "Aussie" would be a borg warner unit, 9 bolt cover. At least im guessing that what tom meant. 82 third gen would be 10 bolt.
4th gen is also 10 bolt cover, but the calipers would be aluminum vs cast iron on a 82.
4th gen has more material around the long bolts that hold the torque arm, 3rd gens are open in that area (you can see the bolts the entire length).
There are other minor differences from 3rd to 4th gen 10 bolts, but id check if those bolts are visible.
I just checked & found our callipers are aluminium
I just checked & found our callipers are aluminium
I think rather than purchase another diff, I’m going to cut down the one I have. Surely it’s better with the aluminium callipers etc plus I’ll get the gears done while it’s apart. I am a certified welder & I hate spending money when I can sort the issue myself
Might look around for a set of IROC wheels, they have "front" and "rear" offsets that pull the rears in an inch or so. Find them in 15 and 16 inch diameters. Cutting the housing would work but finding axles might be a problem?
Comes with a better disk brake system.
Has 28 spline axles but a third gen diff can be upgraded to 28 spline but the posi also needs to be replaced for 28 splines.
Diff is wider so using fourth gen rims makes them fit better.
There is no strength difference between a fourth gen diff and a 90-92 third gen diff which comes with 28 spline axles.
Third gen ring gear size increased from 7.5" to 7/5/8" in 1986 which is the same tiny size the fourth gen diff uses.
So other than a better disk brake system, there is no great advantage to upgrade to a fourth gen diff. The larger 28 spline axles are still weaker than aftermarket 28 spline axles in a third gen. Without changing the rims with a different backspace, you'll have a bit of clearance issues depending what size tires you use.
You can upgrade your third gen diff with better brakes, 28 spline axles and a better posi and it will be better than a stock fourth gen diff plus you get to keep using the rims/tires you currently have on the car.
If you're spending all that money to try and make a 10 bolt better, spend a little more on a better upgrade like a 12 bolt or 9".
I have a 4th gen diff fitted to our 82 Camaro which was done by the previous owner. My problem is I have now fitted factory rims & tires & the back wheels look too wide & I need to narrow the diff. Are there 28 spline axles I can get if I narrow up the housing to match the width of a 3rd gen diff or do I need to shorten my axles as well?
Better plan would be, find some wheels with the appropriate offset to match the rear, and add spacers (the better types, specifically hub-centric) to the front, about 1¾". That also gives you the opportunity to install MODERN high-performance tires rather than the 15" pizza cutters that came on 82 cars. Which, in their day, were YYYYYYYUUUUUUUUUJJJJJJJJJJE wide; but in 2023, they're ... pizza cutters.
Better plan would be, find some wheels with the appropriate offset to match the rear, and add spacers (the better types, specifically hub-centric) to the front, about 1¾". That also gives you the opportunity to install MODERN high-performance tires rather than the 15" pizza cutters that came on 82 cars. Which, in their day, were YYYYYYYUUUUUUUUUJJJJJJJJJJE wide; but in 2023, they're ... pizza cutters.
My problem is she’s an 82 Indy Pace car we are restoring back to as close as original that we can so the factory wheels are staying
I have a 4th gen diff fitted to our 82 Camaro which was done by the previous owner. My problem is I have now fitted factory rims & tires & the back wheels look too wide & I need to narrow the diff. Are there 28 spline axles I can get if I narrow up the housing to match the width of a 3rd gen diff or do I need to shorten my axles as well?
If you shorten the rear axle tubes to match the width of the original 3rd gen you should be able to use original 28 spline axles from a 90-92. I would not recommend cutting and welding the axle but that is just me.
Bear with me here folks. I'm new to the third gen world here. I've done searches trying to find out why the 4th gen swap is so common.
I would presume it's for its ability to withstand more power, but I'm just guess isn't.
LOTS of info in searches for HOW, but nothing about WHY.
It's more common in the salvage yards, it is slightly stronger than '82-'88 axles, and it's a direct bolt in that sometimes comes with better gearing and occasionally a Posi.
If you can get one, you can grab a stronger axle instead. I've done a Dana 60 from a late 1970s Dodge pickup, there are plenty of semi-float 60s still out there. Not that much heavier than the Strange S60, and no more initial cost than a 4th gen rear. The only drawback is if you want tall gears. Adapting the torque arm isn't difficult, but it's a good opportunity to do a shorter, upper third ling instead, like the pre-IRS Mustangs did. 2010 or so, IIRC
The Torsen basically DOESN'T EVER need a "rebuild". It has no clutches. Nothing there TO "rebuild".
You "rebuild" an Auburn by throwing it in the trash and installing a new something else. It can't be "rebuilt". Call em yourself and ask, try to get parts out of em yourself, if you don't believe me. That company and its products are a total steaming bucket of spit. Don't put that garbage in your car.
Tahoe, all ya gotta do, is use wheels with the 4th gen, or C5 or later, backspacing. Just put it in. Doesn't make sense to tear it down and put all that into your existing drum-brake rear.
While Auburns are extremely difficult to rebuild, they work great for normal in-town commuting fun even after 100,000 miles. They are not impossible to freshen up, you just need a machine shop with a welder.
Better plan would be, find some wheels with the appropriate offset to match the rear, and add spacers (the better types, specifically hub-centric) to the front, about 1¾". That also gives you the opportunity to install MODERN high-performance tires rather than the 15" pizza cutters that came on 82 cars. Which, in their day, were YYYYYYYUUUUUUUUUJJJJJJJJJJE wide; but in 2023, they're ... pizza cutters.
I was proving Sofa wrong 15 years ago, and Sofa is still posting things that are not true or factual. A 215/65R15 was not as wide as an old F60-15 from 1970. Corvette had 255s in 1982, which were 1.6" wider, while Countach had 345s, which were 5.1" wider.
Is wider better? Looking, maybe. The Viper and Miata racers will tell you what they do for lap times. But what really matters is lateral Gs. The ability to change direction at speed. Just before the 245/50R16 Goodyear Gatorbacks appeared on the 1984 Anniversary T/A, these cars did 0.85g. With the 245s, the extra 1.2" of width was worth only a piddling 0.02 of extra Gs.
You don't need wider tires.
With 4 posts and a join date of Jan 2024? Who are you trying to kid here?
A 215/65R15 was not as wide as an old F60-15 from 1970.
What does this have to do with a 4th gen rear in a 3rd gen car, and the ability to put MODERN tires that you CAN ACTUALLY BUY in 2024 on wheels with 4th gen offset as opposed to the 215/656-15 pizza-cutters? What the 215/65-15s did on the skid pad in 1984 isn't at issue here; going to the tire store and BUYING DECENT TIRES is.
Auburns are extremely difficult to rebuild
Yeah they sure are... Auburn won't sell you any parts.
they are wider- makes the car look meaner with stock wheels.
In '93 or so, I didn't know this. I blew my 9 bolt, and since I worked at a salvage yard at the time, and DID know that the 4th gen had the "same floor pan/suspension" as the 3rd gen, I was pretty sure a 4th gen rear would bolt in so I grabbed a 4th gen rear out of the yard. I was stoked. Put my car up on the lift in the shop after work, pulled the 9 bolt, slapped in the 4th gen, put my wheels on, and I was pumped....quick, easy fix! I lowered the car down and as soon as the wheels hit the ground I could see the "problem". OMG...it looked SO cheese dick! I drove the car for a few days like that, tying to convince myself that it looked "meaner/bad azz"....but really, I knew. It's looked hard-core, white-trash, MULL-ETT. I made a new plan and swapped that thing out of there, for another 9 bolt.
Last edited by Tom 400 CFI; 01-27-2024 at 11:16 AM.
im thinking someone slapped a 4th gen rear in that pace car. why do people do the swap? same reason there is a 5.3 in everything with wheels now.... its a cheap upgrade in performance that most anyone with wrenches can do..
however, i would yank that thing out and put a standard 3rd gen width rear in there. to me, it does not look mean or whatever, i just see a 3rd gen with a 4th gen rearend in it. will be a cool car once you get it straightened out.
Will 4th gen Camaro axels work in the 3rd gen rear end 7.5 / 10 bolt if I have the torsen zexel or will I have to order new ones?
Originally Posted by 8t2 z-chev
I think a lot of the 4th gen rear swaps is just because a 4th gen rear is easier to obtain in many cases.4th gen rear is the same strength as a 1990 up 28 spline 3rd gen rear-gears are the same as in a 1985 up 3rd gen rear.1998 up posi 4th gen axles have a Zexel torsen posi-the torsen carrier can be installed in a 3rd gen rear end-pre 1990 will need 28 spline axle retrofit.
Zackly. They are EZACKLY the same, except, different. Specifically, they are about 1¾" longer on each side. Not quite 3" total, butt, close enough for gummint work. At a certain level, it doesn't too much matter HOW MUCH they don't fit by; either they fit, or they don't. In this case, they don't.
No biggie though, new ones that FIT YOUR AXLE aren't all that $$$$. And besides, are better in every way than any stock BUTTER CRAP GARBAGE that's already wore out, which they ALL are within 20,000 miles or so of driving off the showroom floor. New good aftermarket ones are ALTOGETHER better than ANY used stock ones. And prolly cost less than wore out stockers plus shipping, anyway.
07-03-2015, 06:04 PM
