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It appears I have the dreaded 2.73 rear gear in my '89 Camaro, and to top it off it's an open differential. I was wondering if I can't find another 3rd gen parts car with a better gear set-up to get the rear end off of if I could swap the gears out of an S-10 pick-up. Seems like S-10 pick-up are all over the place in salvage yards and they mostly use 7.5 or 7.6" rear ends. Also, a person might be lucky and find one that even has some kind of posi unit in it. If this is possible how do I know whether I need gears out of a 7.5 or 7.6 rear end? I've read conflicting information on when GM made the switch: some sources say late 80's other's early 90's. Are there any other vehicles that used gears that fit the 10 bolt rear ends our cars?
If you're talking about getting a different rear end and swap it to your car and then get a third carrier & gears out of another one and if it is a possi you will probably have to rebuild it. You might save yourself a bunch of work/time and just buy a new posi carrier/gears/bearings package. And if you have 26 spline axles you could up date those to 28 spine at the same time. JAT.
7.5 & 7.6 are the same thing. Only difference is, the OD of the ring. Both sizes fit in both rears. I don't think you can buy 7.5s anymore since they're now redundant.
Virtually all GM RWD cars except some B bodies, plus S trucks and Astro vans, have used that rear since the late 70s.
You DO NOT want the S truck "posi". It is the worthless Grenade-Lock, TOTALLLY unsuitable for "performance" usage on pavement. Gears, maybe; posi, no. But since gears only cost $200 or so, buying a used rear axle isn't the best sense way to get them anyway.
Last edited by sofakingdom; Feb 25, 2023 at 05:06 PM.
I didn't realize new 7.5 ring and pinions were so cheap. That would be the way to go.
That's good know about S-10 posi units. Were there any factory 7.5 posi units that were any good? The factory posi unit in my '78 Firebird seems to have held up well over the years, but it's an 8.5" unit.
Might look into a fourth gen rear end? A bit wider than the 3 gen but if you would run some different offset wheels, maybe IROC wheels (?), that extra width might not be a factor. Lots of them around with posi and a 3:23 gear.
Might look into a fourth gen rear end? A bit wider than the 3 gen but if you would run some different offset wheels, maybe IROC wheels (?), that extra width might not be a factor. Lots of them around with posi and a 3:23 gear.
Looks like the 4th gen f-body rear end is 3.5" wider then the 3rd gen one, so it's quite a bit wider. I found a youtube video of a guy doing the swap, however, along with a video of a guy swapping a Ford 8.8 rear end in, which requires A LOT of fabrication. Seems like it would be easier to just have the 4th gen rear end narrowed, if the extra width is a problem. I could see if you're running fairly wide tires and have a lowered the car that extra width being a problem unless you're able to compensate for it with different offset rear wheels.
One thing that would be nice to know is if there is a difference in the track width between the front and back on our cars.
Anyone have pictures of a 3rd gen Camaro with a 4th gen rear end in it? I'm curious how it looks. Also after looking it up I noticed that 3rd and 4th gen F-bodies have about the same rear track, so 4th gen F-bodies must use wheels with more offset to compensate for the increased width of the rear end.
If you put 4th gen or Vette wheels on a 4th gen rear in one of these cars, they fit just like 3rd gen wheels on a 3rd gen rear. Only difference then is, you can actually buy modern tires as a result, since those wheels are in modern sizes, unlike our older wheels.
The difference in wheel offset is about 1¾" to 2" depending on which specific wheels you look at.
If you put 4th gen or Vette wheels on a 4th gen rear in one of these cars, they fit just like 3rd gen wheels on a 3rd gen rear. Only difference then is, you can actually buy modern tires as a result, since those wheels are in modern sizes, unlike our older wheels.
The difference in wheel offset is about 1¾" to 2" depending on which specific wheels you look at.
The difference in wheel offset is about 1¾" to 2" depending on which specific wheels you look at.[/QUOTE]
What does that do to the front wheel/tire clearance when you use wheels with more offset on our cars?
Has anyone here ever compiled a list of things that were carried over from the 3rd to the 4th gen f-bodies? It looks like the wheelbase was the same for both generations, and other features - such as the rear suspension - were the same which makes me wonder if they were both built on the same uni-body.
Fronts with the 4th gen offset won't fit our fronts. They'll stick WAY out farther (that same 1¾ - 2") and rub the fenders.
The front suspension design is completely different, leading the hub to be in a different place.
The designs are fairly similar but have lots of differences, using the front suspension as an example. Couldn't say whether anyone has "compiled a list", or maybe, interviewed a GM engineer or the like.
Fronts with the 4th gen offset won't fit our fronts. They'll stick WAY out farther (that same 1¾ - 2") and rub the fenders.
The front suspension design is completely different, leading the hub to be in a different place.
The designs are fairly similar but have lots of differences, using the front suspension as an example. Couldn't say whether anyone has "compiled a list", or maybe, interviewed a GM engineer or the like.
I was thinking more from an interchange point of view: what 4th gen parts fit the 3rds and are upgrades. Seems like 4th gen f-bodies got more goodies standard.
Why couldn't I just get a 4th generation 7.5 (or 7.6) rear end with a posi and better gear ratio and swap all the parts from it (except the axle shafts) into my current rear end housing? I noticed there's a write up here on installing the disc brakes from a 4th gen car, so I could even switch them over. That would eliminate the wheel fitment issue and it would be a lot cheaper than having to buy all the parts to upgrade my rear end individually. There are so few 3rd generation f-bodies left in salvage yards around here (compared to 4th gen cars) that I doubt I'll ever find a rear end set-up that's any better than what I have.
you can do that-take parts out of the 4G rear and install in the 3G rear You will need to use 28 spline axles from a 1990 up 3G(some'89s may be 28spline also)'93-97 and some '98s may have Auburn posi,'98 up is usually Torsen
Why couldn't I just get a 4th generation 7.5 (or 7.6) rear end with a posi and better gear ratio and swap all the parts from it (except the axle shafts) into my current rear end housing? I noticed there's a write up here on installing the disc brakes from a 4th gen car, so I could even switch them over. That would eliminate the wheel fitment issue and it would be a lot cheaper than having to buy all the parts to upgrade my rear end individually. There are so few 3rd generation f-bodies left in salvage yards around here (compared to 4th gen cars) that I doubt I'll ever find a rear end set-up that's any better than what I have.
If you have the tools and know-how to build a rear end, it is a good idea . The later 4th gens had Torsen limited slip that has no clutches to wear out , all gear simalar to a Trutrac . That is why I would suggest them. One thing to know when you go looking in the salvage yards is that they don't act the same with no load on them as a cluched limited slip would. By that I mean peaple expect both axles two turn the same direction with a possi and oposite direction with an open diff. The Torsens will act like an open diff , don't be fooled.
If you have the tools and know-how to build a rear end, it is a good idea . The later 4th gens had Torsen limited slip that has no clutches to wear out , all gear simalar to a Trutrac . That is why I would suggest them. One thing to know when you go looking in the salvage yards is that they don't act the same with no load on them as a cluched limited slip would. By that I mean peaple expect both axles two turn the same direction with a possi and oposite direction with an open diff. The Torsens will act like an open diff , don't be fooled.
How do you tell then between an open diff and a Torsen, or is it impossible to do without opening it up?
If you can see through the cover, (I can't, but I'm kinda an idiot, but all that aside, don't know many who can) then you can do it without opening it up.
LOOK AT THE PARTS. You have no idea (well, maybe you do) how many people come on here and ask stuff like this. The answer is, always has been, and will always remain, if you want to know what parts you have / want to buy / are offered for sale, LOOK AT THE PARTS, not the Internet.
Last edited by sofakingdom; Mar 5, 2023 at 06:33 PM.
Sofakingdom is right. He's usually right. It's annoying.
But at 20 years old at best for a 4th gen., there's no way to know for sure what you are getting in a used axle at this point. A SPID label might tell you how the car left the factory, but there is NO guarantee that those parts are still in the axle housing. The only way to know for sure, diff. type and gear ratio, is to pop the cover and take a look. You should do this anyway...even if you did possess swami-like powers to know what diff. and axle ratio were in the housing, you still would not know condition. I hate to say it, but a lot of the kids who owned these cars were idiots (I had a Camaro RS as my first new car). Between abuse, no maintenance, or sketchy repairs, you need to put eyeballs on those parts to know if they are A) what you want, and B) worth spending your money on.
The axles are reasonably cheap. 28 spline 3rd gen axles can be bought from Rock Auto, or a lot of other places. Nothing exotic.
I was meaning what years specifically to look at if torsen diffs were only available during certain years. Also, was there an axle code that specified a posi? I know parts need to be examined carefully before getting them but I need a way to narrow it down so I'm not having to pull the diff cover off of every 4th gen f-body I find.
My understanding is that the SS and Z28 from 99-02 have the torsen. auto trans had 273 gears, 6 speeds had a better ratio. I also think that the 3.8 v6 cars with the T5 trans got the torsen, but we are talking about cars that are over 20 years old. As others have pointed out , the parts that started in a car may not be still in there. My Camaro had 4 different rear ends just during my ownership. The 3.8 5 speed cars might be the best choice because of less abuse and a lower likely hood that they have been modified.If I remember corectly the 3.8 cars got 3.23 gears with the T5 trans.
My understanding is that the SS and Z28 from 99-02 have the torsen. auto trans had 273 gears, 6 speeds had a better ratio. I also think that the 3.8 v6 cars with the T5 trans got the torsen, but we are talking about cars that are over 20 years old. As others have pointed out , the parts that started in a car may not be still in there. My Camaro had 4 different rear ends just during my ownership. The 3.8 5 speed cars might be the best choice because of less abuse and a lower likely hood that they have been modified.If I remember corectly the 3.8 cars got 3.23 gears with the T5 trans.
That's interesting that the 6 cylinder cars got the good rear end parts. Of course the 6 cylinder cars also got T5's with really low 1st gears.
I suppose ideally salvage yards and places that sell these parts would have already taken the covers off to drain the oil and inspect them for damage.
A 4.10 gear seems a bit low for highway driving, even with a T5. I don't think I'd go any lower than a 3.42 for now; If I race the car on a road course - like I'd like to do some day with it - then I might go lower, depending on the race course. My Camaro has a Chevy 350 engine in it so I don't think I'll be wanting for a more peppy feeling.
The point was the posi differential, the 28 spline axles, and everything else need to make a beefed-up 10 bolt rear.
Unfortunately you zeroed in on the 4.10 gears. Do the same as John but use whatever ratio you want.
You will need to use 28 spline axles from a 1990 up 3G(some'89s may be 28spline also)'93-97 and some '98s may have Auburn posi,'98 up is usually Torsen 
