10 bolt rear end help

I just bought a 1975 8.5" 10 bolt rear end. I have determined from the codes that it is a 2:56 posi rear end. Maybe firebird or camaro??? The spring perch measures 45.25 on center. Does that match up with a '75 firebird or maro? And is there a difference between firebird and camaro rear ends? Are the ring and pinion sets interchangeable? THanks

 

Camaro and Firebird are the same thing. I think you need to change the carrier to go below a certain ratio. Camaro rear is like 61.5" drum to drum, not sure what the perches measure (I'd have to go measure mine).

 

Not positive on this but ive heard that s-10 rearends are the same as camaro/firebird as well. And yes camaro and firebird are the same. All parts are the same except cosmetics on the outside.

 

thanks. I read on another forum when trying to figure the id of this rear end out, that the R and P of firebird wouldnt fit a camaro. THought that was off since I have owned both and know that they have of lot interchangeable parts.

 

Thanks for hte info. Appreciate the help.

 

1975 is too early to be anything s-10. The only thing an s-10 shares with any f-body GM is the 5 on 4 3/4 bolt pattern and just maybe brake drums, hadn't checked my parts catalogs yet.
If a gear ratio change is desired in the 1975 Camaro rearend with a factory 2.56 ratio, a replacement differential carrier will be part of the puzzle. GM changed the carrier at 3.08 ratio in the 8.5 ten bolt just like needing to change the carrier in a 12 bolt to install 3.73 ratio r&p set.
2.56 gear ratio is too tall to run with an overdrive transmission also.

 

Patrick, thanks. That must be what that other forum was referring to. Guess I'll just make it a highway cruiser! I am gonna run al 4 speed in this truck. So does that spring perch measurement sound like a firebird/camaro?? Great info man Thanks again

 

The break off point for R & P interchange is 2.73 and higher numerically and 2.56 and lower numerically. You can get 4.10 and 4.56 gears for the 2.56 carriers, not sure about other ratios. '71-up Nova, Omega, Ventura and Apollo X-bodies also used the 8.5 through '76 and are about 60" flange to flange. I've heard some '77 and '78's used the 7.5 but have never run across one. All 8.5 carriers through '88 and some early 89's are interchangeable then they changed from 28 to 31 spline axles. The axles from an 8.2 will fit an 8.5 of the same width and vice versa.

 

Thanks Rudebaker. So if I'm getting this right I'm gonna have a tuff time getting other ratios (like 3:08) in that carrier??

 

just shop around for a complete carrier with the gear set you want, used parts for an 8.5 rear are plentiful. check the for sale sections on some of the F body sites.

Doug

 

Thanks Plumber. I may just see how it cruises with those in it. Got a good deal on it and it seems to be in good shape.

 

If this is a daily driver and won't see any 8 Grand Banzai launches with big tires you can always run a ring gear spacer. I don't like them for HP usage but for a DD they're OK. If you're looking for a "new" 3.08 R & P PM me. It was a takeout from a service replacement rear end and was never run.

Oh yeah, if you rather have a 3.42 just go to your local truck yard and look for '88 up Chevy/GMC 1/2 Ton 2WD's. That was the standard gear in most of them.

 

the f body 8.5 rears were 28 spline axles, the newer 8.5s went to 30 or 31 spline I think so check that before ya buy one

Doug

 

Very early 1989 is when the change was made.

 

I wanna get the front suspension in first then its out back I go. Let me get back to you Rude on the R n P. Thanks to all again.

 

FYI if you want to change axle spline counts on 8.5 standard(non posi) rears the spiders swap between carriers

 

Good to know! Thanks z.