which rear to run

[Ishmael]

I've been looking over some of these posts and I'm a little confused. I've got a 68 firebird with a 10 bolt pontiac rearend (8.2) and 2.73 gears,drum brakes. I want to upgrade to a 3.73 posi disc set up. From what I understand, nothing higher than the 2.73 will fit in that case. Is this true?
I assume it is so I started looking for a disc brake donor. What I found is a 9" lincoln with discs and a 8.5"posi, disc rear out of an 81 trans am. Which one am I better off with. From what I understand from http://firstgenfirebird.org/firebird/FAQ/wheel_brake_axle/axles.html, the 2nd gen rear is the same width yet here it says they are different. Anybody know for sure? And if the 8.5 is almost the same strenght as the 9" and I don't need more than mentioned in the other posting (400hp tops) then I shouldn't waste money on buying a posi for the 9".
Which rear do I run? The lincoln 9" or the 81 trans am 8.5" or is there another cheap alternative?
Thanks Scott

[MrQuick]

Hey Scott, the 3.73's will fit in the housing but not the original diff case you have. The gear thickness is different.You can use a spacer ring or a custom gear ring to fit on a 2.73 diff.
The second gen rear housing wont fit a first gen with out modification. It may fit width wise but the perch locations are different. Novas from 68-72 will fit a first gen Camaro. Only 71-72 Nova V8 had 8.5" ring gears.
From what I can gather your original rear isn't a posi unit so I would suggest is to call summit tell them that you have a 68 Firebird with a 8.2 BOP 10 bolt rear end and that you need an Eaton posi unit, 3.73 gear set, 8.2 install kit with 27 spline pinion, and that sould be all that you need.

[Ishmael]

Thanks Vince,
My thought process was that if I could find an 8.5 with the posi, gears and discs already there or a 9" with discs already there then altering the perches and drive shaft, it would be cheaper than installing a posi, gears and a disc brakes on the rear I already have. Any thoughts?

[MrQuick]

its entirely up to you and how much work you got. The 8.5 and 9 would be great strength wise, but either way its gonna cost you one way or another.
The 81 your gonna have to change the perches around and either narrow or get new rims for, plus the rear disc are prone to leaking problems ...
the 9" Lincoln rear is going to have to be narrowed for sure, has tappered axle tubes which may create mounting problems , then new axles to match your bolt pattern and then you got the gears.
If it where me and you need power backing i'd try to find a 71-72 8.5 Nova rear, build it up and put a set of 93-97 Camaro disc on it. Let me know if you wanna sell that BOP rear.

[Ishmael]

The 71-72 nova 8.5 sounds like the best of both worlds. Right width, better strenght. There's one offered in my area now. thanks Vince, I never thought of that.

[MrQuick]

your welcome Scott, make sure its an 8.5 unit, cause they had 8.2's till 72. 8.5 rears usually had a dimple on the 10 bolt cover but pull it to be sure, how's to say they didn't change it.

[Ishmael]

Thanks again. Any other quick way of double checking if he's swapped covers?

[Fuelie Fan]

71-74 Nova's actually. My 8.5's out of a 73

[MrQuick]

Thanks Fuelie, ive run into 73-74 rears where the spring perch is 1" wider than 72's, possibly due to the hatch back? For sake of being wrong I just use 71-72's. Does that sound right? I've never confirmed it. Anyone eles know of any other tricks to find out it a 8.5 unit?

[Ishmael]

Here's one more for you. WHat about a 70' trans am 8.5? I've heard they bolt right in as well. Is this true?

[MrQuick]

no that still a 2nd gen f body, its wider and spring perches are off. If you don't mind relocating the spring perches and changing your back space on your rims it will fit.