Rear end ID help needed
 

All, I'm looking at a rear axle, and need help id'ing it.

Casting number is N 1235542.
Stamping on the axle tube is JA G279 1
Wheel mounting surface width is 60".
I have no info on perch to perch width.

Looks to be an 8.5, but I am having trouble nailing down whether it is a Nova rear end, or a 2nd gen rear.

Target vehicle would be my 67 Firebird, which is already running a Nova rear end with 3.73's. JA looks to be 2.73's, which would be a killer cruising gear.

Any help appreciated, thanks!

If your 3.73 rear is posi I bet the 8.5 2.73 is not if that matters to you?

No, this rear end is not posi. My 3.73 rear IS posi. Yeah, not ideal, but price is right.

Trying to get a perch center to center measurement. If a Nova rear, awesome. If 2nd gen, then I will likely skip it.

A 2.73 would drop my cruise rpm on the highway by a good 1000. 3.73's are a blast, but not great for distance driving, and that's what I am looking more toward doing.

That’s a big change in cruse rpm, where does your Cam’s power band start to haul nice?

Around 2000 rpm it starts to scream. It's a little bit cammed up for a 350. 10 years ago, chasing that extra .1 of E.T. was my rage. Not so much anymore

I looked under my car, and the casting on the pumpkin is a 1235542, from a 73 Nova IIRC. So at least that part matches.

Is there a definitive way to tell by codes and stampings if an 8.5 is a Nova or 2nd gen rear?

Find a camaro/nova site and see if they have the codes.
Some codes were just for camaro or just for nova.

I'd have to search and see if I have them.

:confused:

Found this on the Nova site

Absolutely the most fool proof way.

Stock 68-74 Nova 12-bolt/10-bolt rear axle width is...
60.25" wheel mounting face-to-wheel mounting face, including drum thickness
53.25" backing plate flange-to-backing plate flange
42.75" center-to-center on the leaf spring perches.

There is no casting date on center section?
JA is usually a '73-4 Nova coded 2.73:1, non-posi.

I think the date casting is either an L222 or an I222, either of which translates to a late 1972 production, likely a 1973 JA code 2.73 open rear end for a Nova.

Funny enough, I crawled under my ride, and found my current rear end is JA code, with similar dates. So it amounts to an almost identical rear to what I have, minus the posi and upgraded Currie axles. It's been a while since I built that setup.

I'm gonna pass on it, let somebody else have a crack at it. Steve brings up a good point about power band. I would be probably better off seeking an OD trans in the future to get my cruise rpm's down.

Thanks, all!

From charts that I have the drop in rear wheel torque when going to 2.73 gears would be a big 27%, and all for a gain of about 10% in fuel mileage on level ground.

Like you posted, a trans swap would be the way to go.