Continuing the restore of my 69, I ran across someone who suggested that I swap out the 10 bolt rear end with a 12 bolt, he has one in a 1978 or 79 trans am, how much trouble will this be or should I not even consider it

Zak, It will require you to move the spring perches to a 42 7/16" center line instead of the 1970-1981 45 3/8" spring perch center line.
Next thew drive shaft will need to be shortened about 3/4" All depends on your combo...best way is always to install the rear first then measure for the drive shaft length with chassis loaded (on all 4 tires that is)

Other than that you should be ok.

Is there a reason you think your 10 bolt 8.2 will not hold? Are you planning on racing a lot with trans brake and high stall above 3500? Your 8.2 has bolt in axles to protect your rear quarter in case the axle does brake and if set-up correctly with aftermarket gears and posi it will do the job on the street and even weekend blasts once in a while. Your camaro/firebird 8.5 rear has c-clip axle retention and the same size axle shafts as the 8.2... and if your firebird is original I would keep it original...if not go for it but maybe figure whether you need a c-clip elim kit too.

C-clip retention with aluminum cased ball bearing are really for drag race application only and not meant for freeway driving...Another thought to throw in there.

Jim

Thanks Jim,

All I want to do is drive it around town, take a few trips and maybe just punch it once in a while, I just had the engine rebuilt and I'm putting in a 700 tranny, The guy that was doing the restore for me just really messed the car up, I found someone else and now thing are going, figures right when I'm low on cash, He told me my rear end was not Posi Track and I would benefit from a posi track, Better gas mileage, The engine that came with the car is a 1978 Pontiac 400. and since my car originally came with a 350 and 2 speed tranny I decided to upgrade the tranny which lead to the rear end discussion, plus he is only asking $300 for it. Plus it is out of a 1979 TA, so i still have to move the spring perches maybe I stick with the old one, Are Eaton Rear ends any good?

Thanks
Zak

Not trying to cause confusion, but you said that you think you'll get better gas mileage with the posi trac?... I guess I never heard of that. As for the 69-350 setup, I would have thought it would have come with a th350, 3 speed vs a 2 speed trans. If so, I would think the th350 trans bolted to the 78 400 with the 10 bolt rear would be plenty for cruising and the occasional punching it down. But its up to you, ...your money.. etc.., and yeah, the 700R4 trans does have overdrive which would help with mileage..

You didn't mention what the gear ratios are in the old rear and the new one. That is the only thing that would effect your gas mileage. The posi. alone would have no effect on it.

Gas Mileage... Wow that is a line...lol. If anything it will eat a bit of power...lol. in the turns anyway...lol.
Well I see where your going...BUT you are restoring a Muscle Car. If you start cutting corners on the resto too far you will regret it. Think it through and do not rush the job.

It is a good deal for a 12 bolt chevy rear 300.00 ...WITH posi!!! I would grab that ..BUt makes me wonder... WHY? I hope it is all good or are you headed for another headache.


Please watch going too cheap as you might be setting yourself up for more expenses down the road too. Jim

I would stay with the original rear and upgrade if needed/wanted.

In addition to monaz's post.
For HP, stock 12 bolts are over rated unless you spend alot to make'm strong.
The pinions are smaller then mid 70's TA 10 bolts.
The axle's are only held in with small c-clips.
Not bolted to the flange like Pontiac's are.
If a clip breaks, out comes the axle.
Most everyone has "c-clip" eliminators installed. Not a novice procedure.
If thats been done, and theres nothing wrong with it, $300's a steal.