Have any of you swapped a 12 bolt in a 66 from lets say a 68 Chevelle?
The spring purches are around 3/4 taller,cupped and not flat. Any one have any trouble with driveline geometry from the hight differance?

Also, the rears are 1" longer I think. Have any of you had to compensate with backspacing on this swap? Thanx for any help.

ttft

I put one in my 66 from my 72 wagon.... I had it narrowed 9/16" on each end to match the length of my 10 bolt, then new axles an guts... I have Eibach lowering springs so the purch wasn't a problem!!!!
Rick

Something else to consider, .... according to www.oldmobility.com/interchange.htm[/url] , (GM A-Body Parts Interchangeability) ...... the upper control bushing eyes, on a 68-72 housing, are positioned 3/8" farther forward, than a 64-66'. After a little thought, it seems that ..if using stock 66' upper control arms, with a 68-72 unit, the housing would have to be tilted back ..to line up uc arms, which would raise pinion angle.

I have adjustable uppers,so it should'nt be a problem.It's the width I was more concerned about........

Something else to consider, .... according to www.oldmobility.com/interchange.htm[/url] , (GM A-Body Parts Interchangeability) ...... the upper control bushing eyes, on a 68-72 housing, are positioned 3/8" farther forward, than a 64-66'. After a little thought, it seems that ..if using stock 66' upper control arms, with a 68-72 unit, the housing would have to be tilted back ..to line up uc arms, which would raise pinion angle.

I have a 68+ 12 bolt in my 66 with stock uppers and my pinion angle is like 2 or 3 degrees down. I checked it before and after I installed the ssm bars and everything seemed fine to me???

As far as width, you should be fine. I have A LOT of room with the 26x10 slicks and 15x8 rallies(4"BS)I have on it now. I have a pair pf 27.5x12 Nascar slicks I use for test fitting, I had them mounted on the same 15x8 rallies and they just rubbed the outer fender lip at stock ride height when hitting dips in the road. With a little air in the air bags in the back, they cleared fine. The outer fender lips on my car have been trimmed and rolled so that may make a difference.

Yes, the 68+ 12 bolt is exactly 1" wider than the earlier rear end. Just add .5" backspace to your existing wheel specs and that will put the wheels/tires in the same spot they were before.

Thanx Brandon,Exactly what I needed to know :thumbsup:

No problem, nice 66 BTW. :beers:

No problem, nice 66 BTW. :beers:
Thanx,Right back at-cha :beers: