I have a 67 Buick GS 400 and want to swap the 10 bolt for a 12 bolt. It to looks like the backing plate measurements are the same as a 68-72 chevelle 12 bolt. Are the spring perches and shock mounts the same?
68 - 72 rear differentials are 1" wider than 67 and earlier. They will fit as long as your wheel / tire combination isn't already close to the wheel well lip..
True. I've read that the 65-67 chevelle 12 bolt rear ends are 1" narrower than the 67 Buick 10 bolt. So the 68-72 chevelle bolt would be the same width since it is 1" wider. Is that correct?
From Team Chevelle "Actually it's 65-67 that are narrower and only the 67 will work as a direct bolt in due to the differences in spring design. 65 & 66 have flat spring perches which are not compatible with the later springs. Second, rear axle width has absolutely no bearing on the size tire you can fit inside the wheel well. Rim width, backspacing and wheel well size are the determining factors. So, if the spring perches are the same as your '71 the axle will work with no modification but the emergency brake cables are "application specific" and will have to be changed if they are in fact 2" shorter."
I believe that to be the case, but you'll get different answers here. Best to measure to be certain. You might have to grind a little off the upper control arms to fit the 12 bolt rear.
This is your correct info on the rear end width 65 66 BOP are narrow 54 1/4 8.2 10 bolt 65 66 67 Chevy are narrow 54 1/4 10 and 12 bolt 67 68 69 70 71 72 BOP are 55 1/4 8.2 10 bolt and 12 bolt olds 68 69 70 71 72 Chevy are 55 1/4 10 and 12 bolt 71 72 10 bolt 8.5 rears are 55 1/4 1973-1977 10 bolt 8.5 are 56 1/4 and have totally differet spring, shock and upper control arm mounts. Hope this helps. Jim JD
With all due respect, I've had different results::grin: a 64 Olds F-85 rear and 66 Chevelle 12 bolt I have are both one inch narrower than the 65-67 Special and GS rears I have. Next time I go to the Carlisle swap meet I'm going to measure a bunch of rears!
