Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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'65-70 Pontiac B series used a big Pontiac only style rearend. This rear used an 8 7/8 P series ring & pinion & carrier. Axles were identical for these 6 years, 5 on 5 bolt pattern, 31 spline with sealed axle bearings. '65 & 66 Pontiac B series housings were the same. After '66, the welded on mounts on the housing changed slightly. I've rebuilt a few of these over the years, a GM A-body rear, like the Pontiac 8.2 GTO rear will NOT interchange. Cast upper control arm perches are much wider on the big Pontiac rear. Neither will rears from '65-70 Impalla 12 bolts, or Buick B series rears from this era. Other pifalls... Lower ratio 31 spline posi carriers, as well as nice used condition 3.42 & 3.23 8 7/8 P series (Pontiac) gears are very very hard to find. 3.55 ratio gears were reproduced for this style rear aprox 10 years ago. same clutches were used in the 12 bolt original Chevy car & truck eaton posi carriers.
Narrowing such a rear can be done, I'd def ck what else is in the way... shock mounts, rear frame rails eventually ate the trouble spots. Since new custom axles are going to have to be sourced to do so, if you are happy with current gear ratio, it would be very smart to go to new hsg ends that accept a tapered axle bearing and external axle seal. The stock sealed axle bearings are decent diameter, but as sealed ball bearing axle bearings, they suck holding up to cornering forces. I'd have to pull an original axle out of the racks and measure, but with the size of the hole in the backing plate, a Set20 (3.150" diam) axle bearing & matching housing end might be possible. If not an A-10 (Set20) tapered axle bearing custom axle & hsg ends would be the way to go. If no lineup bar & little fabrication experience, it would be very smart to connect with an experienced local rearend builder/often a race chassis builder. Such a custom hsg and axle narrowing job will run close to 1K, with new Moser axles, and with the work done out of the car on a build bench, then you install.
Last edited by Pinion head; 02-09-2018 at 06:08 PM.