[AROWHED]

Has anyone here put the bulletproof 9.3 Olds\Pontiac rear on a 65-70 Fullsize Pontiac? I'm looking to gain the strength, greater parts availability, and quick gear ratio changes of the 9.3. Got a 63 housing next to a 65 for comparison:
The 63 upper control arm mount locations are farther apart than 65.
The 63 lower control arm mount locations are considerably closer together.
The 65 has all four control arm bushings pressed into the axle housing, 63 they are all pressed in the arms. Will be using adjustable arms anyway but have to change ends.
The axle housing length (without brake backing plates) is identical.
The backing plate\axle retainer bolt pattern is identical.
Coil spring perches different but same distance apart.
Lower shocks mounts vary little.
Both have identical 31 spline axle shafts but the 63 has slightly larger outer diameter axle bearings.
This is gonna be a bigger PITA than I anticipated.

[hurryinhoosier62]

9.3” Pontiac diffs are NOT an economical replacement. A custom 9” Ford would be the most economical route. If you do not believe me, go to Fabcraft Metal Works website and start pricing the components of the 9.3.

[AROWHED]

Thats true but I already got the 63 rear on hand, its just needs refreshed and anyway I've dealt with Fabcraft on my existing 65 rear. However the 65 rear will not survive stick, slicks, 4300 lbs and a 467 stroker.

['ol Pinion head]

Correct geometry upper control arms would have to roughly test fitted, then final verions fabricated. As the upper perchs are not in the same spot, you would be looking at fabbing a custom double adj upper control arm. Similar deal was first done near 25 years ago so custom 8.5 10 bolts & 12 bolt A-body rears could fit in '78+ A/G-bodies. Lower control arm brackets then would then have to be correctly positioned and welded to the 9.3 housing tubes.

[AROWHED]

Definitely gonna be an exercise in geometry and fabrication. I've got a spare 65 GP frame I can do mock ups on without having the body in the way. Should prove interesting.

[hurryinhoosier62]

Contact Brad at Fabcraft directly. He just may know a fabricator that can use your current diff as a jig for placing the control arm brackets in the correct location for your vehicle on an 9.3” housing.

[AROWHED]

Recently completed this adventure. Should note I narrowed the rear 2.50" by cutting off the 63 axle housing ends and welding on 1965 ends, complete with their lower control arm brackets. Custom Moser axles. Then it was just a matter of using adjustable upper arms with heim joints on both ends. I recently modded 2016 Surburban 13" rear disc brakes onto it as well. This rear currently has a 3.42 spool in it, which of course makes for some interesting reactions on tighter turns.

[tom s]

Smart to put the drain plug!Did that to mine when I built the 63 Lemans.Tom

[mgarblik]

That looks like some really nice work. Admire you staying with the BOP 9.3". I was always worried I would break the stock Posi rear in my 2+2, especially with sticky tires. Fortunately it survived at about 400 HP. That had to be near the limit.

[AROWHED]

The spider gear shaft or the gears will be the failure point. When I built up my 65 rear, I used a 1972 posi unit....same 31 spline and a drop in replacement, but has a larger spider gear shaft\gears. It withheld 600HP but I never tried it with slicks...and didn't want to test it. Hence the 63 rear swap and spool.

[Stuart]

Originally Posted by AROWHED

When I built up my 65 rear, I used a 1972 posi unit...

That must have been difficult to find, I would imagine they didn't sell that many of them in 1972.

['ol Pinion head]

Originally Posted by Stuart

That must have been difficult to find, I would imagine they didn't sell that many of them in 1972.

there is wider interchange than that. The '71-76 8 7/8 MP series Eaton carrier is a direct descendent of the '65-70 8 7/8 P series (big Pontiac) carrier. In the 90's up into mid 00's I routinely pulled later MP series Eaton carriers, ones which originally held 3.23 & 3.42 gears. By rebuilding the later posi cases with a '71-76 31 spline side gears & spider set, the resulting carrier could be used in a '65-70 big Pontiac. The high ratio '71-76 MP series posi carriers are still out there to buy & rob side gears & spider sets from. The difficult to find piece will be the low ratio later MP series posi case.

[mgarblik]

Originally Posted by 'ol Pinion head

there is wider interchange than that. The '71-76 8 7/8 MP series Eaton carrier is a direct descendent of the '65-70 8 7/8 P series (big Pontiac) carrier. In the 90's up into mid 00's I routinely pulled later MP series Eaton carriers, ones which originally held 3.23 & 3.42 gears. By rebuilding the later posi cases with a '71-76 31 spline side gears & spider set, the resulting carrier could be used in a '65-70 big Pontiac. The high ratio '71-76 MP series posi carriers are still out there to buy & rob side gears & spider sets from. The difficult to find piece will be the low ratio later MP series posi case.

You have so much knowledge and experience with the mix and match/interchange of these posi-units and years and so forth. I don't think this information is widely available. I know it would take some time and effort, but a chart showing what will and won't interchange between the divisions from 1965-current would be super helpful to many here. It would probably be a winter project, but I would love to know for sure what will and won't fit those Pontiac housings. Learn new things every day.