[Petegto]

Guys I found a complete rear end out of a 66 GP with posti and 278 gears for a fair price. I assume this will swap out in my 67 Catalina Wagon. Rear end is drum to drum .
Am I ok in buying it without any major issues?

Thanks Pete

[rustyrelic]

While you can switch out the center chunks, I believe you will find the axel housings do not share the same control arm mounting points. Perhaps someone else can confirm. Want to say only 67 and 68 are direct housing swaps.

I installed a 3:42 posi in my 68 Bonneville, and truthfully, I wish I had left the open 2:73. The off the line performance change was not that great with the low-po low compression 400, and I lost some of the easy highway cruising ability.

Are you building something with enough grunt and planning to use it in a fashion that really needs the posi?

[Petegto]

Thank you for your reply.
Yes building a 421 HO stoker motor is the reason why I want posi rear. Motor will be around 500 hp.

[rustyrelic]

you might want to consider poly bushings and boxing the control arms.

someone was selling aftermarket arms, but I dont recall who. Maybe RARE?

[rustyrelic]

https://pmtfabrication.com/product/1...-trailing-arms Here is one example

[mr67gp]

I am pretty sure '66 spring perches are different from '67. Not a deal breaker, but something to be aware of.

[rustyrelic]

perhaps it was the spring perches and not the control arm mounting points. I wasnt certain.

[GTOKIDRH]

Originally Posted by PONTIAC LARRY

What he linked above... 1965-1970 Pontiac (FULL SIZE CAR REAR) That is your main difference. The rings are the same 8.875 diameter But that is where the similarities STOP.
Ring gear bolts Pontiac are 7/16" x20 (Right and left hand thread early or late)
Ring gear bolt s Chevy are 3/8 x 24 (right hand thread only)
Pinion shaft on the Pontiac is 1.875
Pinion shaft on Chevy is 1.625
----- -- THIS is the main reason your not going to fit the Chevy gear in a Pontiac housing.
Pinion spline Pontiac is 28
pinion spline in the Chevy is 30
Pontiac rear is bolt in axle 31 spline and the Chevy is 30 spline c-clip axle

In 1971 -1976 The Pontiac rear was used in all the mid HP engine from 400- 350 cube motor with 4 bbl motors Gears will interchange from the 2 eras BUT you MUST use the yokes from each era with the era gears. 1971 -1976 era pinion spline is 30 not 28 like the 65-70 era. The gears will interchange
Axles will again NOT interchange because of the axle bearing differences and also the spline pitch was different too.

1977 -1985 there was a final form of this Pontiac rear and they really down sized it ...remember the cars in this era were way under powered so really the 10 bolt 8.5 would do the job just fine . pinion shaft decrease from 1.875 to 1.625 (basically the same 8.5 pinion was used in the 8.75 10 bot cover with 12 bolt ring design . It was used in the Caddy DeVille and wagons and maybe special tow package ordered cars of the era. Again NO PARTS in the aftermarket for this 8.75 rear.

Hope this help cover the Pontiac FULL SIZE car rear for you. and why you can not interchange the gear sets. Pinion shaft size is too small to transplant into the Pontiac housing - There could also be a different pinion to ring engagement height also But we never really went that far to check... Just not a BIG following for high performance ratios for the rear these days...Most cars have been demo derbied in the past. GM made steep gears for these rears and you can from time to time find a 3.73 3.90 4.33 gear set at a meet some one is selling that they have no idea what it fits we found (2) 4.33 gears that way 7-10 years ago. Sellers though they were truck gears...lol.

Good luck on the hunt.
Jim Mitschke
J D Race

Pontiac Larry, so I have a '67 Executive Safari with a 2.42 posi. I bought a 3.23 posi rear end from a '76 Grand Safari leaf spring car. I plan on swapping internals. What I take from your post is that I have to use the pinion yoke from the '76? You mentioned there being a difference in the axles as well? Do I need to use the axles from the '76 as well? Anything I overlooked?

Sent from my SM-N950U using Tapatalk

[Petegto]

Larry thanks for your reply. I have another question if you don’t mind, I can buy a posi & 3:08 nos gears from a 71 big car Pontiac. Guy tells me that only needs to be done is to change the yoke and maybe cut the drive shaft and that should work. After reading what you wrote I have some doubts about it since you mentioned about the pinion spline is 28 in the 71’s and 30 spline in my 67. Can you give me your opinion on this? The gears are Nos and the posi is rebuilt.
I put in a 421 factory motor from a 66 2+2 with 3x2’s and stroked the motor bored .060.
Thank you

[694.1]

65-70 Oldsmobubble share the same guts as Pontiac. This should expand your options.

[PONTIAC LARRY]

Originally Posted by GTOKIDRH

Pontiac Larry, so I have a '67 Executive Safari with a 2.42 posi. I bought a 3.23 posi rear end from a '76 Grand Safari leaf spring car. I plan on swapping internals. What I take from your post is that I have to use the pinion yoke from the '76? You mentioned there being a difference in the axles as well? Do I need to use the axles from the '76 as well? Anything I overlooked?

Sent from my SM-N950U using Tapatalk

Your 67 axles are fine both are 31 spline , yes just use the 76 pinion yoke for u joint with the 76 gears and differential swap

[PONTIAC LARRY]

Originally Posted by Petegto

Larry thanks for your reply. I have another question if you don’t mind, I can buy a posi & 3:08 nos gears from a 71 big car Pontiac. Guy tells me that only needs to be done is to change the yoke and maybe cut the drive shaft and that should work. After reading what you wrote I have some doubts about it since you mentioned about the pinion spline is 28 in the 71’s and 30 spline in my 67. Can you give me your opinion on this? The gears are Nos and the posi is rebuilt.
I put in a 421 factory motor from a 66 2+2 with 3x2’s and stroked the motor bored .060.
Thank you

He is correct , just use the 71-76 yoke on pinion with 71 gears and posi , as far changing u-joint and or driveshaft length pretty sure its just a conversion u joint at worst may not even need to do that

[PONTIAC LARRY]

Originally Posted by 694.1

65-70 Oldsmobubble share the same guts as Pontiac. This should expand your options.

not all the B body Olds have the 65-70 PONT 8.878 , SOME models years do but not all

[PONTIAC LARRY]

The OLDS B Body interchange is only 1965 and some early 1966 before they switched to their own Type O B body big axle (9.3) similar to the A body OLDS 64-66 used a BOP 8.2 and 67-70 went to the Type O 12/10

['ol Pinion head]

Extremely rare to find a "good" ratio (3.23 or 3.42) P series posi rear in the '65/66 Big OLDS.
Agree with Larry, that usage was only for a little while in big Olds. It's been near 15 years since I've run across a manual trans non AC '65 big Olds, & that was in a monster yard in MN that used to hold onto the old stuff much longer. That '66 had a 3.42 Safe-T-Track under it. Last Fall, two of us PY'ers were in another monster yard up north that had several '65 Olds Station wagons, the wagons are a good place to look. That long row of big Olds had other big Olds of that era setting on top of the wagons, along with trees & saplings growing between each car. No chance of getting any of the wagons jacked up.

On the 8.4" ring gear Type "O" Olds, have had quite a few 3.23-3.91 ratio Anti Spin 442 rears, & have gone though a few more for customers. The Type O's are a restoration piece, for any kind of strong performance, they lack the pinion support of the later 8.5 A-body. Always get a chuckle out of eBay listers noting the Type "O" A-body rears as "12 bolts", or as an OEM usage rear in Pontiac "GTO"s. Only Olds were originally built with Type "O" rears.