GEARMAN69

Calling on Monza JD or others that are familiar with B Body type O rears.
I found this for sale that claims to be posi and was previously modified to fit a 65 F100 it was pulled from. I know there are some Type O B body rear ends that are not the same gears as the A body Cutlass Type O 67-70 but curious if anyone can figure out if this is the 8.5" ring 12 bolt cover Type O or the other one that doesn't interchange. I thought I saw that B body cars could have two different ring gear sizes. I have an email pending reply from seller on this but don't want to waste their or my time if this for sure is not the same gears as A body. Thanks

Also if it is as I suspect B only gears it could be a ratio that someone here might want. I will share more if I can find out.

joe_padavano

The B-body axles of that vintage share nothing with the A-body axles. The only two options were the P-type axle with a ten-bolt cover and a twelve bolt 8.875" ring gear or the O-type with a twelve-bolt cover and a twelve bolt 9.3" ring gear. The drums are hard to find if those are in good shape (no, I'm not looking for any more right now - I've got a small stash of my own ).

GEARMAN69

Yep. I am very familiar with the Pont B body 65-70 10/12 8.878 31 sp rear

I did find some info on the Bigger Type O 12/12 and saw a list of castings for differentials a few weeks ago. So all of these are 9.3 ? I thought there were two B body Olds options or is it the Pont axle as the second in an Olds ?

If this is better than a 2.56 Posi and maybe a 3 series gear maybe I should get it and re sell it ?

joe_padavano

The 1965-66 Jetstar 88 used the 8.5" Type O, but that would have come with the smaller 9.5" rear brakes. If the axle has 11" brakes, the P-type was used on the 1965 cars and 66-70 low power (small block) cars. The 9.3" O-type was used on the 66-70 big block cars.

GEARMAN69

Thanks for the extra info Joe. Good to know. I may also have access to a 68 Delta that has a 71 G headed 455 in it if anyone needs body items. He is pondering on using the drive train in a pick up

GEARMAN69

Finally got a reply with cover off. Looks like it is a 2.93 or a 3.08 but also some pitting on spiders. I told him it is a full size Olds type and I can't use it. I can share the info if someone here want the gears and posi it is cheap enough. He estimated a 3.1:1 ratio he wants $200

https://dallas.craigslist.org/dal/pt...234921733.html

monzaz

Clean the spiders and get us some better close -ups of the spider gear teeth faces.
Some one has been in this rear for sure...CAPS are on backwards. arrows on caps should be pointing out to the wheels NOT in toward the carrier.

MORE LIKELY A 2.56 OR 2.73. IT IS NOT A 3.08 OR 2.93. LOOK AT THE PINION you do not even have 1/2 of it pictured and it counts 8 teeth already you can double that and you get 16 and the only ratio with 16 or 15 teeth is 2.56 or 2.73.

tell him to keep spinning the ring until the stamped numbers are seen on the ring gear outer diameter. get all the numbers and will get you your ratio . example attached

PArt it out and sell it off. Jim

GEARMAN69

These were pics emailed to me I was not there. He is a few hours away. I am passing on this , no use for me.

I see the pinion better on my desk top versus phone yeah it looks like 16 tooth pinion or 15 at the least. I bet it is 2.56 as well.

This guy took 3 days to reply to my email on his new ad and no phone number. I replied and told him what it was and I didn't need it and have not heard back.

monzaz

Yes and as many rears that I have parted out.... Almost all are 2.56 2.73
only wagons and special optioned cars got a good ratio like 3.08 or 3.42 ratio. sometimes you get lucky and get a 2.93 gear....

good luck on the hunt... not trying to be a downer...but just reality if what i see.

GEARMAN69

Its fine I appreciate the extra knowledge like yourself the odder GM gear stuff is still rather gray area. I first saw the ad when I was driving on my phone and thought I had scored a 671 unit for $200 ...LOL

jimbr70

Heck. I want a posi but not 2.56. Not sure what gear I have now but if I change it has to be better than 2.56...

GEARMAN69

You would better off using the Pontiac 8.878 10 bolt cover / 12 bolt ring versus the Type 12/12 9.3 depending on what is in your B Body

That gives you a chance to use a bit easier to find 2.56 2.73 2.93 3.08 3.23 3.42 factory gear/posi or new 3.55 gears and new P trac.

They are all 31 spline and more than adequate

jimbr70

Ugh. So I'd be looking at a full rear end swap, once I find one. What might the definitive markings/stampings/??? be on a "Pontiac 8.878 10 bolt cover / 12 bolt ring"? I'd like to have a 2.93 or 3.08 ratio... gear shops all said no BPO posi units, so I need to find the right diff with the posi unit... geeze - what you needed one repaired? Scary stuff.

monzaz

8.875 even came in 3.73 4.10 4.33 ratios...this was a drag race car back in the day Catalina etc. that big monster.... with stick shift... like drag racing a 1/2 ton Pick Up truck

GEARMAN69

Love the Catalina esp the 61-66 but even a 428 HO 390 hp 4 spd could be had in the 67-69 as well