Type O? Questions.

[Seth]

I have what I believe to be a BOP 12 bolt in the back of an old Chevy truck. It has a round driveshaft flange and a 5 on 5 bolt pattern, 2.72 open.

I'm preparing to replace it with a 10 bolt 8.5 out of a trans am... disc brakes, 3.07 gear ratio and a positraction unit.

The change in width is not an issue as I'm changing wheel as well, but I'm anticipating a driveshaft length difference and was wondering if anyone knew what the pinion length was in a BOP 12 vs a 8.5 10 bolt?
Additionally, is the u joint in the flange a 1350?

Thanks!

[monzaz]

Well if the rear is a 5 on 5 wheel bolt pattern then it is a FULL SIZE 12 bolt OLDS car rear end.

Now probably going from a FULL size car rear to the corp 10 bolt 8.5 you may not need to change the length...BUT you said it has a round coupler with 4 bolts ...does it also have the constant velocity unit joints also. Please post a picture of the yoke area with all the u-joint there?

Are you going to reuse your drive shaft on the truck I am assuming? that is why your asking...
NO car came with the 1350 u-joint.

So no that is not going to be it. Most likely it is a Mechanics 3R u-joint ...GMs most popular u joint. Used in all camaros 1/2 ton truck, all s-10 G-body etc.

[Seth]

Thanks. The casting number on the diff is 406208.

The best I can do on the flange is these pics. Not good, but I can't get the truck up on the lift right now.





No cv on this drive shaft. The new axle is using a yoke with the following measurements.




Is there a conversion u joint?

[monzaz]

Ok well we can sell you a flange to go onto the 8.5 rear you have that might help then you can just bolt it to the drive shaft coupler.

Jim
they are about 35.00 each they are round with the 4 holes like what is on the rear (12 'O' fullsize car)

[Seth]

Perfect solution. I'll call you ASAP.