Hello all, I've got a 72' Cutty that I'm swapping the tranny out on (from a TH350 to a TH400 which I'll be making a short shaft) and I have a question after reading some of the threads on this forum. I want to swap out my 10 bolt Olds for a 12 bolt (as eventually I'm going to a 455 ), and there is a guy locally selling one out of a 66' Chevelle. I know the Olds and Chebby rear ends are different, but I want to know how different and how much work this will be to swap in. I know I'll need to get a driveshaft for it too but I'm just wondering how much modification I'll need to do to the mounts, if the axle will be the correct length, ect.

Thank you!

 

Well if you have a 10 bolt from a 1972 (8.5) The width will be 55.25 flange to flange and the 12 bolt 1966 will be 54.25 flange to flange 1" narrower.
Next the spring perch will be different the 10 bolt olds will have a raised area for centering the spring on this perch. The 66 chevy rear will be a flat perch no raise ring to center the spring. You will need the cup and bolt type system to keep it bolted in and centered. OR you will need to cut and weld.

Everything else will be the same. You can get a conversion u-joint for want ever yoke you use on the 12 bolt chevy. 1310 1330 or M3R joint.

In my opinion I would have just built the 10 bolt 8.5 up. Sell the 12 bolt to supply the funds and there you go. Jim

 

I would keep the 10 bolt.
If the axles have a flange and bolts @ the backing plate then no C clips.