wyocutlass

I have a 1968 cutlass supreme. I am not completely sure exactly which rear end I have. It's been a couple of years since I've pulled the cover off. The cover has 12 bolts if that helps. I do NOT have a posi in my rear end but would like to add one. A guy in my town has a brand new Richmond 3.90 gear set, a posi and a posi carrier. He says the carrier is 12 bolt. He would sell them for 200 for everything. What do I need to do to find out exactly if it will fit and possible to use before I make the purchase.

Fun71

So what are the above pictures from? It looks to be a 673 carrier, which is an O-Type posi carrier for the 2.56-2.78 gear ratios. I can't make out the numbers stamped in the perimeter of the ring gear to determine what the gear ratio is.

12 bolts on the cover of the rear in your car means either an O-Type 12 bolt (original equipment in most all 68-70 Cutlass models) or a Chevy 12 bolt that could have been swapped in at some point. You would need to check for the number of bolts holding the ring gear to the carrier, which for the O-Type would be similar to the above picture showing 10 bolts.

If his carrier has 12 bolts holding the ring gear on (meaning Chevy 12 bolt), it won't work in an O-Type, which has a 10 bolt ring gear.

wyocutlass

thank you for your reply. I will remove the cover and see exactly what I have. Those pictures are the posi and carrier and the gear set he has for sale. He sent those to me.

svnt442

The easiest way to tell if it's a type O or a Chevy 12 bolt is to look at the ends of the axles with the drum off. If there is a hole in the face of the axle to allow an extension through to remove a plate the holds the axle into the tube then it's a type O. If the face of the axle is solid and there is no plate holding the axle in the housing, then it's a Chevy 12 bolt.

wyocutlass

Another question is since the carrier is a 673 can the 3.90 gears work on it?

monzaz

You do not even need to pull the drum... just look at the housing tube flange where it meets the backing plate. If the tube tappers down to 2.5 inch before tit get to the flange that holds the backing plate on it is c-clip Chevy
If the tube stays the same size or even gets a bit larger in diameter it is a bolt in axles being a olds 12 bolt with 10 bolt ring.
Also the chevy rear you will see the nuts that hold the backing plate on where as the bolt in axle will normally have slug heads and the nuts will be in the drum brake hardware area under the drum.

hOPE THAT HELPS TOO.

Also 673 carrier will need a spacer plate to work with aftermarket Richmond gears. Will not work at all with GM 3.90 gears.

Jim
J D Race

wyocutlass

Where can I get a spacer? So if I get the spacer the 673 carrier and the Richmond gear set 3.90 will work?

monzaz

I can make one for you, PM me. Jim