BAMiller

Working on a 1970 cutlass for a friend. The rear axle has a 12 bolt cover but the ring gear has 10 bolts it is a 2.56 posi. it has the bolt in axles I am thinking it is a type O axle after reading some posts here. Does this axle use the same gears as a 10 bolt like out of a 1978 f body? I have a set of 3.08 gears from a 1978 f body and also a posi unit for the same axle. Will any of these parts work in the oldsmoble axle? If not would a need a carrier to upgrage to the 3.08 ratio?

joe_padavano

Yes, that's a Type O axle.
No, nothing else interchanges.
Worse news, the 2.56 carrier is unique. The aftermarket thick gears that Richmond sells only fit the 3-series carrier used in axles with ratios of 2.73 to 3.23.

olds 307 and 403

Interesting, I thought the 2.56 and 2.78 used the same carrier. I thought the aftermarket gears were designed to work with 3.08 and 3.23 carriers. What is the complete carrier breakdowns for the O axle?

joe_padavano

You are thinking of the Chevy 12 bolt. The Type O for A-body cars used carrier P/N 398698 for 2.56 gears only. P/N 393126 carrier was used for 2.73, 2.93, 3.08, 3.23 ratios. These are the open diffs. Anti-Spin diff cases have different P/Ns obviously, but the ratio splits are the same.

monzaz

Just correcting this info

This is for the 12 bolt OLDS 8.5 A body 1966-1970
2.56 - 2.78 are the same carreir
3.08 - 3.23 are the 3 series carrier the 3.42 and 3.90 aftermarket gears fit.

10 bolt 8.5 corp 1971 - 1998 does not interchange with the 12 bolt cover 8.5 rear. Sorry.

I think your getting the FULL size Olds 9.3 12 bolt cover 12 bolt ring ratio break mixed with the Mid size Olds 12 bolt cover with 10 bolt ring.
JIm
JD

joe_padavano

My apologies. Jim is correct. I missed the "exc F85" note in the parts book listing. I was quoting info for the 9.3" Type O. Sorry for the confusion.

BAMiller

thanks for the replies I will talk to him and see what he wants to do. I am thinking a strange 12 bolt rather than investing money in the olds rear axle.

joe_padavano

The real question is, what are the plans for the car and what is the budget? Lowest cost solution for a mild to medium street driven car is the 71-72 10-bolt. This uses the corporate 10 bolt diff and gears, so parts grow on trees, and strength is more than adequate until you get more traction and torque. Slicks and a built BBO? I'd go aftermarket.

monzaz

To Joe, It all good... I just want to make sure as much as possible to get the info as correct as we can.
I still get the full size breaks messed up

I have 2.28/9, 2.41, 2.56 on the 1st carrier
then 2.73, 2.93, 3.08 on the second carrier
and 3.23, 3.42 on the last 3rd carrier

On the 9.3 olds what is the steepest gear ? this 9.3 should cover 1965-1970 (28 spline pinion yoke) and 1971 -1976 corp era. (30 spline pinion yoke)

I have the Pontiac 8.875 rear
same deal
2.41, 2.56 1st carrier
2.73 2.93, 3.08 2nd carreir
3.23 3.42 3.73 3.90 4.33 and steeper ??? 3rd carrier I know 4.33 was a GM over the counter gear i have had 2 sets FACTORY

Anyone got the booKs that can confirm or correct this info. Please help.

Thank you. Jim
JD

BAMiller

Its a olds 455 built like a W-30 engine I was told I did not build this engine my friend bought it already done. will have a turbo 400 transmission the eng should have lots of torque. He decided to order a new Strange 12 bolt complete axle for like $2300.00 seems like a good option. Thanks for all the info I'm not real up on this Oldsmobile stuff. I am thinking something between a 3.42 and 3.08 ratio not sure what the options are they are sending a form for us to fill out to order the axle. It will be a street driven car maybe a few trips to the dragstrip.

VC455

In spite of what the factory ratings show, the W-30 engines have less torque than a standard 455. And the torque comes in at a higher rpm. A 3.42 is the shallowest gear you should choose and the T-400 should have a looser converter to help it move at lower speeds.

The best choice would be a 3.91 rear gear with a Gear Vendors overdrive unit on the output of the T-400. With that, the car will feel very lively and still will have lower cruising speed (effective axle ratio with OD will be 3.05). You should be able to find that GV unit used at a decent price.

After some bad experiences with shallow gears, I chose something similar to what I recommended and I am very happy with the flexibility--I have good acceleration and low cruising rpm.

BAMiller

OK after talking to someone at Strange axles they don't make a bolt in 12 bolt for a A body. I am now looking at a complete ford 9 inch kit from Quick Performance about $1900.00 plus shipping. Anyone have any experience with this company? The price is much lower than others I have found almost seems to good to be true. I think they rebuild some of the parts rather than using everything new.

monzaz

Moser Engineering makes the 12 bolt chevy rear





for the a-bodies I assemble and make them all the time.

monzaz

Just need to know how you want one built. Jim

BE CAREFUL WITH QUICK PERFORMANCE AND THOSE 9" REARS. tHEY GIVE YOU THE BARE MINIMUM. THE CENTER SECTION IS ONLY GOOD TO 400HP AS IT IS A STOCK CASE
THEY ARE USING ...USED STOCK FORD HOUSING NOT NEW HOUSING WITH THICK WALLED TUBING.


BE CAREFUL!!! IT IS CHEAPER FOR A REASON.