Schnets

Hello all!!
I’m in my third year of my restoration and am working on the differential and desire to put a non-slip in.
I’m looking for some good reading material and recommendations on what gear ratio to install. I’ve beefed up the engine with a 10-3/4:1 cr and the turbo 350 has been rebuilt to handle the additional HP.
I don’t really want to pull the body off the frame, but am willing to if ya’ll think it is best to remove the rust from the frame. I did the front part of the frame when I pulled the engine-trany.
I like the original look, but want to beef up the suspension. What makes sense to keep and what makes sense to restore, I.e. the control arms etc. I’m Leary of doing the differential rebuild myself so any input on this would be great. Some reading materials on overall retoration would also be helpful. Thanks for all your knowledge in advance.

Cutlass Fan

Welcome to the site. Your questions are kind of all over the place. Was the rust on the front part of the frame bad enough that you think it may be a structural problem or a potential one on the rest of the frame? If not only remove the body and
clean the frame if you want a show car.
We need to know your driving habits before recommending a rear end ratio.

Schnets

Thanks for the reply. My driving habits will be only for summer drives to car shows and short car club road trips.

oldcutlass

Welcome to the site, we do like pictures.

Cutlass Fan

Also what year is your car and what engine does it have?

Schnets

I have the 350 V8 in a 1970 cutlass Supreme conv. I replaced the factory heads with 1970 W31 heads, an aluminum 4 bbl intake with a 750 cutlass holly and headers.
thanks

Fun71

Well, if you have the original O-Type rear, your gear ratio choices are extremely limited.

Below is info about the O-Type that I copied from Brian Trick many years ago:

O-Type 12 Bolt

Here is a list of the posi units & what gears they will fit:
#673 = 2.56 & 2.78 ratios, 28 spline
#671 = 3.08 & 3.23 ratios, 28 spline
#588 = 3.42 & anything numerically higher, 28 spline
#672 = 3.42 & anything numerically higher, 31 spline
***The 31 spline axles were offered in late 67-68 OAI cars only.

Today, the only aftermarket O-Type gears are 3.42, 3.90, and 4.10 and they are made to fit the 671 series carrier. Here's a link to Richmond Gear's catalog. There may be other companies making them now, but I don't have that info.

https://www.richmondgear.com/wp-cont...n1.pdf#page=31

There is also a limited slip diff that is a Ford 8.8" carrier that is machined to fit the O-Type gears and housing, and I think it fits only the 3.08-3.23 series gears.

If you have an O-Type and plan on keeping it, you should contact monzaz (Jim Mitschke of JD Race) or 507olds (Brian Trick) as they are our resident differential experts and have intimate knowledge of them and parts for them.