Hi All,
I have a 70' Cutlass S Holiday Coupe I bought 85% restored and I am bring the final projects to a close this winter. The 350 Rocket and TH350 were nicely rebuilt and is running about 300HP now. It does have the original 2.56 gear ratio in it, and I have the build sheet stating so.

Not a racer, but I want more out of the hole quickness when needed. I am thinking of going to a 3.08. a 3.36 or a 3.42 to get this done. Way back when in 1979, I had a Trans Am with a 2.73 I had switched to a 3.42 and it was a night and day difference on quickness. (It had the torquey 403 Olds in it, by the way..)

Lastly, I assume from everything I look up, that this is a 10 bolt 8.2 inch setup? I will obviously have my mechanic check it out, but thought I would ask you guys.

Looking forward to thoughts and opinions.

Thanks,
Bryan

 

It has been redone as a W-31 clone.

 

If you want to complete the W31 disguise they were either 3.42:1 (code TM) or 3.91:1 (code TO) in 1970.

If that's a stock rear end it won't be a 10 bolt, it will be a 12 bolt O type rear. You know that the 12 refers to the number of bolts that hold the ring gear, not the number of bolts that hold the diff cover in place...

 

Thanks, Allan. I liked the 3.42 back in 1980, I will probably go with it again, especially considering the info you just provided. Since the rear end work is not in my wheelhouse, I will let my mechanic determine and order. :-)

Thanks again.

 

The 70 Cutlass/442 came with a 12-bolt O-axle. Good rear,but currently no gears are available for them. There is possibility that they will be available in April,but there have been delays before.

 

With my 70 when I restord it I found it easier to change the whole rear. My car had a 2.73 12 bolt Olds rear but the cover has 12 bolts the ring gear had 10! I put in a rear from a 69 Chevelle 12 bolt posi with 3.23 gears and had a new driveshaft made because the yoke was different. Works great and that was done back in 1997.

 

You can also use a yoke from a Canadian 12-bolt Chevy,and make it a direct swap.

 

I looked at the build sheet last night-It says *G96 PLN Axle 2.56.

Assuming that is still the case (I am sure it is, but my mechanic and I will verify soon.), is that more than likely a 8.2 inch or an 8.5 inch?

 

The 12-bolt O-axle is a 12-bolt cover,with a 10-bolt ring gear,28-spline bolt-in axles,and a 27-spline pinion. This rear is unique to itself. No other parts fit it.
It is not an 8.2 and it is not the common 8.5.

 

So based on what you said here, a company like National Drivetrain is incorrect when they say they have a Richmond 3.42 that will fit it?

 

Pretty sure ALL of the differential vendors are out of gears for the O-axle,as many others have searched everywhere for them.
Ask them if they are for the 12-bolt O-axle. 12-bolt cover with 10-bolt ring gear.

 

Will do. Thanks for the help.