Rear Differential for 51 buick

[ratrod51]

1951 Buick Special Straight 8 w/ 3 on the tree, air ride on all 4 corners.

Ok, now that I have the adapter plate to run my 700r automatic transmission on my original straight 8 motor, what rear differential should I be looking for? I heard that an 80's Capris Classic used the same bolt pattern and was of the same width as my stock 1951 rear differential.

What about gearing? What should I be looking to get? The 700r has 4 speed with ovredrive. I am not looking for acceleration, I want to be able to cruise at high speeds (75) and run the lowest rpms possible.

I know that i will have to then find an external drive shaft that will fit the length of the tranny to diff and I will need to install a four link to stabalize the new rear diff. I have already found one that is designed to work with air ride suspensions, so any help on the diff will be greatly appriciated in completing the new drivetrain for my old 51 daily driver.

Thanks.
Yaril

[bebop138]

They say you should run 3:70 gears--suppose to make the tranny work better in overdrive. If the rear has coil springs look for a rear end of the same length that had coils and you would`nt have to put in a four link just swap spring perches--same for leaf springs. I think your right on the Caprice set-up. You will have to make your own traling arms and panner bar set-up---the four link is still a option, either way you have your work cut out for yourself. Good Luck. [img]graemlins/thumbsup.gif[/img] [img]graemlins/thumbsup.gif[/img] [img]graemlins/thumbsup.gif[/img]

[big gear head]

The 3.42 is the most common ratio used with the overdrive 700R4 transmission. You don't want something around 3.08 or 2.73 because the engine will not turn enough RPMs at around 55 MPH. It will lug too much. If you go with a 3.73 or 4.10 you might find that the engine turns a few too many RPMs at 75 MPH. Just my opinion. I have a '91-'96 Impala rear end with 30 spline axles and an Auburn posi in it. I don't remember what the width or the bolt pattern is.