Rosco920

All, I am in search of different options for the rear end. I have a 1972 Cutlass Convertible w/ 350. I plan to drop a 455 in it sooner or later. I was told that the best thing to do is start building the rear end first and then move forward...to ensure that the components are strong and capable of handling the performance of the 455.

Anyway, this is new to me, so I take the question to you guys.

What is reputable site/brand for a new rear end? I'm not sure if I should just add the posi + upgraded gears to the original housing I have or swap it all out.

I do know that I do not plan on taking to strip. I want highway driving jic I take it on there + be able press the pedal and dance a little. I've doing some research and it says to probably stick to mid 3s......like 3.42 or maybe a 3.73?

I have stock wheels now, but will upgrade to 20s rally wheels.


Am I thinking correctly with the 3.42 or 3.73?

2blu442

If you have the original rear end it will be the 8.5 inch corporate rear end. These are easy to find parts for, both GM and aftermarket as they were used in a lot of GM cars from the early 1970's through the 1980's. If you want to add a posi and change the gears you'll have a good selection. Picking a gear ratio will be impacted by the height of your tires. Not the rim size, but overall height. If you want to cruise on the highway in comfort I'd lean more toward the 3.23 or 3.42. But back to what I shared earlier, if you wind up installing tires that are significantly taller than stock you might be OK with the 3.73's.

We have a member here who sells parts and restored rear ends, he goes by monzaz. If he doesn't reply to this thread you might send him a PM or email to talk this over with him.

John

RetroRanger

Second for Monzaz he knows his stuff.

I have 3:42 w ~27" tires. It revs about 3k ish on the highway. If I did it over again I think a 3:08 would suit me bettter

Rosco920

Thanks for the info. I'll give it a little time before I send him a PM. I really want to get this Diff done. The open one sucks ha


You can't do anything other than change the wheels? Correct me if I am wrong ( I probably am, but love to learn), but is this what the OD can fix? Also, what size wheels do you have? I've just curious so that I can get a visual.

Rosco920

Also, I'd imagine by sticking with the original diff housing, I can add on disc brakes too....something else I wanted add in the midst of upgrading diff.

RetroRanger

Tires are ss3s w 255-60-15s I could swap ring n pinion or go to an OD auto trans, but I would really rather convert to manual 5 speed trans. I don't do a ton of hi way so it's ok but it revs more than I like as us now