I've got a '70 455 442 convertible that I am restoring as a driver. The engine is a mild rebuild .040 over with very mild cam. I plan on keeping it as stock as possible to run through the TH400 trans. My question is, what suggestions on rear ends? I am definitely fitting with posi, and leaning 3.42's, but open as there's a lot of expertise here. Thanks for the input!

 

With small diameter tires (14") and a lot of highway driving, 3.42. With taller tires or mostly town cruising, 3.91.

 

It also depends on your definition of "highway driving." If you seldom get above 60 mph, the 3.42 gears will be great. But if you live out west and/or love to cruise at 75 - 80 mph, you might want to consider 3.08 to 3.23.

 

I agree with this selection and reasoning.

I second this vote.

WHAT rear do you have as this could become an issue in finding a GEAR RATIO you need. Jim

10 bolt 8.2 olds/pontiac
12 bolt 'o' type
10 bolt 8.5
Other?

 

The car should have a 12-bolt O-axle,unless it has been changed.A lot can happenm in 40yrs.If it still has the original 12-bolt O-axle in it,it should have a decent gear in it already,like a 3:08 or 3:23.If that is the truth,then maybe all you need is a posi carrier.

 

Great, that's what I'm looking for here. Truth is, I probably will be driving around town with an trip out once in a while. I live in WI, so only parts of the year on highways and limited at that. I need to check my current axle to see, but sure it's not posi. I will not be tracking this thing, so not worried about drag times, etc. Suggestions on where to pick up a good posi carrier?

 

3.42 4u

 

Jim(monzaz) has some carriers available now.I'm all out at the moment.If you have a 3:08 or 3:23 in there now,then I would just leave it,and add a posi,especially if you have a 3:23 because there won't be much difference between the 3:23 & the 3:42,to justify buying new gears.Look at the 2-letter code on the backside of the passenger side axle tube,and let us know what it is.It might be upside-down,depending on when the car was built.

 

Thanks guys, this is really very helpful info. It's amazing how much you can read up on these, but when it comes down to it I trust the guys who have the cars and build'em. I'll check the code and get back here. May save me some $, and I most certainly will need it in other areas of the car.

 

Price out a posi carrier for that Oldsmobile "O" rear end. Might realize it's really pricey for used stuff .

507OLDS seems to be the resident expert rear end guy here, and Monzaz.

THere's a thread that shows the codes on your right passenger side axle tube so you can see what gearing it came with from the factory.