Looking into some rear gears.
I've got the 12 bolt "O" axle on the 70 442, but the only gear options I'm able to find are either 3.43 or 3.90 (Oldsparts.com).
Initially I'm more interested in the 3.73 but I don't think anyone makes them for this particular axle?

Current Tires:
Rear: BFGoodrich Radial T/A - 275/60-15
Front: BFGoodrich Radial T/A - 225/60-15

Transmission:
Th400 or 350 (beefed up) haven't decided as I'm prepping for the engine.
Engine numbers should be around 500+hp/600tq.

What do you guys recommend between the three?

Car will be an everyday driver. City, highway, road-trips etc. The way it's meant to be.

 

Your choices are 3.42 or 3.90 with the original carrier. You can swap carriers & go with original 3.08s or 3.23 gears also. All of these are hard to find.


You never stated what your current gear ratio is. So what gears do you have now? There are no gear sets between the 3.42 & the 3.90.


For a driver the 3.23 gear ratio is the best of both worlds with a stock 26.5" tall tire but since you have a 28" tall rear tire go with the 3.42s.

 

I'm not sure what gear is back there, I'm assuming it's stock. Regardless it doesn't feel like anything special. I was leaning towards the 3.42 as well. Any experience with Oldsparts.com? Do they sell quality?

 

I don't know anything about olds parts.com but they likely sell Richmond Gear ring and pinion sets. You can look on the Richmond web site to see what's available, but as Dave posted its very limited with just 3.42 and 3.90 gear sets that are made to fit the 3.08-3.23 carrier.

 

And all those gears work on the 3.08-3.23 OEM carrier.


We need to know where you are starting to help you get where you want to go. Figure out what you have. Do you have posi now or not? Pull the cover, read the axle code or whatever it takes to figure out what you have currently.

 

Seems I was editing my post as Dave was typing. I checked the Richmond site and they no longer list the 4.10s.

As he said, you gotta figure out what you currently have in order to know what you can do.

 

Oldsparts.com is another name for Brothers Automotive. Buyer Beware! Do a search here under that name and take the results seriously

 

I have a set of (actual three (3) sets) that are in excellent condition 3:23 ratio gear set from a rally 350 that had 78,000 miles when removed. $265.00 plus actual shipping cost.

 

Don't have time to open it up but these are the stamps I found outside. "402227",
"CFD 5" and the the letter "P" (at least I think it's the letter P).
So assuming it's stock what's on the inside?

 

You need to tell us what the two letter code that is stamped on the passenger side axle tube. It usually faces the rear of the car but can also be stamped on the other side. It will be two letters like TM. That will discern what gear ratio was originally installed in that rear end when new. No guarantee that it is original to the car or that the gears have not been swapped. Only way to do this right is to get dirty & pull the cover.

 

That is the casting information on the pumpkin. It means nothing to what gears are inside. The same pumpkin was used on all the A bodies unless it was a W27 all aluminum which it doesn't sound like you have.
402227 is the part number, CFD (Central Foundry Division) - 5 means it was likely cast from mold number 5. CFD provided castings for all GM divisions. P? Dunno.

Here's an example (taken from another post on this site) that shows you an example of what the axle stamping might look like. This is from a Pontiac I believe.




If you can't pop the diff cover to find the ratio, this is a quick excerpt from one of our knowledgable experts. It assumes the car is jacked up and both rear wheels are off the ground.

 

contact supercars unlimited

 

I'd avoid like the plague...

 

Not a Pontiac - that is a pic I posted of the original 8.5" 10 bolt rear from my 1971 Cutlass Supreme convertible. An O-Type will have just a two letter code and not the numbered date code. Below is a pic of the axle ratio code on my 1970 O-Type 2.56 rear:

1970O-Type12boltcodelocation.jpg

 

Sorry, my bad Kenneth.

 

No worries. The more images such as these get posted, the more people will be exposed to them. It's good for knowledge sharing.

 

The stamp on the axle is an "R" I can't make out the second number for the life of me. So I'm probably looking at a 2.?? rear end.
Regardless, I'm probably going to order both an aftermarket Anti-spin and ring/pinion set from super cars.
So I should be in the clear if that's the case, right?

 

R2 = 2.56:1 gear ratio, open differential so you are on the right track for parts.

 

Ah yes ... you've got time (and money) to swap gears but not to figure out what you've currently got. How much time and money will you have after you find out you've purchased the exact same gears -- or you've installed something you find really irritating?

Don't trust the stampings. Either open it up or else spin the wheels and count driveshaft revolutions. You have time.