posi

[70CHEVYBB]

I can pic this up for 150 what do you think? He says it rebuilt.

[Xeen]

$150 is a great price, they sell for $500 new, what gear series is it for?

[70CHEVYBB]

its a 4 series but I think I can get a 3:73 ring and pinion for it ?

[Bigdav160]

They do make a thicker gear (or spacer) to fit a lower gear to a higher case. Like a 4 series gear to a 3 series case or a 3 series gear to a 2 series case. I'm not sure if they make a thinner gear to go the other way around. The ring gear would be pretty dang thin.

You'll spend a couple hundred bucks if you want to replace the clutches in that unit. And i would make sure the area for the side bearings is going to clean up.

[70CHEVYBB]

He claims its been rebuilt already. I am going to make the deal sight unseen and take my chances. I do see Richmond makes 373 gears for a 4 series carrier.

[leftybass209]

I've done a lot of research on carriers recently. 3 or 4 series doesn't matter anymore other than for purchasing purposes as far as aftermarket ring and gear. That's a good price on a carrier. Hopefully it's as expected.

[Mike C]

3.73 is the break point on trucks for the 4 series carrier if memory serves. So factory gear set would work if that's the case.

[davepl]

I wonder if he has any receipts for rebuilding it. I'm going to assume not. Maybe someone more knowledgeable can suggest a way of finding out if he actually did rebuild it or not.

After all, who rebuilds an old posi to sell it without any proof of rebuilding it? If it's still a deal at $150, OK, but you'll be into it for a couple of hundred more if it wasn't rebuilt. And more if you don't know how to do it yourself.

[70CHEVYBB]

He said he was told that it would fit his 12 bolt chevelle rear end. I am going to take my chances. I will keep you posted and thanks for all the input.

[Bigdav160]

What's the difference between a car case and the truck case?

In all the application guides I see they are different part numbers.

[70CHEVYBB]

not real sure but I did just buy it for 125.

[davepl]

12 Bolt Truck != 12 Bolt Car

Or so I've always been told. At a minimum the car version pinion stem is larger. Posi carrier won't fit either, different ring gear flange offset even within the same series (2, 3, 4, etc).

All numbers are Timken. And yet, in spite of all that, I've heard it can be done. Which makes no sense to me, but what do I know? I found one guy trying it in his '68 Parisienne (it's a Canadian Pontiac kind of day today), and here are his part numbers. Maybe this is what he did to convert by using different bearings.

Car 12 bolt ----------------------- M802048 cone, M802011 cup -------- 1.625" inside, 3.250" outside, 1.045" thick.
Truck 12 bolt ---------------------HM89449 cone, HM89410 cup ------- 1.4375" inside, 3.000" outside, 1.1563" thick

Then the conversion bearings:

Car gear, Truck housing ------- 24781 cone, 24721 cup --------------- 1.625" inside, 3.000" outside 1.000" thick
Truck gear, Car housing ------- 25570 cone, 25519 cup --------------- 1.4375" inside, 3.250" outside, 0.9375" thick