Olds Posi ? Whatta u think ?

Ok, guys been thinking long and hard on weither to buy a posi rear end for my 68 skylark. Non-track car, just cruiseing and the occassional red light "tire burner"... 455 with a turbo 400 transmission now, but in about 3 weeks an installed 200/4R transmission.

Option 1: 12 bolt Posi Rear with a 3.08 gear ratio out of a 1970 442 Olds Cutlass,"Freshly rebuilt", like 3 weeks ago. ($700.00)

Optiion 2: 12 bolt, non-posi out of a 72 monte carlo, needs posi unit/gears and all, plus installation into rear end.

 

Option 3-- Buy a new 8.5 GM corporate carrier and gears from Monaz

 

if freshly rebuilt means all new bearings and seals and a reconditioned posi unit, then $700 is a decent price. If its got new gears in it then its a real good price.

The 12 bolt will cost you a bit to build, they are quite strong and quite popular.

Of the two I would take the O.

 

I guess another question IS Do either of the rears have the ratio you WANT? Is 3.08 the ratio you were shooting for? Or are you looking to change the ratio?

IF you are going to swap a ratio then take the 12 bolt chevy as the ratio for the O type 12 bolt is 3.42 or 3.90 and the gears are 300.00 + JUST for the gears.

10 bolt 8.5 will cost you less... I have one for sale with 3.08 RIGHT NOW...lol. than the 12 bolt chevy but for the 700.00 on the olds unit...it is still a pretty good deal AS LONG AS IT IS rebuilt. That is the BIG KEY Huh? tough call.

Mine is listed at 1000.00 at least. May work a better deal if someone is interested.

Jim
JD

 

The price for the type O 12 bolt seems on the high side, my el camino has a type O 12 3:90 posi and I have about $400 in it and thats what i thought I was going to get out of it when I upgrade. Maybe the market for those are better than I thought

 

I may be wrong but the 3.08 ratio may be a little high geared behind an overdrive. The $700.00 rear end might be a deal if actually rebuilt. As mentioned it might be a 10 bolt with a 12 bolt cover. A friend of mine had one of those rear ends in an 11 second Olds with no problems. It will probably cost you more than $700.00 to build a rear end whether its a 12 bolt Chevy or a 10.5
Parts and labor ain't cheap.

Bob H.

 

I am sure the rear is a OLDS 12 bolt which IS 12 bolt cover and 10 bolt ring gear. Nothing wrong with the rear...JUST more expensive to build as gears and posi units are a bit harder to find and more expensive.

Thgat is why IF it is already re build it might be a good enough rear...IF you like the 3.08 gears for your application...??? ALL depends.

IF the 12 bolt covered rear has BOLT IN AXLES it is a 'O' type 12 bolt and will have 10 bolt ring gear. 'O' typr olds 12 bolt also use a 1 1/4" nut to hold the pinion yoke on. The 12 bolt chevy uses a smaller 1 1/8" nut hex head.

Take care and good luck in your choice. As I stated if you need any parts or prices to see what way you want to go just PM me.

Jim
JD

 

Hello.

I know it has been a while, but did you purchase the 12-bolt with the 3.08 gears? If not, do you know if they are still available? I am looking for a 12-bolt with that axle ratio, or even just a #671 posi carrier.

Thanks,
Anthony

 

Neither, ended up getting a olds 10 bolt, 3.73 posi for allot cheaper. Busted an axle bout a year ago, but besides that been all good.

 

IMO the 3.08 gear is to high for an overdrive tranny. I think the engine might lug in overdrive with a 3.08. Most people that install 2004Rs go with at least 3.42 and many go as low as 3.73 or 3.90 depending on what type rear you have.