Has anyone dealt with Precision Gear Inc.? It looks like they sell a posi for the O-type rear.

I'll have to save my money over the winter!

Any suggestions for a good differential ratio for a B body with a 455? I would like to be able to drive the highway, lay rubber (of course) and be competitive with other street machines block to block. The cam is around 300 duration and .500 lift.

The link for Precision is attached below.

http://www.precisiongear.com/gmtracklok.htm

 

Send a PM to Brian Trick. Never seen a diff question he could not answer.

 

Thanks!

 

Yeah, for the 8.5" ring gear axles used in the A-body line, not for your B-body.

 

I tried to install their (GM10/LS"O"3) into my 68 442 and the installer said it wouldn't work. Don't know why. I think these are ford posi's turned into olds units.



Can anyone help me identify if it would work with my 68 442? I believe my rear end ratio is 3.08. I calculated it based on RPM and MPH in driving. I don't think I have ever found the code to my axle. I'd like to use this Posi unit but as it stands I may have to sell it if it doesn't fit.

 

Send a pm to Monzaz, very knowledgeable and can get you what ever you need.
https://classicoldsmobile.com/forums...rs/monzaz.html

 

If you have a A-body GM 12 bolt cover 12 bolt guts it will fit... with 3.23 3.08 Factory gears and 3.42 and 3.90 aftermarket 3 series Richmond gears.
IF you have a FULL size 65-70 B Body Olds 12 bolt cover 9.3 ring diameter with 12 bolt ring gear bolted Carrier OBVIOUSLY it will not fit.... TOTALLY different rear

The 8.5 and the 9.3 are the most outside diameter of the ring gear ...tooth side not ring gear bolt side.

Sorry will not fit a B-Body car as stated by another member.

I know it is hard to tell BUT it is really easy to know they are totally different...JUST count your ring gear bolts. 10 vs 12.

Jim
J D RAce
Akron, Oh

 

Without taking a picture, I am sure it looks like the first picture. I have 12 bolts on the cover but no clue as to the ring gear. I don't think I should be taking the cover off to find out as I don't want axle goo all over my garage floor.

 

Well then good luck with the purchase as that 88 rear never came with a 12 bolt cover and 10 bolt ring rear. If your not going to help yourself... we can help no further. Only way to be sure. you can pull an axle shaft too . full size car will always have 31 spline axles. Most 12 bolt a-body will have 28 spline except for w30 rears which had 31 spline axles and 29.75" long.

There are NO aftermarket posi units for the full size 12 bolt olds rears.

 

Never said I had an 88. I have a 68 Olds 442. The point I was making is that I would not be able to identify what ring gear I have (10 or 12 bolt) unless I physically went into the differential and counted bolts. I am not setup for that. But based on what you are saying, it seems to me that since I have a 12 bolt cover (this I know) and I must have 28 spline axles. So in essence this device should work on my car. The only thing that may defy this logic is maybe I don't have a 3.08 rear end. I have tried many times to find the code on the axle housing and have never found it.

Chris

 

There are two different rears with 12 bolt covers that fit into your car - the O-Type (12 bolt cover, 10 bolt ring gear) and the Chevy 12 bolt (12 bolt cover, 12 bolt ring gear). From the factory, Canadian cars got the Chevy 12 bolt and all others got the O-Type, but after 48 years anything could have been swapped in (even a different gear ratio into the housing), so you really need to verify exactly what you have.

An easy way to get an idea of what ratio is in there is to lift one rear wheel, put the trans in neutral, turn the wheel and count the driveshaft revolutions. Divide what you get by 2 to account for the differential action since only one wheel is turning. Turning the wheel 10 times helps get a better driveshaft revolution count. Post up what you find and we can help decipher the ratio. This won't help with Chevy 12 bolt vs O-Type, though. If you can post detailed pictures of the side of the center section and the U-joint flange, that would really help to ID the rear.

The most direct identification is pulling the rear cover off, counting the ring gear bolts (to ID 12 vs 10), and checking the numbers stamped into the edge of the ring gear (this will give the number of teeth on the ring gear and the pinion gear, divide them and get the ratio). If you have an oil change drain pan, use it to catch the gear oil. It's really not difficult.

 

I was answering with the first poster on the this thread ...did not realize there were multiple posters ...
too many different things gong on in one thread.

Should start your own thread post for that one.

So a picture of a box number and no picture of your rear diff still does not help us answer your question. we need to see what rear cover you have under your car. The posi unit you have pictured will have 10 ring gear flange bolt holes and probably be 28 spline side gear unit.
That unit pictured should fit the 3.08 and 3.23 12 bolt OLDS rear with 12 bolt cover and 10 bolt ring. bolt in 28 spline axles. That unit will also for the 3.42 AND 3.90 Richmond gear sets.

The code on any axle tube is only good IF you know the car has never been messed with and over 40-45 years I would NEVER trust the axle tube code anymore.
YOU have to remover the cover and read the ring gear edge it will have the ratio tooth count stamped on the edge. Just spin it around till you find the part number of the ring gear and then after that the tooth count and the date code will be stamped into the ring gear outer diameter. (pictures are examples of how it will be stamped... NOT ACTUAL 12 bolt olds ring gear numbers)

THIS is the ONLY true way. Sorry. change the oil anyway...probably needs it.

 

I just saw this posting. I would try and remove the cover but I don't want axle grease going everywhere. I think maybe I need to take it to a shop and have them determine the particulars.

 

Removing the cover is a ten minute job just place an oil change pan under to capture the lube. Before refilling I let the cover sealer set up overnite and refil the diff the next day to help avoid leaks

 

Sounds like a simple task. I have several oil catching pans I can choose from to use. So this may be a dumb question but where do I put new fluids? I know there is a venting shaft at the top of the axle. It is small and I wouldn't think to add it there. How much should fluid should one add?

 

there is a fill hole w a square drive plug on the front of the diff not very convenient but i usully put a small hose on the bottle to make it easier IIRC its like 2.5ish qts.

Look in your CSM for the exact fill amount and type of fluid

 

I just talked to the guy who fixed my tranny and who also does posi's and he was saying that the bolt pattern was wrong. So this is kind of telling me that I have a 12 bolt ring gear. Any thoughts?

Also now I know where to look for axle codes! On the driver's side, front facing side of car! I was looking on the passenger side back facing of the car!

 

Don't over fill, the level should be about 1/2 to 3/4 in below fill plug hole. It takes 90w gear oil and can be had at your local auto parts store.

 

The codes are on the passenger side axle tube.