Just got this oldsmobile 98 handed to me from a customer who got it for the drivetrain but it's only got 60k miles power windows decent Interior and it's solid plus anytime I can save a bog car from the derby boys it does me good. I'm in the process of getting parts to make It a crusier and I'm having trouble identifying the rear diff it's a 12 bolt rear but it's gigantic has a full round cover and gigantic drums I've been trying to I'd it but haven't had luck I got some numbers off of the center and the axle tube from what I read online and the tube letters are ethier OO or QQ or a mix of the two because bottom of the letters didn't get stamped all they way. Main reason why I'm looking into It is I want to run overdrive because I have a fresh built one sitting around and I want to change gears but if it's a 3:42 I'll leave it. So I decided to join and ask the experts who know alot about these oldsmobiles. Thanks for letting me join hope to learn a lot.

 

9.3 Oldsmobile rear end? I've mentioned before that I'd much rather disassemble a radio instead of tinkering with the 3rd member.

One of our members @monzaz should be able to hook you up with info, if not some parts. Here's a good place to start.

https://classicoldsmobile.com/forums...ll-size-93232/

 

3.42's weren't available in the '68 98. 2.56:1 were standard. You shouldn't need O.D. with those gears.

 

could be QQ which is 3.42 ratio ...non posi open
BEST to open that rear up and get the stampings off the ring gear edge.
You will need to physically see the condition of the parts anyway to be sure it is all good. + oil likely needs a changing.
Jim
JD Race

 

could also be a QO which is 3.23 - as you can see in the picture the parts of the stamping that are not visible are the lower right of each letter and that is how you can tell a O from a Q... lol

Also, From the forum we are looking at it seems to have 1966 axle codes??? This again is why OPENING the rear is the ONLY TRUE best way to know what you have.
Jim JD Race

 

Thanks for the info Jim. I knew you'd be able to steer the OP right. Hopefully he opens up the differential for that code and you can get him some parts.

 

Welcome and hope to see more of your 98. According to the PIM. QQ is a 2.56 open. Three ratios were available for these cars in 68, 2.56 (std ratio) 2.73 and 3.08. Hope this helps you-and post some pics of your Ninety Eight!
Dave

 

Thanks for all the info I'm going to definitely tear the cover off as soon as I can I don't have a garage and the car is at my work. when I get caught up ill pull it in and find out for sure what I have. I would really like to run my 700r4 but if it comes down to it I'll just locate a turbo 400 and live with the highway gears for now.

 

Had time after work tonight to pull the cover and found 2:56 gears and it is the big olds rear 12 bolt 12 bolt 9.3 inch ring gear. So what are my options regardless if I find a different transmission I'd still want a lower gear I know parts are hard to find but don't know if there is a direct rear end swap.

 

That 2.56 rear end wouldn't work well with a 700R4 or 2004R. Hopefully you can get some parts to at least rebuild it.

 

My local rear end shop (old timer) had a set of 323s for an olds 12 bolt I couldn't drive over fast enough to snag them. 80 bucks was a good deal plus he included a ring gear spacer he custom made because of the case break.

 

There're a couple different Olds 12 bolts, and the A-body has 12 bolts on the inspection cover but 10 bolts on the ring gear. As shared by another member 3.23's were not available in the 1968 full sized. You may need to check the numbers before tearing your rear end down to make sure they will fit.

 

I'll double check for sure but it is a 12 bolt ring gear over 9 inches just have to double check pinion but so far this old timer has been right on most stuff but knowing my luck something will be off.