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1970' Oldsmobile full size 12 bolt

Posted: Thu Sep 24, 2009 7:56 pm
by BigBlockMan
I have a Oldsmobile 12 bolt rearend (actually i have 3) 1 is from a 70 Delta, 1 in a 72 Delta, and 1 in a 73 Wagon. This is not the 10 bolt ring version both cover and ring have 12 bolts. Housing casting number is 383300, carrier is a casting of 698. Also on the carrier is a "GG" a "387" and a "2". I assume the 2 would be the series the GG and 387 must just be other casting info. The 698 appears on both the backside of the ring mounting surface and the tooth side of the case. The other 3 id's are all on the tooth side of the case. I am looking for a 3.73ish gear set for this housing/carrier.
The current gears are 2.56's. I want something a little steeper, if available I would even settle for a 3.40/3.55ish set. You seem to be the man with oddball rears figured it was worth a shot. The ring gear measures 8.5" on the mounting surface outside to outside, roughly 9.375 from edge of gear tooth to edge..where does one measure a ring gear? I have managed to find bearings that will allow the pinion sizes to match up between a "C" Type pinion and this housing but I am just not sure about pinion length and ring size.
I do have a few pics if needed but will need to get them to my computer first.

Re: 1970' Oldsmobile full size 12 bolt

Posted: Thu Oct 08, 2009 12:24 pm
by monzaz
WOW BBM, Sorry ti took so long to return this post...MY Fault.

Ok well not to burst your bubble here BUT about 3.42 might be as high as these rears ever got.

I have a set of 2.73 that is about as high as I have seen so far under a car with the FULL SIZE 'O' Type rear.

698 2 series 2.56 ONLY and 700 next step up 2.73 -2.93 3.08 maybe.

I am usually THE MAN.... But even I am still learning the full size cars because every GM division is different and almost from year to year they change... :(

I do buy rears just to learn and measure etc from time to time...but that does not pay the :D

No Aftermarket gears are available at this time for your 12 bolt FULL SIZE olds. So what is out there is it. I always appreciate and help the customers can offer in the casting numbers and tech GM books out there that are obsolete. They give an idea on if were on a witch hunt or not on steeper gears like 3.73 4.10 in this olds 12 bolt rear. Jim

I can tell you that the Olds a body and the Olds full size do share the same clutch packs and preload spring...Even the spider gears will interchange if you you need them too. axle spline count will be different.

Re: 1970' Oldsmobile full size 12 bolt

Posted: Tue Oct 13, 2009 12:07 pm
by BigBlockMan
I think your correct about the 3.42 being as steep as they got from the factory. I need to open up a couple of the other rears I have and see what they are.
I may have hatched another plan however. A little back ground on the project may even help you understand why I am attached to these odd ball rears. I run demolition derbies, with the beating the cars take the bigger and stronger the axle the better. Up until this point I have been using a Cadillac 12bolt which you also can't get parts for. I will send some casting numbers and pics if you deisre to add to your ID page, these rear ends where available with 2.73's and a special towing option of 3.15, axles are 1.3125 diameter, 28 spline bolt ins. Similar to a 9" Ford the drivers side uses a shorter axle than the pass. The pinion bolts in the front of the case and uses a pilot bearing by the carrier, the carrier itself drops out the rear. I'm not sure what diameter they are as I have never measured.
I wanted something equally as heavy to fit under normal GM fullsizes (Cady uses a different width upper control arm mount) and happened to have this Olds 12 bolt. Axles are the same size but 31 spline, and I thought the possiblility of finding say a 3.73 ratio was better.
That being said I think I have a 8.875 Corporate rear (need to investigate but cover looks right), and I see they also use a 31 spline axle. Do you know if a 31 from this Olds will fit the corp? If they do I can cut and weld the tube ends to accept the bolt in axles. (Update I tore into one the the suspected corp rears, it is a 10-12 and the Olds axles will spline up) This is all based upon the fact that the standard Chevy 12 bolt gearset will fit in the corp. this is question #2, are the sets the same?
As far as the posi factor goes I just use a "Lincoln locker" and haven't had one break yet. I may even have a posi unit for the corporate rear but again I need to investigate. If these are rare or whatever I would be interesting in parting with it as I have no use for it. (Update #2 it is a posi, 4 spring and clutch type, 2.73 ratio, casting looks to be a 250)
As far as you being the man I understand there are a lot of oddballs out there and very little information available. Most everything I can find is muscle car related, not so much for the fullsizers. You knew more than I did about it so good enough for me. Like I said if you want I'll send pics and measurements from this Olds and a Cady if you want. Maybe the info will benefit someone else down the line.
Thanks again for the help.

Re: 1970' Oldsmobile full size 12 bolt

Posted: Tue Oct 20, 2009 8:41 pm
by monzaz
12 bolt corp rears were bolt in and c-clip version.
early ones really were PONTIAC full size rears from 1965-1970 these were all 31 spline same as the olds 31 spline and were all bolt in axle rears.

Then in 1971 -1980ish were used in HD application they were all c-clip and first 71-74 ish were 31 spline then in the late seventies went to the 28 spline axles...pontiac full size, caddy's, 1976-1980 olds buick full size, a-body 73-75 elcaminio monte carlo etc

PROBLEM again are gears....crap.

NO the 12 bolt chevy gears will NOT fit...wrong bolt size and the pinion shaft is wrong length.

The pinion shaft is the same as a 10 bolt 8.5 with a 12 bolt ring gear and the ring gear bolts are left hand thread bolts 7/16" diameter.

Re: 1970' Oldsmobile full size 12 bolt

Posted: Tue Oct 20, 2009 10:51 pm
by BigBlockMan
Did some tear down today on what I thought was a 8.875 is what I found:
Carrier Bearings LM603049/LM603012
Outer Pinion M88048/M88010
Inner Pinion M804049/M804010
Carrier casting 250 (2.73 ratio, eaton style posi)
Housing casting 480633 (From a 72 Chevy wagon)
Axle code 7D P293 (7 may be a mis-stamped Z) no letter after digits findable
31 Spline 1 5/16 (1.3125) diameter C-clip axles (measured at the splines)
Pinion diameter 1.872/1.310, 30 spline
7/16 LH bolts on the ring gear
Ring gear diameter is 8.875 with a smaller inner measurement that a 12 bolt Chevy, (Chevy ring fits but is not tight on the carrier)
The plug seen in the cover in the picture is the only opening for oil to be added.

I also have another plug in pan rear in a 74 Olds Delta 88 (housing casting 480632) so it's not a wagon only thing.

What do I have here?

Re: 1970' Oldsmobile full size 12 bolt

Posted: Sat Oct 31, 2009 10:19 pm
by monzaz
Should be the same 10 bolt cover 12 bolt gut/ ring gear, pontiac 31 spline rear. All these carriers should interchange from housing to housing. with correct yoke interchanges.

Same design was used into the mid seventies with minimal changes ...BUT the rear became c-clip rear and the splines changes to 28. :( Jim