O Type

robs70monte
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O Type

Postby robs70monte » Sat Aug 06, 2011 5:46 pm

I have 12 Bolt in a parts car (1972 Monte Carlo) I know its not the factory rear end but it doesn't look like a Chevy 12 bolt it has a smooth diff cover (doesn't have a lip on the pan like the Chevy 12 bolt) i think its a olds 12 bolt it has ears on the bottom kinda like the chevy 8.5 10 bolt,Its a open diff the its said to have 3:73s in it but i have not checked that yet,I want to get a mini spool for it and possibly 3:73 gears-4:10

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monzaz
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Re: O Type

Postby monzaz » Sun Aug 07, 2011 9:29 am

Rob- That does sound like the 12 bolt 'O' type please reference the pictures of the rear covers in the ID Differential section of this web site It will also give you all the dimensions and other info bearings axle spline count etc. you need.

We also can provide you with the bearing kit - limited slip unit (posi) We have power trax units that will fit right into your open NON POSI carrier just as a mini spool too.

We do have the MINI SPOOL if this is what you prefer-

GEARS - Now gears will ALL DEPEND on what ratio is in your 12 bolt now. IF you have 2.56 2.78 3.08 3.23 we can get you aftermarket gears that bolt right in and the available ratios will be 3.42 or 3.90
3.73 is NOT available for this rear.

Jim - J D Race.com
J D Race

robs70monte
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Re: O Type

Postby robs70monte » Sun Aug 07, 2011 12:27 pm

http://s1092.photobucket.com/albums/i41 ... 1_1768.jpg
Heres a link to a pic of my rear end
It looks to be a type O form what i see ill have to look for numbers on it later
I would like a mini spool and 3.90 gears this rear end is replacing the 8.2 10bolt bop rear in my 1970 Monte Carlo witch is a open with 2.56 gears

robs70monte
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Re: O Type

Postby robs70monte » Tue Aug 09, 2011 6:55 pm

My rear end is 100% A O type 12bolt(10bolt) So how much for a mini spool and can i find out the spline count with out pooping the cover.Did they make the 31 spline open diff

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monzaz
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Re: O Type

Postby monzaz » Tue Aug 09, 2011 10:23 pm

Yah doubt they made a OPEN 31 spline diff for the 12 bolt olds. Was a W30 option in 67 68 cars

Yes we can get you that mini spool

Problem- You will need to change the carrier to move up to the 3.42 or 3.91 FROM 2.56 or 2.78.

What is the purpose of this car that you need to LOCK the rear axles solid.? Jim
J D Race

robs70monte
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Re: O Type

Postby robs70monte » Wed Aug 10, 2011 6:32 pm

Its a street strip car right now i have a 8.2 10bolt (BOP) in it with 3.73s and a mini spool and Moser axles im fine with it for now but i want a stronger rear.
Im on a budget also and im sure that a mini spool or full spool is cheaper then the posi unit not
to sound cheap

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monzaz
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Re: O Type

Postby monzaz » Fri Aug 12, 2011 8:32 pm

Well - The 'O' type 12 bolt really is not much bigger in the ring gear (8.4" 'O' compared to 8.25" Pontiac)
The only real difference in the BASE 12 bolt olds compared to the PONTIAC 10 bolt is the inner pinion bearing size (1.625 'O' type compared to the 1.438 Pontiac 10 bolt 8.2)

Axles shafts are the same 28 spline and are interchangeable too.
Yoke is the same as a Pontiac 10 bolt 8.2 (both are 27 spline and the SAME Identical part number)

Only big difference is the trac lock posi unit (clutch type 12 bolt 'O') compared to the cone type posi unit ...BUY even the Pontiac had a more heavy duty posi unit with 4 pinion spider gears...

10 bolt Pontiac also had more heavy duty main bearing caps.

FOR this reason PONTIAC stayed with there 10 bolt 8.2 until 1972.

In 1973 GM made all GM cars use the corp rear 10 bolt 8.5.

Jim
J D Race


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