10 bolt 72 cutlass driving me crazy 8.5 or 8.2?

mmcilroy
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10 bolt 72 cutlass driving me crazy 8.5 or 8.2?

Postby mmcilroy » Tue Oct 20, 2009 8:37 pm

Looking for some help.
Have a 72 cutlass convertible with a 10 bolt olds rear end (based on what I have been able to find out). I believe it to be around a 2:73 ratio. Would like to get to the low to mid threes if possible but can't find a positive answer if its a 8.5 or 8.2?? Also if parts are available.

Can anyone provide some guidance?

What I do know:
NO C clips
"O" cast into both sides of the differential
non-posi
10 bolt cover with lip from 12 to 3
U joint has bolts with clamp NOT a u bolt with nuts

Does any of that make sense.

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monzaz
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Joined: Tue Nov 13, 2007 7:56 pm
Location: RICHFIELD, OH

Re: 10 bolt 72 cutlass driving me crazy 8.5 or 8.2?

Postby monzaz » Tue Oct 20, 2009 8:47 pm

mmcilroy, VERY familiar with this rear. It is the corperate 10 bolt 8.5...same as all the 70 rears and used all the way up to 1987 grand nationals and it is still used in the trucks to day in a slightly modified carrier bearing and axle spline way.

Your diff will be identical to the 1971 1972 Buick skylark...LOOKS a little different BUT that same guts.

We have plenty of new and used parts for this rear, rebuild kits, posi units reconditioned and new.

You have many many many choices out there with this rear and it is plenty strong to boot. It is a keeper.

you have a 10 bolt 8.5 rear. ALL 8.5 8.6 gears will fit your differential from 2.73-5.57 ratio and all in between.
J D Race

mmcilroy
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Joined: Tue Oct 20, 2009 4:41 pm

Re: 10 bolt 72 cutlass driving me crazy 8.5 or 8.2?

Postby mmcilroy » Wed Oct 21, 2009 11:28 am

Thank you for the quick reply. I'm not a differential expert but I imagine I'll learn this one inside and out before this is all over. I appreciate the insight. Do I need to know how many splines it has before I can purchase the right parts. If so whats the easiest way to find out?

Thanks again in advance, your site is great, most informative site I have seen regarding this topic!
I'll be shopping soon I hope.

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monzaz
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Re: 10 bolt 72 cutlass driving me crazy 8.5 or 8.2?

Postby monzaz » Sat Oct 31, 2009 10:12 pm

No you do not need to as I amn sure this is what it is and it will be 28 spline 45 degree spline.

You will need a 3 series posi

we have 3.08 gears good used GM for 45.00
we have 3.23 gears good used GM 95.00
3.42 New aftermarket for 139.00
3.73 New aftermarket for 139.00

Rebuild kits

New posi units or reconditioned factory GM units for sale all the time also. Jim
J D Race


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