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Old 02-19-2011, 09:12 AM
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1st Gen Monte rear end questions

I have a 72 Monte Carlo. The current rear has a blown axle bearing. Its a Corporate 10 bolt, non posi unit. Well, what an opportunity to upgrade. I am thinking of a 12 bolt, but curious if my current drive shaft will work and I am wondering about pinion angle if I go the route of a 12 bolt or if there are other things to consider. Lastly, should I invest in the current 10 bolt and upgrade it to a posi unit, might be cheaper, not sure. As far as horsepower goes, I would not expect to exceed 400 - 500 at some point in time, assuming I swap the current motor.

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Old 02-19-2011, 10:26 AM
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Keep the 10-bolt if it is, in fact, a 8.5" and not the 10-bolt 8.2" diff.

The 12 bolt diff has a slightly larger ring gear, but the pinion diameters are the same. The corporate 8.5 will handle the power levels you mention.

But be sure you actually have what you think you have (I do not know how much you know, etc. so bear w/me). From a thread on another board, posted by BGH:
Most of the '71 and '72 Monte Carlos had the 8.2 10 bolt, but there were a few that got the 8.5 10 bolt. The 8.2 has a 1 1/8 pinion nut and 3/8 ring gear bolts with 9/16 heads. The 8.5 has a 1 1/4 pinion nut and 7/16 ring gear bolts with 3/4 heads and left hand threads.
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