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Old 02-04-2006, 03:10 PM
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Ring and Pinion Swap in a 2nd Gen Firebird

Hello guys,

I'm building a 1981 Trans Am and am having an issue with the rear end.

The powertrain of the car is pretty custom, Chevy 350 with an M-21, and a Rear end out of a 1976 Firebird. I was told the rear end was a 2.41 Posi, and seem to remember running the numbers to confirm it...

Anyway, given the very high first gear in an M-21 and the rear end, it is making the car near impossible to drive, so I was looking into changing the ring and pinion to be a 3.73 like was designed for the transmission.

I've been looking and found there are two different carriers for this particular 10 bolt rear end, and the ones I've found are for the larger of the two carriers. I've also been told that I can purchase a ring spacer for my rear end to put these gears into my rear. So, my question is, can such a simple fix allow me to change out the gears? And if so, will that spacer weaken my rear end significantly?

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Old 02-04-2006, 06:58 PM
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Buy the correct posi carrier for the differential. Ring gear spacers do not allow the ring gear to be centered and positioned on the carrier. The inner bore of the ring gear is meant to be firmly seated on the machined OD of the carrier; ring gear spacers destroy this location. I'm sure there are many who have done the ring gear spacer, however, it is not a recommended device. Using them places all the torsional load on the ring gear bolts which will lead to broken bolts.
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Old 02-04-2006, 07:03 PM
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Chazmac is absolutely correct.

Find a gear set that will bolt up to the 2-series carrier you have, or replace the carrier with a 3-series.

Of course if you replace the carrier, you can get any limited slip or posi you choose that will fit your axle housing.

Your 1976 housing should contain an 8.5 inch ring gear.
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Old 02-10-2006, 09:18 AM
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Just to clarify, it would just be the carrier that I would have to replace and not the whole axle? Would I have to replace the axles themselves as well?

Does anyone have a location to get a ring gear for a series 2?

What are the differences between the series 2 and series 3 axles?

Finally, if I'm using this axle for the street, what sort of life expectancy should I expect from a spacer'ed axle?

Sorry for all the questions, I'm trying to get a very quick education on these rear ends, and thanks for the help guys.
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Old 02-10-2006, 10:57 AM
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Changing carriers doesn't necessarily mean changing axles. The carrier break for the 8.5" GM rears is 2.56/2.73, and you'll want the carrier for the 2.73 and up gears, along with the gearset and installation kit.
Call West Coast Differentials in Sacramento and they'll have all the numbers you need. 800-510-0950
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