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Old 05-09-2013, 09:36 AM
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8.5 Posi

Hey guys, I'm trying to find a factory posi unit for my 10 bolt 1979 Camaro. In the past I've dealt with 12 bolt and 9 inch rear ends; but, what I'm doing to this car won't need it. If you can steer me in the right direction to get one I'd appreciate it very much.

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Old 05-09-2013, 06:46 PM
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CHECK OUT CRAIGS LIST. I have found some bargains there. Be careful what you are told, and know what your buying. Not all 8.5 10 bolt posi will fit. I got one from a friend several years ago for $75.00 and that included the 3.42 gears. Also go to the swap meets in your area. If you don't know, ask a friend to tell you what you need to look for. Don't be ashamed to ask, I'm still learning and its from asking.
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Old 05-10-2013, 06:11 AM
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There are several differentials for the 8.5 10 bolt. Be carefull of what you buy. The 2nd gen Camaros used the Traction Lock, whcih is a clutch type differential with a S shaped preload spring in the center. These were made in 2 and 3 series. The 2 series has the casting number 410409 and the 3 series has the casting number 410408. You will want the 3 series for gear ratios from 2.73 to 5.13. These were all 28 spline.

In '90 GM increased the axle size from 28 spline to 30 spline, so if you are using the stock 28 spline axles you will need a differential that was used before this upgrade. GM started using the Auburn differential in the 8.5 around this time. I would not use a brand new Auburn in anything that I own, and I will not install one in a customer's car, so I sure would not bother with a used Auburn. Don't even think about using one of these.

The trucks used the Governor Lock differential. You do not want to use this differential in a performance car. These were just barely strong enough for a stock GM truck with stock tires and can not handle much abuse. These were made in 28 and 30 spline. In '98 GM increased the size of the ring gear to 8 5/8 and they increased the size of the differential bearings to the same size as the 12 bolt. There are bearings available to adapt these differentials to the earlier housings.

I would recommend that you skip the search for a used differential and just get a new Eaton Posi or Yukon Dura Grip. These are almost exactly the same thing and are rebuildable. A new set of clutches for a used Trac Lock are about $250, so for just a little more you can have a new differentail that you know is in great condition. You can get these in 28 or 30 spline, so if your axles are worn and need to be replaced you can just upgrade the rear end to 30 spline and make it stronger in the process.
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