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Old 03-09-2010, 03:08 PM
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GM 8.5 Posi

I have a 28 spline posi unit that the spider gear on one side is junk. How hard are these to rebuild? any help would be cool. Thanks Bruce

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Old 03-09-2010, 07:17 PM
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Is this the one that you have? If it is then the gear isn't too hard to change, but finding one will be hard. They are not available anymore, so a used gear is your only hope. The gears from the standard differential will not fit. If you can pick up a 2 series you can get the gears out of it and put in yours (assuming that you have a 3 series). The 2 series is not desirable, so they are cheaper.

If this is the one that you have then the gears are not hard to get. I have 2 new ones on the shelf. Changing them is a problem. You must have a special tool to disassemble this unit, and the tool is not cheap.
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Old 03-10-2010, 08:47 AM
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Gm 8.5

I Haveone of each. Sounds like it might be better to just get a different unit.
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Old 03-10-2010, 11:27 AM
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Spider or side gear?

I am assuming you have the S-spring type, I believe it is type 2 if less than 2.73 and type 3 if 2.73 and over. It is not really clear...at least to me which gear you need. The spiders are on the large pin that transverses the carrier while the side gears are parallel to the clutch plates. I think the spiders are common to both open and posi diffs, the side gears are unique to posi's, I'll verify when I'm home.

This is a good type of posi to rebuild if you can find the parts, the gov-lock type should be avoided.

A link that maybe useful. http://www.buickperformance.com/posi.htm

Last edited by weedy64; 03-10-2010 at 11:34 AM.
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Old 03-10-2010, 01:57 PM
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I found a guy who has a 2 series for sale. I can connect you with him if you are interested in fixing yours. http://www.chevelles.com/forums/showthread.php?t=311122

Last edited by big gear head; 03-10-2010 at 07:57 PM.
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