I've purchased two posi units, one is from an 87 GN, and the other is an Eaton 28 spline, 10 bolt, 8 1/2". Neither seem to fit. I don't know much about them, but the shop showed me what happens when they install it. The flange on the posi is pressed up pinion gear. Anything obvious that I may be doing wrong?
Did they reset the crush sleeve to set pinion depth? Did they reset the carrier bearing shims?
There's really no difference between 8.5" units (the later 8.5" units in the trucks have different axle splines, I think) so they should all fit. Sounds like either a wrong part or they shop doesn't really know what it's doing?
I don't think so, but I really don't know. I doubt both posi's are the wrong unit. I'm not even sure who I need to take it to that might know what they are doing. If they didn't set pinion depth or carrier bearing shims, would this cause the problem I described? They let me look at it while it was in, and the flange of the posi was resting right against the pinion gear.
Are you sure you don't have a 7.5" rear end?
It sounds almost like they are trying to put an 8.5" posi on an 7.5" carrier?
I have an 87 GN. Did they come with 7.5" carriers? I thought the 87s had 8.5" rears.
They came with the 8.5, but if it was replaced somewhere along the way, it may have gotten the smaller one. Sometimes people find out they have the 7.5 with 3.73 gears. Which to me sounds like they got one from a Monte SS, and the guy putting it in thought since it was from an SS that it was as good or even better than the original.
Brian
While they came with 8.5" units, its not unheard of for someone to snag the 8.5" out of one and replace it with a 7.5" unit before selling it.
This can also happen with cars that are put back together after theft recoveries, as the 7.5" is _much_ easier (and cheaper!) to find.
It might be worthwhile to pick the rear up and check your ratio real quick by spinning a wheel and checking driveshaft revolutions. While all the TR/GNs had 3.42 rears, most of the plain V6 cars with the 7.5's seemed to have 2.41 gears. If you find you've got 2-series gears, that would be a good sign that something is wrong.
Since you're buying posi units, I'm guessing your car is lacking one. Check for code G80 on the sticker in your trunk. If you have G80 on your sticker, you should already have a posi. If you have the code and no posi, that'd be another sign that things had been monkeyed with. See http://www.gnttype.org/numbers/rpo.html for more RPO codes.
Actually, I believe the Monte's got the 7 5/8" unit and not the 7.5" unit.
Any way to tell without taking anything apart what size the unit is? I remember when I was in the guys shop, he pulled something out of the rear end and placed it next to both posi units. I'm not sure what that unit was, I think whatever it is in the rear end that is in place of a posi. When he put them side by side, he placed a yard stick across the top of the three units. The thing he took out of the car was a little shorter than the two posi's that I bought. Maybe by .5 - 1" shorter. This may shed some light on the situation.
You might try to ID it by looking at the cover. See http://www.precisiongear.com/GM.htm for some pictures of the different GM housings.
Also, compare your housing's gasket shape with those at http://www.drivetraindirect.com/html2/gm7pt5.html and http://www.drivetraindirect.com/html2/gm8pt5.html to help narrow it down.