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Swapping to a 4th gen rear, namely a 2002 Trans Am disc, posi, 3.08 (Auto car, pretty sure that's the ratio)
I would like to change the ring and pinion before installation but I am seeing lots of different options for part numbers. Going to a 3.73 and I'm looking particularly at this set from ebay.
My concern is that I see some listed as "Fits 3.23 and up" or "thick" gear and I want to be sure that this part will fit properly on the first go round. Will this 3.73 set fit my carrier? I intend to rebuild the complete axle assembly during the install. I have done the older GM open units but this will be my first posi overhaul. I appreciate the input, thanks in advance!
However, that particular vendor DOES have the special "thick" gears that you would need for your situation.
To understand what's different, remember that the gear "ratio" is NOT ONLY the ratio of the # of teeth on the 2 gears, BUT ALSO the ratio of their DIAMETERS. Therefore as the ratio INCREASES, the pinion diameter must DECREASE, since the ring diameter is the same for all ratios. So as the ratio increases, the thickness of the ring must also increase, because the pinion teeth are farther away from its teeth, so to speak.
2 series on the left, 3 on the right. Note how the flange that the ring gear mounts to is in a different place: the 3 series in this model of axle is about .400" closer to the pinion.
The factory does it that way because gears tend to warp during heat treatment, which obviously scraps them and drives up the overall cost of making them. The thicker they are the more they scrap. So they locate the ring flange at some point far enough away from the pinion to allow for a thin ring gear in the lowest ratio they'll ever make which I think was 2.29 in this model, then as the ratio increases, they make thicker and thicker ring gears; up to a point, where the scrap rate is expected to get too high, at which point they move the flange over and start over with thin rings, and then they get thicker again as the ratio steps up.
In this model of rear the break occurs between 3.08 (12 & 37) and 3.23 (13 & 42).
There is no difference whatsoever in rebuilding a rear with a posi carrier vs one with an open. If you know how to do the one, the other should present no problem. Expect however, that the posi will be mostly if not completely worn out, being an Auburn POS; which incidentally is not rebuildable. I'd stongly suggest checking its posi action THOROUGHLY before spending any money putting it into a new buildup.
Last edited by sofakingdom; Apr 30, 2020 at 01:51 PM.
Yes the LS1 cars came with a Torsen, not an Auburn. LT1 cars still had the old disgusting POS.
AFAIK no 4th gen V8 car came with a 3.08. I could be wrong of course. It's happened before.
One of 2 things is going on here: either you don't know what you've got or are looking at buying, or some scammer is yanking your crank.
Pull the cover off and LOOK AT THE PARTS before you lay out one single dime. Maybe even pull an axle and measure the length. Get a photo of the brakes and post em, that'll help identify the car they came out of.
Well joke is on me, didn't spend much on this so I'm not extremely angry, but this diff is not posi. Can I just swap in a used carrier from hawks to get posi?
Well joke is on me, didn't spend much on this so I'm not extremely angry, but this diff is not posi. Can I just swap in a used carrier from hawks to get posi?
Almost the same thing happened to me. I got one from a buddy who was told when he bought it it was from a 99 T/A LS1 car. He didn't really care as he just wanted the tubes for his 8.8 build. He ended up getting a 9" so I bought the rear for $100 I got it home and it was an Auburn posi with 2.73 gears. So must have been out of a V6 car. I have a torsen and 3.42's to put in it at some point.
