View Full Version : 7.5" rebuild/gear change help

04-30-2012, 01:48 PM
I am very new to the rear end gearing and building. I am looking to put a set of 3.90s or 4.10s in my 7.5". I know its better to go with a better rear end, i just dont have the money and i need the car on the road. When i started looking for gears i saw that some gearsets cant be used with the stock posi rear end. Can i not just go and buy the ring and pinion gear and the matching instal/rebuild kit and slap it in? Some say i need a block plate of some kind and im not sure what to look for. Any hints and info would be great. Again i am very new to this gear swap stuff.

I have a 99 trans am M6, and dont plan on to much track time.

04-30-2012, 04:22 PM
99s' would have come with a 'Torsen' posi. A torsen posi requires a modified 'paddle/block' to be re-inserted after the installation of 4.10s. Users modify/grind the original or purchase a SLP 'split paddle'
Don't know what the situation would be with 3.90s as they're not commonly used.

04-30-2012, 04:31 PM
Just call the dealer and they said my car had a g80 diff. They said it wasnt the torsen diff. How can i know for sure?

04-30-2012, 06:35 PM
G80 is the code for positraction/limied slip,an Auburn is a G80,a Torsen is a G80.
98 and earlier got Auburn,99 and later got Torsen.
pull the cover and look



04-30-2012, 08:33 PM

read that, I just did it, you need some things in addition:
I used a ratec solid spacer instead of a crush sleeve. you really need a tapered installer and a good bearing splitter, not one from harbor freight. you need either a pipe longer than the rear so you can knock the wheel bearings and races out, or a blind puller with a slide hammer and 1/2x18 threads. you may need a dremel, I had to cut 3 of my bearings off and you need to be very careful. pm me if you find yourself cutting.

save the inner race of your inner pinion and carrier bearings, hog them out so they slide and use them to drive on the new bearings. I recommend buying an extra set of pinion bearings, hogging those out and using them to set pinion depth. reuse the old nut as it'll go on/off easier.

you really need a good impact wrench (I use an aircat) but you must have a dial indicator w/ mag base and a set of calipers.

it is a lot of work and requires particular tools that you may not use again. I did it for the experience, I don't recommend doing it if your only aim is to save money.

04-30-2012, 08:36 PM
extra bearings weren't for depth, that's preloaded. sorry. . .hard to post right on a phone

04-30-2012, 10:04 PM
Wow, thanks! Where can i get the "slp split paddle" i called around all day and everyone just sent me back to the richmond gear tech. And then he would tell me to contavt an slp dearler, and so on and on and on. Really a funny day, made me laugh.

04-30-2012, 10:11 PM
SLP 'split paddle'

04-30-2012, 10:20 PM
sorry, might just try calling slp? see if its available? I have the slp auburn so didn't need it.

also, if you freeze the pinion and heat the bearing I was able to get the inner pinion bearing in 90%. cheap old trick, but still awesome.

05-01-2012, 08:09 AM
Would it be better to just go with a whole new diff? If so are there any recomendations or better options? And am i correct in understanding that the stock axels are 28 spline?