topher01

hey yall i have a 4thgen rear end to go in my 91 rs. i have built a vortec 350 for the car and swapped in a t56. im swapping the 4th gen rear end in to gain rear disc brakes and the posi. it has factory axles and gears in it. gears are 332. im thinking of doing 410s or 388s, any input on gears. car will be street strip car. also i now the stock axle shafts arent very strong. any recomendatins on upgrading those also. engine should be close to 400 horse havent dnyoed car yet, 400 is machinests guess. i dont want to snap and axle my first trip down the strip, thanks in advance everyone!!

big gear head

The 4th gen axles are 28 spline AAM. There is no upgrade from that for the 7.5. The weak part isn't going to be the axles.


If this is a '93 to '97 rear end then it's going to have the Auburn differential. Good luck with that. Be ready to change it soon. If it's a '98 to '02 then it will have the Torsen, which is MUCH better.


The gears will likely break before anything else. Correct set up is very important to the strength.

topher01

the axle is out of a 94 z28, what set up would you recommend for this axle? i would like to build this axle up for the disc brakes and i already have the axle lol

sofakingdom

iTrader: (1)

There are no 3.32 or 3.88 gears for that rear.

Gears always are a ratio of 2 whole numbers (count of the teeth); usually at least one of them is a prime number and often both; pinion teeth are in the range of 15 down to about 9, and ring teeth anywhere from 37 or so up to around 44.

Not all possible numerical combinations are actually manufactured for all rear end models, for a variety of reasons. For whyever, there are fewer ratios available for these, than for most others.

3.23 (13 & 42), 3.42 (12 & 41), 3.73 (11 & 41), 4.10 (10 & 41), 4.56 (9 & 41). The 41 ring is different for the last 3 even though they have the same tooth count. There are lower ratios too.

A 94 rear will have the Auburn posi. A steaming pile of manure. Chances are, it already is mostly wore out if not completely.

For a T-56 I'd suggest 3.73 minimum. That's what I have (just the weenie stock ratio) and it's borderline too low. 4.10 would probably be ideal.

big gear head

What do you want to do with the car? Will it be drag raced, auto cross or other? The differential that you choose should be matched to the use of the car. There is the Eaton Posi, Eaton Truetrac, Yukon Dura Grip, Detroit Locker, Power Trax Grip LS and a few others, but each one has it's uses.

topher01

Car will be a street strip car, I would like a posi not a limited slip. I work on big rigs. A big company we use is eaton. Not sure how there automotive parts are far as quality wise. Thanks go the help!

big gear head

Posi and limited slip are the same thing. Posi is Eaton's trade mark name for their clutch type limited slip differential. Somewhere along the line people started using Eaton's Posi name for all limited slip differentials. Posi is Eaton's name, Power Lock is Dana's name, Sure Grip is Auburn's name, Safety Trac is Pontiac's name.... These are all limited slip differentials.


The Eaton Posi is a good choice. The Yukon Dura Grip is almost an exact copy of the Eaton Posi with a different clutch material. The Power Trax Grip LS is also a clutch type LSD copied off of the Traction Lock. Any of these would be a good choice. If it's going to be more strip than street then the Detroit Locker would be better. Clutch type LSDs don't hold up well to repeated water burnouts.