T/Atime

Ive been toying with the idea of doing a gear swap for a while now. A few things are holding me back from getting this done.

First im aware that the stock 10 bolt is not the first choice in rear end selections. But on a mild 350 with 260 rwhp I dont think this would be an issue. Some people have said to save my money and build a 12 bolt. This might not be a bad idea because i will be building a (383 hsr) in the future but my original L98 is still running great. So a guess my question would be what are the limitations of this rear end.

I would love to get a set of 3:73s im assuming that i have 3:08s now. The car is a 91 GTA L98 it has a stealthram intake, headers, flowmaster with a pcm for less tune. Its driven 90% in the city so 2200rpms on the hwy is not an issue. In the future it would be nice to go to the track with a 383 motor with drag radials and make a few passes.

Does any one have a similar set up with 3:73s? If so what can i expect around the streets? ET reduction?

big gear head

Parts needed, new Eaton 3 series posi, 3.73 gear set and a high quality installation kit. You will need to take it to someone who knows how to set the pinion depth, bearing preload and backlash.

RedHawkLB9

you NEED to make sure what gear you have now......to see what series carrier you have...i have a 10(2.73) 2 series thats goin to a shop next week and puttin in THICK 3.73s for the 2 series carrier....but you say you 3.08 that calls for the thick gears like me....the gears and install kit is all you need tho lol

big gear head

I listed the Eaton because if it has an Auburn in it now it is probably just about shot. The Auburn is not rebuildable, so replacement is the only option. The Auburn is close to the bottom of my list of good parts to use, so I always recommend replacing it with an Eaton. As an Auburn wears it fills the rear end with powered metal, which runs through the bearings and gears. They also wear out a lot quicker than the Eaton.

gurkgurkgurk

yeah u can get an eaton posi at summit or any other parts seller. because the first thing u wanna do is get rid of the one u currently have, chances are the cones are worn pretty good, and once the cone is gone the only way to fix it is to grind it down, but even thats a temporary fix.

to let you know, along with going into steeper gears, your gas mileage on the freeway will go significantly down. you also bring down your top speed because of the fact your rear end gears are getting bigger so the transmission has to turn it even faster to go the same speed it went before on the highway. but if this is just a race car, then forget what i said.

also your gonna want to get the rebuild kit, id actually check out randysringandpinion.com they specialize in rear ends and differentials and will help you get where u want to on the track. theyre also pretty affordable. another thing is if your a do it yourselfer and u have a workbench at home and access to a press or a torch, you can do it entirely yourself, which is good because its always nice learning something new just incase u need to do it again down the line. there are tricky things like setting case bearing preload, and pinion preload, backlash, and all that jazz. if you do end up doing it yourself, get 2 crush sleeves, because the most common mistake that people make when setting pinion bearing preload is that they think theyre no where near specification and then they turn it just a tad too much and then theyre over specification and they have to start over again, and since crush sleeves can only be used once, its cheap insurance to get an extra one.

T/Atime

Thanks for all the great advice!

Ive got a transmission shop that i trust to build up my diff.
Do i need new bearings with all the parts. And what about the limited slip components... i was told that this is the weak link in this diff?

About the ratio selection... i dont have any real world facts about this? Gas milage is always the main draw back in choosing a suitable gear. If i decide to pick 3:73s my rpm will jump 300 to 2200 at 65mph. This does not seem like it would kill my mpg, cuz its a 700R4? 3:73 will also put me at the end of the 1/4 mile just under red line in third gear. I am prepaired to sacrifice a little gas milage to gain a usable powerband. Im not that interested in exceeding 140mph at this time. With the stealthram i have lost that bottom end but gained a lot more top end... Kind of miss the tpi lowend grunt... just a bit..

This is going to be one of those fun seat of the pants you can feel modifications. I respect all of your opinions and if i left out any factor worth considering i would sure like to hear about it.

big gear head

That is why I listed the installation kit in the list of parts. It will come with all of the required bearings, except the axle bearings. You can get axle bearings and seals with the other parts or pick them up at you r local parts store.

There are no rebuild parts for the Auburn, which is probably what you have. These are throw away differentials. When they wear out they are scrap metal. Just replace it with a new Eaton.

T/Atime

Thanks!
when i bring my car to the shop ill tell them to price out the eaton 3 series with the kit.

dabird07

iTrader: (10)

this thread was really helpful i just bought a rear end gear 3.73!
and ive been told mix things imma hold off on installing untill i get a posi and ofcourse new tires
THANKS!!!

Ron U.S.M.C.

With that gear ratio the last thing you want is a one wheel peal. With out the posi. you will be disappointed. The hole point in doing a gear change (IMO) is to make it a posi. (and the gears of course.) I recommend the Eaton . I have one and it feels great on a launch and is perfect in the turn.