Gonna drop an LT1 in the 91 V6 soon, just want to know if my rear can hold it if I punch it? I know it would be better to replace it with a 9 bolt (I think its 9 bolt) but don't have the money for a new differential yet, the car came stick so it should have a higher gear ratio right? Thanks.

stock u should have a 10 bolt 3.42 gear ratio, very certain its a no posi being a v6. i think it will hold up fairly good, being a non posi u might be having alot of traction issues though..

Lt1's only seem to have alittle more horsepower and a tad less torque than a L98 350 tpi. and most 10 bolts can hold pretty good power having street radials on.

my original v6 rear with 3.42 gears held up fine to my 350 i swaped in. and it makes more power then a stock LT1 for sure

a v6 10-bolt rear is the same as a v8 10-bolt rear, other then gear ratios, and a posi unit in some cases.

your rear end should be fine behind an lt1 for while until you get more money saved up.

Great, I really want to put POSI on the rear and I heard their actually was a kit or something or other that goes on to these differentials. Anyone got a link? If not I guess i'll go looking for a 4th gen rear.

You have the same rear. You just need a posi carrier for it, and better gears (if your application needs them), then you'll have pretty much the same thing as in the fourth gen, except the right length for your thirdgen!

Alright, sounds good to me. So where can I find a POSI unit to install? Anyone have a link to a site or manufacturer # or something similar? I don't have any idea what to search for. Also, my rear has drums , how hard would it be to convert to discs? Thanks.

Converting to would be easiest to use a disc rear to begin with. Here's a tech article about converting from drums to LS1 style discs: Thirdgen.org tech article on LS1 disc conversion

There are many options on what posi carrier to go with. If they're still out there, the take-off units from SLP (what came OE in fourht gens) are the Zexel Torsen's, and from what I've heard are pretty good. I've seen them as cheap as $99. The heavy duty version can also be had, I think around $400.

Ok just got a bunch of results on ebay searching for 10 bolt posi unit. Is it the 28 spline that im looking for? Is 3.42 gears a good set to have and will 3.73 make that much of a difference? One more thing, how hard is it to install the unit? Thanks.

I have a rear end out of a V6 car in mine. With decent power you can't get it to hook up hard enough to hurt it. I am getting ready to install an Auburn posi this winter so I guess time will only tell.

Thanks for the link .

Awesome bro, just ordered some after seeing it for 99 from the manufacturer, I love this site . Ok so how hard is it to install this unit? Just pop off the diff cover and just bolt the POSI on? Also, would it make a huge difference going from 3.42 to 3.73? Thanks again bro.

SLP online. Thier offices are closed currently so it won't be processed until Jan 4. Im praying they have some in stock.

LOL, I didn't mean it literally .

You need to have it installed by a pro that knows how to do it right with the right tools. It is not your typical bolt on at all. So be prepared to fork out a few hundred but it is well worth it if you ask me. The SLP posi probably has less than 5 miles on them when they remove them. They go from the GM plant right across the street to SLP's plant. Well they used to when they made them. One thing that you may need to check. Is your stock 3.42's for a 2 or 3 series carrier. If they are for a 3 series carrier than the take out posi will work. If your 3.42's are for a 2 series carier you need different gears to work with that posi. I am not sure if the V6 3.42 is the same as the V8 3.42. Same rear but you may want to look into that.

It's actually fairly easy to install, Ive changed a few in 4thgens. You need the later axles 90+ somthing like that with the larger spline count. But be warned a good aftermarket unit will outlast the SLP so you might consider this before you order.

What do you mean by fairly easy? I definatlye don't have the money to have apro install and i've seen the depth chart tools go for $100 .

Most of the time, installing the new setup with the exact same shims, in the exact same order will get it really close. For the most part, it's the axle housing that has the variation, not the gears and carriers. Many times, I've done this and not have to make any changes. You most certainly need a dial indicator to check the backlash, and an in-lb torque wrench for pinion bearing preload. After getting these right, check the pattern.

I'm NOT telling you to just throw the new carrier in there with the same shims and you'll be ok, you absolutely MUST check it! I'm just stating that most of the time, the way the old one came out is close for the new one. If you don't have any idea of what you're doing, get a manual, and if you still don't, leave it alone, and get someone to do it for you. Maybe you can get someone to help you do it, so that you can learn by watching them?

I've never used a pinion depth gauge, and I do this stuff for a living.... I'm sure I probably should get and use one, but it's never been an issue for me!

So can someone go into some details on how to install the unit?

I can tell you how I installed my eaton posi. Might not be the most correct way but it worked for me (so far).

-Pull off cover
-Unbolt the cross pin, and pull it out
-Remove C clips, then axles. (make sure they are the right splines for your posi)
-Maybe change bearings/seals while your there
-Take out old diff, this can be tricky. I had to pry mine with the wooden handle of my hammer.
-Take ring gear off old carrier, install on new one (in my case)
-I used my old shims (had a shim kit just in case)
-Popped in the new posi. Install the shims. (fat shims last)
-Bolt it up, use dial guage to check back lash. Used some grease to check gear contact area
-Torque it properly, install axles, c-clips, cross pin. And your done.

I may of forgot something but i'm pretty sure that is all

Ok waht exactly is a dial guage? Also how can I check if I have a 28 spline axel? I believe all 90+ models came with a 28 spline. Whats a cross pin? What do you mean by popped in old POSI? I have a haynes booklet that I can look up for the cross pin and such items, but I definatley do not want to tear up my rear =/.

Actually, I do, but last time I brought my vehicle over there to be checked for an idle, the stupid college kids were putting ratchets, nuts, bolts in my headlight pockets and I bitched them out saying they could scratch my paint, not to mention the instructor wasn't overlooking anything they were doing 1/2 the time.

Although I may be new to the area, I don't feel its rocket science and im not afraid to try anything new, however I do want to know as much facts as possible before I start.

Honesty if you dont have any of the tools and no experiance with using a dial indicator buy a power trax unit and same yourself a headach. You will get a better unit that wont break under load and no special tools are needed to install.

Got a link?

Dial guage=Guage which measures depth very accurately

Splines=fancy word for teeth on your axles


Had a nice long detailed explanation but it got lost while submitting

Sorry for the spelling mistake on "popped in old posi"

edited it and fixed it

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