Alright, I am sure this question has been asked a million times, but I couldnt find any info with search.

I have a 90 formula with 305TBI, T5 Tranny, and what must be the 3.08 rear end (not sure how to tell, but I read in in the 90 firebird info).

Everyone says that the best thing to do is just get a whole new rear end, but the junkyards arounf here never seem to have f-bodys. Plus, as much as I would like 3.73, I dont want the speedo off at all. Finally, I like where my RPM's are on the highway in 5th now, i actually get pretty decent gas milage.

So my question is, is there any kits that you can buy online to convert your stock rear end into posi? I cant stand the one wheel squeel in the rain. Plus the 1 leg burnouts.

I remember reading somewhere that there was a kit for like $90 that a tranny shop could put into your stock meatball to make the car posi. I dont really understand how the diff works, but I cant afford anything expensive. Even if it only lasts for a little while then goes back to open that would be nice.

If I cant find something cheap, i might look into how to make a Lincoln Locker. It cant be that hard. But I would rather have the drivability of a LSD.

Thanks for any help!

 

Nope Nothing usable for under $400 + other parts (bearings, seals, shims).

Lincoln locker or mini-spool is kinda dangerous, WHEN it fails.

You can just put a new plastic gear in the tranny to get it to read correctly again, if you're putting in new gears. That shouldn't be a reason not to upgrade your gearset.

If by "meatball" you mean differential, that would probably be a mini spool. Again, dangerous when it fails.

 

#1. If you can't recalibrate the plastic speedo gears, don't bother installing a posi. There is no reason your speedo will be off after changing gears if you do the math and buy the right plastic gears (that will cost all of about $10 for both of them).

#2. A Zexel-torsen posi can be had off ebay for about $150. They are stock from 4th gens. You must have 28 spline axles to use them (pull some from a late 3rd gen that came w/ 28 spline axles). OR you could use a $150 ebay Auburn cone (stock 3rd gen) posi unit, which would keep your 26 spline axles. You could also keep the 3.08 gears if you really wanted to. If you haven't set up gears before this option is probably not for you. If you keep the 3.08s, all you would have to do is use a dial indicator with a mag base, check the backlash of the stock gears and carrier before removing them from the housing, and then reinstall the ring gear on the posi carrier and put it back in using the stock carrier shims, check backlash again, and if it is the same, put everything together, if not, buy a shim set up kit and adjust the carrier shims until your backlash is the same as stock.


You don't want to change plastic speedometer gears, but you are going to manufacture differential parts yourself?

 

You sound like the perfect buyer for a Powertraxs No-Slip Traction system. It's a bolt in LSD and you don't remove your ring and pinion, so there is no backlash setting or shimming necessary and you use your stock axles. So if you're rear end is operating fine, this would be an option. The unit is around $400 new...it's not exactly cheap, although I did get mine used for about $100 off this site. I don't know if they are in abundance used. I just stumbled onto mine while browsing the parts section.
You could put it in yourself. Installation time is about 4 hours for a first timer. There are some tips to use to make the job easier. If you go this route, PM me and I'll dig up the website. If you took it somewhere for installation, it shouldn't be much because as stated, you don't remove the ring and pinion.

http://www.powertrax.com/noslip.html

 

Yea, the powertrax is a slightly easier install since it goes INTO your stock open carrier, rather than replacing it. But pricing is about the same as the rest. Some users love the powertrax, but most hate it. Do a search on that for more info.

327 mentioned used (ebay) options. I didn't even think of used, but that's an option. Just be wary of "like new" units that are cracked or something. As far as i'm concerned, going to a new posi, you're looking at spending $600, when the smoke clears (tire smoke that is )