i have a 91 rs that originally came with the 3.1L now it has an lo3 305 tbi! what i want to know is will a posi unit from another third rear end fit" i really don't want to replace the entire rear end! also are aftermarket posi units fairly easy to install?

 

I read you do not want to swap out the whole rear, but I have to let you know I was able to find a fourth gen rear with 3.42 gears, posi, and disc brakes, for $325. I think you would spend more than that on the posi and install kit and probably the same amount of time on labor .

 

it will fit but the pinion will have to be set and the ring gear lash will have to be set. As sully91rs said if your not building it for racing it's almost cheaper just to swap complete rear ends. At least when you swap a whole rear end you can upgrade to rear disks at the same time. 4th gen rear bolt right in. They are slightly wider, 2 inches each side, but it's not really noticeable.

 

it's an easy swap and the pinion depth doesn't need reset. you don't even have to touch the pinion. the back lash has to be checked and reset if needed. there's no need to buy any sort of install kit.

 

so your saying all i would have to do is find a posi unit from another third gen and install the unit? is there any fairly priced aftermarket units?

 

If your keeping the same gears and just swapping in the posi carrier that simplifies it a bit.

Like EDE said, only backlash needs to be set then. You dont even have to so much as lay a finger on the pinion.

 

just make suer you find one that is the same "series" as your old one so that your gear will bolt on. Then, simply put it together with your gear and set backlash.
- It'll probably take around $100-$150 for a decent take-out posi, and with a whole rear with discs around $300-$400, that's up to you.....

 

i definitely want to keep my gears! i am fairly sure they are 3.43. i get this from reading other threads that most v6 rs have the higher gear ratio! how could i find out for sure? run the nubers on the bottom of the housing? or will my vin tell me? also the donor camaro for my 305tbi was anothe 91' rs could it have a posi unit or did the units only come in the z28's? by the way i appreciate all this help! man do i love this site!!

 

Limited Slip rears RPO G80 were a option. People who were buying V-6 and RS models with a low power V-8's are not going to spend money on that option. Also the cars on the Dealers lot in most cases came without a Limited Slip rear.

 

A nice way to find the gears is to jack up the rear and spin the tires. As you spin the tires, count the revolutions of the u-joint. The revolutions of the u joint for every revolution of the tire will be the ratio.
I did this test on my friends 86 v6 camaro, and the u joint spun about 3 and a half times for one tire revolution. I looked it up, and v6 86 auto had 3.42 gears. I did the same test with my 91 rs v8 auto, and the u joint spun about 2 and a half times for every tire revoltuion. thats about 2.73 gears, which is what 91 rs v8s auto came with .

 

hey sully91rs!! di your test and i came up with 3:42! thats what i wanted to know! ok, now can i keep this gear ratio and just install a posi unit if the donor was a different gear ratio?

 

as long as the posi carrier is a 3series you can drop your existing gears on no problem.

3.08 and numerically lower = 2 series
3.23 and numerically higher = 3 series

 

your 91 should be the 28 spline axles, meaning older 26 spline units won't work, and I wouldn't down-grade axles....

 

my donor car is a 91 rs v8 could it have a posi or do most rs not have posi units!

 

i've never heard of an rs with posi. plus, if u take off the cover, u shuld b able to see if ther is a posi unit.

 

posi in an RS was an option just like in any other model, the thing is if the guy who originally bought it didn't opt for a TPI car, odds are low that they did opt for a posi. - most RS V8's were 2-series, open carrier....

 

ok, does anyone have a pic of a posi unit? never done any work on a rear end before! lots of engine work but no rear end...... ok maybe on chicks but not on cars.....

 

been checking out the aftermarket units (mostly in summit) and this seems like a great way to go i just don't wanna spend $600 for one any ideas?