Limited slip differential (Posi)


Asked by Dec 06, 2009 at 05:27 PM about the 2001 Pontiac Firebird

Question type: General

I have an 01  firebird v6. I am trying to figure out if my car has a posi (LSD) rear end. I have lifted the rear wheels, and spun one of the rear wheels forward, and the opposite one did not move. I spun the same wheel backwards, and the opposite wheel then spun in the opposite direction.   ????      I also tried burning out. I accelerated from a stand still, and there were two marks on the pavement. ???    Thx.

15 Answers


try jackin up one wheel and spinning it, if it wont spin u got posi( spin it at least a little while). otherwise take the differential cover off and look if there are clutch packs (about 3 inch circles about an eight of an inch thick in a group of at least a few) in line with axles on either side of the big gear in the middle u probably have posi. otherwise if u know what 75w90 gear oil smells like then the friction modifier for the clutch packs really stinks in comparison also an indicator. And if that picture is of your bird the u have a killer lookin one.


I will try that as soon as I can Thanks a lot man, for the help and the compliment.


Im pretty sure a rear limited slip posi makes sure both wheels dont rotate at the same speed, (eg. corners) so if you jack it up, and spin one wheel, and the other doesnt move at all its a L-S posi.


oh, and if you can do a burn out its a LSD (posi) either that or a Pro-drag racing rear diff. (which i highly doubt :P)


cool thanks alot bro


No probs man. My shop teacher just explaind some of that stuff today, and I remembered your question. Have a good 'un.


Ok so I got the chance to test this out. I jacked up one wheel, put the car in drive and tried to spin the wheel. It was able to spin forward easily. Then I spun it in reverse and it wasn't able to spin as easily, so according to you I do not have a posi diff. However, when I accelerate quickly and peel out, I leave two wheel marks on the pavement, indicating that they both spun. I am real confused. What ya think man?

2 tire patches side by side means its a posi. have for with that killer chicken.


hey man sorry I didnt get back to u very quickly. you can get them to lay 2 patch rubber with out posi but if it wants to spin both tires I say let it and dont worry . oh if the car was in drive when checked, I would try that in neutral. but in honesty my '02 T/A was a little temperamental about both tires goin for a while but if she does a two wheel burnout then i would say your odds r good of havin posi.


hey I have the same car, it has an open differential not a posi (stands for positraction or lsd). basically when you lifted your car and spun your wheel back it was the pinion of the two axles spinning. basically the driveshaft goes into your differential and spins a big gear with your axle running through it. an open differential is set so that when both tires have the same amount of traction the torque is distributed evenly. when one wheel slips (or spins in a burnout or a turn) the pinions of the wheel going faster takes over and the other is left to be spun by centripical force or the force of the car being moved by the other wheel. once the traction is even again the two pinions recieve equal amount of power. the idea of it is to help turning because the outter wheel has to spin more, and seeing as we have the lower model of the car they didnt want to spend time putting a posi-traction or limited slip dif in. If you have more questions lemme know -kirby

1 of 1 people found this helpful.

a posi or lsd means if 1 wheel loses traction it will lock the other, but it will also allow both wheels to spin at different speeds (like when going around corners)


I have a question I have an 99 Firebird v6...pretty sure its not posi because it feels like only one wheel is spinning, how can I convert it to posi affordable other than welding the gears?


Heres how i do it without opening the case. I jack up both wheels , car in nuetral, turn the driveline by hand as if the car is driving forward, if both wheels turn? Posi. One wheel turns? Not posi

2 of 2 people found this helpful.

No I think he has a limited diff. If it was an open diff. then the tire would be able to spin freely going forward because it sends more power to the "slipperiest" tire which would be the tire in the air.

I have a 2002 firebird 3.8 v6 and I can only make one line in the road.what can I do to make it posi?

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