I have a 1987 Pontiac Formula they guy that sold it to me said it was posi but he is pretty stupid so I dont really believe him. So I went out and looked for the code on the inside axle tube passenger side but its caked pretty bad with grease and junk so I could'nt really see it. How do I tell if I count the bolts on the rear end housing and its a 9 bolt is it definatley a posi or not.

The guy said it has WS6 suspension and im pretty sure if it does it has posi but it has rear drum brakes so?? Anyways the car was originally a 305 TPI with a 5 Speed the motor has been switched to 350 nothing else changed.

 

if its a 9 bolt its prob a posi...go outside in the steet and do a burnout if thers 2 marks its posi and if its one its a open carrier.. thats the easiest way

 

Yep I figured that was coming haha, well the other day I was backing into the driveway and my tires spun for a quick second but I couldnt tell if both were spinning, is posi engaged all the time or does it engage as soon as one of the tires start spinning?

 

if you don't want to waste your tires, just floor it on a rock driveway, and then go look at your tracks.

 

My tires are bald anyways from the previous owner burning out all the time it looks like a pretty even tread wear.

 

thats not totally true, if you do a burnout with an open rear you do, most of the time, spin both rear tires. if you are turning and light them up, you will only spin 1. easiest way to tell is to jack up the rear of the car, put the car in neutral and turn one of the rear wheels. if they both spin the same way, posi, if they spin in different directions, open.

 

mines open carrier and both tires will spin in the rain,dirt or rocks lol...feels nice can wit to get posi!!

 

Im gonna try that as soon as I get home for class tommorow seems like the easiest way to tell. Thanks.

 

If the tires spin different directions it could also be a burnt up LSD. Not uncommon for 20 year old vehicles...


Just pop the cover and take a look at it, the oil is probably long long long loooonnnnnggggg past due for a change anyways!

 

- Trosional type posi units will let the tires spin opposite on jcak stands. They don't make a torsional for the 9-bolt, but it's still not a good "test".

Pull the cover and look. I'm sure it needs the fluid changed anyway.