I'm going to the boneyard, what is the easist way to tell if a rear is a posi? I heard that with the car in the air if you spin one tire by hand and the other one moves its a posi. Is that true? After i find one I will pull the cover and count teeth.

 

Ok.....3 easy ways to go about this.

1. Raise car, spin tires. If BOTH tires spin same way - Posi.
If they both spin oppsite of each other - non-Posi

2. Look for a tag bolted underneath one of the cover bolts. If tag reads "Use limited-slip lube only" - Posi

3. Look in the center console at the RPO tag. If the same is true as it is for G-body GM's, the code for a posi rear should be G80. I maybe wrong on this last one though.

HTH!

 

I thought Posi acted like a normal Diff untill there was enough torque going through it to lock down the plates? Is this right?

 

I have a Posi and if I raise one end and spin the tire , the other tire turns in the opposite way and on my tag coming off one of the bolts it only reads a number. (well mine does)

 

Anyone else? Now I'm really lost.

 

Do you have a haynes? Mine has the TUBE axle does for each year firebird to tell what ratio and if it has posi or not. The code is also on the axle OR OR OR you can look on the RPO codes for that ONE number like he said above but I don't think that tells you the ratio. BUT THERE A CODE ON THE AXLE and those numbers are in haynes.

 

do just what justa6 told you to do. if both tires spin in the same direction, posi. if they spin opposite, open rear. the RPO code for posi is G80. if that is on your RPO sheet, you have posi. however, the clutches inside the unit do tend to wear out over time. a common problem is people saying that they know they have posi, but when they spin em, they only see one line. this is due to wear on the posi clutches.

Beene, posi is the name of the system. limited slip is the name GM gave to their posi units. Limited slip works likes this. Both rear wheels will turn at the same speed going foward unless the torque of the engine overcomes the posi clutches. when you take a turn, the unit allows the inside wheel to slow down and "slip" so you dont get wheel hop. spools, on the other hand, keep both wheels moving foward at the same rate ALL THE TIME. this means when you turn, the inside wheel will lose traction. mini spools are more appropriate for drag cars, not street cars.

 

Take off the cover and look. Tags are useless, people change all sorts of stuff all the time and don't put on new tags.

All posi is, is a set of clutches inside the carrier, that "clutch" the axles to the carrier. They have a spring that puts tension on the clutches, so no force is required to "lock up". The clutches basically force both wheels to turn at the same speed, unless theer is enough traction to be able to apply enough torque difference between the 2 wheels to slip the clutches.

Justa's directions are almost right, except they should be:

• Raise the rear end off the ground.
• Leave the trans in Park if it's an auto, or in gear if it's a stick.
• Rotate a wheel.
• If the wheel turns and the other turns the opposite way, it's not a posi.
• If it takes 60 ft-lbs to turn the wheel, then it's a posi.

Mkos, if your wheels can ever turn in opposite directions with less than about 60 or 70 ft-lbs of torque, then you don't have posi; or your posi is completely worn out.

 

Hmm I'm going to have to check. I do have posi so maybe i'm thinking of my other car. hmm

 

I think a little more accurate way is to have the car in neutral, and give the driveshaft a sharp twist, and if both wheels spin, it's a posi, and if one does, it's a std. The reason for that is, like someone else here mentioned, they can have posi, but the same/opposite spin test doesn't work, it's because you come across some worn posis out there. If it was new, it would work. If not, then you'd have confusing results. This way that I mentioned, always works (well I shouldn't say always because someone will find a way to prove that wrong, too..hehe).

 

THERE IS A CODE STAMPED ON THE AXLE HOUSING. GEEZ.

 

We all know about the code. The code doesn't tell you what the rear has, only what it came with. People change what's inside the housing without changing the code all the time (speaking for myself of course ). The code is essentially worthless on a 15-year-old car.

Take off the cover and look. It's utterly foolproof and infallible. Everything else has a chance of error.

 

Thank you for all who helped