I have an 87 TA 5.0 4bl. It was passed down to me from my father. For the longest he swore the thing was dual posi and I didnt believe him. Reason being that evertime I burned rubber only one side spun and thats the passenger side. Still he swore it was posi and said they both always spun for him. Anyways, One day we were messing with the timing on the car and he asked that I held the brakes and peeled/burned out. To my astonishment they both started spinning. I thought the problem was fixed and it had to do with the cars timing. Now since then I notice that the driverside doesnt spin all the time only sometimes. Now we still didnt get the cars timing to be perfect, but it is better than before. Now my question is, Is it really related to the cars timing or was that a coincidence and there is something else wrong that would cause this? Any and all feedback would be appreciated.

Positive traction(posi) in no way shape or form has anything to do with the timing.

Usually open diff(non-posi) cars will spin the passenger's side and not the driver's, since there is more traction at the driver's tire due to the engine's rotational torque.

That said, the only proper way to know if it's a posi or not is to pull the diff cover and check, and it would sound to me as though this has probably never been done to the car, therefore it is probably over due a fluid change anyhow.

Unless things have changed, you can jack both rear wheels off the ground and turn one wheel with the car in neutral. If the other wheel turns the same direction, its a posi, if it turns the opposite direction, its not.

Sounds like its not, though.

Im not the smartest person when it comes to cars. I know my **** for the most part, but terminology is what always gets me. Im the guy thats like "the thing under that other thing by the (fill in blank, for example exhaust manifold)". So excuse me for making an *** out of myself, but where is the "diff cover" because I've never messed with that on any car or I've simply never heard the name and just dont realize what your talking about. Im sure your gonna tell me something and im gonna be like "oh that thing" or "so thats the proper name" and if not I'll be happy that you taught me something new.

ya my car does the same posi here and there it usually on new pavement...but it open carrier not posi hate it lol

the "diff" or differential (sp?) cover is the big semi round thing dead center between the axles. it has a couple (9-10 depending on rear you have) bolts running around the perimeter.

some people call it a pumpkin to

Though the diff cover in the following pic (the silver thing) is after market, you'll get the idea:

https://www.thirdgen.org/forums/atta...-89-guides.jpg

JamesC

If you shock an open diff hard enough it will appear to be posi because there is NO traction at either wheel and both will spin.

What redlightrunner said is the quickest way to tell-----just jack it up and spin one wheel and watch the other.

Things have changed. If the car happend to have a torsional type posi(it wouldn't have factory for the year) they'll spin opposite. Torsionals only lock down when shocked from the driveshaft.

like I said, pull the cover and look. I'm sure it needs the fluid changed anyhow.
and yes, I mean differential cover. The one between the axle tubes, located on the housing/pumpkin.

the way i do it at the junkyard is put it in neutral and have some 1 hold the opposite side and see if there is strain...if theres not its open diff...

this still doesn't work for later-model torsional type posi units.

There's a good chance it's a worn stock posi, that would explain it locking sometimes, but not always.
Remember, a posi is ~$400. Yikes eh?
And yea, there are cheaper ways, mini-spool, lincoln locker, used, etc - but you really get what you pay for here.