1984 F-150 Positraction

It doesn't. Positraction is a GM feature.

Translation: GM calls theirs positive traction; Ford calls theirs Limited Slip. They do the same thing, afaik. You should be able to look at the axle tag, and probably the door placard, to find out if it does or doesn't have it.

Because these units use internal clutches, they lose their effectiveness with miles; therefore, it might be a moot point unless the purchaser plans on tearing down the axle to replace the clutch packs.

CJB

Jack up the rear end, spin one rear tire by hand. If the other rear tire spins in the same direction, it's a limited slip. If the other tire spins in the opposite direction, then it's an open differential.

Spdloader

Or a non-function Limited slip....

No, limited slip (Fords version of GM's "positraction") is an option, not standard. Somebody would have had to pay a few hundred extra dollars for that option. If it has a factory limited slip/Traction-Loc then the tag on the rear end will indicate that. The tag will say something like 3.25 for an open rear end and 3L25 for a limited slip/Traction-Loc rear end... For the truck you are asking about it is much more likely to have an open rear end, not a limited slip.

True, clutches could be "done" by now.

Spdloader

This test will work a lot better if the transmission is in neutral:)

Al

Thanks to everybody for their suggestions/ideas. I put it in neutral, jacked up the rear end and spun each tire. The opposite tire did not move.

When I put it into second gear and tried again, the tires turned in opposite directions - so I guess I have an open differential.

Thanks again.

Yep, open diff.

Spdloader