LSD Not working

[z28gsxr]

My truck has roughly 141k. I bought it a few years ago at 127k and am not sure if the LSD ever worked. A few weeks ago i was out offroading a bit in the sand and I noticed that the limited slip was not working. One wheel was spinning just digging into the sand.

Maybe 6 months ago I swapped out the fluid in my differential and replaced it with Royal Purple. I don't remember the exact weight but it was the recommended weight listed on this forum. I also read that with Royal Purple you did not need the limited slip additive that you normally add to the oil. Could this be my issue? Should I try adding the additive?

[z28gsxr]

Do they all come with a factory limited slip? i have an 02 f250 lariat 7.3L auto 4x4.

[SuperCrutyPS]

You're right - I looked up the RP Max Gear and it says it's formulated for LSD use. So...it could be your limited slip isn't working.

I don't know what year your truck is, but from the '01 F350 Owner's Manual, it states:
"2 Add 236 ml (8 oz.) of Additive Friction Modifier C8AZ-19B546-A or
equivalent meeting Ford Specification EST-M2C118-A for complete refill
of Traction-Lok axles."

So...does RP Differential oil meet this Ford Spec? Would it hurt to add it? I wouldn't think so. Plus, it might be a cheaper way to check before having it torn down.

You can check your truck's owner's manual here:
https://www.fleet.ford.com/maintenan...ls/default.asp Look under Fluids and Specifications.

[z28gsxr]

Its a 2002 f250

[letitsno]

No they don't all have limited slip.
The clutch's have most likly worn out, with that kind of milage.
Not that hard to do, hardest part I had was getting the right parts.

[wsigo]

Are you sure your truck came with that option? Check out the tag on the diff cover. I don't off the top of my head remember what you should look for, possibly an "L" before or after the gear ratio listed on the tag.

The additive would actually cause a Ford limited slip to "slip" MORE... it's designed to keep down the "chatter" while turning by letting the clutches slip past each other.

[STIgone73]

This is something I need to address on mine as well. I have an 01 f250 4x4 w/off road package and mine does the one tire frier as well. Most likely needs a rebuild. Mine has 152k on it.