I am experiencing an issue that I think relates to the rear differential in my truck. It is a 2002 F150 Supercrew 4X4 with the 5.4 and it has the limited slip differential.

Around town, I never really notice any issues. However, if I drive it on the highway for any distance, I then notice issues after I slow down. Once back in town, it will shudder when I pull away from a stop and will creak when I turn corners.

I am assuming that it is an issue related to heat. When I drive around town at lower speeds, it probably does not get as warm as it does on a highway run.

When it gets warm, something must be tightening up.

I have had a couple of suggestions.

One, is that I need to make sure it has some sort of friction modifier lube added because it is a limited slip differential. I do not think it has that in there now as it was checked and re-filled. I do know it is synthetic lube in the diff now.

A second suggestion that came through someone my younger son knows is that there is some sort of technical bulletin relating to these differentials suggesting that a shim package is available to fix the problem.

A third suggestion is that the pinion nut was tightened a bit too much when the pinion seal was changed out a year or so back due to leakage.

Anyone else suffering similar isssues and have the answer?

I am going to have to take it somewhere and get someone to have a look at it. I don't want to cause additional problems by ignoring it.

I do more highway runs in the summer and of course it likely gets hotter in summer so I was able to essentially ignore it for the winter, but now the time has come to get it fixed.

Randy

 

If you're sure the diff is filled with the correct fluid, try adding some limited slip additive. If you're getting shuddering around turns, it's probably the clutch pack grabbing too much from none or not enough additive. Add until the shudder just goes away so that it still grabs when you want it too.

Mike

 

you can buy a 7 oz tube of friction modifier at Auto Zone, put the whole tube in and see what happens after 50 miles. THe stuff is magic in a tube.

 

I second what Steve says, I had the same issue with my 01....had a nice arguement with the dealer about the friction modifier...they didn't know what it was!! I followed Steve's info....The book manual calls for 4oz, but I put in abot 7oz, and it took about a hundred miles before it quioted down.Trust us on this one!!
Rich

 

Slip modifier

 

Napa sells friction modifier also...good stuff!

worked for me!

 

Never heard of slip modifier...hey ya learn something new everyday!

 

i say you swap the whole thing out for a DETROIT locker, then add a MAG-HYTEC diff cover (which holds 2 more qts of fluid!) - then make sure you go full synthetic - then get back to me!!

drj

 

I'd be happy to do that...can I borrow a couple grand?

 

i think as long as your not swapping gears too - the DETROIT is a few hundred - plus labor - and the diff cover is only a couple hundred too...

i bet you could put the whole rear end together for less than a grand!!

but i have to tell you - with the rear end locked - i NEVER get stuck...in fact - i usually end up getting other people UNstuck.

i did have to modify my driving habits a little bit to accomodate the DETROIT - but its not that big of a change.

drj

ps - i could extend you a loan - but my interest rates are ridiculous!!

 

Well, the Detriot locker for the 9.75 is around $650 and the Mag Hytec covers are around $250. Plus install it would be at least $100...