Hello! I just bought a 2000 F150 ext. cab short bed 4x4. Its got the 5.4 engine and 3.55 LS rear end. Anyway, the tires chirp and "grind" around the corners as if the axles are locked together. The rear end isn't leaking any fluid. The truck has 100,000 miles on the clock. The differential doesn't make any vibration and seems to be great except when taking tight turns. It feels like the axles are locked together, and I am sure the rear end has never even been opened so everything should be factory. It feels like its got a detroit locker in the back. What would cause the limited slip to lock up like this?

Would it help if I changed the rear end fluid and put some limited slip clutch additive stuff in there?

Has anybody else ever had this problem?

I just don't want to hurt my limited slip clutches or tires because of this.

 

I think you just answered your own question.

 

Change it and then drive it in a figure 8 several times to work the limited slip lube into the clutches. Sometimes you may have to replace the clutches though.

 

I had the same problem after my stealership replaced the fluid....they originally added 4oz of the friction modifier and it still did it...they added a total of 8oz and it solved the problem.
if it ever stops snowing here, i'll be changing again, to Amsoil and adding their FM even though they claim you don't need it.

 

Why do they say you don't the FM?

 

I had the same problem and so did my fathers SCREW... we both but royal purple in the rear ends with some ford FM... took care of the problem completley...

 

not sure...Amsoil thinks their stuff doesn't need it...but since it's $5 as a prefered customer and it can't hurt, i'm adding 4oz.

 

Royal Purple says their gear oil doesn't need FM but I always add it in my truck. It can't hurt. I need to change mine soon.

 

you might have locker and not know it.

drj

 

Ford doesn't make a locker, only limited slip!

 

How long has it been since they dropped the Trac loc any way?

 

i know that ford does not make a locker - but it IS a used vehicle with high miles - so it IS possible that someone had a locker installed and you would never know without opening it up. he did say that he just bought it. so before we all decide theres something wrong with his truck...you have to consider other options.

i only suggested that - because i have a detroit in the rear and the symptoms are IDENTICAL.

drj

 

go to Auto Zone, get 2 quarts of synthetic 80w 140 gear lube and the 7 ounce tube of friction modifier and your problem is solved.

 

UPDATE:

I opened the rear-end (which has never been opened before BTW). Everything looks good inside. The fluid was brown and foamy. It didn't look like water had ever been in it or anything. I replaced the fluid with Mobil One Pure synthetic 75W140 and a 7 ounce tube of Ford Friction modifier, but I am still having the same issue. I tried doing a bunch of tight figure 8s to get the fluid around in the clutches. Will it take a few miles for the change to happen?

Any other advice?

 

i think i read within 200 miles the problem should be solved....if not, new clutch packs.