My 2002 psd seems to lock-up the rear-end sometimes when turning. Even in 2wd it will clunk and sound terrible. It started doing this shortly after mechanic changed gear-oil in rear-end. Any ideas?

 

Some trucks were equipped with what is called a "limited slip" (although I like to call them "limited traction") differentials that use clutch plates to minimize the "one-wheel-wonder" effect commonly associated with "open" differentials.

These clutch plates require an additive to be used that allows the clutches to slip and release. Without the additive, clutch binding and friction material failure are common.

I would have the tech add "friction modifier" to the fluid. It will take a little bit of driving around corners to work into the friction material, but you should be fine.

 

I agree. Sounds like a friction modifier issue. Just make sure the mechanic did use a synthetic fluid and not the old 80-90w gear oil.

 

I couldn't remember if you were supposed to use synthetic or if you were NOT suposed to use synthetic. Also do I have to use Ford's synthetic or just any additive for the rear-end.

 

Yes....Friction Modifier.....Needs to be add and is required in the rear end differential of your truck.

 

Tony,
These guys are right. I was on the way back from Texas one night when mine sounded like it was coming out. We were at a rest area and it honestly sounded like the lugs were loose on one side when you pulled up (you know that rythmic clunk at slow speed). I checked everything and figured it had to be the rear but at 3am didn't have much choice but to drive on. Had it checked by the stealership and they added friction modifier (they said there is a service bullitin about it) and it stopped. They also recommended that I change the fluid about every 15k miles if pulling a trailer.

Good luck,
John
2003 F350 CC 4x4 dually, 6 speed, K & N FIPK, Quadzilla Commander, Superchips Max Microtuner, RDS 91 gallon tank/toolbox combo,

 

The tag on my diff says it came with syn in it. If you use Royal Purple you don't need friction modifier. The tech should have known better.