RS603

I just had my trans rebuilt in my '05 F-150 XLT 4x4, and when I went back to have it checked (shop policy), they noted the rear posi has a minor chatter. Is this a driveway fix or should I start calling my general mechanic?

SCORGE

How many miles? Rear diff fluid may need to be changed. What do you have as far as gears go? ratio, electronic locking, etc

RS603

Has about 145500 on the clock, electronically-controlled locker. Don't know what the gear ratio is.

SCORGE

I would try a fluid change and cleaning. If i'ts E-Lock you don't need friction modifier. Will also give you a chance to look inside.

RS603

Got it, thanks!

SCORGE

Sure thing

PerryB

Are you sure about the e-lock, because I don't think they existed before 2011. You probably have a conventional clutch-type locker and its pretty common for them to get chattery with age. If the clutches aren't too glazed a fluid change (along with fresh friction additive) might make it quiet again. If you have a chattering e-locker you have a serious problem with it.

screamineagle

Yep, no e-lockers on these trucks.

casey.mikl

Does a friction modifier have to be added with synthetic fluid? I changed mine about 2k ago and haven't added a modifier yet.. I haven't had a chance to get to ford.

PerryB

Yes. If you have a clutch-type posi (Trak Lock) you need friction juice.