I have a 2003 Ford F150 with a 5.4V8 Triton 4X4. The truck is about to roll over 200K here soon. I am feeling/hearing a vibration/grinding sound coming from the truck when I am moving slowly and making turns, either left or right turns. Seems to happen more so on left hand turns. I have changed all power train fluids and filter, and still does it. I do not feel or notice the vibration/grinding when I am going straight or at highway speeds. It is only when I am moving from a stop and making turns. Any suggestion on how to diagnose, find out, repair, fix this issue?

 

did you add the friction modifier to the rear axle ?

https://www.ford-trucks.com/forums/1...f-rebuilt.html

 

No I did not. Is that something that should have been done?

 

Yes if you have a limited-slip axle. Check your door jamb for axle code and look it up. It used to be that if the axle code was a "9" for example, that was a 3.55 axle ratio, open differential. A "H9" was 3.55 ratio with limited slip differential. Your codes are probably different, but you could search or post your code here and someone can tell you whether it is open or limited-slip. The differential on a limited-slip axle has a clutch pack between the side gears. The special additive gives the proper slip-stick shearing effect. Without the additive, it acts grabby when cornering.

 

jerky motion when turning, but no problem when going straight line is 100% = lack of friction modifier with an LS unit.