OK here is the problem that has me scratching my head. I have a 2005 F-150 Screw Fx4 and whenever Im driving slow either in a parking lot or dirt road I hear a loud popping sound coming from somewhere under the truck.... here is the thing it only does it some times. there is nothing that makes it happen it just ramdomly does it. It pops about 8 times then stops. Iv replaced the rear U-joint so I know thats not it.. so whats next?

 

Front u-joint?

 

I checked that when I changed the rear one it felt good and moved smooth every way so I dont think its that.

 

is it a 2004 or 2005? you said 05 but your signature says 04. couple of different problems have popped up in those two years.

any idea where it is under the truck? somewhere up front? rear? transmission/t-case area?

 

Ok sorry it is a 2004. and its coming from the rear end somewhere. When it pops its almost sounds like its in revolution with something like a pop...pop...pop. First time I heard it I thought something had wrapped around the drive shaft and was hitting the frame when it spun around. I let a mechanic listen to it and he says he has no idea what it could be.

 

go to your local ford dealer, or look online, and put a bottle of friction modifier in the rear end.

i don't know if it's just there wasn't enough put in initially or what but that sometimes helps.

 

You only use friction modifier in limited slip rears - if yours is an open rear, it won't help.

 

the fx4 will have a l/s axle.