So here's my problem...

I got a 2001 F150 Supercrew 4x4 Lariat with 100k miles. When I'm driving my truck and I let off the accelerator and go into a "coast" and then get back on the accelerator I get a clunk or knock of somekind coming from somewhere under the truck.

It never clunks from a dead stop, ONLY from a coast.

Any suggestions? Thanks for the help!

 

I am guessing you might have u joint going.

 

Yeah sounds like a u joint to me. an easy way to tell if your u joint is going bad is to grab the yoke and try to shake your drive shaft. If it has play than you got a bad u joint. Dont just do it in the rear though also check by the t case.

 

did you ever figure this out because mine does the same thing...?

 

does anyone know if greasing the yoke spline will help this?

 

when the slip yoke is sticking you cant hear it you can feel it. If you can hear a clunk it is most likely a driveshaft. Block the tires put the truck in neutral and see if you can move the shaft up and down or side to side by the joints

 

The only way I can explain it is a thump feeling. I definitely feel it....i guess clunk really isnt the word. I feel it under the cabin.....so if the shaft moves when in nuetral then its a bad driveshaft?

 

oh yeah, it only happens in overdrive

 

Might be the torque converter. But I would check like suggested the u joints and transmission mount.

 

sounds like a universal joint