Hey all, had this problem for a while now and it seems to be getting slightly worse. While cruising at 50-70 mph (cruise control or not), when I am coasting or at 5-10% throttle (about 20 inHg vac if anyone else runs a vacuum gauge) I get a pulsing vibration coming from the truck. Once I apply more throttle or step on the brake it fades away. It feels like its from from the rear of the truck more than the front, and feels like its getting slightly worse (or I'm getting slightly more bothered by it). I replaced the fuel filter about 1000 miles ago and didn't find much silt in the old one, which I know some people suggest to be the problem. Stock tires still in balance.

89 4x4 F-150, extended cab, 5.0 if that has anything to do with it. Anyone else have this problem?

 

Would you better define 'pulsing vibration'? How fast (frequency), how much (amplitude), where does it feel like it's coming from, etc.

Offhand, suggest to inspect your u-joints.

 

ujoints, as wde said.

 

Feels like its coming from under the truck, around the center line. As for freq, maybe 2 Hz/cycles per sec. Amplitude is enough to compete with road noise at highway speed.

Will a haynes manual have a procedure to check u joints or do you have a link to a writeup here? I'm sure I can find a general one online if not.

 

To check ujoints, put on emergency brake, put key in run but dont start, take truck out of gear, go under truck and shake drive shaft, also roll it back and fourth, if there is even a slight movement in the joint change it. 99% of any vibration in the drive train are the ujoints.

 

That truck should also have a carrier bearing...if it's not the Ujoints, I'd suspect that as well.