Hello All!
I bought an '85 F-150 4WD with a inline 6 back in '95. It's been a good truck up to a couple of years ago. First thing to go wrong was the engine, it acted like it didn't have enough power to pull it's own self at times. So I bought a 5.0 4b out an '84 Mustang, checked it out, listen to it run and made sure it good oil pressure. Me and my son swapped out the two engines. I ran it for about a month when one day it wouldn't start. After checking it out and adjusting around with it, we figured that it had probably jumped time. We pulled it back out, I found engine re-build kit on Ebay with my choice of cams, a high speed cam or a torque cam - I went with the torque cam since it was in a 4WD. OK the engine has a fresh new build to it, we put it back in with dual exhast all the way out the back. Next to go was the AT. So I found and bought an '93 F-150 with 5 speed tranny. Yep, you guess it, we converted it an automatic to a standard. I also have 33x12.50x15 tires mounted on 10" wide rims. OK - enough of the history on this beast!

I noticed a shimmy in the truck when you let off the fuel pedal. It seems like it's coming from the front end but I'm not sure because you can feel it in the whole truck. It don't do it while you're giving it gas. I've jacked up each side of the truck in the front to check the wheel bearings by shaking each wheel and both front wheels seem tight with no play in either side. Does anyone here have any idea of what might be wrong?

 

Have you checked the ball joints?

 

Check the condition of the u-joints and carrier bearing (center bearing) in the rear driveshaft if your truck is so equipped. Also check to see if the rear yoke on the differential has come loose. All of the above can cause a vibration when the truck is in motion and little to no power is being applied.

 

OOOPPSS! I forgot to mention that it's a short wheel base 4WD. As far as I know it has never had the ball joints replaced. How do I check them and are they hard to change?

 

+1 on the driveline, u joints eapecially

 

+2 on u-joints. u might also check the I-beam and radius arm bushings as well, cause when mine went bad, i had all types of vibration up front.

 

It's not a vibration. It's more like a wave or a rocking type motion. I got my son to drive it while I followed him and it looked like it had a sideways type of shake in it from front to back. It's kinda hard to explain, I ain't never seen nothing like it before.

 

You might try rotating the tires front to back. It is free and could eliminate the problem. I had the same issue on an F250. It shimmied and shook (but was a solid front axle). I tried all sorts of things I read online. On a whim, I tried to change the wheels/tires with another truck. It was gone!