Just bought a '98 F150 XLT long box. To certify, the rear UJ was replaced. It has a two piece shaft. Hanger bearing okay. I get a vibration, that is felt in steering wheel also at around 50kph. Once over 75kph, it disappears. One the highway, it's smooth as silk. Any ideas?

 

Could be a tire out of balance, or bent rim, or tire with flat/bad spot. Also could be a bent or out of balance driveshaft. How badly torn up was the old u-joint? That could be an indicator of a driveshaft problem.

 

I had the same problem on my explorer..what i did was rotated all four tires and it went away..my steering was a bit crazy going low speeds and smoothed out at highway speeds just like your truck. i hope its not the drive shaft you are having a problem with..let us know how you made out

 

The tire rotaion idea is something I had forgotten about. Sometimes it can be the smallest fix. I'll let you know how it turns out. Presently I am in Colombia, and cannot get back to the truck until July. The tires were all re-balanced and the U J was just a little sloppy. Can the two pice shaft be changed with a one piece, if such a thing exists ?

 

I would agree with the tires, it is amazing how much of a difference they can make. If the shop that balanced them did not correctly calibrate their machine, then the balance will be incorrect.
Double check the U-joint.
You might also want to check for an alignment problem.
Let us know how it goes.

 

You may want to ask this in the 97-03 truck forum. Those guys over there are more experienced with the trucks (not that we aren't). It is nice to keep the "Truck Tech" talk out of the chapters because there is a lot more info/help in the tech forums.

-Matt