I have a 98 screw F-150 4x4 with an 8 inch lift and 35" tires.While driving
at lower speeds there is a violent vibration/front end hop, that seems to smooth out after reaching 55-60 mph, then returns around 65mph.
I have replaced upper and lower ball joints, passenger side front wheel bearing, new rotors/pads. I noticed yesterday that the idler arm has a little
bit of slop(am replacing it tomorrow).I have also had the tires balanced by
two different shops/each time they were way out of balance.It has been
about six months after the ball joints were installed(with an alignment).
Could it just need to be aligned? Any Ideas!
Thanks, Phil

 

I think that it might be your tires, When you get bigger tires like 33's and above they are really hard to balance. I have the same thing, except in the rear. Slight bumping hopping around 45mph then goes away then back again around 65mph

 

Any vibration that comes and goes at different speed is a moving part that would be worn or out of balance. It could be tires, wheels or a bad combo of both. Check your wheel weights on the inside and outside of the wheel. If the weight is in excess of 8 oz on either side the tire needs to be indexed(spun) on the wheel. A hub bearing could also cause this but would have to be quite bad.

Try and be in the shop when they balance your tires and look for a hop in the tire to indicate an out of round or a separated tire as well.

It is in the front as the vibration is in the steering wheel. If the vibration was in the seat or floor it would be in the back end.

Good luck....