I need some help. I have a 1967 F100 with a 460 in it. Im not sure what transmission it is but it's a manual. At about 25 mph my truck starts to vibrate gently. The severity of the vibration progresses as I pick up speed until about 60 mph. Then it just stops and drives smooth like nothing is wrong. As long as I stay above 60 mph its fine but as I slow down the vibration comes back at about 60 mph. I dont think its related to the wheels because the vibration goes away at high speed. Any ideas

 

My guess - and the cheapest fix - is wheel balance. You can approximately locate the source of the vibration by feel. Does it come through the steering wheel or the shifter?
Eric

 

Yes you can feel it through steering wheel and stick shifter

 

check U-joints and carrier bearing if it has it. Also check to make sure there is no slop in the front wheel bearings.