I have a 99 F150, V6, 5 speed, 4 wheel drive. It hs a little over 56k miles on
it.
I have been experienceing a shudder everyonce in awhile when it has been moving
for 10 minutes or so at around 55-60 miles an hour. It really starts to shake
for a few minutes and then will die away as I slow below 40-45. If I put the
clutch in and let the engine drop off and it still does it. I tap on the
brakes and other then slowing down as the truck slows a little it still
persists. It was just in for brakes and the mechanic looked everything over
while it was up on the lift and inspected the tires and said it all looked
fine. He looked at the drive shaft and joints and those looked ok to him too.
He drove it and couldn't get it to do it so said to bring it back in when it
starts doing it more.
Any ideas on this???

Thanks in advance,
tom

 

Could it be a tire that is out of balance?