I just bought a 2000 F-150 extended cab 4X4. It is a very nice truck and had only 18,000 miles on it. When I first got it I didn't realy motice any problems. Latley when I get up to 40 - 45 mph the rear of the truck begins to vibrate. It dosen't seem to be the u-joints although that was my first suspision. I have also heard from other people that this is just somthing that these tucks do. If that is the fact then I will be very disapointed. If anyone has encountered this problem or of you have any ideas on how to repair the problem i would greatly apprecate any information you could provide.

Thank you

 

I had the same problem. After chasing everything including tires/balanced, etc. I finally found a bent driveshaft. Jack up the rear end and put the truck in drive and watch/touch (lightly) the driveshaft (near the diff). You will notice if it is a bent driveshaft.
good luck..

 

If you want a tech answer, don't post in the GCF. Try 97-03 F-150 forum.