Triumph Repair: vibration in Spitfire 1500, wheel vibration, speed vibration

Question
Hello, I am hopeful you can help me with this.  My spitfire developed a serious vibration at the rear of the driveshaft, I had the U-Joint replaced, next long trip the vibration is coming back.  Any ideas?

Answer
Hi Michel,
There are two "U" joints on the driveshaft and one on each axle. When you say "vibration" you need to try to determine at what conditions and at what speed your vibration is most noticeable. If you already felt what a "U" joint vibration feels like (a high speed vibration) on a driveshaft as compared to a out of balance wheel vibration (lower frequency) Even though you can get into an area where a problem is by the symptom, I found that any vibration or a noise should be diagnosed by putting the car on a lift and have the car run up to the speed in gear that the vibration is most noted and look and listen under the car to see where the problem is. A "U" joint vibration can even be seen as it shakes the driveshaft and with the car stopped you can feel each "U" joint for free play and look for signs of rust at any of the bearings in the joint. No free play is acceptable in a "U" joint.
Howard