Toyota Repair: Tacoma, side mirror, defective tire

Question
Ted,

I have a 99 toyota tacoma 4x4 extended cab.  It started vibrating at between 50-60 mph about a year ago and seems to be getting worse.  I had the truck aligned and all the wheels balanced.  Last night I looked out my side mirror and it looked like the bed of the truck was vibrating causing the shaking in the cab.  Could this be a problem with the shocks or leaf springs?  Or maybe something in the front end?  I would realy appreaciat any thoughts that you may have.

Thanks so much,

Ray

Answer
Possible driveline problem, a vibration is caused by a rotating part or parts, it's not caused by shocks or springs, since the wheels were balanced already I will rule them out, I recommend checking for a possible out of balance driveshaft or a bad U-Joint.
If the vibration is of high frequency and harsh, it's the driveshaft, if the frequency is lower and it can be felt in the steering wheel there may be a problem with a bent wheel or a defective tire but this will be at lower vehicle speeds.