Volvo: V70 Vibration, rear drive shaft, drive shaft

Question
2000 V70 XC Driving Vibration Problem

When I purchased the car 6 months ago (107,400 on odometer) there was at the time a vibration at higher speeds 60 mph+.  This is the best I remember – may have noticed something different if “lived” with the car before repairs were made.  I may be dealing with a different problem now.  At the time the Volvo mechanic (Volvo dealer) found a missing weight on the rear drive shaft (bevel gear box to back of car) and replaced the drive shaft.  Since then I have had a vibration that starts at 40mph – peaking at 45 mph – a little better from 50 to 60 mph – but worse again at 65 mph – tapering off at 70 mph.  I took it back a couple of times but they could not make it any better.  The tires have been balanced (good) and I measured the circumference – two are exactly the same, third is 1/8 in and fourth is 3/16 in larger.  Driving in third gear does not seam to change the speed at which the vibration occurs.  I have noticed that on a smooth road the vibration seems to decrease when I let off from the gas maybe 25% but does not go away completely.  Could the rear drive shaft have been installed incorrectly or is there a different problem?  I have tried looking at the motor mounts but they are hard to see and I am not sure what a bad one would look like.  Please let me know if there is any other information you would need to help diagnose the problem.   I would appreciate any information you can give.

Thank you,

Kelvin  

Answer
Kelvin,
There has been a lot of trouble in the drive shafts and the bevel gear, so any of those could be the cause. There should be some makings on the driveshaft for line up. Speak to that dealers sevice rep from Volvo and see if he/she are able to help. If weights are missing from that shaft it may not have been balanced, just a weight put in it's place.
Looking at the left side sub frame just under the trans, there should be a small rubber pad and there should be 6 to 8 mm clearence there. If the clearence is less it is likely that the motor mounts are bad.