i get a hum/vibration when i get to about 65 mph, it stays the same until i get to around 75 mph. the tranny has been rebuilt (not to well either) and the motor changed(supposedly, but i have my doubts). any ideas what could be causing this? i've exhausted my ideas, brakes, rear end, tires,i've gone as far as to loosen up the tranny and drive shaft and make sure that they are true and tightened right.[sm=feedback.gif]

 

Sounds like the driveshaft is out of balance. That can happen with transmission work.

 

wouldn't the noise be present at all times? i think changing the U joints may be the answer.

 

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U joint should be fairly easy to check wether there is play in them (don't rule them out unless you'vechecked). As for the drive shaft as long as the transmission is the same model size ect the drive shaft shouldnt change balance. They are balanced seperatley on a lathe type machine. Can you tell wether the vibration is coming from one erea more then another? As for a hum that is a common tire problem a vibration can be caused by something as simple as a thrown weight.

 

i thought of a weight /balance being off, had them rebalanced. going to check the u joints, and if thats not it then it's time to open up the rear end and check bearings.