Nissan Repair: 2004 Infiniti G35X vibration, 2004 infiniti g35x, wee tad

Question
My wifes vehicle has a vibration between 65-75 mph. I found the front driveshaft joints to be inflexible, replaced with a new shaft about 2 months ago. Vibration is a harmonic, no noise but the mirrors shake and I can feel it throughout the vehicle at those speeds. Originally the problem was more evident at 75 mph and above, and seemed to go away after the new front driveshaft, but has returned even worse.

AS a retired auto mechanic of 39 years, I think it is still something in the drivelines, at least feels like it. Engine speed has no effect, tires are fairly new and balanced. rotating them makes no difference. I can find no slop or looseness in any of the CV joints. I hope to have time to look at the underside tomorrow, make sure the front shaft hasn't come lose, and disconnect the rear shaft to check for similar u-joint issues.

As a volunteer here also (in Ford), I appreciate the time involved in helping folks out. Thanks for any thoughts you might have on this problem.

Answer
hello it does sound like it is coming from the drive shafts and it maybe just a wee tad out of alignment and this is what could be causing the harmonic vibration i would try to put the car on axle stands and start the car very carefully and place it in drive to see what the balance look like from underneath or if you know any trained machinists they could put one of the measuring tools they use to check for trueness in the drive shafts