1990 driveshaft

[BCC93QT]

Replaced driveshaft with used. Inspected before install. Gravy. Almost perfect. 4 tires are new
Brakes and rotors. New. Alignment. Good
Vibration from 60-80. Makes it undriveable hmm

[VStar650CL]

First step is find out if the vibration is from your new tires or the new shaft. If it has the stock P215/65R15's with a 26" rolling diameter then 70 mph is about 15 Hz. With a 3.538 diff (I think that's right for a '90) that means the driveshaft will spin at about 53 Hz. Getcha a Treysit sirometer, take it up to 70, and see which frequency you have.

[BCC93QT]

Its not from the tires. Ive been chasing this issue for a while.

[BCC93QT]

4 tires New. Balanced. Rotors brakes. Done. Car rides... as smooth at the other side of the pillow

[BCC93QT]

Vibration...

[VStar650CL]

If you're certain it's from the driveshaft, it takes some work but you can locate and compensate the imbalance using worm-drive radiator clamps. Those are always heavier on the screw side, so rotating one in successive approximation and seeing if the imbalance gets worse or better will let you gradually zero in on the angle which best cancels the vibration. Then add more clamps one at a time at the same angle until the weight is right. I should add that a Treysit is useful for that too, since the amount of deflection on the spring will be proportional to the intensity of the vibration. That lets you quantify the better-or-worse part instead of judging it subjectively.

[Ryantzer]

My money's on it being the driveshaft as well, very common on the Q45s - the one on my '90 is causing a vibration also that I have yet to deal with. Was looking at getting a one-piece aluminum driveshaft made for it but am not sure what other issues it may introduce, after all, Nissan decided on a more complicated two-piece driveshaft for a reason. I suspect there's something to do with the maximum speeds of a driveshaft of a certain length, and the top speed of the Q45 could potentially create issues with that. This place can build either an aluminum one-piece or a stock replacement two piece: https://driveshaftspecialist.com/alumin ... ort-sports

[BCC93QT]

Driveshaft. Balanced in a performance shop...