[SixBanger]

'73 240z....Ok this may be a long shot but can somebody help me out here? About a week ago, my car developed some serious vibrating at speeds higher than about 30mph. This all happened gradually, but within about one day (i drive 40 miles/day).
The symptoms:
-entire car shakes as speeds increase, but seems to fall in and out of harmonics where it shakes less or more....
-the shaking is bad when in gear, but doesnt completely go away when coasting in neutral...
-engine doesn't shake at idle and revs freey as ever when car is stationary...
-no thumps or supension creaks, just shaking and mild humming...
-i had the car up on jackstands this weekend looking over the suspension, nothing wiggles or seems to be loose. didnt check tranny or motor mounts (maybe they sheared?)
-wheel bearings are fine, no play and spin freely when i checked this weekend.
-steering wheel shakes a bit, shifter is sturdy as always
-clutch grips fine
-Ujoints are fine

I've been bashing my head in trying to figure this one out. Obviously im not looking for a solution but rather any ideas you guys may have. Could the engine cause this? (it seems to run fine in neutral but lost some pull sinse all this started--i dont know if its an engine problem or just the vibrations killing horsepower). Ever seen a driveshaft get out of balance for some reason? Seems to me the vibations are from somewhere in the drivetrain (my tranny has been leaking oil). Any and I mean any ideas are appreciated.

Thanks,
Alex

 

[helowrench]

jack your car up and take a very very close look at your tires, sounds like one on the rear may have started to separate. look for an out of round condition
better yet take it to a tire shop and have them balance them
slight chance that a ujoint could have become offcenter but check tires first also look for a spot where a wheel weight could have slung off

 

[escanlon]

If you've gone through the car's suspension, it's linkages and other items that would be OBVIOUS first time checks, I would definitely agree with helowrench. It definitely sounds as though you have a bad tire(s).

Years ago I had a 76 Mercury Capri II with not one but two bad tires in front. The inner steel belt on both had broken and were causing the vibration you are feeling. Mine would be real bad till about 35-40mph then would smooth out, then would pick up again at about 50-55mph. At times you would swear that the car was going to vibrate out of control. Could be that mine were worse than yours are, but went to the tire shop and they showed me the out of round and the lump on both tires.

Hope this helps.

 

[SixBanger]

already checked that, everything seems fine. besides, if i had separation i think the tire it was on would really stand out. the entire car seems to shake, as if its coming from the middle... thanks for the reply

 

[silver77280z]

I had the same problem and it wasnt the tires!, to my supprise. My driveshaft bolts where loose at the diff. I couldnt tell from the visual. I had to jack up the car and turn the bolts to notice. I put some heavy duty lock tight on and it seems to be holding tight. My vibration started about at 50 and the entire car vibrated like a crazy. That might be your problem.

 

[SixBanger]

thats one thing i havent checked yet, but i'm suspecting. I've had the driveshaft apart before when i rebuilt the rear end, and the noise seems to come from the middle of the car... might just be it, I'll see tomorrow when i put the car up on jacks again... thanks

 

[helowrench]

middle of the car would be about where the front ujoint on the drive axle is, might check that and the trans mount