My '86 Z28 will vibrate at high speeds (65+) The whole car vibrates, the dash, the seats, the steering wheel, everything.
It has aftermarket 3.73 rear end and runs about 3000 RPM at 75 MPH.
I think it might be the drive shaft, any other ideas?
Thanks, I should get it back it about a week from being painted.

 

Driveshaft sounds right. If not, maybe a tire(s) isn't balanced correctly. But yeah, check on that driveshaft.

 

SLP has a new steel driveshaft with dampener installed on the transmission yoke for around $225 I think maybe less. I would start there as well
HTH
Chris

 

is it speed related or rpm related? If its speed related you can almost be certain that its either the drive shaft or a wheel

 

I think the first thing I would check is the U-jionts , just to be on the safe side you don't want that thing dropping out at speed. Then check the shaft,and or wheels. Where does the vibration seem to come from ,under the car,front ,back ? It could be the convertor if it seems like the front,could be a bearing in the rear if it seems like the back,but my guess would be shaft related.

 

Driveshaft. Time to replace or upgrade. it's always nice to have a reason for an upgrade.

My car with 3.73's when I bought it vibrated BAD above 75mph. Stock shaft was just really out of balance and that can get very dangerous over 100mph.

 

It seems to be speed related.
The whole car seems to shake.
I'm leaning towards the driveshaft. When I get the car back from painting, I'l check out the drive shaft.
Thanks for the help.

 

I had that same problem. i mean it would shake BAD. my dash pad looked like it was going to come off It was my tires. They had worn down funny and it was causing a vibration. im guessing if your allignment is ok and your tries are wearing properly it would be the driveshaft.