Ok, a while ago i posted about a bad vibration in my 91 Z. I was told to get it to happen put it in nuetral and see if it goes away. It didng go away. So i am assuming that it means the vibe is in the drivetrain. Could it be the motor mounts? it happens at like 60-65mph, and around 90+mph it shakes extrelemy bad.Does anyone have a clue whats goin on here? I wanna find the prob and fix it b4 the spring. TIA guys

 

ttt

 

Check your motor mounts, tranny mounts too

heres the tranny mount i had



heres the location



heres levering the tranny to line it up, mind the graphics, some jokes were being commented upon at time of picture

 

check ur tire pressure

 

It's a little worse vibration than that.......i have the same problem....starts around 60-65....goes away, but then does it REALLY bad at bout 90MPH. My motor mounts are fine, so i'm thinkin the driveshaft is outta balance

 

I've never seen a one piece driveshaft just get out of balance.
From my experience a driveshaft balance problem will get worse with speed but not change.
Tire balance and drivetrain geometry problems, and sometimes bad u-joints will cause a come and go type vibration.
Sounds like a tire problem.
Could be the alignment also or worn bushings somewhere in the suspension.

 

I know a driveshaft doesn't just "get out of balance"....but I've only had this car a year and a half of it's 13+ year life....so who knows what happened to it the other 12 years....it's done it since I got the car. It's not tire balance.....new tires...I balance my own tires at work, and check them periodically. And there's a difference between this vibration and vibration caused by tires out of balance....I know this because I have to diagnose these things 10 times a day at work. Not the alignment....had that done. Worn bushings could be a possibility, I haven't replaced any of them, but i dunno if worn bushings would cause a vibration this violent (at 90MPH), but i could be wrong. When i decribed the vibration, it doesn't change, it gets worse w/ speed, doesn't change like i made it sound.

 

I wish you had mentioned all that earlier.
Have you done a visual check of the driveshaft and u joints?
Torque arm and transmission mounts? might cause a pinion angle change. Axle and rotor runout?
rim run out?
high speed miss?
My personal opinion on trying to give advice on noise and vibration problems over the internet is that it's useless.
There are so many things to look at. You apparently work a some kind of shop, I'd like to think someone there could actually drive the car and give advice. It's a huge shot in the dark trying to diagnose this having never even been within several hundred miles of the car.

 

Replaced the ujoints not to long ago, so it's not that. Yea you're right, it's hard to diagnose these problems w/out ever riding in the car.....but i figured that out of all the thirdgen guys on here, a few would have had the same problem and fixed it....wasn't really expecting an accurate diagnosis, just someone's personal experience. Thanks though man.

 

Sounds like a problem that I had...now this isn't very likely but my tail shaft in the tranny was twisted, cracked, and bent all at the same time..............Like I said not very likely but worth checking, just pull your drive shaft out and turn it if its bent you won't be able to turn it......