Hi all heres my problem, when i get to highway speeds of 70mph and faster my whole car starts to vibrate. What i notice the most is my dash starts to vibrate. I just had my tires rotated and balanced. My steering wheel still vibrated at 40-50mph so i took it back to discount tire co and had them reblance my front tires. That preety much solved my steering wheel problem but i still have the problem with vibration at high speeds.I ran a carfax on the car and as far as i know the car has never been in a wreck. Do you think my rear tires just need to be rebalanced or is something else wrong? My car is a 1989 pontiac T/A with a gm goodwrench 350 in it. I have the 700r4 auto tranny in it. Any thought would be greatly apparaciated!

 

Vibration at 50-60 that goes away above that is usually tire balance as you seem to have gotten taken care of. Higher speeds like the 70+ are often driveshaft balance, or u-joint issues. I have the same deal on my car, and it is really annoying! I have recently new u-joints in it, so I think I'm gonna have to get the driveshaft balanced when I do the engine or trans swap.

One other thing to look at is to make sure the driveshaft isn't bottoming out on the output shaft of the transmission, and that the splines slide freely on the output shaft.

 

I think the tight 3rd gen suspension, and overall ride of an sports car is the main reason for any rough ride. Maybe kick it up to a 100, where my 3rd hugs the road like a benz :rockon:

 

i have the same problem, but it goes away at 100. i was researching this and i stumbled upon a site that does driveshafts and they said this.

Put your rear wheels on jackstands and put a bucket of water on the pass side floor. accelerate untill it starts vibrating and if there are very small ripples it is probably engine torque convertor or tranny vibration. if it is large ripples, probly driveshaft or wheels.
either way, you should also try it with your wheels off, but put your lug nuts back on to hold the drum, put all 5 on so it is balanced. if the vibration left, it is the tires or wheel, if it is still there, its a bigger problem. also, if the vibration goes away just by putting it on stands, i would check alignment and suspension.

 

I had a similiar problem with my TA right after I bought it. I finally traced the problem down to the harmonic balancer. The rubber inserts were coming out of the balancer itself. This probably doesn't apply if you have a newer engine, but that was my problem.

 

Another thing I thought of today as I was experiencing the vibration, and I'm sure it's a contributor to my vibration, and that is the tail shaft bushing in the rear of the transmission. I know mine is pretty well worn, and it is most likely part of my problem.

All in all, I know that I'm gonna get the driveshaft balanced anyway, and the transmission is getting replaced also (once I get another built to put in it's place!) so in the end I should have everything eliminated. (I elminated the rear-end by replacing it with the 9-bolt, and I still have the same vibration). Nothing I plan to do to the car is specifically intended to get rid of the vibration, but with everything I'm doing, I'm sure I'll find it!

 

i knew a guy that had the same problem and the fix was a new drive shaft.

 

I have the same problem at 60-65 MPH with new wheels and tires. After removing my 200C, installing a 700R4, and using a diff driveshaft, it's still there, but not as bad.

I was reading an article somewhere that mentioned GM put something inside the driveshaft to absorb noise (foam, mystery goop,etc) and that after a long period it would shrink and/or shift throwing the driveshaft out of balance.

Anyone ever heard of this??

It would explain how the driveshaft could become un-balanced and still be straight and have the original weights still attached..

 

I dont know that they would put anything in a steel drive shaft, but maybe on an aluminum one....

 

yeah, my T/A does it also at speeds of about 80. but when you go faster, like 100 or 110 it goes away. why is it there only at certain speeds?

 

That's the way vibrations go! Example is tire balance. Typically tire balance will only be noticed at 45-70 MPH range (Usually a narrower range than that, but different tire sizes will be a different range) but over the upper speed it will go away. To explain it any further, I would have to take a physics class!

 

this is kinda like a story my friend kevin told me. "i go into the local pontiac/gm dealership one day and i talked to the service manager (he knew the guy well and still does) and i told him that when im driving my Iroc-z at 150mph i get this vibration, the service manger says Kevin where the f'ck would u like me to test drive the car around here at those speeds?!!" and it was all laffter after that. also Kevins car is a 1990 Iroc-z 1LE, the first of 28 for that year with a 350 in it.

 

I had the same thing on my 90 TA. Except it was 65+ MPH. I had the stock steel driveshaft balanced, and it really didn't help. Got the 1LE Aluminum and problem solved. I have sinced put another recently balanced steel driveshaft in and it vibrates again. My TA does not like Steel driveshafts.
Good Luck!

 

mine has the stock aluminum driveshaft, could it be out of balance?

 

Hey everybody thanks for the info! Im going to take it back to Discount tire and have them check the wheels and tires again, hopefully that will take care of it.If not ill let everybody know what i found out.

 

The cause for the vibration at the higher speed is the pinion angle. You don't need a new driveshaft or need to get the current one balanced. You can make pinion angle changes by adding or removing the shim in the transmission mount. If you add shims make sure you have the correct length bolts. Get a pinion angle finder (Sears or aftermarket) and set the pinion angle to the service manual specs. Alignment will not cause that kind of vibration. Also, if you are going to make a habit of 100 mph then you need to get an on-car wheel balance.

Sorry about the late post/reply.

Scott

 

I got a Spohn Torque arm and installed it and adjusted the pinion angle. Then I had a front wheel on-car balance. That made all the difference in the world. The guy here in Cincinnati, Bill Burcheck (spelled wrong, sorry) did the work and said they were way off. I highly recommend you find someone in your area that can do the on-car wheel balance. Have them balance your rear tires while they are at it. If they do on-car then they are good. Not everyone can still do it. Cost $20 per tire. Also, it is called strobe balance. Remember to match your wheel to the rotor since if you reclock your wheel then the balance will be out.
Scott