Vibration over 84

[tigmaned]

i know most tire place balance tires at 55 mph right. i have new tires up front, front wheel bearings up front are tight and just had a 4 wheel alignment done too. she rides great till times when i take it up a little and as soon as i see the dash read 84 i get a pretty good vibration up front and even see the hood shakeing too. does this happen to any one else?? i am thinking about checking all the steering parts next too and tire pressure also. got 275/40-17 on right now but think i have like 35psi per tire and not sure thats to hard or to soft for this size rubber?? i am going to play around with that too, put a little more in and see how it feels and go down from there?
oh, forgot this is happening to my 1986 vette with 89K miles.
Thanks for looking any help you have time for!!

 

[Chris Kennedy]

One question: When you get the vibration, does the steering wheel also vibrate/shake quickly back and forth in your hand? If it DOESN'T, then what I think may be going on is that the tire/wheel are in balance, but what you may be getting is a general structural vibration, not wheel balance problems. What I have noticed in my own car (an '89 with same size tires) is that I occasionally will get a similar vibration on a surface of road, yet will NOT get that same vibration at the same speed on another type of surface. Also, the steering wheel is steady as a rock at all times and speeds. The front ends on our cars seem to have a lot of flex (especially with the roof off), and certain types of road surfaces aggravate this and give the impression that something is out of balance---I think the physics term is something like "sympathetic vibration" or something else (don't quote me!). I have thought of looking at some of the brace supports which RD Racing offers, but in the meantime, I would suggest that you try this: For normal driving LOWER the tire pressure from 35 to about 27-28 (I run my new BF Goodrich KDWs at this pressure). That's more than enough tire pressure unless you are on a track, and I think what you will find is that at the lower pressure the tire will absorb many of the road jolts BEFORE they are transmitted to the car's structure and start the structure vibrating. I also found that if you live in an area with crummy roads like I do, the car will be much less jittery and twitchy, you will stress it less, and actually the car will handle much better since it isn't skittering on the crummy roads.

/s/ Chris Kennedy

 

[kiwi vet]

Hey tigmaned

You've obviously tried all the usual things for vibration, balancing, wheel bearings, shocks etc.
The level of tire pressure should'nt contribute to any vibration, unless the tire carcass is failing, which would be obvious also.

I have had an issue in the past with cars that are not driven a lot, flat spotting tires from sitting in one place to long, particulary on soft performance rubber. When run up the speedo they then have a vibration.

The only other thing Ive experiance like this was an out of round rim (turned out to be from a damaged car), but that easy to check by rotating the rim on the car (free wheel) and measure rim bead against a straight edge for wobble. But your wheel balancer should have picked this up if it was an issue.

Hope this helps, good luck.

Grant

 

[tigmaned]

just checked my tire pressure and i was wrong they were at 28psi, so i put them to 32 psi and see if i like that better and if not i can always lower it.
i feel a little of the vibration in the steering wheel. i dose seem like a wheel out of balance to me so i may take the rims back to be checked? i know its a 20 year old car so i am sure parts are worn, just wondering how common this is? i have noticed my front sway bar end links are metal to metal in a few places so i wonder if that would cause the jitters over some roads?