devilfish

When i reach 90mph, i start to feel vibration in the car. Not so much from the steering wheel. But I feel it in the seat aswell as on the shifter.
If I press down the clutch the vibration is still there. So its NOT following rpm.And if I go abow 100mph it gets less. My guess is a bad driveshaft. I have new u-joints on the driveshaft, but not on the half-shafts. I cant remeber if I got the vibration before the new u-joints. As that whas the first thing I changed when I got the car ( changed clutch, so I changed the u-joints aswell ). Can bad u-joints on the half-shafts cause this?
Any tips would be great.

VetNutJim

All four wheel bearings ok?
Any bad u-joint could cause this. Could be a 'dry' joint that is buzzing.
When they go bad the needle bearings will grind into the joint end so once that happens it won't stop until the joint is replaced.

Why does it manifest itself at a particular speed?
The drivetrain is comprised of components that all have their own 'resonant frequency'.
Frequencies(vibration forces) outside of the 'natural' range for a component are damped by a particular component.
Frequencies that are 'in range' will transverse thru the component and may even me amplified by another moving part.
Thus it depends on the resonant frequency and the vibratory strength and frequency of the 'input' force.

Another couple of things it could be:

1) Transmission output shaft bushing in the tailstock of the tranny.
2) Pinion bearing

I had a very similar problem a couple of years ago on my 1973 Super Cheyenne truck.
It had vibration at 78 MPH. Faster was ok, slower was ok. It actually felt like a 'growl' that could be 'sensed' more than anything else.

After replacing the front wheel bearings, u-joints, transmission rear mount, tire balance ,ect, it FINALLY just went away.
I think each thing I replaced reduced the tendency for the drive train to oscillate.
I never could say what 'fixed' it. It just got less and less with everything I did.
Loosening the tranny rear mount bolts after I replace the transmission rear mount seemed to have the greatest effect.
After everything 'settled' where it wanted to beI tightened up the rear trany mount bolts..
The vibration has not returned.

VetNutJim

BTW, the FIRST thing I'd get done is a brand new wheel balance.

5pinball

generally if steering vibrates its front end. if back of seat vibrates it r. end

devilfish

Correct me if im wrong. But wount that feel in slower speeds, and in the steering wheel? Nevertheless, I will take care of that.

devilfish

Thanks for the answer. I search the forum and found that you can isntall the driveshaft "wrong", and that re-install it, rotating it 180degrees is a thing you can test?!? But I thought all the driveshaft on the corvette where individual balanced from the factory? And if that is the truth this wount matter?



1) Transmission output shaft bushing in the tailstock of the tranny.
2) Pinion bearing

I really hope its not one of those things. I better test all of the other things first

Im going to check the wheel bearings, and get back with a answer.

Regards

VetNutJim

Nope, the vibratory inputs unbalanced wheels/tires make can manifiest themselves at particular speeds. Same as any other part that generates any force that feeds into the structure.

Tires can have hard spots in them and soft spots.
These generate a force that the suspension tries to absorb.
At some frequency the vibrations won't be adsorbed and the vibrations are fed into the chassis structure and felt by the driver.
Tires can be just plain out of balance and do the same thing.
They can feel ok until you reach the 'magic' speed where the vibration isn't absorbed and then you will feel it.

An out of round tire usually will be felt at all speeds.

Can you find anyone that has a Hunter GSP9700 balancer that does the Road Force Variation test?
This machine test for bad tires. This tire fault CANNOT be found with any normal digital tire balancer.

Know anybody you can swap wheels/tires with?

Here's an example for you:

I bought a new set of BF Badrich tires for my '84 Vette.
They exibited 'shake at 56 MPH.
Took them back to the store. They replaced two of them.
The vibration was less but still there.
I BOUGHT two more NEW tires of the same type/size.
Vibration got a little better but was still there.
Took the car to another tire shop. THey replaced TWO more of the tires at my expense.
Vibration was still there. By this time I'd spent a TON of money trying to get a set of those BF Badrich tires on the car that wouldn't SHAKE.
Finally gave up and bought 4 new Goodyear GS-Cs'

Vibration was GONE and hasn't come back.

I STILL have SIX of those BF BadRich tires, mounted up, back in my garage.

I recently put 2 of them on my 98 Z28 while I had 2 other new tires mounted.
Guess what? NO VIBRATION at all on the Z28.
Why? Different natural resonant frequency of the suspension.
They CAN'T be run on my Vette but they are FINE on the Z28.

BTW, when this whole ordeal started, I had a worn out set of Kelly Springfield tires on the car. Worn out but didn't vibrate. So, I KNEW the problem was the tires. I just never could get a set of those BF BadRich tires that wouldn't shake and vibrate.

BTW, I'll N-E-V-E-R purchase another BF BadRich tire the rest of my life.

I have had tires that would feelok until the car hit a pothole or crossed a railroad track. Then, they would start doing a hula dance.
Would darn near take the steering wheel out of your hand.
Nothing was wrong but the tires.

Get those tires checked out before you spend a lot of time/money on anything else.
Don't rule out ANYTHING as a possibility until you have absolute proof that something is ok.
Keep an open mind when looking for something like this.

VetNutJim

Bad FRONT wheel bearings on your Vette can normally be felt in the steering wheel. The 'grind' or vibration changes with the speed of the car and are most easily felt below 30 mph.

Bad REAR wheel bearings on your Vette will most easily be felt when going around a sharp curve at low speed.
Sometimes you can hear them and othertimes you'll 'sense' a vibration from the rear while turning.

The fronts are real easy to check. Jack it up, rotate the wheel by hand and listen/feel for any 'roughness'.
Check for looseness too. The bearing can still be 'good' but have too much 'play' in it. These don't normally cause vibration however.

The reason bad bearings can be felt more at lower speed is because the vibrations are too fast at faster speeds.

This is a tenhnique the factory usesto minimize vibration of the driveshaft.
They reccomend marking the position of the shaft and reinstalling it back in the same position it came out.
I'm with you on this. If the driveshaft or half-shaft is balanced properly it shouldn't matter.
I tried this with the truck mentioned above. Took the drive shaft out and put it back in 180* from where it was.
It didn't help in my case but it is something to try in pesky cases.

Find someone that can do the "Road Force Variation" test on your tires. That's a good starting place for this problem.

devilfish

All bearins seems fine. I do got a tiny play on the right front bearing. If I grab the tire with both hands I can move it in and out 3-4mm. But no grind sound.
I also noticed that my tiers got uneven wear pattern. I think I need a 4 wheel alignment. Cant that cause the vibration?

Thanks

VetNutJim

Anders,

Alignment will cause your tires to wear out prematurely. (Toe both front and rear)
It can cause the tires to wear on the edges...
Can cause the car to pull to one side. (Cross Caster or Cross Camber)
Can make the steering harder or easier (caster)

It won't cause vibration however.
At least I haven't encountered that, not that I know everything, cause I don't

Got a few questions for ya, please:

1) Is the vibration felt in the steering wheel?
2) Does the mirror shake of vibrate?
3) Is the vibration felt in the seat?
4) Is it worse when you lightly apply the brakes as you begin to stop?
5) Is it worse if you pull the parking brake up slightly (hole the release button when you do this)
6) Did it ever NOT have any vibration with the current set of wheels/tires?

VetNutJim

Here's some of the 'Jimbus' School of Thought on the DRIVESHAFT and the factory reccomendation to put it back on exactly as it was form the 'fattri'.

The driveshaft is balanced.
The transmission output shaft is balanced.
The differential input or pinion shaft is balanced.

All three of those components are checked for 'RUNOUT'.

All THREE of those components have SOME UNBALANCE and SOME RUNOUT that GM does not spend the timeto get out.
THESE ARE NOT JET ENGINE TURBINE WHEELS.

The 'Tolerance Stackup' , at times can cause a particular SET of these parts to contribute 'In Phase' vibrations in the driveline.

Once the car is assembled there is only ONE of the components that can be used for 'TUNING' the vibration out of the driveline.
That component is the driveshaft.
It is being used to counter some force that is created in the drivetrain.

What puzzles me is I DID NOt see a 'station' at the factory in Bowling Green that did a particular test for driveline vibration.
If this isn't done HOW THE HECK do they know which way to orient the driveshaft???????????

Did I miss something on my tour of the factory?
Bueler, Bueler, Bueler

devilfish

1: no, well i can feel the vibration in hole car. But its not a "extra" much in the steering wheel.
2:Yes it shakes, but the right and left "outer" mirrors does not shake.
3:Yes whery much so. And the door rattles.
4:No, it just decrease with lower speeds.
5:no diffrense
6:Hard to say. I did not push this car before i changed the,clutch,u-joints,shocks etc as well as tiers. BUT i did not feel any vibration when i picked up the car. But then again, I did not run it at 90mph or abow.

I must say that the place I can se/feel it the most is on the gearshifter and the seat. But that dont say much, sorry. The vibration is not huge. Its not like I can speak in the car. Its more "fast" tiny vibrations.
I know that I droped the driveshaft on the ground when i changed the clutch. Not a long fall, but it did make a tiny mark on the aluminium, i dunno.

devilfish

Going to rebalance the tires tomorrow...