hi all.....

the problem...drove aon the highway yesterday, drives smooth until i hit 120km/h = 75mph and then starts to shake from rear ..or somewhere else, but feels like comig from behind the seats

i have three year old falkens on it, had them balanced twice and always shake at higway speeds

how can i hunt down this prob?

thank you

 

How are your u-joints and rear wheel bearings ??

 

rear wheel bearings are new, 5000 miles on them, no play in them, u-joints are original, 30kmiles on them, feel also tight, no play

but i will check them again ( did it only 20 times :D )

can simply the tires be "not good"?

 

I would say the tires, f you have kocked off everything else.
Is it an auto or 6 speed?
I'll take a stab at this....
but I had a slight vibration in mine and whe the tranny was rebuilt in aug it was gone.......
I have a 700r4

 

Boy I had this problem on my 96 LT4 Vert after the dealer fixed a diff leak and they were never able to get it worked out of the car. It started exacly where your does....the car ran fine without technical problesm for years, but this vibration was always there.....the tech manual has an entire section on harmonic vibration in it so it must occur more often .....I would have a Corvette specialist do a vibration check on a roller set up.....

 

its a 6 speed

i will try it tomorrow, to run it on jack hoists without tires and see, if it starts to vibrate again...

Corvette Specialists in Austria...i think, they are hard to find in USA, and even impossible to find here :(

 

Update!!!!


put my car an jack stands, and spinned it up to 70mph...usual vibrations

then i removed tires, spun it to 150mph..minor vibration, but absolut no vib´s at 70mph

then i put it in 1st and watched the spinning of the shafts

both axle shafts have a slight runout, about 0,03inches, also the driveshaft

is this normal??

i dont think that they are machined absolutely straight frim factory, or i´m wrong??

hope you can give me some input

thanks

 

anybody??? :confused: :(

 

You have a tire(s) that is not balanced properly/has radial runout OR had RFV.
(Radial Force Variation)

If you can find someone there that has a Hunter GSP7000 (I think that's it) they can find this for you. May not be able to fix it without replacing a tire(s) but that's probably 99.99% a good bet what it is.

USUALLY with bad ujoint(s) the vibration changes under acceleration or deceleration and you can FEEL it change.

I've been through this SEVERAL times with my Vettes and my old Prelude beater.

Good luck with it.

 

Hi vetnut

the vibrations i have begin slowly at 55mph and became really annoying about 70mph, independent if 5th or 6th gear used

the vibrations doenst change if accelerating , decelerating, or just coasting, alsways there

can you say something about my driveshafts? is it normal, that they have a slight runout?

thank you :cheers:

 

Your driveshaft runout is normal. They ALL have it.

The shaft runout is so close to the centerline it has to have quite a bit of runout or imbalance before it makes much distance.
Plus the shafts are aluminum and don't weigh much to begin with.
Tires on the other hand are rotating out there on a pretty long 'arm'.
All the suspension pieces are lightweigh so it doesn't take much imbalance to transmit vibrations through them into the chassis/steering wheel/seat mounts,etc.

You will probably find the vibration goes away or diminishes as you go on past 75 or 80. Seems a lot of folks (me included) experience vibrations around 55-65 mph.

I replaced my driveshaft, half shafts, u-joints and even the rotors trying to find the cause of the vibration.
This was after I had the tires balanced 5 times and two of the tires replaced under warranty and bought two more so was on the second set of crappy BFG Radial TA's.
I WILL NEVER spend another penny on BFG tires (no flames, please).
Anyway I got a set of wheel adapters and put the tires/wheels (Goodyear GSCs) off my 91 Vette on the 84 Vette. Guess what? NO VIBRATION.
NONE,NADA,ZILCH.
Result? Tires with Radial Force Variation were the problem. They would balance just fine. Just STILL had vibration.

Don't make it be any more complicated than necessary.
Have those tires checked out with the Hunter GSP wheel balancer.
It's is the ONLY one I'm aware of that does the RFV test.
Go to Hunter's web site and read about it.
I'm not associated with Hunter in any way, BTW.

This problem just about drove me NUTZS before I figured it out.
(Took TWO years before I got the vibration out and NONE of the things I replaced helped one little bit.)

Thought all sorts of things must be wrong.... just like you are thinking.

If I hadn't experienced it first hand I wouldn't post here about it

Cheers.

 

BTW:

If the vibration is in the steering wheel, it's one of the FRONT tires out of balance.
If coming from the rear or you feel it in the seat, it's a rear tire out of balance.

Got anybody you can borrow a wheel/tire from for a short test run?

 

If you are running the same size wheels and tires, rotate them front to back and see if the vibration moves.

 

hi all

yes, it feels like coming from back of the seat...

sorry, but i don´t know anybody who can borrow me a wtire/wheel, assy, vettes are reallly rare here...

i hope to find a hunter balancer, im going to polish my wheels in Winter, than they must be bealanced anyways

thanks