I found a vibration in my vette between 3100 and 3200 rpm about 2 weeks ago. Further investigation found it only occured while in gear.

First I talked with my mechanic and among the possibles he mentioned it might be the wheel balancing. We/he would have to look into it. Which made sense. I also talked to my car building brothers and got their opinions too. Then being thorough I sent an e-mail to Bill Boudreau the zfdoc outlining my problem and asking if he had any ideas from many miles away.

Bill replied with his thoughts, one of which was the balance again and with the type of computer balancing machine that would answer the question if it was the balance. Well using the link he provided I found a tire shop near me that had the right balancer. Took it to them, they were off a little and the problems is gone. Several test trips - including a warning by the local deputies - and it is totally gone. I have written to Bill with my thanks. Just wanted you all to know sometimes the simple questions to the right people will make a big difference in the end and pocket book.

I am amazed and happy.

 

can you elaborate on the balancing details (type of machine etc.)

Thanks

 

That's awesome that you got it fixed! I've never heard anything but good things about ZFDoc. Just curious, though - why would and out-of-balance tire/wheel vibrate only when the car is in gear? It's the tire itself causing the vibration, so shouldn't it do it at a certain speed (which, in a given gear, corresponds to a certian RPM) regardless of whether the clutch is in or out???

 

Hi Brookman,

Here you are.

First my questions to Bill:
Here is my concern/issue/problem:
I have a '92 coupe with just over 41k miles on it. I got it in the spring and it has spent a lot of time since I got it in the shop at Dreamworks Performance here in Denver.
I just got it back late last month. The one area not worked on was the transmission, a ZF 6spd.
Well this last weekend I noticed a vibration while driving it.
The vibration is only felt with my hand on the shifter and it is there at roughly 3100 rpm in any gear. It is not there while out of gear.
I first noticed it when I drove along a seem of new and old asphalt on I-25.
I first thought it was the seem; however, it continued after I got to smooth asphalt and even on concrete.

So I kept looking for it in my attempts to isolate it.

It was there both Sat and Sun, not there on Tues and again was there clearly yesterday.

My mechanic, the owner at Dreamworks thinks it might be the input shaft, among other things. That is the reason for this note.

Any ideas on your part without looking at it?

I realize the end result would be to send it to you or bring the car down to you. I am looking for possible answers and of course some idea about time and possible cost. Which I know is hard to pin down. I am just looking for ideas at this stage. And of course how long I might be able to drive it.

Thanks,

Dave Gross



Next, Bill's reply:
Such an abrupt change in vibration feedback leads me to believe that you may be experiencing vibration feedback from downstream of the transmission. The only scenario that would allow for the bearings to go south so abruptly would be if the vehicle was drove at a fairly high speed over a square curb causing the main case to fracture at at least two of the five front bolt eyelets. Otherwise, I would start at the rear wheels and have them balanced on a HunterGSP9700 wheel vibration control system. See http://128.242.141.111/ for where the nearest system is to you.

Also inquire if the drive shaft was removed for any reason and if so was it reinstalled with the same index to the differential pinion yolk or put back 180 degrees by accident.

Next, consider the half shaft and drive shaft u-joints.

Let me know what you find out and we can take it from there.

Best regards,
Bill Boudreau
ZR51 Performance
http://www.zfdoc.com
Cave Creek AZ 85331
(602) 319-6575


The results:
Here is what was found at the tire shop.
All 4 wheels were slightly off. As they did each wheel they checked it via a spin on the machine and then if needed and they were they took all the weights off and got a new reading and then put the tape wts on directly under where the hub would be and then rechecked it before remounting the tire on my '92. Sounds simple. And when I wrote each wheel was off it was not by much in 3 out 4 it the right wt, just the wrong horizontal location (on the edge and not directly under the hub). And the vibration was only felt with my hand on the shifter.

 

Perfusion,

Not sure I am qualified enough to answer your question. My guesses are that at roughly 3150 rpm is where I felt it. I got pretty analytical in pinning it down, thought that might help diagnose the problem. It was there both going up and coming down in the rpm range on all types of asphalt and concrete.

When I discussed it with Mike Meyers on Monday. He thought it was related to the wts being not right under the hub location and by just being off center if you will that at certain rpms it made itself known. He originally thought wheels and perhaps a lost wt. among the possibilities. It was not a lost wt just off center.

I do know that the rebalance fixed the problem. Again I had my hand on the shifter and that is how I noticed it. There was no vibration from the steering wheel.

And since you asked my '92 came with Nitto tires. Yes, they are very noisy.

Hope that helps.
Dave

 

That balancer is the bom... if I remember rightly, it is the "run out" type, that actually loads the tire.

super trick.

Bill is da man! He really know's his stuff!!!!

 

Brookman...IIRC, Discount Tires in your neck of the woods should carry that machine. I believe they call it "Road Force Balancing," but you can check out the machine firsthand, as I never had any problems going into their bays when I lived in Phoenix.

 

I've talked with him on the phone, great guy!