Wheel balancing

[William C. Brown]

Gents,

I'm having limited success balancing the wheels on my 68 coupe. I have brand new rallye wheels and have had them balanced on a computerized balancing machine, but there still seems to be some shake. Should I have my wheels balanced on the car, instead of on a tire machine? I have all new suspension components as well as new rotors and the car has been aligned both front and rear. The only thing I haven't done is replace the motor and transmission mounts, but I don't feel any shake in the shifter so i'm assuming (probably incorrectly) that the mounts are not a problem. Any suggestions?

--Corey

[Joe L.]

Re: Wheel balancing

Corey------

At this point, I would recommend having the wheel assemblies balanced on the car. Assuming that you can find someone anymore to do it this way, you will need to mark one wheel stud and the corresponding wheel stud hole after balancing for indexing purposes. After on-car balancing, the wheel and tire assembly has to be returned to the same relative position when re-installed after removal for any reason. Also, you will not be able to rotate the tires without re-balancing.

If you have replaced your rotors only, without replacing them as a unit with the hub, there is a good chance that this will remedy your problem. The rotors were originally balanced as an assembly with the hub (fronts) and spindle (rear). Seperating and replacing the rotors will usually destroy the balance. Although aftermarket-type replacement rotors are usually neutral-balanced, the hub was never balanced this way. So, if the hub was very far off in balance to begin with, this would have been "compensated" for by the original balance with the rotor installed. When you install a new neutral-balanced rotor, everything is "off".

Balancing the wheel assembly mounted on the car essentially balances the entire rotating mass. Usually, though, only the fronts will need to be done this way. The rears can usually be balanced close enough off-car to avoid vibration/shimmy problems.

If the on-car balance does not solve the problem, as it may not, then that means that there are other problems. These could include a bent wheel or wheels OR they could involve a defect in the tire(s). If the current off-car balance job evidences the need for a lot of weight (5 oz or greater) on one or more of the tire/wheel assemblies, that might "hint" at a defective or poor quality tire.

[Wayne K.]

Re: Wheel balancing

William,

I don't know what kind of computer balancer was used but if it wasn't a Hunter 9700 they may still be out of balance. The Hunter 9700 matchs the best positon for the tire on the wheel and checks to see that the measured road force is within spec. Balanced this way may solve your problem.

[Duke W.]

Re: Wheel balancing

If you still have shake after a good wheel balance, there is probably an out of round or radial force variation problem in the assemblies.

The Hunter 9700 can diagnose and correct most problems. It measures both radial and lateral wheel and tire runout plus road force variation.

Find a local shop with a 9700. The following link might help.

www.gsp9700.com

Duke

[Terry M.]

Re: Wheel balancing *TL*

I highly recommend the Hunter 9700. My personal experience - not on a Corvette, but on the former police car - was very positive. I never had a smoother ride in anything.
The 9700 will be able to detect a bent rim or shifted plies, and a skilled operator can match the high point of the wheel to the low point of the tire so that minimum weight is used.

[Craig S.]

Re: Wheel balancing

Terry - sounds great. Now to find one in town.....and the skilled operator part.....usually the tire shops in Tucson seem to have just out of high school kids that you have to stand over to make sure they get the balance to at least read "00" on the readout after balancing....and without 5 ounces of lead....

[Jack H.]

Could be another problem....

if tires were run for any appreciable distance on non-true wheels. Once tread had taken a 'set' and wants to 'squirm' down the highway all the balance techniques in the world can be futile....

[Craig S.]

Re: Could be another problem....

Been there and done that! I had one alloy wheel (American Racing 16.5" x 8.25") 8 lug on my 81 pickup....went through problems with one of four always getting out of balance after 1000 miles. They always said the wheel was fine, only a slight out of round...was about 1/16" in an area of about 30 degrees out of the 360. Finally, I bought another wheel...and...end of problem. Fought it for years....several sets of tires....and brands....samo samo....until replacement.....Craig

[Jack H.]

Re: Could be another problem....

Me too, Craig. Original steel wheels on my '71 had been curbed real good. Since they were dated originals, I had them re-trued and went to watch. VERY interesting!!!!!

Fella used an axle stub to mount the wheel and turn with dial gauges following the horizontal and vertical axis of the rims. Spec he wanted to see was true in both directions within 7-mils. He'd mount the wheel turn it mark high spot(s), dismount, lay on a cushioned floor, select a hammer from roughly 20-30 hanging on the wall and KAWAAANGGGG, make an 'adjustment'.

Picked the wheel back up, re-mounted it and did the process again. Took about 1-3 hours per wheel and he wore ear protectors. Said he used to work on wheels without the ear protection until he couldn't shake a constant ringing in his ears one day (hum, wonder why....).

After the wheels were trued, the car STILL had the shakes. Went back. They told me to 'dump' the tires (only 5K miles on 'em). I didn't believe 'em, but once fresh rubber was installed ALL my shake vibration problems EVAPORATED. So there can be an interaction between wheel and rubber....

[Craig S.]

Re: Could be another problem....

Wow...interesting process. I agree on the rubber/wheel. Once the tire has the jounce....it just won't go away until replaced. I proved it time after time on that one wheel. All I can think....is if I hit a pothole hard I don't remember....since these were alloy cast wheels and turned. But I sure don't remember ever hitting anything....

[Terry M.]

Hunter 9700 *TL*

The Hunter 9700 is not the typical entry level balancing machine. It costs well over 10K - I can't remember if it was 15K or 19K that I was told. The place I went to had a very skilled operator - Hunter provides the opportunity for extensive training. Of course, you can lead a horse to water..... My electronic conversations with others who have had tires balanced on this machine reveal skilled operators at other locations.
If there are any wheel/tire issues this machine will find them. Of course if the new rotors were not balanced as part of the manufacturing process.....well that is another story.
It is worth stopping by a place with one and watch them balance a tire. It puts a whole new spin on computer balancing. BTW: my charge was $7 a tire, but I brought them the tires and wheels already mounted and off the car.

[Craig S.]

Re: Hunter 9700- Thx Terry! *NM*

[Henry Pozzuoli]

Re: Wheel balancing

At what speed do you feel the shake? If its at slow speed it could be radial tire squirm. I had a few tire that had to be replaced it's the way they were built. I even had Goodyear shave one set of tires to try to stop it then they replaced the tires.

[William C. Brown]

Re: Wheel balancing

Thanks for all the help guys. The problem may very well be with the cheapo tires that were mounted on this car when I got it. I plan on replacing them but have not done that yet. I'll try the on-car wheel balance first and then opt to replace the tires.

Thanks again

--Corey

[Dave Suesz]

I had great results...

Based on something I was told about '68s. My C1 got a new set of "Firestone" repro tires 15 years ago, and no matter how carefully they were balanced, the car had some tire 'vibe. A real pain on the highway. I spun the tires while on a lift and they appeared to be not perfectly "round". I was once told all '68s were supposed to be delivered with factory-shaved sets of 5 bias-belted tires. I had this done, and spin balanced again. Smooth as glass, to this day.