Very Specific Vibration

[Bill S.]

I have a vibration in my 66 coupe that is a bit perplexing.
The vibration occurs only at 70 MPH and is virtually not existent above or below that speed. It shakes the front of the car (not real pronounced) and the hood will "bounce" a bit at this speed.
I have new tires on the car and they have been balanced twice. I have checked the front trans mount, rear end mount, replaced the shocks, checked the ball joints, and front wheel bearings.

If some thing were out of balance, like the drive shaft or a bad universal joint then wouldn't the vibration continue up th RPM range???
Thanks
Bill

[Clem Z.]

Re: Very Specific Vibration

out of round tire,disk brake rotor out of balance

[Verle R.]

Re: Very Specific Vibration

Bent wheel?

Verle

[Dick W.]

Re: Very Specific Vibration

I think that Clem and Verle have it nailed. Driveline is more of a "harmonic" type vibration, usually feel it at a lower speed and then at double that speed, ie 35 and 70. Take your car to a reputable tire store and have them trued. It does wonders for the ride AND increases mileage, as if anyone puts enough miles on their Corvette to wear the tires out

[Phil P.]

Re: Very Specific Vibration

bill---i returned from phu cat viet nam early 70 and purchased a 67 350 hp 4sd vet from lew williams chev in the scaramento area---i had a shimmy, or out of balance wheel issue with it---went to a tire store and they said the the front tires were out of true---i let them spin the tires on the car and lathe, true them---cut rubber off as they were spinning---all seemed good as the car lost the light vibration---not so later on---long story short i found the nuts on top of the shocks were loose---tightened them down and all was well---good luck,phil

[Jack H.]

Re: Very Specific Vibration

Yes, wheels that are out of round (not 'true') WILL generate RPM specific vibration defying attempts at balancing the tires! Continued driving with fresh tires on out of round wheels will cause the tire tread to take a 'set' and once that happens you can essentially 'pitch' the tires. Short of shaving the tread to get them back to their factory original shape, they're 'gonners'...

Any decent wheel man can remove the wheels, one at a time, dismount the tires, and check the wheels for proper concentricity using a stub axle fixture and dual dial calipers.

You can also do a little to fault isolate drive line vibrations. When the vibration is present, push in the clutch or put the transmission in neutral and see if the vibration goes away as soon as the drive line is allowed to 'idle'. If it doesn't, you're probably fighting a wheel problem.

To diagnose a front vs. rear wheel problem, generate the vibration and take your hands off the steering wheel. If it's a problem with front wheel(s), the lion's share of the vibration will 'seem' to go away (transmitted from the front wheels to you via the steering). It it's a problem with rear wheel(s), you should continue to feel the vibration through the seat of your pants. All bets are off if you have BOTH front and rear wheels that are out of round....

Last, if/when you determine you have a problem with wheels not being 'true', what to do is a toss up... If you shop hard, you can buy fresh replacement steel wheels for $80-120 apiece. Shops that do wheel truing for a living generally get this much (or more) for their labor to true a steel wheel.

So, you're between a rock and a hard place on which way to go (fix or replace). It's not unusual to find wheels out of round on Shark cars because novice owners take a while to 'learn' where the nose of the car ends and wind up 'curbing' the front wheels until they come down the learning curve...

[Don Y.]

Re: Very Specific Vibration

Hunter Engineering makes a wheel balancer that will not only balance the tire/wheel assembly but can tell you about the force variation or hard/soft spots around the tire. You can have a tire that is perfectly round and balanced and it will vibrate from a hard or soft spot in the tire that occurs during manufacturing. If you think about the air in the tire and the body of the tire acting as a spring holding the vehicle off of the pavement you will get a visual of the force variation. The tire may have a hard or soft "spring" at some point around the tire that will cause it to roll unevenly when loaded. This balancer has an arm and roller that mash into the tread and give a comparative reading of the force that pushes back as the tire rotates. We use these to troubleshoot vibration concerns. You may want to check with your local shops or tire retailers and see if someone there has one and is versed on how to use it to solve vibration concerns.
Don Yesacavage

[Jim T.]

Re: Very Specific Vibration

Go to www.hunter.com and you can enter your city and it will tell you what shop has the GSP9700 road force balancing machine. The local Goodyear store has had one for a few years.

[Duke W.]

Re: Very Specific Vibration

It's called a Hunter GSP 9700.

www.gsp9700.com

Duke

[Clete M.]

Re: Very Specific Vibration

Don. Good description of the GSP9700. You would make a good sales rep for Hunter. They build the best equipment in the world.Clete

[Don Y.]

Re: Very Specific Vibration

I work for an MB new car dealer. Our group also includes Porsche and BMW so we have clients with very high expectations. I also was a line technician for this and other new car dealers in addition to my dad having been a factory rep for a major tire manufacturer. The Hunter equipment really works well for us and helps solve problems.

[John H.]

Re: Very Specific Vibration

The Hunter GSP-9700 does a great job of identifying/quantifying both radial and lateral runout, plus road force variation, and suggests remedial action to the tech to resolve those issues. Just "balance" isn't enough. Our local Chrysler dealer has one (and a tech properly trained to use it), and that's where I take my wheels/tires.

[Clete M.]

Re: Very Specific Vibration

John. If you liked the original 9700, take a look at the new model. Has new software features including SMART WEIGHT technolgy. It uses 30 to 40% less weight and actually improves vehicle ride quality. Also has a laser line to guide the operator to the exact location for stick on weights. Most previous models can be upgraded to this software package. Clete

[Pat #25912]

Re: Very Specific Vibration

Could Ralley wheel trim rings, caps or hubcaps affect wheel balaned? Maybe some of the repos are made in China with too much lead paint on one side

[Clem Z.]

Re: Very Specific Vibration

don't laugh because those locking wheel nuts that use a special tool to install and remove will cause wheel balance problems because the are much heavier than the original wheel nuts