C3 / 71 Vibration

[Gerard Q.]

I've been trying to trouble shoot this problem for a while now without luck. Hopefully someone can point me in the right direction.

I've got a 1971 s/b auto convertible. It is a frame/off restored car. I get a vibration at around 65mph 2500rpm which I can feel in the steering wheel and the seat of my pants.

If I run it up to 2500rpm in neutral I get no vibration, so that leads me to drivetrain.

Here's the puzzling part. If I'm driving myself (no passenger) and less than a full tank of gas I get no vibration. It's only when I have a passenger and or gear loaded in the rear and more that 1/2 tank of gas do I get the vibration. So it's load related. When I feel it and let off the gas it diminishes.

So far I've had the wheels spun balanced, the u/joints checked and the driveshaft rebalanced.

Any help as to where to look next would be greatly appreciated.

[kelly theaker]

Re: C3 / 71 Vibration

tires , i would start there are they old, or been stored sitting on them . put them on the balancer and stand to the side or use a guage.

[Jim T.]

Re: C3 / 71 Vibration

Feeling the vibration in the steering wheel even though you have had the wheels balanced you check for a wheel rim that does not run true. Put your spare time on the front and see if you still have the vibration. Does your tire balancing facility have the equipement to check for wheel trueness?

[Gary S.]

Re: C3 / 71 Vibration

Have you tried this with a standard four wheel tire rotation?

Gary

[Gerard Q.]

Re: C3 / 71 Vibration

Thanks for the tips.
The tires and wheels are new. Would a tire and or a wheel problem be more evident as the weight (load) of the car increases?

[Terry M.]

Re: C3 / 71 Vibration

Some tires, even new ones, are notorious for an out of round condition. Normal balancing machines will not detect this defect. The expression is: even a square tire can be balanced on conventional spin balancing machines.
The state-of-the-art for vibration control in the tire industry is currently the Hunter GSP9700 Wheel Vibration Control System. Note that they don't even call it a tire balancer, and for what it costs they shouldn't. Go to the link below and look for a shop in your area with such a machine. Talk to them before you bring the wheels and tires there to determine if they have a trained operator. This is a very sophisticated machine, and to get the most from it requires a good deal of training from the manufacturer.
If you have the capability, take the wheels and tires there, if not take the car there. You will be amazed at what that machine can do in the hands of a skilled operator. It can tell the operator how to index the tire on the wheel to compensate for out of round in both the wheel and tire. It will also locate an out of round condition on the tire and determine if that can be compensated for or if the tire has to be returned to the manufacturer.
The change due to loading is a little puzzling, but after the Hunter System has done its work you will be able to eliminate the wheels and tires as the source of the problem.
There is also a link on this page for Hunter GSP9700 locations in other North American countries than the USA.




Locate a Hunter GSP9700

[Gerard Q.]

Thanks Terry, I'll have them checked out. *NM*