My 68 6 cylinder 3 speed manual drives as smooth as silk up to 60 mph. Beyond that speed, there is a general vibration throughout the car, some of it felt at the steering wheel but not excessively. In order to cure this, I was thinking, for starters, of having the four wheels rebalanced, then the driveshaft. If those steps don't cure the problem, how should I proceed? Opinions and recommendations would be appreciated. Thanks, Joe.
Don't just have the wheels "balanced" - you can perfectly balance a square wheel on a machine, but it won't roll smoothly. Go to www.gsp9700.com and use the locator feature to find a shop/dealer near you that has a Hunter GSP-9700 balancer - in addiition to balancing, it also identifies radial and lateral runout, and applies a road-load to the tire to check road-force variation as a function of runout and tire construction, and shows the tech how to re-orient the tire on the rim to minimize it.
If that checks out OK and you still have the vibration, the next step would be the driveshaft.
John, thanks for the info and the link. There are 41 shops with the GSP-9700 in my area. I will have the tires and rims checked out as a first step. Joe.