I have a 67 camaro, 3 speed, 327 with an est 400 hp and the original 3.08 peg leg. Problem is that when we get up to around 60-65 mph the whole car vibrates. I can also hear a muffled winding sound kind of like going over the speed strips that are placed at slight intervals on the highway to slow you down. Its done this for a couple of years and it is my intention to change the rear out to a 3.73 posi with a 4-5 speed trans but money needs to come first. Could this vibration be as simple as an unbalanced drive shaft or u-joints? Any ideas? Any suggestions would be greatly appreciated. Oh, the front suspension has been rebuilt so I know its not coming from up front.

Sounds like it could be pinion bearings. Usually drive shaft imbalance shows up at lower speeds but a bad pinion bearing could cause this. Make sure your wheel balance is ok, then have a driveline or tranny shop check the car. Better to spend a little now than a lot later.
Jim

It could be tire noise due to low airpressure, misalignment, slight out-of-balance. Change tires from side-to-side, reverse their present rotation, and examine what happens.

Well thats the thing. The front end has been rebuilt, all new ball joints, bushings etc and I still had vibrations from the rim and tire combo I had on prior. Nothing has ever been done to the car from the tranny back....

“whole car vibrates” indicates drivetrain or rear wheels to me. If changing rims & tires had no effect, sounds like rear, tires are out.

Do you have long tube headers? How is exhaust mounted to body? I have had this same problem at speeds you described. New tires and wheels, differant motor, trans, trans mount, new drive shaft, all axles within runout. let motor idle and pop in netural at 80 and coast down to 50,,, sounds like my caddy. But cruising,,, a harmonic vibration is there,, to see in mirror 60-65. Been there ever since car was new. Still suspect vibrations from long tube headers. Not in engine balancer either,, have ATI.

I worked at a car dealer once and we had a car with a bad vibration at 55-60 mph. It turned out to be a bent axle tube

Well I guess I'll keep digging. I'll be swapping the rear out next winter anyway along with the tranny. I was just hoping it would be something simple to make cruising better for this summer. I would not call them long tube headers. They are Headmans with standard collectors.

I've been through this before, sorta' a BTDT. To figure out what is causing the problem need to basically run the vehicle with the back end up on jackstands (under the axle tubes). Then proceed to unbolt items until the vibration goes away. Like this:

Place rear of vehicle on jackstands under the outer ends of the axle tubes. Just high enough to get the rear tires off the pavement. Run up the MPH and verify vibration exists. If so, remove rear tire/wheel asemblies and place the lug nuts back onto the car. Run up the MPH and verify vibration.

If no vibration then the problem is in the tire/wheel assembly(s). Otherwise, pull drums off (or disks if so equipped) and verify vibration. Note: DO NOT use the brakes with the drums off, makes of mess of the wheel cylinders. Next step is to pull the axles, then the differential carrier, then the driveshaft, with a run up to MPH after each is removed.

In my case is was the differential carrier that was out of balance.

Bob.