Have the wheels and tires been checked for excessive run-out? It is quite possible to have a bent wheel give the symptoms you describe.

_________________
Joshua

The alignment shop checked the runout, and the wheels came off another car I owned, and they were never damaged.
The rear tires have not been checked for runout.

OK, I'd check the rear wheels and the axles too. Just because the tires are new don't give them a pass. Check everything.

_________________
Joshua

Hmmmm.....a custom drive shaft with ball & trunnion joints. You might want to double-check those, along with your trans mount.
If the vibration is felt in the whole car, and not just concentrated to the steering wheel, I would suspect something in the driveline.

Roger

No B&T...the custom driveshaft was built so I could eliminate the ball & trunion.

I've had driveshaft imbalance on other vehicles, and it always increased or decreased with speed. This comes and goes with no identifiable pattern. It's just a random shake that affects the whole car. The steering wheel shakes, the seats and mirror shake, and the motion seems as much corner-to-corner, as sideways. It really feels strange, and unlike anything I've experienced in the past.

The restoration shop showed me something I wasn't aware of, and that was some type of inert fluid-filled dampers mounted in each corner of a Camaro convertible. He said it was intended to minimize cowl shake, but I've experienced identifiable cowl shake on rough roads before, and this doesn't feel the same.

I've always been fairly successful troubleshooting car problems, but this one has me scratching my head.

Tomorrow, I'm going to jack the car and check the tire and driveshaft runout, and look for anything obvious. Then it's off to Discount Tire to have them check their tires.

Does it happen on the rain-grooved streets?

The tire rib pattern may just be catching the grooves........

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

We don't have rain grooved streets around here, and it happens on freeways, rural highways, unimproved-oil back roads, and even crossing a parking lot. Sometimes it's noticable as slow as 10 mph, and it happens a bit more often at cruising speeds up to 70...which is as fast as I've had it.

If this is not caused by tires:

Would you describe this feeling as quivering, more side to side than virticle? Not so much as any motion, but a feeling that something is connected to a bowl of Jello?

I have experienced this feel in full sized cars as recently as this winter with a 2010 Charger I rented while in Florida, as far back as 69 with Dad’s new Fairlane which felt like it had balloons for tires, and other large cars & pickups in between. I think it is caused by rubber bushings that are on the soft side, lots of new tread, and everything being tight so that the smallest motion is transmitted to the seat of your pants.

As the chassis rolls on some miles, and imperceptible wear creeps in to add a wee bit of slop, the feel will be more abrupt eliminating the quiver with a more of a sharper jolt which most folks regard as normal road feel.

Enjoy the new mid sixties car ride…

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

It's definitely not a mid-60s car ride. I was selling new Plymouths and Chryslers in 1964, and this condition is not normal for a stock or high performance suspension.

The closest to this feeling that I can remember in a car was when I drove a Nextel Cup car at Texas Motor Speedway. At speeds over 150, the tires skip over minor defects in the pavement when the shocks can't respond fast enough.

It's not like a vibration or up and down movement, but more like multi-directional...corner to corner...fore and aft, and side to side horizontal movement.

If it is tires, they are all bad. One bad tire is easy to identify, as is an out of balance condition on one or two tires, but if all were out of round, it might act the way it does.

Check the front wheel bearings. If they are not seated right they will cause the "jittery" effect.

Update, if anyone is interested.

I jacked the rear end and ran it at low highway speed to check for an out of round tire and found both tires were about .12 out of round. I didn't check the front, but if they are as bad as the rears it's no wonder the car is doing a multi-directional dance.

I also checked the newly fabricated driveshaft and measured a runout of about .05 right behind the front U-joint when turning. Not sure how bad that is, but since there isn't a shop that can balance a driveline within 70 miles I'm going to try using a hose clamp to see if I can affect the balance. If it turns out to be misalignment instead of balancing, I guess I make the long drive.

Nothing like multiple problems combined to give odd symptoms.

Update: While checking further, I found the left front shock had not been tightened properly by the restoration shop. There was a quarter inch gap between the rubber pads and the shock mount. Tightening it fixed 80% of the problem.

I then took the car to the tire shop and they found the right rear tire to be out of balance. That fixed another 10%, and explained the multi-directional movement.

The tire people did not think the minor out-of-round condition was a problem, but there is still a small amount of side-to-side steering wheel movement. Discount Tire is good about honoring their warranty, so I'll drive it for awhile and see if anything changes.

I do plan to install new shocks as I think the low-mileage ones on the car are not damping properly. The increased spring rate of the V8 torsion bars and new springs probably requires better shocks to do the job.

Any suggestions for a new shock that improves ride? The car is a cruiser, not a race car, so ride comfort and smoothness is primary.