I don’t need to go to Mythbusters or anyone else to find out what happens when the front u-joint fails and the driveshaft hits the pavement – it actually happened to me, in a ‘65 Chevy sedan. I was barely underway when the driveshaft dropped and hit a raised manhole frame.

I wasn’t doing more than 10 mph, but it was enough to raise the right rear tire off the ground and push the rear of the car sideways about three feet. Fortunately, there were no parked cars or pedestrians in the way.

Pole vaulted? No. Dangerous? you bet your ass!

I think they did that episode with that Crown Vic they keep beating on.

Edit: Jeff beat me. That’s what I get for having 12 tabs open and not refreshing before commenting.

Myth: Car going at speed could have its driveshaft fall off and cause the car to pole-vault.

Busted: Implausible that the scenario would actually occur, and unlikely the car strong enough to actually vault on the driveshaft.

Read about it here.

That’s a good idea. Whether or not I hear replies from the folks originally making the inquiry is another, but maybe I can have a Piston Slap update to accomplish just this.

Just submitted this to Mythbusters…I, too have heard about this before…

A while back I was traveling cross country in a MB 450se, when the underdash parking brake release handle started vibrating so violently I though it would crack the dash! In panic, I thought maybe the brake cable had somehow gotten wrapped around the drive shaft, so I immediately pulled over and started crawling around under the car – and found nothing. Got back onto the highway, and around 50mph the crazy dash shaking panic inducing vibration started again!

Several stops and starts later I happen to notice that the chrome trim on top of my windshield had come loose. Giving it little thought, I pushed it back under its clip… and when I got back on the highway the vibration was gone! It didn’t actually cross my mind the two events were related until the vibration came back a few hours later, and when I got out, I noticed the trim had pulled loose again. Pushed it back on, vibration gone. I kept this up until I could hit a parts store and buy a little adhesive to help hold it under the clip. After that the vibration never came back again…

It was a real lesson in the power of sympathetic vibration – a 10″ piece of chrome trim on top of the roof vibrating in the wind made my parking brake handle try to tear itself out of the dash.

And that’s why mechanics hate oddball vibration issues.

In retrospect, I would probably have tried to fix it myself but I didn’t know what was wrong or how to figure it out. If you get up under the truck and grab hold of the driveshaft (the long tube from transmission to differential) and then yank it around, you might be able to see it wiggle or have too much play — signs of a u joint problem.

The carrier bearings and U-joints may not be bad. If the carrier is improperly shimmed or the axle pinion angle is off the misalignment could cause this.

Or wheels out of balance. These types of problems can drive you nuts.

My old 86 did this at about 50 mph and quickly went away. Perhaps not same problem as Chris here, but never did track down the problem.