Mith-Busters Driveshaft a Pole Vault

I had a 1973 Ford Van that two things happened at two different times. The first thing that happened, I was on the expressway going about 70 mph and the exhaust broke at the front of the muffler, causing the muffler to drop down and picked up the rear wheels about 2 feet in the air. It scared the S**** out of me but I did not hit anything. And the second thing that happened about 1 month later the drive shaft fell out at the back u-joint, the drive shaft slide out of the transmission. The front dropped down and the rear of the drive shaft hit the under side of the body and lifted the rear of the van about 4 feet off the ground. I was doing about 35 mph and almost had a heart attack and got lucky that I did not hit anyone. I coasted into a parking lot, went back for the drive shaft that was laying in the middle of the road. No one had hit it and when I picked it up, the only thing wrong with it was the broken u-joint.
George

 

Dumped the rear uni a couple of times on my daily driver, first time was a long way from home so it had to be towed and repaired at a shop. Second time was luckily close to home. Took it to my fathers shop and put it on the hoist. Discovered that the cup had one stripped thread that had obviously been bad for a long time, one bolt hole that was cross threaded. No wonder that ****er came out.
Lost a front uni in a mates ute once, it picked us up pretty high and pushed us sideways. Came down so hard my mate has permanent back injuries from it. Bent the drive shaft into a big Z.
Doc.

 

I'd forgotten about this but when I was in high school one of the kids a year behind had this great big goofy 4x4 Chevy wagon - like a '71 Impala wagon, body and frame, set on top of a Chevy truck frame of some sort, so it had 4x4 and like 36 inch tires all around - a redneck party wagon, I suppose. Eventually he wrecked it and got killed in the accident. We saw the carc*** come into the nearby garage (from a great distance) on two rollbacks - the truck frame with the motor and all, broke away from the car body, which they brought in upside down. The front of the roof was smashed down a little, but the body was mostly intact. The story that went around was that one of the driveshafts had come loose and come through the floor and took a chunk out of his skull in the process. Don't think I ever heard if that was what did happen, or if it was something else, though.

 

If you want to incorporate the driveshaft safety loop into a crossmember, they sell U and O shaped mandrel bends made of tubular steel just for that purpose. I like the ones that are mandrel bent out of 1x2x 1/8"-wall rectangular steel tubing. If you buy two U shaped pieces, you can make a loop whatever height you want. For lots of safety you can have a front AND rear one. Remember to account for the up and down travel of the driveshaft. If your rearend is located by a panhard bar, there will be a slight amount of side to side motion. If your yoke on your pumpkin isn't exactly in the middle of the rear axle, you need to mount the driveshaft loop(s) off center a certain amount. It's a good idea to stretch a string between the center of the output shaft of the transmission and the center of the yoke on the pumpkin to make sure you'll have enough clearance through the whole range of motion of the rear axle.

 

One of the main causes for u-joint failure is when people overtighten the little u-bolts and crush the bearing caps out of shape, which shortens the lifespan of the bearings a whole lot, and then everything rattles to pieces. Try to follow the torque specs carefully on those. If it calls for only 25 foot pounds, don't just crank it as hard as possible with your longest wrench. And use the correct nuts that come with the new u-bolts.

I also heard that u-joint crosses with a drilled hole for a zerk fitting are more prone to breaking than un-drilled sealed type crosses. The hole for the zerk fitting makes a weak spot where it's more likely to crack.