I read that NHRA wants a loop within 6" of the front u joint, which sounds like it would obviously help limit damage and mayhem should that go out. What I'd like to do is keep the driveshaft from exiting the underside of the vehicle in case of a front *OR* rear u joint failure. As a matter of fact I did some real world testing the other day and determined that if the rear u joint goes then your driveshaft hits the road in about half a second! I know its closing the barn door after the cows have gotten out, but what do you guys use as a safety loop on your driveshaft, front or rear, or what do you think I could/should use to retain that bugger should the rear u joint go?!? My car isn't especially fast or anything so NHRA legal isn't strictly important, I'm just trying to get it ready for a 5,000 mile round trip soon and trying to cover my bases. It'd ease my mind knowing if that happens again I won't have to worry about causing a hazard on the freeway. Thanks all!
put a loop on the front, and put strong enough joints and yokes at both ends so it won't break. you could put a loop at the back too. Just make sure it's tall enough that the driveshaft won't hit it at full up and down travel.
I would not try to keep the driveshaft in the car. NHRA requires one for the front of the driveshaft, because when the front of the driveshaft comes away from the transmission, and the rear u-joint is still connected to the pumpkin, the front of the driveshaft will dig into the ground and it will pole-vault the car and cause it to flip over. However if there was a u-joint failure, and the driveshaft became dislodged from the rearend, I do not want that driveshaft anywhere near the spinning rearend yoke. If you keep the driveshaft from falling towards the ground, you will have a rear-end that is spinning at 65mph x what ever gear ratio, and a driveshaft, which is just long enough to contact this spinning yoke, and is also spinning at the engine rpm. When these two metal pieces happen to come back into contact it could cause the driveshaft to twist, or the rearend lock up, or more carnage to an already broken car. I understand that you do not want to be a hazard in the road, so just make sure that your car is as safe as it can be, and just hope that everyone around you has taken the same precautions. Brian
There are just millions of cars on the road that have driveshafts that have been there all that time, running 100's of thousands of miles. If you are worried, replace the universals and I will bet it will go at lease double your range to 10,000 miles.
Two stories on drive shaft failures, well one bellhousing actually. A guy buys a new modified has a powerglide in it, with no rear mount. First time on the track. He pulls out in turn two slowly rolls down the back straight. Enters turn three, wraps the throttle setting the car sideways. The bell housing breaks, the u joint let go, dug into the track and sent him tumbling. He never even completed a single yellow flag lap with the new car. Second, I had a suspension mount let go allowing the rear to rotate, breaking the rear u joint. The front U joint is right under my right elbow. The safety loop is along the back edge of the seat. The shaft flopped so violently that it bent the safty loop! It started beating the right side of the cockpit tub. All I know is that I was looking for a way out thinking it was coming in the car with me. If it ever happens again, the faster that shaft exits out the back of the car the happier I'll be!!!
I wouldn't worry about it for the rear. Replace the rear joints like hotrod said, keep a spare in your tool box and enjoy the trip.
I totally agree. Not to mention the damage to your floorpan and human passengers when the driveshaft is spinning and trapped under the car beating the crap out of anything within its reach.
If you are that worried, then put one in front, bolt-in or weld it in. Then make a removeable one that bolts in for the rear. Also, it wouldn't hurt to get some bearing girdles with grade 8 hardware for the rear. Yes, NHRA/IHRA and other sanctioning bodies require one because is can pose a problem to the car but totally will distroy the surface of the track. I drag raced for 20 some years and never had a drive line come apart and I drove some pretty healthy 500+HP cars with over 600lbft of torque. I made one for my modified Model A frame only because I want to take it to the Drags occassionally and want to be able to pass Tech. IMHO
Here is a picture of the U-joint girdle, cheap insurance if you are worried. Used them in racing for more years and never had any failures.
Most universal joints have a heavy duty version available (truck, van, station Wagon, etc.) have your parts guy check or better yet go to a driveline specialty shop and ask. Utilize the best (and ,yes, they will be the most expensive) and drive away. You'll have 10's of thousands of miles before you have to worry about it. Frank
I don't think my shaft can escape....at least the front end of it. I designed eveything so it can't come through the floor or fall from the front. I have stout enough parts and damn good angles so I minimized the chances of u-joint failure anyway.
If you want to low-buck it, bolt a piece of heavy chain to the floor pan towards the rear of the drive shaft. Allow enough slack so it hangs an inch or two below the shaft. I had one blow once and it kept the shaft from hitting the deck. It was a new Mr. Gasket u-joint that I paid $30 for. Since then I use brand-x u-joints and have never had another failure. Bob
WHAT IF ? What if i break a U~Joint ? What if i Blow a tire ? What if my Trans siezed up ? What if a Tie Rod Breakes ? Spend to much time on What If's your going to get Ulsers ! I have spent time on L.A. Freeways & i would be more worried about EVERY driver out there before i worried about a U~Joint breaking & cuasing a Hazzard. Every Driver on the L.A. freeway is a Hazzard ! the 5, 101, 134, 60, 210, 170, ALL of them a a personal Road course for the Welthy in BMW's & MBZ's and the stupid Cell phone wielding Paris Hilton Wannabes
I have broken three uni joints. Two in a 496hp daily driver, both were rear uni's. After the first one let go I made a loop for the tail shaft. When the second one let go it flopped around in there and tore up the floor pan pretty good, resulting in a lot of work and a bent tail shaft! I got rid of the hoop, I want that fucker gone out from under there if it happened again. Third one was in a mates ute, changed gears going around a round about and it dropped the front uni. It dug in enough to hop the car sideways with enough force to cause a crush fracture in my mates back! I guess it was lucky he was so damn drunk at the time! What did I learn? Fuck all really. Have one at the front I guess but I would rather it get out of there. Would I be right in thinking NHRA are more concerned by where a tail shaft may end up rather than what it will do to the car? I saw one pop out some years ago and it took off at a million miles an hour into a fence. Mess you up nicely if it hit you. Doc.
Did you already lose a driveshaft? If you did, I think you would want to look at why. This is for your Merc, right? You mention the NHRA, but you're not gonna race it, are you? I'm guessing you have a stock 302 and an automatic, which should be very easy for the driveshaft to handle. It's good that you're thinking about safety, but you may be overthinking this one. Thanks, Kurt
If you pop a rear joint under hard acceleration, and your shaft doesn't slip quietly out the back of the car, your drive shaft could thrash round like a cake mixer and shred the contents of the car, so put a loop at the back. If the front breaks, the rear end is still driving it, so it could thrash around like a cake... You get the picture. I covered both options, even though this is just a street car with a stock big block Ford;
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