Hey, got a question, been thinking about it for a while and decided to see what others though. I'm planning on buying a universal driveshaft safety loop. I've seen many people put on 2 driveshaft loops which are located near the front and back of the driveshaft. I really only want to put on one and only one of these on, so here's my thoughts.

If I put the loop more towards the front (front of the car) of the driveshaft then if the driveshaft snaps it'll be contained as it spins wildly, until I realized something has happened. But if it breaks past the loop and the rear part of the driveshaft digs into the pavement, it could catapult the car and possibly break the rear end, if not the rest of my car. But if I only put it near the end, then if it breaks, the driveshaft front would spin around bashing everything until I stop the car or the yoke flys out of the transmission.

I was thinking about putting it towards the end and measuring the smallest amount of length needed for the rear part of the driveshaft to dig into the ground. So I would place the loop right before that mark.

I still want to hear what others think before I do anything.

 

Put it at the front, about 4-6" behind the U-joint. Driveshafts tend to break at the ends, near the yoke weld, rather than in the middle. You want it near the front to keep from catapulting the car if it breaks at the tranny end.....if it breaks at the back it will just bang up the floorpan.

 

I would think NHRA sets there rules for a reason, and in the rule book is says.. Driveshaft loop must be within 6" of the front U Joint.

The loop is there for only 1 reason. To hell with the car, and car parts. It's your life that it needs to save.

If the rear U joint pr pinion breaks all it's gonna do it let the shaft drop and drag the road.

If the front U Joint breaks you in for a world of hurt, maybe even death.

The front can break, drop to the ground, and as the car moves foward, the shaft will "dig" in and could cause the car to flip rear end over front end

 

getting a universal fit one is a joke. you'll end up using it for material to make one from. they sure don't fit without some changes.

 

Also the idea is Say the rear breaks and it trys to catapult the car>>>>it WONT...because as soon as it trys to force the car up the shaaft will pull/fall out of the tranny...

But when the front breaks and the shaft drops in the front and the rear stays fixed it acts like a pole vault and launches the car>>> OR it will beat the sheeeiiittt out of the tranny tunnel and could possibly break into the drivers compartment..

 

I have a Spohn Loop for sale. Let me know if you want it

 

Sorry, buying one for $15 shipped. Unless you can beat that.

Anyways, Everyone who has posted here has just restated exactly what I said, but there was some confusion. I wasnt talking about the u-joints, I was talking about the actual shaft breaking in between the u-joints. So we're all getting at the same exact point.

The reason why I was stating in between the u-joints was because my friend ripped his apart right in the middle of the damn thing and his front loop did absolute **** in that case, that's why I was considering the rear.

Now if you think about it and do some measurements. If you mount it in the rear, and the driveshaft breaks anywhere, it'll look like:
__break
\_ ______________| |___/
__ ______________| |___|
/________________\/___ \
tranny___________loop____rear end
Forget about the bottom 2 lines and the one near break I needed to put them there in order to keep the figure from condensing. The 2 lines under the word 'break' is the driveshaft, that's all you need to look at.

Everything will be contained if the length between where the driveshaft falls to hit the loop and the angle of depression it creates is not enough so that the opposite side, won't hit the ground. Essentially a triangle, where the straight top line is the driveshaft normally, and the hypotenuse is the driveshaft after it falls and is held by the loop, and the vertical line is the length the driveshaft fell form the original place (at the breakage) to the bottom, where it rests due to the driveshaft. (Again forget about the middle lines).
_____
|___/
|__/
|_/
|/
Hope everyone remembers the math they thought they'd never use .

Anyways. If the angle at which the driveshaft fell is minimized to where the length of the driveshaft (the end to the breakage) can be contained to above the road, then the driveshaft would be safely contained.

This would also prove beneficial to where it broke on my friend’s car. Having the loop mounted in front, and having the driveshaft break beyond the loop, it still catapulted his car. Now if the loop is in the rear, it can contain the driveshaft no matter where it breaks.

Hope I didn't lose anyone, I'm not too good at explaining my view but I can draw it all up better. If I need I can scan the page and upload it to this post. But I still want to hear what you have to say.

 

your math and theory work on paper and I fully understand your logic...but I can't help but feel your missing some. Maybe variables...such as the strength of a driveshaft loop and by placing it just past the contact point of the fallen driveshaft stresses the driveshaft loop material to a point where nhra required it further foward. Now I know nhra is a little on the overkill side when it comes to saftey but I don't feel the loop will hold if the driveshaft breaks at the joint and starts swinging at 2000-5000 rpm's and the loop is further then lets say 25% of the driveshafts length or say a 12/18 inches on our cars. Of course one could pull some calculations on the strength of steel(driveshaft saftey loop material) and the moment of inertia and energy of the driveshaft on the loop, but one would be wasting their time as NHRA conducted these calculations and tests, along with the consideration of millions of 1/4 mile races over the last 50 years to make thier educated rule.

/in other words 6 inches or less from the front yoke joint.

/and if your that concerned buy another one for the rear to save your floorpans.

 

I hear what you're saying, but the NHRA's 'calculations' were probably nothing more than watching a bunch of u-joints snapping or MAYBE a little calculationt o determine that the u-join was the weak point. Nothing more. But still, in my friends case, that didnt happen.

Now, the metal is about 1/4-1/3 of an inch thick. It doesn't have to last long if it is going to give way, just long enough to realize somethings wrong and stop. I doubt that strength is that big of an issue being that thick.

 

1st off 99.97 or 99.98% of all breaks in the driveline is the U joints. They are the weak point, not the shaft

You just don't break driveshafts!!. Your buddy had 1 of 3 things..

BIG HP number (800 hp or so) and real sticky tires.

A weak, rusted driveshaft

Or the driveshaft angle was all messed up from side to side and up and down, which placed a greater stress on the shaft, till it just broke.

Out of years of going to the track, and working on cars, I seen 1st hand 2 driveshafts break (never happened to me), and atleast 200 U Joints break

The 2 that broke the shafts...

One was a buddy's race car (vega), running 8.30's (1/4 mile), and launching off a trans brake and shooting 150 hp of n20 on his 5K rpm launch. Broke as the car lifted the front wheels and took off good (about 10 feet out)

Another one was one guys S-10 truck. The shaft looked like it had been sitting in a junkyard in the open for 20 years. There wasnt a spot on it that wasnt rusted to death. When it broke, he had just hit a BIG pot hole going about 75 mph on the road. I guess the impact and bounce of hitting that pot hole was enough along with the torque of a 383 SBC to just break the rusted shaft

Then when it comes to U joints.. Heck I was snapping the cheaper U joints twice a mo. on a 15 sec full size truck .

On my 84 camaro a few years ago, I would break atleast 1 U Joint a weeend at the track. Broke so many on that car, I got where I could pull the shaft, and replace the joint in the pits in less than 15 min.

So far useing the stronger "brute force" forged solid body joints, I aint broke one yet (knock on wood), but just in case I got 2 in my car (one for front cause its a bastard joint for my th-400 conversion) and 1 for the rear), so I can change them on side of the road, or at the track, when/if I break one.

 

Yeah, that's what I keep hearing. Friend has 475 to the wheels and had a ls1 aluminum driveshaft, it looked perfect, street tires too. Maybe just a faulty shaft . Heard stories of other braking their shaft too. I guess I'll just put it less than 6" from the front. Me nor any of my friends have ever broken u-joints and they're not slow cars. Seems pretty odd. Before anyone yells at me for wasting this much time with a driveshaft loop when I havent even broken a u-joint, let me just say in advance, better be safe than sorry.

Thanks for everyone's thoughts.

 

I've seen lots of U-joints break but never had one myself.

All the u-joints I've seen break were always on the starting line and mostly rear ones. Either a u-joint fails or a yoke fails.

Even my 15 second daily driver truck has a front driveshaft loop. When I raced it and crossed the finish line at 87 mph, a broken front u-joint can still do lots of damage. Even 60 mph on the highway is dangerous.

The factory aluminum driveshaft is very weak. It's not a performance item. The aluminum is too thin and the yokes are too small.

 

ls1 driveshafts are actually very rigid. Guy I bought my rear end from's ls1 is deep in 10's and it's still fine through countless drags.