Fragged U-joint: How Dangerous?

[Lowell W]

In recent threads on CC concerning driveshaft loops, there seemed to be unanimous agreement that a means of restraining the driveshaft in the event of a broken U-joint is an essential safety feature; also that the smaller the area the broken driveshaft has to move around in, the better.

Several suggestions were made: A) that a single loop is sufficient; B) that a loop at each end of the driveshaft may be required for adequate protection; C) that a centrally located ring, slightly larger in ID than the diameter of the drivshaft, may be an ideal, and simpler, solution; and D) that some kind of a shield over each U-joint may also be necessary, or at least desirable.

The central ring arrangement would be the simplest to design and build, especially for cars with IRS. If that would provide adequate protection; great! I did fabricate a front and rear loop system with 1/4" steel shields over the U-joints which certainly is strong enough, but now that I look at it on the bench, it looks way too heavy and clunky. Actually it looks like it belongs on a tractor, not a Cobra.

Before proceeding further with design and fabrication of a driveshaft restraint device/system for my car, I decided it would be a good idea to see whether anyone has had any experience with a U-joint coming apart. Assuming the driveshaft itself is restrained with some kind of safety loop, how much force is imparted to the U-joint pieces or yokes? Enough to send them through the tunnel? Enough to warrant the use of a shield over the U-joints? If so, how heavy is heavy enough? Anything else I'm missing that I need to consider?

Thanks,

Lowell

[Three Peaks]

I think the problem is that once the u-joints let go, the end can swing around cause huge damage. I think the u-joint protectors are more to keep the driveline from taking off in flight than keeping pieces of u-joint from causing damage. But I could be wrong

[SJK2]

Buckshot is making a nice tunnel:

http://buckshotracefab.com/tunnel1.html

[aldersonjames20]

I just had both of my U-Joints replaced on my car. They both had excessive play in them and a whole lot of noise and vibration was coming through the car. I have not got a lot of experience with this stuff, but I think the danger lies in that if the U-Joints come apart, they can take out the fuel lines which usually are running fairly close to that area, and along with that is the battery cable... so sparks and fuel... kaboom. At least this is what I was told anyway.



Does anyone happen to know what manufacturer these buckshotracefab tunnels are built for, looks like a Superformance, but can't tell for sure.

James

[Yetiman]

Originally Posted by aldersonjames20

James

You might want to seriously consider re-routing that power cable.

[Ant]

In my years of racing, and giving vehicles a hard time I have never had a driveshaft fail, but it only needs to happen once and cause injury....!

So this is what I have done from the strength of parts point of view, and of course a regular check for wear and tear is very important. Buy good quality U/Joints, and as big as possible I used 1350 series, with a Mark Williams machined yoke for my Jerico, and I also purchased top quality weld on driveshaft parts etc, including the U bolt 8.8" differential pinion hub to cope with these large style U/joints. The driveshaft is only going to be well under 2' long, so I will fit a hoop made out of 1/8" strap, about 2" wide securely attached probably top and bottom, quite frankly you can make your hoop out of 1/4" or bigger but its a waste of time and excessive weight if it isnt supported properly, and quite close to the driveshaft tube, so in event of failure the least angle the better!

Also the requirement here is to have the Hoop more to the front of the driveshaft according to the certification guy, but that may depend on where the seats are!

[aldersonjames20]

Originally Posted by Yetiman

You might want to seriously consider re-routing that power cable.

I agree with you wholeheartedly, but I looked at it and because of the position of the battery I think it would be hard to get the power away from the fuel lines, or do you mean just close to the driveshaft? Are most battery cables not close to the fuel lines on cobras?

It does seem dangerous to me, kind of like a woman, snackhouse is way too close to the outhouse...bad design.

James

[Juggernaut]

Originally Posted by aldersonjames20

I agree with you wholeheartedly, but I looked at it and because of the position of the battery I think it would be hard to get the power away from the fuel lines, or do you mean just close to the driveshaft? Are most battery cables not close to the fuel lines on cobras?

It does seem dangerous to me, kind of like a woman, snackhouse is way too close to the outhouse...bad design.

James

I have my fuel lines running down the left side of the chassis & the positive battery cable running down the right side, just makes me feel better keeping them apart.

Great thread on driveshaft loops, I'm in the process of getting one for mine!

Randy

[aldersonjames20]

Originally Posted by Juggernaut

I have my fuel lines running down the left side of the chassis & the positive battery cable running down the right side, just makes me feel better keeping them apart.

Great thread on driveshaft loops, I'm in the process of getting one for mine!

Randy

For some reason I thought my setup was unique, turns out that this is the standard routing of the lines for fuel and power on SPF's. I have EFI so I have higher pressure and a return line, but thats the only difference from stock. I am waiting for this driveshaft armour cover discussed above to be finished before I look at rerouting the lines... they probably shouldn't be that close to each other anyway, but if I can mitigate the risk by spending some money for the cover then I will just do that. I know if I start to reroute I will screw something else up... I alway do.. my wife tells me so..

James

[Lowell W]

Steve,

Yeah, thanks, I looked at the Buckshot. It completely surrounds the driveshaft and does cover the U-joints. As a matter of fact, I think that's what got me thinking about containing the U-joint fragments in the first place. It would need to be removed to grease the U-joints and I think it would be difficult to clean inside. I still like the idea of surrounding the driveshaft with a 1/4" thick steel loop.

James,

I'm sure they're made for SPF; not sure about other makes also.

Lowell

[Rick Parker]

Lowell:
It's not the fragments of the U joint that is the concern, but as ThreePeaks said the (insert your # here) HP powered broken driveshaft flailing about in an ever increasing arc and taking out YOUR HIP or THIGH! If it breaks at the front joint it may not reach the ground but if you are under speed it is powered by the momentum of the car. Scary thought.

[Lowell W]

All your points are well taken. Assuming the driveshaft IS adequately restrained, is there any danger from the pieces of the yokes and the U-joint that come loose when something fails? Has anyone experienced or heard of an injury from a loose fragment; NOT the driveshaft itself?

Thanks all,

Lowell

[olddog]

Originally Posted by Lowell W

Assuming the driveshaft IS adequately restrained, is there any danger from the pieces of the yokes and the U-joint that come loose when something fails?

Here is my gut check. Assume the U-joint is 4 inches across (cap to cap). Pi times diameter give a circle arc length of 12.56", which I will round to 1 foot. Assume 4th gear (1:1 ratio) and 6000 rpm at motor (same for drive shaft). This is 100 revolutions per second, and 1 rev is 1 foot. So the tip speed of the cap would be 100 feet per second. That would be the maximum partical speed.

The slowest hand gun velocities are around 800 FPS at the muzzle. So you are nowhere near gun velocity, but particals could be heavier than a bullet. Granted I wouldn't want to be hit by it, but the floor should stop it or slow it considerably. Also your much more likely to loose it in a lower gear, at lower speeds.

What amount of risk is acceptable? It doesn't take much to loose an eye. I guess everyone will have to decide for them selves. I would put it in the lower risk catagory, when you consider these cars were not designed to safely transport diplomats.

[767Jockey]

I'm no math wiz, but lets give this a shot to put it in perspective:
100 ft/secondx60=6000 ft/minute
6000 ft/minute x 60 = 360000 ft/hour
360000 ft/hour divided by 5280 (5280 feet in a mile) = 68 miles per hour, about the speed an average 15 year old throws a baseball. I wouldn't want to get hit by a U joint cap thrown at me by a middle school kid, but it wouldn't exactly kill you either, unless it hit you in the temple or something odd like that. It may crack fiberglass, but I highly doubt it would penetrate the floor and hit you. Assuming my math is right, it's much ado about nothing. Good topic of conversation, though.

[sllib]

U-joint girdle?
Bill Stradtner

[1985 CCX]

Great thread!

In the past I have only had trouble with 4x4's u-joint failure. When large V8's, mud, and 38"+ tires get involved stress is a major factor which usually raised its ugly head with driveline failure. In that instance it usually was not anything that could cause for alarm since noise would alert one that a problem was under way. I never experienced a breach where a shaft went wild and wrecked the general area surrounding it.

With a Cobra driveline failure can be a problem depending on the time and place. This forum is really a great place to air issues so we can all keep these cars safe. In original CSX cars the hoop was simply a ~0.5" steel bar bent up into the tunnel area and braced to the frame. The rear tube of the chassis was there to keep the drive shaft from dropping to the ground. Is this all that is needed or is there a need for more protection? Has anyone that drives a street car ever had serious issues with thie failure or is this more of a racing need. 99.9% of the time my car is on the road and after 22 years has never had an issue. Regular PM and upkeep seems to be working.

I guess what I am asking is has anyone ever really had a failure that caused massive damage and injury? Now it seems obvious that you would not want your fuel line and battery cable packed next to the driveline. However it looks like it might be standard for SPF? I have never heard of an SPF going up in smoke from driveline failure. How much is enough and where does overkill start to take hold building panic?

Let's face it in a general accident our cars are not up to 2007 standards. That said it also holds true for most OEM 1960, 1970, and 1980 era cars. I would think building a shroud that can build heat would not be the best way to thwart failures. The steel box is great for racing purposes but for long road trips would increased heat build create problems that would never have been there in the first place with a simple hoop?

Thoughts,
Jeff

[aldersonjames20]

Originally Posted by 1985 CCX

Now it seems obvious that you would not want your fuel line and battery cable packed next to the driveline. However it looks like it might be standard for SPF? I have never heard of an SPF going up in smoke from driveline failure.

If your referring to the picture of my SPF's battery and fuel lines, don't consider it to be standard, ain't a damn standard thing on my car.... previous owner redesign... almost all of it for the better I would say, but I am not certain that SPF's are set up this way in general.

James

[Lowell W]

Jeff,

Here is a link to photos of driveshaft damage.

http://www.clubcobra.com/forums/show...ht=scary+noise



Bill,

I think the girdles support the caps but don't restrain the fragments if the cross or yoke break.


Ant,

Yep, I'm giving some thought to having a driveshaft built with 1350's.


James,

ROFLMAO!!!


So far, the consensus seems to be that if the driveshaft movement is limited, the lighter particles with less centrifugal force shouldn't present much of a threat. At this point, I'm leaning towards using a 1/4 x 2" hoop around each end of the driveshaft, similar to Dean's arrangement here http://www.clubcobra.com/forums/show...404#post717404
and then welding a lighter (ie. 14 ga. or so) shield around the top 180° of each hoop, wide enough to extend over the U-joints.

Lowell

edit: Removed another link to a confidential site which I had posted inadvertently. Sorry...

[Jerry Clayton]

Lowell

If you build a drive shaft with Spicer spl 1350 joints you will gain tremendous increase in strengh
First they have no grease fittings--the greasable u joints are not as strong as the non greasable ones
Second they are much bigger and stonger


Third--the SPF cars I have seen (including the ones pictured in these driveshaft threads) have an excessive drive shaft angle that is unnecessary --with the irs this is a constant misalignment whereas with an live axle the rear would fluatate. So you have an shaft that is always seeing an eccessive amount of wear and tear leading to possible premature failure--your drive line angle can be corrected dramatilly by shimming the tailshaft of your trans by 1/2 to 3/4 inch higher which probably will only change the engine level front to rear by less than ONE degree!!!

Correct the drive shaft angle and the failure possiblity goes down--change to higher strengh/quality components and you will virtually eliminate it.

Note--with a ONE FOOT long driveshaft the force at the end of a flailing about shaft will equal your torque/rpm numbers on your dyno sheet--of course the rpm will be reduced if you are in one of the lower gears/increased if your in an overdrive gear.

There are 4130 and carbon fibre parts available from drag racing or sprint car racing that can be adapted to your car.

Next time your at the train station stop in

Jerry

[767Jockey]

This isn't an urban legend. I actually happened to a guy who lived a few doors down from me growing up. It happened in the late 70's in a fairly new at the time Pontiac Trans Am. He had put quite a bit of work done on the car, and was street racing at fairly high speed. Accident investigation proved that the chain of events was that while at speed his front u joint failed. The front of the driveshaft fell to the ground and stuck into a joint in the concrete highway. Apparently it stuck just long enough and with just enough force to unload the rear end and put the tail of the car out of control. He hit a phone pole at high speed and died at the age of 19. Every high performance car I have owned since that day had had a driveshaft safety loop. His name was John Schellie (sp?), and it happened on Montauk Highway in Bay Shore, NY. Perhaps there's a report out there somewhere that some of you more internet savvy guys can find. I know that his family sued Pontiac. I don't know what the final disposition of the case was, as the family moved shortly after.