Fragged U-joint: How Dangerous?
 

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

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 ;)

Buckshot is making a nice tunnel:

http://buckshotracefab.com/tunnel1.html

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.

http://www.clubcobra.com/photopost/d...INE_REAR31.jpg

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

James

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

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.

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

Driveshaft failure
 

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!

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

U-joint girdle?
Bill Stradtner

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

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. :LOL:

James

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

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!!! :eek: :LOL:


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...

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

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.

U/J Failure
 

Come to think of it I had a C Clip come out once at 100mph, this destroyed the Universal joint, ie the needle rollers turned into paste with the grease, there was a horrible vibration and the alloy bellhousing fractured badly, all this was after the engineering shop modified the shaft, and I failed to check it when I installed it.........!

I havent read any articles on driveshaft failure, but I wouldn't think there is any need to cover the U/Js, as normally when they are worn or break the needles and cross get all munched up, and I assume if the cross comes out all together its the actual D/S that causes any problems, but I could emagine a huge whip and boom if under a drag racing situation!

The old cars with the enclosed D/S were very safe, and when modern D/S's came out I guess there was skepticism on the safety of them! Run a hoop and fit a cover of 14- 16 gauge metal close over the top half of the shaft!

Jerry,

Thanks for the tip. I recall you asking me about the driveshaft angle at the party. The driveshaft does angle quite a bit to the right from the transmission to the diff; I'll check the horizontal angle too. I've been considering having another driveshaft built with solid 1350's. I'll give you a call at the shop in the next day or two regarding setting up my rear end with a Truetrac.


767,

I started wondering about a car "pole vaulting" over the driveshaft long before I ever heard any of the horror stories. Makes ya wonder why the manufacturers don't put in a front loop.


Ant,

Yep, that seems to me to be the best alternative.


All,

The big advantage of the totally enclosed "Buckshot" system is that you can probably leave the fuel and electric lines where they are and still be pretty safe in the event of a separation. Everything has its pros and cons...

Lowell

For the low cost of $24.95 Summit Racing offers a loop that passes requirements of both the NHRA & IHRA authorities. The loop is in four parts and appears to be very versitile for mounting to just about everything auto.

It is part #SUM-G7900......................

Cheap and easy installed insurance!
Jeff %/

With battery and fuel system comp[onents in the rear--much care and thought should go into the design and routing of components--any battery cables/connections near anything in the fuel system could be very nasty if your upside down
The possibility even exists to do damage with a jack in your garage

Jerry