Broken rear axle !

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Larry E Long
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Post by Larry E Long » Fri Oct 27, 2006 4:06 pm

JAB wrote: I have to disagree. There is no "drive gear" on conventional differentials. I think this is one of the most often perpetuated myths concerning differentials. The reason the right rear usually spins (looses traction) is related more to the fact that the driver is seated on the left side (more weight) or due to road surface conditions or that the vehicle is turning a tight right (right side "lifts" allowing traction to break) more than any other internal friction factor. Look at how the carrier assembly is built, (not including posi, etc. units) & you'll see that no side is favored over the other. They each have their own side-gear which meshes with other gears that are nestled in the carrier. When the carrier rotates the side gears rotate with it but at varying speeds comensurate with the load. If you play with it on the bench it will look like one side is going backwards; while it's possible to do that, in-use it's usually that both sides are actually rotating forward but that one side is rotating at a much slower rate than the carrier itself, which gives the appearance that it's going backwards. Which wheel slips on an "open" rear-end is determined by the load/traction condition, not which side it's on. It is a length thing as all other factors are essentially equal from the mechanical standpoint.
I never mentioned a "drive gear" and have no idea where that came from. The driver sitting on the left is irrelevant. Playing with it on a bench has no relation to actual road use but what you're describing is the function of the spider gears and that is relative to driving around corners. It's a matter of physics and how the turning of the gears applies torque to the differential and rear suspension. As the clutch is engaged torque is applied to the driveshaft which in turn applies it to the pinion shaft. When the pinion gear transfers that torque to the ring gear, however, there is a secondary effect which is torque twist. The differential and suspension are twisted. It's similar in effect to what happens on the front axle of an MB when the brakes are applied hard which twists the axle which causes a steering problem. That's why the front torque spring was added. As the rear differential suspension is twisted there is an increase in downward pressure on the left rear tire and a decrease in downward pressure on the right rear tire. The power being transferred from the motor to the driving surface will follow the path of least resistance which is to the right rear tire. That is why, on open differential (no powr-lok etc.), leaf sprung, rear wheel drive vehicles the right rear tire spins first.

The reason the axle breaks is because each time the tire spins loose, even a little, the torque to the splines is increased significantly at the moment the axle regains traction. After a while the splines get twisted, cracks occur, and eventually it breaks, and there is no predicting when or under what load that will happen. That does not mean that a left rear axle can't break but it's far less likely. There are situations, however, when a left rear axle can become stressed. If you are stuck in snow and you rock the car back and forth by shifting from forward to reverse and back again you can alternately stress one side then the other. If you stop at a red light on a hill and go to start again the vehicle may roll backward just a bit before you engage the clutch. That changing from one direction to another can stress the left rear axle as the afore-mentioned differential twist plants the left rear tire. I've also seen axles break because there was a defect in the metal.

I've built and raced a lot of race cars in my day and I know something about how torque affects traction, how to control it and where the weak points lay. The way to control torque twist on an open differential, spring leaf rear suspension is with a pair of traction bars. With traction bars it's possible to break either axle or, as a fellow racer of mine did, blow the ring gear right through the back of the housing (1962 Chevy 409, 4 speed, 4.56 posi.).

Also, remember that a spring leaf suspension is entirely different than coil spring, trailing arm or any type of independent suspension and reacts entirely different to applied torque.

And comparing torsion bars to axles is like comparing a steering wheel to a tire. They look similar but are entirely different things. How about grease fittings and brake bleeders? I actually watched a rookie apprentice try to shoot grease in a bleeder once but that didn't mean they were the same. Don't compare apples to oranges.

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Post by artificer » Fri Oct 27, 2006 4:48 pm

Larry you are entitled to your opinions but an axle is (both axles are) a torsion bar/s and that's a fact!!! If you don't think so explain what an axle actually does besides transferring torque and in that process always twisting some. Sometimes twisting the end right off which is a broken axle. This is not rocket science.
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Post by Larry E Long » Sat Oct 28, 2006 6:24 am

The metalurgical properties of a drive axle versus a torsion bar are entirely different. Torsion bars are designed to twist, axles are not. You're right, it's not rocket science but it's not a guessing game either. Next thing you'll be trying to tell the good folks here on the Gee that driveshafts must twist too because they look similar to torsion bars. And of course the mainshaft in the transmission must twist, how else will it absorb the torque? What nonsense. Do some research. Nuff said.

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Post by artificer » Sat Oct 28, 2006 9:57 pm

Mark Williams Enterprises......."This treatment provides an ultimate tensile strength of 225,000-253,000 psi along with exceptional ductility (the ability to change shape or form without breaking). The shaft surface hardness is about 50 Rockwell-far less brittle than an induction-hardened carbon steel axle. When these forgings are subjected to thousands of lb-ft, they twist and rebound like a torsion bar instead of snapping like a wishbone".

All axles twist in service and are designed to do so and there are lengthy papers available on this subject. They are also designed to break at a certain point to protect other component parts, something I mentioned many posts back regarding LandRover and the hemisphere failing because the axles were too good (ungiving).

Larry says:
"What nonsense. Do some research. Nuff said".
Larry do your own research, I did enough when I lectured in Automotive Engineering in the 70's. Just get over expert opinions you formed after building (or looking on and helping others to build) a few hot rods and probably reading some magazines written by career journalists.
As well the wheel which has less load looses traction first....doesn't matter what side it is on. And your description regarding differential action is faulty. Additionally you are right, drive shafts do twist and they don't look anything like torsion bars........surprise, surprise!!!

David sorry your post was hijacked. You have some good info from a number of reliable sources in reply to your boken axle questions and you are back on the road. Great.
Last edited by artificer on Sun Oct 29, 2006 11:14 am, edited 1 time in total.
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Post by Remko » Sun Oct 29, 2006 5:33 am

Hi,

photo's look very familiar (could be mine)... i had it back in 1998, same result.

it happened while goiing up a hill low gearing 4wd, not completerly reaching the top and pushed the clutch.... stumbled down and while going down, my foot slipped of the clutch... my luck only the rear broke (could also be a front axle to break which is a lot more difficult to change.

had to take the diff apart to get the pice out. at first i tried to tap it out from the other side with a broom but no effect, (center-pin of the diff made it impossible).
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Post by sergio » Sun Oct 29, 2006 2:16 pm

JAB wrote:Which wheel slips on an "open" rear-end is determined by the load/traction condition, not which side it's on. It is a length thing as all other factors are essentially equal from the mechanical standpoint.
You guys are something. You don't seem to be able to distinguish between cause, effect and correlation. Which side it's on is what determines it's load/traction condition!! I can imagine you attending a basketball game and concluding that bouncing a ball on a hardwood floor makes you tall.

It's very big of artifical to allow Larry his opinion, especially since Larry's 100% correct. For every action, there is an equal and opposite reaction. It's that simple. As Larry said, the right rear wheel drives in opposition to the rotation of the engine. If the engine spun the opposite way, the LR wheel would drive. Prove it to yourself by doing a burnout in reverse. Watch a drag race and see how the chassis reacts. Upon dumping the clutch the car torques to the right, loading the RR wheel and in a perfectly set-up chassis, lifting the LF wheel to show a peek of daylight under the tire. (RR wheel down, LF wheel up; another equal and opposite torque reaction.) Watch his video:

http://www.dragstuff.com/techarticles/v ... nsion.html

Then go to: 69 Camaro Launch - Slow Motion Video

See how the rear bumper starts out (almost) perfectly level and then lifts on the left side as the car launches. That is the reaction to driveline torque that loads the right side. This is why which side it is on matters. The bumper is actually out of level a bit even at rest because the chassis is tweaked a little from previous hard launches. The next step in the progression for unibody cars like the Camaro is for the body to become so twisted that the doors cease opening and closing and eventually, on a hard launch, one day the rear window breaks.

That brings up the next point; artificial's claim that everything that gets twisted is a torsion bar; sooo wrong. An axle is not a torsion bar,no matter how many ditties he finds from other uninformed folks that say it is. Your axle is not a torsion bar, your driveshaft is not a torsion bar, your crankshaft is not a torsion bar and the unibody of that Camaro is not a torsion bar, no matter how you may twist them and wind them up. As someone else said the design and metallurgy of a T-bar are entirely different. Your axles, driveshaft and crankshaft, despite being torqued are engineered to resist those forces completely, not to work within a range to exert them. Look also at the dfference in the nature of their failures, T-bars just stop holding a car up and rarely break, axles, driveshafts and crankshafts twist very little before they break. In fact, the way to predict driveshaft or axle failure is to paint a line on them when they are new and then use the line to measure the degrees of twist. The acceptable range is in the low single digits of degrees whereas some T-bars can be turned nearly around and still be within their elastic range.

As far as axle failure being a length thing, it is but the length hurts you, not helps you. Don't think so? Try to find slat grille scalloped axle shafts. You'll find 10 short ones for every long one. Think of the extreme case; shorten the axle to where it doesn't exist, bolt the diff directly to the hub, no axle, no failure.

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Post by artificer » Sun Oct 29, 2006 3:11 pm

Too smart for your own good Serpico, go back to the political clap trap where you are a master of the outrageous.
Of course there is a torque reaction provided there is good wheel traction then the engine will try to rotate around itself especially if you are still doing wheelies or burnouts at your age.
This twists the frame/chassis hence wheels lifting off the ground and all that other stuff, which relates to loss of traction as the wheel is spinning and not transferring drive effort to the frame.
Common sense unless you're still trying to destroy diffs and axles reliving your youth doing rollbacks, indeed!
Then again you are an extremely literal animal.
Axles aren't torsion bars, in the literal sense but they certainly act like one, are designed to and do twist as you allude to later by drawing lines on axles in your nebulous argument.
It is my belief Mark Willams Enterprise are not some "uninformed folk" But we all know there are some that can and do plus other commentators who don't and can't.
I'll stick to my guns and you should watch out for your foot if you are handling that weapon again.
Axles function like a torsion bar
The wheel with less traction will spin first
And the short axle in Jeeps is most likely to fail (all other things equal)
Last edited by artificer on Sun Oct 29, 2006 5:20 pm, edited 1 time in total.
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Post by sergio » Sun Oct 29, 2006 3:40 pm

artificer wrote:Of course there is a torque reaction provided there is good wheel traction
No, if there is torque there is a reaction. Doesn't matter of there's good traction or bad. The reaction is in response to torque, not in response to traction or the lack thereof.
then the engine will try to rotate around itself especially if you are still doing wheelies or burnouts.


God only knows what this means.
Axles aren't torsion bars,
I know, that's what I said.
...are designed to and do twist
No, they are designed not to twist. The fact that they do twist in spite of that means they have a finite lifespan.
This twists the frame/chassis hence wheels lifting off the ground and all that other stuff, which relates to loss of traction as the wheel is spinning and not transferring drive effort to the frame.


God's territory again here.
Common sense...
There is no such thing as common sense, it is implied empirical knowledge.
But we all know there are some that can and do plus other commentators don't and who can't.


Yes, I agree, it has become painfully obvious that whatever you may have done was totally by rote and without any understanding whatsoever of what you were doing or the principles involved or being applied. But it's never too late to learn...
The wheel with less traction will spin first
Not true. The wheel with less traction relative to the drive being applied will spin first. If a wheel, say the RR, has more traction but even more force being applied, it will spin first.
And the short axle in Jeeps is most likely to fail
All things being equal, a longer axle will snap first.

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Post by iowa » Sun Oct 29, 2006 4:35 pm

there was an interesting artical
in the latest JP magazine about
axle strength.
they stress them until they break!!
there is a pic of a whole row
of broken brand new axle shafts!!
i know it meant for later jeeps
but thot it might interest some.
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Post by artificer » Sun Oct 29, 2006 5:11 pm

Serpico:
Semantics is your forte, it's all yours. Bye.
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common nonsense

Post by Chuck Lutz » Mon Oct 30, 2006 11:00 am

Gee, can anyone play in this sandbox? You got experts, he got experts, so what? The term "common sense" was bantered about so I guess a shade tree mechanic like me can use MY common sense here also.

1) Traction Bars: Used by hot-rodders to keep BOTH wheels on the ground and avoid spinning the tires and thereby wasting power that could be used to get your car down the track...

OK, as I get it, you could even pre-load them with DOWNWARD force as you attached them. Still, as you took off from the line, that spinning (or wheel-hop?) wanted to happen but the traction bars prevented it. In doing that, the traction bars would distort and twist and GIVE a little, but still effectively keep you from burning rubber and wasting time getting going. The design of them ALLOWED for some twist and distortion.

2) Axels: Designed to NOT twist, since in doing so that leads to failure. The fact that they DO twist somewhat, is what they designers are trying to avoid. They are trying to avoid it because they will BREAK if they twist at some point. The metalurgy of them is designed to NOT break or they'd be breaking them all the time....but they DO give and once they start to give theny will eventually snap. Don't confuse the fact that what the designers are trying to AVOID with what can happen (twist & failure).

I don't buy that the axels are DESIGNED to twist, on the contrary, we know if they DO twist, they will fail. So if the whole point here is to avoid twist & failure, then the axel can't be compared to the TRACTION BAR whose very design enables it to twist & NOT fail.

I disagree with one thing though....it was stated that there is no such thing as common sense, that it is implied impirical knoweledge.

Actually common sense is empirical knowledge....but the definition is correct.....derived from observation or experimentation. Not something you are born with or that fell out of the sky or you picked up at COSTCO. So Common Sense....does exist.

So can anyone explain in detail why we find an extrordinary number of one size axels and not of the other size axels? If both were made in the same quantities, then the disparity between the number of one over the other these days would tend to make you think that one size had failed in a disproportionate number to that of the other size...

But then that would be common sense telling you one size had a higher failure rate over the other unless other information was available. All the engineering, metalurgy and physics aside....this would be pretty "definitive" wouldn't it? (God I love that word...)
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Post by artificer » Mon Oct 30, 2006 1:09 pm

In the interests of quality information and I will not take up any more space than necessary on David's post:
Mark Fenning U of Qld 2002 Extract from paper presented:
"1.6 Torsional Stiffness
The axle driveshaft (refering to axles not tailshaft) in any vehicle serves as a relative torsionally elastic member and in it's simplest form is a torsional spring connecting two masses each of which have a relatively high rotational inertia."

QED and no need for the Holiday Inn Express.
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???

Post by Chuck Lutz » Mon Oct 30, 2006 3:48 pm

Let's just see if we can try to all actually understand what the guy that wrote a paper for U/Qld was saying....since we don't have the entire artlcle in front of us we are at a distinct disadvantage in terms of understanding the CONTEXT in which the sentence offered is.

So, while he isn't discussing the axel shafts at all, as mentioned should we even give any credit to the statement the gentleman made? Well, as pointed out previously by another poster who seems to understand this pretty well, this is comparing apples to oranges.

BUT, since it is offered as some sort of PROOF.....let's give it a go.

1) He's discussing "Torsional Stiffness"...OK, wood has torsional stiffness. Bone has it, axels (or driveshafts, whatever) have it. Titanium steel has it. Some items have more torsional stiffness than others, obviously, it takes more force to twist the end off an axel than it does to twist the end off a stick. Or to twist a human leg bone enough to splinter it in the middle....still that is torsional stiffness being demonstrated.

2) TORSION....defined as: a) twisting or turning, b) the stress caused when one end of an object is turned in one direction and the other end is held motionless or turned in the opposite direction.

OK, Mr. Fanning has just made a statement that the DRIVESHAFT is a:
1) RELATIVELY torsionally elastic member.
2) ...is in it's simplest form is a torsional spring.
3) ...that connects two masses that have rotational inertia.

So it would seem that when the wheels are stopped and the clutch is released and power applied....that
1) The driveshaft actually gives somewhat as power is applied.....OK, we don't know what his definition of RELATIVELY is....are we talking millemeters of elasticity or microns?
2) The "tortional spring" he speaks of....by that are we to assume that the metalurgy of the driveshaft allows some TORSION (twist) before it's spring characteristics take over and it compensates by catching up to the revolution/force of turning? I would think so or it would not exhibit any "elastic" properties.
3) "Rotational Inertia"....inertia: a) the tendancy of a body to resist acceleration; b) the tendancy of a body at rest to stay at rest or a body in motion to stay in motion in a straight line c) resistance to motion, action or change.......OK, by this definition we understand why the axel in your jeep BREAKS by virtue of both "A" and "C".

So, what have we learned here....

1) Mr. Fanning has reminded us that even the driveshaft has "torsional" issues and by the definition of that word we know that TORSION occurs to all objects subjected to the situation described....anything can exhibit it.

2) The driveshaft exhibits a SPRING like effect. I certainly can find no fault with this reasoning and would agree that even the AXEL will exhibit the SAME effect.....up to the point where it FAILS and breaks.

3) That "Rotational Inertia", as defined, is why the axel breaks and why any component subjected to "torsion" can and will at some point fail if the stress point is reached.

So Mr. Fanning's sentence seems perfectly clear to me and certainly supports the idea that while the AXEL is not designed to twist and break that since it is subjected to "TORSION", once it's SPRING characteristics or tendancies have been stretched to the limit, "Rotational Inertia" will BREAK that axel.

Yep, I think Mr. Fanning has described the failure of your axel to a tee....thanks for posting this valuable scientific contribution.
Chuck Lutz

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Post by sergio » Mon Oct 30, 2006 4:22 pm

artificer wrote:Mark Fenning U of Qld 2002 Extract from paper presented:
Well, I suppose if you live your life by relative standards, everything is something it's not, relative to something that is even less so. I'm a giant relative to a midget and a midget relative to Shaquille O'Neil. So which am I? A giant or a midget? The reality is, I am neither.

So an axle twists more than the differential or the wheel/tire combo so compared to them, it's a spring.

I have an aircarft tug with no suspension, axles bolted directly to the frame. I suppose you would say that the tires function as a spring relative to the two hunks of steel bolted to each other but despite those "springy" tires, you still need to wear a kidney belt and be prepared to lose fillings when you drive it.

Who's Mark Fenning? What grade did he get on this paper? Maybe his teacher wrote on it, "D+, Mark, relative to the other kids on the short bus, who all got D-, you're smart."

JP

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Broken axels

Post by Ernie Baals » Mon Oct 30, 2006 4:50 pm

Hi Dave;
Glad to see that you are back on the road ( I am going to pretendall the post in the middle don't exist for now :lol: )
Axels braking are a common problem in the MBs and GPWs, also dodges WCs and M37s.,

Other than age and flat out abuse, larger and different tires can play a major role.
I know from my and a friends experience that when you run snow tires or even radials on a GPW it will brake axel shafts quicker that with non directionals. Always the short on too, but M37s always seem to brake the long ones.
the reason being, that on new snows or radials you have quite abit of tread in contact with the pavement and all times.
while with a non directional the foot print of the tire is much smaller.
there for the snow or radial won't slip as easy as an old non directional.

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