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I would like to know exactly what the guy at the Ford shop meant by break the front axle. I'm not sure his understanding of mechanical forces, or engineering statics, was accurate. He may have been speaking from just expearence. So the reason an axle broke may not have been what he thought was the reason. I'll try to explain so you can understand what things are important. Here is how it works. The weight of the loader, tractor, etc. that is held up by the front axle ALL must be carryed by the front axle pin. Widening the front wheels does NOTHING to change that weight. Assuming the wheels are the SAME distance from the axle pin, they both carry half the total weight on the axle pin. NOW if you set one wheel to the 72" width position and the other to the 48", the closer will carry a greater proportion of the weight. But the axle pin still has the SAME weight on it. When you reach the point where one wheel is "in a hole" so it is not touching the ground, then and only then will ALL the weight (obviously) be carried by the remaining wheel. NOW if ALL the weight STILL were passing trough the axle pin, then there is an unbalanced torsional force set up WHICH IS NOT ALLOWED! SO, the weight is transfered from the axle pin to the axle stop. That is ALL the weight that was on the axle pin!! That is because the stop is in between the wheel and the axle pin. The axle pin now actually pushes up on the axle, to keep it from pulling out of the front of the tractor. The force of the wheel and the axle pin is up and balances the force of the loader and tractor being applied down at the axle stop. All forces are balanced so things are "static" - unbalanced forces cause acceleration and things to MOVE! So it is no wonder that the axle stops are a little bent. They were subjected to the whole front end weight. AND that weight was most likely not applied slowly, rather BANG! like a hammer blow. Now to be complete, I must say that widening the axle WILL put added stress on the axle between the wheel and axle pin. Think of it this way. If you were to make a cut thru the axle half way between the wheel and the axle pin, what forces would you have to apply at that point to keep the tractor in balance. First you would need a upward force equal to the force on the wheel that the ground provides. BUT now that force is only half the distance to the axle as before. Now you have an unbalanced torsion force - force times the distance equals torque. The torsion force is balanced by a force at the top of the axle pushing (compression) and an equal force at the bottom of the axle pulling (tension). An example of this would be when you break a stick, the one side is compressed and the other is pulled. Usually the pulled side will break first. But sometimes before it does you can see the compression side bark bunch up as it is pushed together. Therefore, with the axle spread out the half way point is further from the axle pin and thus a greater torque is created. Given the size of the front axle AND the fact that the overlap section is right where the half way point is, I don't think that will be the "weak" point of the axle. Regards,
Larry ps. Since I took Engineering Statics twice - had to, fluncked first time - Nailed it second! - I can do force diagrams in my sleep. :-)
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