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Very interesting post this!
I haven't been unfortunate enough to break an axle yet; however; I always engage high-four whenever I drive on a loose surface, even if it is a well made road. Perhaps that is why I have escaped.
Aaron; can you explain why having FWD engaged will stop a bouncing rear axle from breaking?
Cheers Charlie
What breaks axles (or at least fatigues them so they break later) is torque/shock loading in low range offroad. If you never use the vehicle in low range offroad you will probably never have any problems.Quote:
Originally Posted by chazza
I have lost count of the number of series (10 spline) axles I broke - both in SWB or LWB vehicles. I was mechanically sympathetic, but would drive anything I thought I could (though with minimum wheelspin).
Unless you are really hammering them, they will usually only start to fail (plastically deform), and fail completely at a leter date. Half of them failed on-road - one while driving downhill!!!
My father hasn't used his 88" offroad for quite a while (apart from beach trips) - and hasn't broken any axles in years!!!
I know that bigger tyres increase the stress on axles. I didn't break any axles while my 2a was on 205s, but I've done three short axles since fitting 750s. I prefer the extra ground clearance, fuel economy and speed of 750s though.
Dan.
69 2a 88" pet4, 74 3 109" pet4, 68 2b FC pet6.
When you are driving along with an amount of throttle applied and a wheel leaves the ground (due to corrugations), it will accelerate it's angular velocity (spin faster). When the wheel comes back down and contacts the ground, it must decelerate instantaneously back to the speed required for the current forward motion. As this deceleration happens over a very brief period of time, the negative accelaration is very high. This imparts a high torque on the drive axle, resulting in it being repetatively stressed over time.Quote:
Originally Posted by chazza
If the front axle is engaged, any wheel that leaves the ground can not speed up. This is because the two wheels on the other axle are still in contact with the ground, and prevent the system (the back axle is linked to the front axle) from speeding up. This assumes that only one axle has a/any wheel/s off the ground at any one time.
This theory is not perfect, as there is an amount of backlash in the system. This does allow some amount of rotation between the front and rear axles, but overall, the damaging effect is reduced when the front axle is engaged on loose terrain.
I hope this helps.
Aaron.
Aaron
I thought that the bottom of the wheel was always stationary and it's only the rear half of the wheel that is accelerating while the top of the wheel is at double the velocity of the vehicle and the front half is decelerating?
Diana
P.S. Has that got anyone scratching their head! :) ;)
In my previous post, when I was talking about accelerating and decelerating, I meant angular acceleration and deceleration. This means increasing and decreasing the angular velocity (RPM) of the wheel/axle. I was not refering to linear acceleration and velocity.
Your anology about the bottom of the wheel being stationary, with the top of the wheel having twice the velocity of the vehicle is also correct, if you are looking at the instantaneous linear velocity of a small piece of the extremity of the tyre.
Ben, seeing as you are the Physics lecturer, check my work. I have only completed first year physics.
Aaron.
__________________________________________________ _______Quote:
Originally Posted by Olive Drab
I will sell a salisbury rear axle complete inc springs from a 109 and through in the tail shaft all for $220
Hodgo
The last one I broke was clutch starting my 109 in reverse on concrete in the driveway. Somebody must have left the lights on. This turned out to be a tuff day as I had already broken a front axle and had to get my brother with his landcruiser to push me back up the street and back into the driveway. i hate listening to toyota owners
I'm not surprised - if not the axle, something else was likely to go. Clutch starts should always be in top, or at most third; use anything lower and you risk damage to the axles, drive train and particularly gearbox, especially in first or reverse.Quote:
Originally Posted by Olive Drab
First or reverse will usually skid the wheels before the engine turns unless you engage the clutch very suddenly (using the rotational momentum of the wheels to help), which applies shock loads to the entire drive train. A very slow push or tow in top will turn the engine at cranking speed, and it will start unless there is an engine problem, just declutch as soon as it fires. This does not require sudden engagement, and will not apply an unfair strain on the gearbox as will using a lower gear.
John
I am not a physicist - just an engineer - buy i do claim from time to time to be a physical chemist...Quote:
Originally Posted by Aaron IIA
There are 2 different scenarios (assuming open diffs front and rear).
(a) You lift 1 wheel in 4x4, but have sufficient momentum/traction to maintain forward velocity/motion.
(b) you lift 1 wheel, and at least 1 wheel on the other axle has insufficient traction to maintain forward motion.
Case b is easier. The wheel that lifts off the ground will start to spin at DOUBLE the rotational velocity (rotate twice as fast). e.g. for a 4.7:1 diff, it will suddenly rotate like a 2.35:1 diff. This exacerbates the problem. Since 2 wheels are now spinning at 2.35:1 (quite fast) - the shock loading when the wheel returns to the ground can break something - as the wheel must come to a dead stop. A wheel on the 2nd axle doesn't need to lift, just have sufficiently low traction to spin (compared to the alternate wheel).
case a - the wheel that lifts will still turn twice as fast as the other 3 - since the other wheel on the same axle will be effectively receiving NO DRIVE. However, when it comes back to earth, the shock loading won't be as high.
I don't think you could ever break anything (in a 2.25P/D) by driving dirt roads in high range 2wd.
dandylandyman and JD:
High loads when reversing are very hard on old axles which have already been stresed in the forward direction. It was always a joke with thye comp vehicles running GQ axles and 35's. They could sit at the redline going forwards and not break a thing. As soon as they had to reverse - snap - broken CV stub.
As I mentioned earlier - I once broke an axle in an 88" going downhill. I had just turned a corner and I think the slight loading in the reverse direction (due to diff action) was enough to finish off an already doomed axle.