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Thread: so what causes an axle to break?

  1. #1

    Post so what causes an axle to break?

    i have heard everyone say "dont run that tire with that axle or it will break!" but what actually causes the break? Being too heavy on the gas? coming down too hard? Well, those are the types of things that i would think. So, here's what i need cleared up:

    Is a 4cyl or 6cyl more likely to break an axle? or doesnt it matter? Is it related to the amount of torque you have?

    If you have stock gearing with say 35'' tires, are you more likely to break 'em than if you have regeared the stock axle's with say 4.88's?

    would lockers increase your chance of a break?

    What terrain would most likely cause the break? Mud or rock crawling?

    I am still debating if i should go SOA or SUA, with 35's or 33's. I have a 4cyl with stock axles, and i have heard numerous people say that 35's will work fine and others say i'll have problems with 33's. So, just need to know what actually causes the break and what i will need to look out for! Thanks
    '00 TJ Sahara

  2. #2
    Geezer Jeeper Jerry Bransford's Avatar
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    Anything that causes the torque sent to that axle to exceed its normal rating will cause it to deform, twist, or break.

    An axle normally never sees more than 50% of the available torque. That's in perfect conditions. Put a locker on that axle with one wheel in the air, the axle connected to the wheel on the ground is now seeing 100% of the available torque... double what it's used to.

    Installing lower gears will increase the amount of torque sent to the rear axles. With 37" tires and 3.07 gear, you know that very little torque is being seen by the axles. Reverse that and install a Tera 4:1, 4.88 gears, and a small 33" tire, you can see that enormous increase in torque the rear axles would see. Add a locker to that equation where one wheel is getting all the torque because the other wheel is in the air and you can see it's a recipe for disaster.

    Limited slips usually don't cause much mischief because they seldom transfer more than about 30-40% of the available torque to the working axle, as opposed to a locker's 100%.

    It's all about balance. Too big of a tire is hard to turn so you apply a lot of torque to the axle to get you moving. Put small tires on with low ratio gearing and the torque could be enormous if it is suddenly transferred from both axles to one axle via a locker.

    There are a bunch of specific ways an axle can be broken, others will bring up all kinds of scenarios and guidelines.

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  3. #3
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    Well, i'm not going to tell you which combinations are most likely to break. But it seems like most of the times an axle breaks it's when someone is stuck and they're trying to "Gas it" out of the stuck, especially if the front end is bouncing, then you have sudden shock to an axle that is spinning free and then has weight on it when it lands. And I would say that when it comes to lockers, manual lockers specifically (ARB,OX) that if you engage it when one wheel is airborne and spinning fast allready your setting yourself up for trouble.

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  4. #4

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    btt, anyone else?
    '00 TJ Sahara

  5. #5
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    Its amazing how easily the Dana 35 can snap under the right conditions. I broke my 35C with 32" BFG MT's, 4.10 gears and a truetrac (6 cyl engine). It happened on a steep sandy hill climb. The sand was wet and offered great traction. Just as I was beginning to bog down there was a loud pop and the axle snapped.

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    It's all about your right foot

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