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post #11 of (permalink) Old 01-07-2005, 10:11 AM Thread Starter
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Re: Drunken Gear Ratio Torque Physics Question

The question wasn't realy directed at a mog axle. I was looking at drive shaft options and the oversized u-joints in my axle shafts compared to the common 1310 drive-shaft joints. This setup is going to be opposite of what I'm used to seeing with 260x joints up front.

I don't understand how a later gear reduction would effect the torque on a prevoius component. But that dosen't seem to be our real world experience, does it.

Which u-joints would be in the most jepordy of breaking?
The ones between the tranny and divorced transfer case?
The ones between the transfer case and axle?
Or the axle shaft joints?

Do the drive shaft joints need to be larger than the axle-shaft joints? (I mean, that's the way thay show up from the factory)
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post #12 of (permalink) Old 01-07-2005, 11:40 AM
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Re: Drunken Gear Ratio Torque Physics Question

well theres a lot of stuff at play in these types of situations.

the reason a U joint sees more torwue after a gear reduction is that a gear reduction works as a torque multiplier. If you engine has 100ft/lbs of torque, and your first gear is 4:1....then at the output of your tranny you can measure 400 ft lbs of torque....neglecting the friction of gears and other loses. that means that any component after the gear reduction will see 4 times the load as before the reduction. this is why we never really have to worry about beefing up the output shaft of the engine.....unless we run insane amounts of power theres no need to worry, we just build up the drive train to handle the insane gear reductions

the reason a guy with higher gears blow Ujoints is because of the dynamic loads on his drivetrain.....this is how i managed to Explode a D35 with a stock 4 banger. spinning the tires, spinning the tires...then they suddenly caught....Blamo! no more d35...i dont miss it.

The U joint in your driveline thats the most vulnerable assuming they are all the same size, would depend on the ratio of your gearing to your tire size. A big tire, as we all know, cancles out the effect of the low gearing in your differential as far as torque applied to the ground is concerned

let pretend we have 2 jeeps with identical drive trains....except one has portal axles for a total of 4:1 gear reduction (2:1 in the Dif, and 2:1 in the portal) in the axle....and the other has a regular axle for a total of 4:1 reduction in axle dif .....both axles have same size shafts etc.........if we had a situation where the tire was NOT MOVING...no slip at all....frozen in mud from getting stuck last night..... and you gassed it realllllly hard and then let go of the clutch (no clutch slip...this is a perfect world). the portal axle ujoint would have a better chance of living than the U joint on the normal axle. because it will see half the torque that the conventional axles ujoint will.

in my crazy lil engineering world the axle U joints have to be tougher. but by how much depends on the tire size and all that
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post #13 of (permalink) Old 01-07-2005, 05:43 PM
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Re: Drunken Gear Ratio Torque Physics Question

[img]images/graemlins/tongue.gif[/img] FUDD nailed it for you.......as RPM goes up, torque goes down. Taking the last bit of reduction in a planetary hub like the off road machinery usually does, is a way of keeping the drive train components smaller and cheaper. Interestingly enough, MERCEDES trucks have done that for years with a spur gear reduction at the ends of the axle. Their axle shafts actually turn backwards from normal because of that set of gears......leave it to the Germans to have something like that. [img]images/graemlins/crazy.gif[/img] FARM TRACTORS had the differential UP-RATIO from the rear axle and that way they didn't blow the spiders out so easily. The differential fed into two spur gears and those gears turned the big bull gears that were splined to the tractor axles. [img]images/graemlins/tongue.gif[/img]
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post #14 of (permalink) Old 01-07-2005, 07:08 PM
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Re: Drunken Gear Ratio Torque Physics Question

oh yea.....

The axles for the Big Huge monster wheel loaders that Caterpillar makes also have Planetary hubs to reduce the size fot he shafts.....so you know they gotta be beefy :-)
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post #15 of (permalink) Old 01-08-2005, 06:46 AM
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Re: Drunken Gear Ratio Torque Physics Question

[img]images/graemlins/smile.gif[/img] As if your brains weren't fried enough, here is another question for you...... "What is the DISADVANTAGE of taking a tremendous reduction in the rear axle of a conventional vehicle? (not a planeteary hub) Heck, why not take ALL OF THE REDUCTION THERE?" [img]images/graemlins/tongue.gif[/img] Cut your brain loose......let it float.....and really think about the question. [img]images/graemlins/tongue.gif[/img] Imagine yourself as a pinion gear in order to find the answer to the question. [img]images/graemlins/crazy.gif[/img] If you give the correct answer, you win permission from the "Dictator For Life" to continue spending every dime you have on Jeeps. [img]images/graemlins/wink.gif[/img]
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post #16 of (permalink) Old 01-08-2005, 11:27 AM
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Re: Drunken Gear Ratio Torque Physics Question

well i dont know if this is the answer you're looking for.....

but w/o thinking to hard if you just had a regualr Ring and Pinion....

The Gears would have to be HUGE! or your pinion would have to be teeeny tiny small.

theres a limit to the number of teeth you can cram on a gear before you cant gear it any lower...so i assume if you did a 40:1 or 50:1 you'd have about zero ground clearance


im sure thats not what you were looing for, but i just woke up so im not gonna think too much...got a clue as to what direction you're thinking with this
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post #17 of (permalink) Old 01-09-2005, 05:47 AM
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Re: Drunken Gear Ratio Torque Physics Question

[img]images/graemlins/wink.gif[/img] You are rubbing up against the answer; it is because the speed of the pinon gear relative to the ring gear gets to be so high that you can burn out the rear axle gears very quickly. Also as the ratios get lower and lower approaching 5:85 to 1 for example, the pinion gets smaller and smaller until it can no longer carry the amount of tooth contact area needed to transmit the HP. So having a low geared rear axle is good for the rest of the drive train, but then you have to Pay the Piper with that tiny pinion and not enough tooth area touching to hold the pressure. [img]images/graemlins/crazy.gif[/img] Back in da fifties when the Double-Rocker Chrysler hemi engines were the King of the Road, we put lots of them in trucks, but the drawback was the lower rear axle gears that were required, and the subsequent high pinion speed which led to a shortened gear life. But oh how those early hemis did run!!! [img]images/graemlins/cool.gif[/img] [img]images/graemlins/cool.gif[/img] [img]images/graemlins/cool.gif[/img]
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post #18 of (permalink) Old 01-09-2005, 05:47 AM
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Re: Drunken Gear Ratio Torque Physics Question

[img]images/graemlins/wink.gif[/img] You are rubbing up against the answer; it is because the speed of the pinon gear relative to the ring gear gets to be so high that you can burn out the rear axle gears very quickly. Also as the ratios get lower and lower approaching 5:85 to 1 for example, the pinion gets smaller and smaller until it can no longer carry the amount of tooth contact area needed to transmit the HP. So having a low geared rear axle is good for the rest of the drive train, but then you have to Pay the Piper with that tiny pinion and not enough tooth area touching to hold the pressure. [img]images/graemlins/crazy.gif[/img] Back in da fifties when the Double-Rocker Chrysler hemi engines were the King of the Road, we put lots of them in trucks, but the drawback was the lower rear axle gears that were required, and the subsequent high pinion speed which led to a shortened gear life. But oh how those early hemis did run!!! [img]images/graemlins/cool.gif[/img] [img]images/graemlins/cool.gif[/img] [img]images/graemlins/cool.gif[/img]
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