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Old August 13th, 2012, 08:01 PM   #1
cerial
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Default Stupid traction question(s)

First off let me say I have never tore into and wont pretend I know anything about transfer cases.

If you have a old school jeep with a Dana 20 transfer case and the hubs engaged in 4wd Hi driving lets just say 55 on a country road coming up on some rail road tracks.

What happens to the power when you hit the railroad tracks and one of the axles goes into the air before coming down?

Is there any feedback or is that loss simply transmitted through the tires?

Is it transmitted into the LSD? What if for some strange reason Both lockers were engaged?

Is there a clutch type "thing" in the transfer case to prevent tearing up the gears when the front drive shaft stops suddenly with the rear still spinning at full speed?

Or is all that feedback sent back to the transmission's clutch or torque converter?

The reason I ask is if there is a "clutch type thing" in the transfer case it will require a little design tweaking. It is not a big thing if I catch it now. But, if it will prevent me from grenading my Brown Lipe aux trans (which is between the trans and transfer case) it is worth asking.

Thanks for any help.
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Old August 13th, 2012, 08:12 PM   #2
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With a standard 4wd t-case the front and rear driveshafts are going to spin at the same speed no matter what.
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Old August 13th, 2012, 08:46 PM   #3
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Quote:
Originally Posted by cerial View Post
First off let me say I have never tore into and wont pretend I know anything about transfer cases.

If you have a old school jeep with a Dana 20 transfer case and the hubs engaged in 4wd Hi driving lets just say 55 on a country road coming up on some rail road tracks.

What happens to the power when you hit the railroad tracks and one of the axles goes into the air before coming down?
the wheels keep spinning

Is there any feedback or is that loss simply transmitted through the tires?

Is it transmitted into the LSD? What if for some strange reason Both lockers were engaged?

Is there a clutch type "thing" in the transfer case to prevent tearing up the gears when the front drive shaft stops suddenly with the rear still spinning at full speed?
Your U-joints work pretty good as a weak point. No clutches or anything that I know of.

Or is all that feedback sent back to the transmission's clutch or torque converter?
Feedback is sent through your drive line

The reason I ask is if there is a "clutch type thing" in the transfer case it will require a little design tweaking. It is not a big thing if I catch it now. But, if it will prevent me from grenading my Brown Lipe aux trans (which is between the trans and transfer case) it is worth asking.

Thanks for any help.
I will take your brownie box off your hands if you are worried about it. Honestly though, I have money to spend else where.

See above for some info. Transfer cases like the D20 just split the power between front and rear, they also give you gear reductions.

Last edited by Coyote Red; August 13th, 2012 at 08:49 PM.
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Old August 13th, 2012, 08:54 PM   #4
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I have just been reading up on the Torsen differential for days now and wondering if there was something similar clutch wise used in old school transfer cases.

One less thing to replace I guess.

Thanks for the info.
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Old August 13th, 2012, 09:46 PM   #5
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A dana 20 is just a fixed gear drive, both axles directly coupled together, and coupled to the transmission.

Dont think its a 50/50 split, thats a overly simplified way to think about it.

You are going 55mph, so the only power is that needed to keep the car at speed (wind resistance + parasitic drag).

It doesn't matter if that total force is spread across 4 tires or 2 or whatever, it doesn't change the output of the engine/transmission.

So in the over simplified model, say you needed 20 horsepower to move down the road at 55, perfect equal traction, you've got each wheel putting 5 hp to the ground. So, if the front tires go up in the air, then the rears will put down 10hp each.
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Old August 14th, 2012, 09:07 PM   #6
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The rail road example was not the best one. I was thinking in terms of shock load feedback. Such as your stuff a tire against a tree but the rear axle is on pavement or some other surface which would give good traction and load up.

If you had say beefed up locked 5 ton axles and 1450 joints the transfer case output shaft would twist/break once the front axle suddenly stopped and the rear kept trying to move?

Seems there would simply be a loss of friction at the rear wheels causing them to spin in that case. But, for some reason I kept thinking in terms of some kind of center diff in the transfer case that would remove power from the front and apply it to the rear to avoid breaking the output shaft or separating the case itself.

Over thinking stuff again I guess. Stuff the front wheel into a tree and the rear wheels will just spin gotcha. No need for any over engineered center diff/clutch BS system.

Thanks for the input.
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