Interesting Trail Fix...?

[harriw]

Hey folks!

I've been staring at this and thinking for an hour now, and just had to post this:

http://thereifixedit.failblog.org/2...-true-craftsman/comment-page-1/#comment-73417

Some of the comments are just ridiculous, but there's plenty on the right track too (and some real gems too - any excuse to bring up the zombie appocalypse works for me). Seems to me it's a trail fix just to get 'er home, as plenty have suggested. Here's my question though (the "Bill" comment at the bottom is me):

Here’s my question: the whole point of an open diff is that it allows the wheels of one axle to spin at different speeds as you go around a turn, reducing tire wear (outer wheel wants to spin faster than inner wheel). This also means if you hold one half shaft stationary (like the wrench is doing), the spider gears in the diff. will force the other shaft to spin twice as fast, right? So your front axle will spin twice as fast as your rear, pissing off your Transfer case. You might be OK in the muck, but once you hid solid ground, something would give. SO… what are the chances his rear is shot too, and this is actually a ONE wheel drive trail fix???

So did I go horribly wrong somewhere in my thought process? Or am I right that his pass. side front wheel will be spinning twice as fast as his rear axle?

disclaimer: I keep my truck on pavement so I don't pretend to be an expert in such matters, and am neither praising nor criticizing what's pictured here - I just had way too much fun noodling over this, and thought I'd share.

Thanks, and enjoy!

-Bill

 

[cammeddrz]

if you hold one half shaft stationary the spider gears in the diff. will force the other shaft to spin twice as fast, right?

uh no......i really don't know where to begin to point out the flaws in that but here goes: spider gears just allow power to be transfered to one half-shaft or the other. whichever has least resistance. the speed at which the half shaft is turned is not doubled just because one wheel is locked. the speed stays the same.

but even if this was correct and it somehow turned that shaft twice as fast (which it doesn't) and he was correct (which he's not) that this phenomena would be due to the spider gears. it would not "piss off the transfer case" because the spider gears are "after" the ring and pinion in relation to the t-case so there would be zero feedback to the t-case anyway.

and another hole in this whole "pissing off the t-case" scenario is that the t-case would be the one propelling the shaft, as opposed to the axle shaft turning the t-case. the only way that it would "piss off the t-case" would be if there were some outside force trying to turn the driveshaft (not axle shaft) "twice as fast" as the rear driveshaft.....yeah, that'd "piss off the t-case"

now all that being said, based on my understanding of spider gears. if you wanted to create such a situation to get one side to spin twice as fast. would be if you were somehow able to turn one half-shaft backwards at exactly the same speed multiplied by the gear reduction to equal the speed of the drivshaft. the other half-shaft might possibly turn twice as fast. but the speeds would need to be exactly equal

 

[gwaii]

uh no......i really don't know where to begin to point out the flaws in that but here goes: spider gears just allow power to be transfered to one half-shaft or the other. whichever has least resistance. the speed at which the half shaft is turned is not doubled just because one wheel is locked. the speed stays the same.

but even if this was correct and it somehow turned that shaft twice as fast (which it doesn't) and he was correct (which he's not) that this phenomena would be due to the spider gears. it would not "piss off the transfer case" because the spider gears are "after" the ring and pinion in relation to the t-case so there would be zero feedback to the t-case anyway.

and another hole in this whole "pissing off the t-case" scenario is that the t-case would be the one propelling the shaft, as opposed to the axle shaft turning the t-case. the only way that it would "piss off the t-case" would be if there were some outside force trying to turn the driveshaft (not axle shaft) "twice as fast" as the rear driveshaft.....yeah, that'd "piss off the t-case"

now all that being said, based on my understanding of spider gears. if you wanted to create such a situation to get one side to spin twice as fast. would be if you were somehow able to turn one half-shaft backwards at exactly the same speed multiplied by the gear reduction to equal the speed of the drivshaft. the other half-shaft might possibly turn twice as fast. but the speeds would need to be exactly equal

actually the op is right.give it a try,get a spare diff from the scap pile and hold one end.the other end will turn twice the ring/pinion ratio for every turn of the pinion.that's how spider gears work.
any time the two wheels are turning different speeds the total of their speeds will be twice the ring gear's speed.
if the ring gear is held still,and one tire is turned forward,the other will turn backward the same speed-for a total of zero-the ring gear speed times two.
if both wheels are going the same speed,they will have a total of twice the ring gear speed(each is going the ring gear speed-there's two of them)
if one wheel is going 1.3 times the ring gear speed,as in a corner(outside wheel) the other will be going .7 the ring gear speed...so it adds up to two.

if one wheel is not turning,the other will go two times the ring gear speed.

try it.

 

[kimcrwbr1]

Is it me or wouldn`t just unlocking the hubs take the stress off of the transfer in 4WD the differential will still take a beating not to mention the u joints flopping around not being under a load.

 

[harriw]

Thanks you Gwaii for confirming I'm not crazy

cammeddrz - I'm sticking to my guns on this one: pinion gear spins the ring gear. If load on both wheels are the same, spider gear stays stationary, spinning both output halfshafts at the same speed, right? When you turn, the difference in turn radius between the inner and outer wheel makes them want to spin at difference speeds (due to contact with the ground). This is made possible by the spider gear turning slightly inside the diff, allowing differenct speeds for the two output shafts. As Gwaii pointed out, this can be seen by holding the input shaft still (just jack up the front of your truck (both sides) - the engine will hold the input shaft in place for this test). spinning one wheel will force the other to spin backwards - since the ring gear is not spinning, the spider gear has to. This makes the other wheel spin backwards.

So if one wheel is held still while the input shaft turns, the stationary half shaft will force the spider gear to spin as the ring gear (and the entire carrier) spins. With the spider gear spinning in this direction as the carrier spins, the output speed of the other output shaft will be doubled. Right?

it would not "piss off the transfer case" because the spider gears are "after" the ring and pinion in relation to the t-case so there would be zero feedback to the t-case anyway.

I'm refering to the fact that when going in a straight line on dry ground, contact with the ground makes both axles want to spin at the same speed (assuming same size tires, etc., etc.). If the T-case and differencial are making one axle spin twice as fast, it's going to bind. Either you'll hop all over the place as the front wheel slips and sticks, or you'll tear apart the T-case and/or something else along the drivetrain. Right? Same reason why you don't turn on dry ground with old-school 4x4 (U-joints) on.

Thanks.

-Bill

 

[kimcrwbr1]

The one front wheel will want to turn twice as fast as the rear wheels you have to unlock the hub or somthing will break as in transfer driveshaft or diff.

 

[kimcrwbr1]

Or craftsman wrench

 

[cammeddrz]

try it.

i shall

so if a car is doing a burnout with a 1-tire-fire, that one wheel is rotating at twice the speed as the d/s input would normally create

and as the car slowly accelerates towards the speed that the wheel is turning, that single wheel will simultaneously decelerate until the opposing wheel accelerates to half the speed the first wheel originally turning?

so if i power braked a car with an open diff and held it so the speedo read 30 mph: the one wheel would spin at 60 mph until i released the brake.
at which point that wheel will literally slow down (as the car speeds up) from 60mph to 30mph as it got more traction?

 

[country0001]

Further on down in the comments, someone had mentioned that it was just to hold the axle in place. It wasn't even a trail fix.

 

[heptofite]

i shall

so if a car is doing a burnout with a 1-tire-fire, that one wheel is rotating at twice the speed as the d/s input would normally create

and as the car slowly accelerates towards the speed that the wheel is turning, that single wheel will simultaneously decelerate until the opposing wheel accelerates to half the speed the first wheel originally turning?

so if i power braked a car with an open diff and held it so the speedo read 30 mph: the one wheel would spin at 60 mph until i released the brake.
at which point that wheel will literally slow down (as the car speeds up) from 60mph to 30mph as it got more traction?

yes, exactly this.

 

[The_Dealer]

would craftsman still replace this under warranty??

 

[gwaii]

i've found that while they are mechanically simple devices,open differentials are one of the most misunderstood parts of a vehicle.
it drives me nuts when you hear people talking about putting in a locker so they can 'get equal torque to both wheels'....a locker allows exactly the opposite.
an open differential will ALWAYS have equal torque at both wheels,a limited slip will allow a difference in torque in an amount equal to the clutches friction force,a locker will alow a torque difference equal to the available traction and the engine's abillity to produce torque.

 

[cammeddrz]

people talking about putting in a locker so they can 'get equal torque to both wheels'

i've never heard that one, i thought it was obvious that locking the wheels together (with an l/s, locker, or spool) is a matter of traction not torque right?

 

[gwaii]

you want to hear that one,watch powerblock on sundays.

love the shows,but that's a common mistake there,as it is elsewhere.you've never heard anyone referring to 'the driving wheel' in an open diff?or calling it a 'peg leg' because only one wheel is driving it?

even if one tire is spinning,the one that isn't spinning is pushing the vehicle with exactly the same force as the one that is.

 

[cammeddrz]

watch powerblock on sundays.

actually i tune in to comedy central to get my comedy......

the powerblock is propaganda, bought and paid for