centre diff lock Q

[SteveG]

if you remove the front propshaft and lock centre diff lock. The diff lock will divide the torque equally between both front and rear outputs whether there is a load or not. Therefore the front propshaft will receive 50% of the torque.

True or False. If false give your reasons

Cheers

Steve

[white90]

if you remove the front propshaft and lock centre diff lock. The diff lock will divide the torque equally between both front and rear outputs whether there is a load or not. Therefore the front propshaft will receive 50% of the torque.

True or False. If false give your reasons

Cheers

Steve

I was under the impression torque is the force req to overcome resistance, with no front prop there is no resistance so the rear will get all the available torque applied.

[Diff]

Without the front prop fitted, but with the diff locked, there is nothing for the torque to turn at the front output flange, so 100% of the engines torque will go to the back wheels/axle.

If you think about it like this: You don't lose half the vehicles ability to pull a trailer up a hill just because you took the front prop off and locked the diff.

Hope this helps,

Regards, Diff

[SteveG]

if you think about a single axle with the diff open. You raise one wheel in the air, the open diff will give the wheel in the air 100% of torque - Yes?

Ok so if you now lock the diff, both shafts will now share the torque equally and rotate at the same rate-Yes?

So does the front diff truly divide the available torque because it can't give both 100%. If any engine gives out 200lb of torque at say 2500rpm, there's not 200lb at each wheel. Surely if each wheel has the same amount of traction the each will be getting roughly 50lb. It couldn't be giving 200lb to each otherwise you would have a 200lb engine putting out 800lb on the road. Would be good ifyou could, but it's not going to happen.

If your examples are true and let's say you had front and rear diff locks and centre diff lock all in the locked position and let's say you have three wheels in the air. That means that the single wheel on the ground would be getting 100% and all the others 0%. But if that's the case why does the other axle with two wheels in the air turn?? And if it were to find traction it would have the force to move. The diffs wouldn't start to suddenly put the torque back - it's because it was there all along. Surely this is correct? Yes?

So what's happening. Surely with a centre diff lock in and just one prop-shaft it's going to get half the torque irrespective of whether there is load or not, or am I wrong?

Cheers

Steve

[white90]

if you think about a single axle with the diff open. You raise one wheel in the air, the open diff will give the wheel in the air 100% of torque - Yes?

Ok so if you know lock the diff, both shafts will now share the torque equally and rotate at the same rate-Yes?

So does the front diff truly divide the available torque because it can't give both 100%. If any engine gives out 200lb of torque at say 2500rpm, there's not 200lb at each wheel. Surely if each wheel has the same amount of traction the each will be getting roughly 50lb. It couldn't be giving 200lb to each otherwise you would have a 200lb engine putting out 800lb on the road. Would be good ifyou could, but it's not going to happen.

If your examples are true and let's say you had front and rear diff locks and centre diff lock all inthe locked position and let's say you have three wheels in the air. That means that the single wheel on the ground would be getting 100% and all the others 0%. But if that's the case why does the other axle with two wheels in the air turn?? And if it were to find traction it would have the force to move. The diffs wouldn't start to suddenly put the torque back - it's because it was there all along. Surely this is correct? Yes?

So what's happening. Surely with a centre diff lock in and just one prop-shaft it's going to get half the torque irrespective of whether there is load or not, or am I wrong?

Cheers

Steve

There can be no torque applied if there is no resistance to the turning of the output flange.

the wheels in the air turn as the wieght of them and the other drive train components offer a resistance so torque is applied far less then the wheel on the ground that if it were a front one wold quickly destroy the CV anyway

hence the need for care when any wheel is in the air as the torque being applied is greater.

[LandyManLuke]

Torque is turning force, the engine has only so much torque it is able to produce.

Considering a landrover with all three diffs locked, and three wheels off the ground. the three wheels in the air require only a few Nm to spin them, the one wheel in contact will take all the torque it can to rotate the wheel, so that wheel will be able to produce say 95% of the total available, the other 5% turning halfshafts and wheels that are spinning in air.

Torque is going to be at a maximum/minimum under acceleration/braking or gradients/boggy ground when rolling resistance is high.

Consider a LR with both props in place, accelerating from 0 - 60, the same LR accelerating in the same time with only one prop still requires the same about of torque, so this has to go through the one prop.

[SteveG]

There can be no torque applied if there is no resistance to the turning of the output flange.

the wheels in the air turn as the wieght of them and the other drive train components offer a resistance so torque is applied far less then the wheel on the ground that if it were a front one wold quickly destroy the CV anyway

hence the need for care when any wheel is in the air as the torque being applied is greater.

How can this be with a locked diff. Torque is just a measurement of force required to move an object over a distance. With a locked diff there is no way the force on each half shaft can vary. Yes? Otherwise it's just like an open diff.

So the force is there all along whether there is a load or not. True?

As you know with an open diff the reverse is true, if there is no load there it gets all of the force. If the wheel suddenly finds traction you have to be careful as you are for an instant putting all of the force through a single wheel.

With an axle diff lock in locked position both wheels are turning at the same rate all of the time irrespective of load on each. With it locked there can be no way that the force or torque is varying between each wheel.

Cheers

Steve

[LandyManLuke]

How can this be with a locked diff. Torque is just a measurement of force required to move an object over a distance. With a locked diff there is no way the force on each half shaft can vary. Yes? Otherwise it's just like an open diff.

So the force is there all along whether there is a load or not. True?

As you know with an open diff the reverse is true, if there is no load there it gets all of the force. If the wheel suddenly finds traction you have to be careful as you are for an instant putting all of the force through a single wheel.

With an axle diff lock in locked position both wheels are turning at the same rate all of the time irrespective of load on each. With it locked there can be no way that the force or torque is varying between each wheel.

Cheers

Steve

An axle with a locked diff is just a single solid shaft.

Consider a turning shaft, such that if you were to grip each end with one hand it would stop. ie you have overcome the torque available.

now consider gripping the shaft at one end, but with both hands. will it stall? yes. the same torque is still all thats available, its just been used in a different place.

torque is directly proportional to resistance to rotation, at a constant speed. if torque is greater than resistance, the shaft will accelerate, if it is less, it will slow down/stop.

i think...

Luke

[Turbocharger]

How can this be with a locked diff. Torque is just a measurement of force required to move an object over a distance. With a locked diff there is no way the force on each half shaft can vary. Yes? Otherwise it's just like an open diff.

So the force is there all along whether there is a load or not. True?

As you know with an open diff the reverse is true, if there is no load there it gets all of the force.

Sadly a locked diff isn't a torque splitter. You're constraining rotation, not torque.

Imagine for a moment you have rubbery elastic halfshafts and it becomes clear (I hope).

• Locked
  With a locked diff (in an axle), in a straight line on good tarmac, both shafts twist by the same amount so equal torque. If you picked one wheel off the ground then the other halfshaft would twist twice as far, while the lifted wheel's shaft would remain straight (neglecting the inertia of the wheel).
  
• Unlocked
  When you unlock your diff, it means both halfshafts twist by the same amount - which is the minimum of the two shafts (so if one wheel is lifted in the air, both shafts deform by the minimum, which is zero).
  

[D9OSV]

Have I missed something..???

Or is this all as strange as I first thought....

Does it matter ....?

If the Center diff is locked it is supplying equal load to front and rear as a fixed shaft,

so again,

Have i missed something

confused

Jim

[LandyManLuke]

Have I missed something..???

If the Center diff is locked it is supplying equal load to front and rear as a fixed shaft,

.......only if all four wheels are on the ground, with equal forces acting on the wheels of both axles

[D9OSV]

Yeh, But in that situtation does where the ,Eerrrr, torque go matter????????

Surely you just want to get everything back to normal as soon as and crack on....

Or is this one of those wierd scientific threads and i'm once again out of my depth??????

Errrrrrrr......

Jim

[Mark90]

With a locked diff there is no way the force on each half shaft can vary. Yes? Otherwise it's just like an open diff.

It's like Turbo says. With locked diff you are applying equal amounts of rotation not equal amouts of torque. You can't have torque with out resistance, but you can still have rotation witout resistance.

Remove the front prop with a locked diff and yes both output flanges will rotate at the same speed but all the torque will be transmitted through the rear prop as that is the only one offering any resistance.

[SteveG]

Yeh, But in that situtation does where the ,Eerrrr, torque go matter????????

Surely you just want to get everything back to normal as soon as and crack on....

Or is this one of those wierd scientific threads and i'm once again out of my depth??????

Errrrrrrr......

Jim

Of course you can have torque without resistance.

Power = Torque x RPM (or rotational speed)

HorsePower = (Torque x RPM)/5252

No resistance or load factor in any of those two equations

And an open diff is a torque splitter. The problem I had before was understanding that when it's locked it's providing the same amount of torque to both axles.

Cheers

Steve

[FridgeFreezer]

Steve - you think too much!

[02GF74]

if you remove the front propshaft and lock centre diff lock. The diff lock will divide the torque equally between both front and rear outputs whether there is a load or not. Therefore the front propshaft will receive 50% of the torque.

True or False. If false give your reasons

Cheers

Steve

As explained, with or without the use of rubbery props and half shafts, diffs allow half shafts to rotate at different rates and has nowt to do with torque. In fact torque does not exist at all unless there is something that it is trying to turn something else that offers resistance. *

To justify the last sweeping statement, conisder an engine. If you put it in neutral and run it a 4,500 rpm, how much torque is it producing? None as there is no load. (ok, there is a bit to overcome the inertia of the rotating bits - pedant mode off]. Now fit a large caliper to the flywheel so it acts as a brake and apply pressure thus offering resitance; now the engine is producing torque that can be calcualated.

Now going to the unlocked axle diff with one wheel in the air. The diff allows the free wheel to turn as it offers no resistance and you will find the engine torque has magically vanished so the engine turns effortlessly. If you have both wheels on the ground and apply brakes, the engine will stall as it cannot producce enough torque to overcome the reisistance of the brakes. You can try this at home but be sure the wheel that is in the air is supported safely.

This can be extroplated to any number of diffs. locked or unlocked.

No rubber half shafts were harmed in providing more confusing 5h1te.

* Don't be confused by your engine's torque/power curves; the torque is the maximum that can be produced at the given rpm and only when the engine is loaded so most ofthe time it is way below that value.

[Mark90]

Of course you can have torque without resistance.

Ok look at it this way. Torque is "rotational force", right?

You can't build up a force without an equal and opposite reaction or you get acceleration, simple physics, Newtons laws etc. So once the disconnected prop flange (or lifted wheel in locked axle) has been spun up to speed the only torque being delivered to that side of the diff is to overcome the frictional forces in the system, ie negligable in the grand scheme of things.

Oh here's another way of looking at it. Take your torque wrench and a slack wheel nut, no matter how fast you spin the nut you won't be able to apply any significant torque while the nut is freely rotating. Only when it meets the wheel rim and an equal and opposite reaction is present wil you be able to develop any torque.

Without the resistance you won't be able to develop the torque.

And an open diff is a torque splitter. The problem I had before was understanding that when it's locked it's providing the same amount of torque to both axles.

It only provides the same amount of torque to both axles if they both present the same resistance, ie have the same level of traction.

[jbergholm]

if you remove the front propshaft and lock centre diff lock. The diff lock will divide the torque equally between both front and rear outputs whether there is a load or not. Therefore the front propshaft will receive 50% of the torque.

True or False. If false give your reasons

To add more confusion, maybe.

Let´s say that you somehow can get the tip of your finger between the teeth of the gears in the transfer box. Would you then prefer to have your finger between the teeth on the rear output axle, which is propelling the vehicle forward, or, would you like to have it in the front output axle where you have removed the propshaft, thus the shaft is rotating without resistance. Torque is, as I´m sure most of you know, a force x radius (distance to turning centre) so the pain in your finger will (to a point anyway ) be proportional to the torque transfered in the gear. I know what I would prefer.

That said I belive Turbochargers rubber shafts is the best way presented to understand the problem.

[SteveG]

Ok Mark I get it know

And yes on this subject I'm thinking too much and it hurts so I give up now.

Cheers

Steve