Confused- How a diff Diff Lock work

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Tk88

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Hi there,

I have been reading some information on the diff lock system in the Land Rovers but I can't get my head around a few things. My understanding is that there is three differential: front, middle and rear. The middle diff locks the front and rear together. The idea being that if you loose traction you still have power going to a front and rear wheel. However why is it beneficial to send all the power to the wheels that have no traction (assuming that the vehicle is stuck), wouldn't there be more chance of becoming unstuck if power when to all 4 wheels or the wheels where there might be traction

Take the below video

YouTube

When the vehicle becomes stuck when not in DL why isn't power being sent to the wheel that has traction (left wheel) and not being wasted on a wheel that doesn't (right wheel). Secondly when in diff lock why is the power sent to the wheels front and back that don't have traction.

My further understanding is that this is where traction control comes into effect...as the abs is applied to prevent the tractionless wheel from spinning and allow power to be sent to the other wheels that do have traction. But my question still remains....why in the first place is the power being sent to the wheel with no traction.

My second question is regarding transmission windup in which a 4x4 is placed in diff lock and driven round roundabouts and other corners where all wheels do not move at the same speed. Can someone provide a detailed explanation of the causes and dangers?

Many thanks,

Tom
 
A diff works by sending the drive to the fastest spinning wheel else cornering would be near impossible.

On a corner the rear wheels are inside the line of the fronts so spinning slower. If centre diff is locked the drive is equal front and back so the difference has to be made some where.....ie...skipping tyres, stressed drive shafts, u/j's, halfshafts and transmission windup.
 
Okay, so in order to turn, both wheels must be independant but why is power sent to the wheel with no traction rather than to the one with traction? Is it something to do with energy (power from the engine) taking the route of least resistance (ie the wheel with no traction)?
 
Tk88 said:
Okay, so in order to turn, both wheels must be independant but why is power sent to the wheel with no traction rather than to the one with traction? Is it something to do with energy (power from the engine) taking the route of least resistance (ie the wheel with no traction)?
Click to expand...

That's exactly the reason - the power will always take the path of least resistance, hence if a wheel loses traction it'll just spin all the power away. The idea of a centre diff lock is if a rear or front wheel loses traction you will still have traction from one or both the remaining front/rear wheels at the other end.

For example: Front left wheel loses traction, without centre diff lock the vehicle will just sit and spin that wheel. With diff lock engaged the power will still get sent to the rear wheels as well as the one front spinning wheel. If one or both rear wheels still have traction then you will still move :)
 
Last edited:
DreXeL said:
If one or both rear wheels still have traction then you will still move :)
Click to expand...

Almost right. ;)

If you lose traction on the rear axle aswell as the front you will go no where. Its called getting cross axled.

The centre diff in your standard defender dosent send 25% to each wheel it sends 50% to each axle.
 
blue beasty said:
A diff works by sending the drive to the fastest spinning wheel else cornering would be near impossible.

On a corner the rear wheels are inside the line of the fronts so spinning slower. If centre diff is locked the drive is equal front and back so the difference has to be made some where.....ie...skipping tyres, stressed drive shafts, u/j's, halfshafts and transmission windup.
Click to expand...

Which is exactly why if your driving on ice with diff lock on you may not turn as fast as you would want to ;)

T'is all down to technique, get used to flicking diff lock in and out as required.... easier said than done. Which is why vehicles with VCU's are so good for folk that don't know how and when to use diff lock.
Neither system is infallible it can only ever be as good as the nut behind the wheel ;)
 
BIG_GINGA_BEARD said:
Almost right. ;)

If you lose traction on the rear axle aswell as the front you will go no where. Its called getting cross axled.

The centre diff in your standard defender dosent send 25% to each wheel it sends 50% to each axle.
Click to expand...

Of course, my mistake. Yes, if one one rear wheel loses traction as well as a front wheel then the front and rear wheels without traction will just sit and spin.
 
A Landy is in permanent 4 wheel drive with no center dif engaged. I always thought that meant one wheel with power on the front and one on the back.
If the center dif is engaged and 50% power goes to the front and 50% goes to the back, what changes..?
I have never got my head around all this.
 
JonnyP said:
A Landy is in permanent 4 wheel drive with no center dif engaged. I always thought that meant one wheel with power on the front and one on the back.
If the center dif is engaged and 50% power goes to the front and 50% goes to the back, what changes..?
I have never got my head around all this.
Click to expand...
a landy is permanent 4x4 as long as all wheels have good traction ,the 3 diffs enable this whilst doing high speed a cornering etc on the road ,but on poor ground 1 wheel can spin and lose all drive to the rest so your left standing still ,locking cdl means the center diff is no longer working as a diff and both axles are driven regardless and you need to lose traction and spin a wheel on both front and rear axle to standstill
 
JonnyP said:
A Landy is in permanent 4 wheel drive with no center dif engaged. I always thought that meant one wheel with power on the front and one on the back.
If the center dif is engaged and 50% power goes to the front and 50% goes to the back, what changes..?
I have never got my head around all this.
Click to expand...

Without difflock it is only 4wd in the sense that power can drive any or all wheels depending on traction......for example when cornering all wheels may be rotating at different speeds but all receiving drive, only when traction is completely lost on one is the drive to to other 3 lost.

With difflock engaged traction has to be completely lost on a wheel on both axles before drive is lost
 
jamesmartin said:
a landy is permanent 4x4 as long as all wheels have good traction ,the 3 diffs enable this whilst doing high speed a cornering etc on the road ,but on poor ground 1 wheel can spin and lose all drive to the rest so your left standing still ,locking cdl means the center diff is no longer working as a diff and both axles are driven regardless and you need to lose traction and spin a wheel on both front and rear axle to standstill
Click to expand...

I must learn to type faster :p
 
jamesmartin said:
a landy is permanent 4x4 as long as all wheels have good traction ,the 3 diffs enable this whilst doing high speed a cornering etc on the road ,but on poor ground 1 wheel can spin and lose all drive to the rest so your left standing still ,locking cdl means the center diff is no longer working as a diff and both axles are driven regardless and you need to lose traction and spin a wheel on both front and rear axle to standstill
Click to expand...

Thanks for that James n Blue. I get it now :)
 
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