centre dif lock concept?

[ROGQ]

can someone please explain the centre diff lock concept as i am confused... they are on constant 4 wheel drives right? and it locks the shafts together provides 50-50 tourque to fron and read diffs yeah? but if you have to lock it in to engage 4x4 then how is it a constant 4x4? am i way off track with this?

[DaveS3]

Think of it like a normal diff.
Normal driving everything is transfered reasonably eaqually to both front and rear diffs, then in other circumstances the drive transfers fully to either front or rear (eg when one wheels off the ground, power transfers to the side of least resistance)

Dave.

[ROGQ]

dont you have to lock it in via an incab switch or something?

[kirragc]

Put it tis way if you didnt have the centre lock you only need to lose traction on one wheel to stop the car.

Rangies had a vacuum activated lever in cab

[lay80n]

Constant 4wd's need a centre diff to allow the front and rear shafts to rotate at different speeds whilst cornering etc (as the rear and front follow different arcs, different distances, therefore to keep the car speed constand they must have slightly differing speeds, same as left to right). But having this diff there means that potentially one wheel loosing tractions will stop the vehicle, as all the drive will go to that wheel. Locking the centre diff is the equivalent to sliding a transfer case from 2H to 4H pretty much. It locks the differential in the transfer case so that the drive is now distributed 50:50 front to rear. Usually a push button system.

Layto....

[ROGQ]

if one wheel is in the air without the centre diff locked in and it sends all tourge to that 1 wheel then technically it's not a "constant" 4wd is it?

[lay80n]

if one wheel is in the air without the centre diff locked in and it sends all tourge to that 1 wheel then technically it's not a "constant" 4wd is it?

Why isnt it. On solid ground, all 4 wheels recieve drive. Whats not constant about it??
Most rigs from the factory are designed to have wheels in the air. If your in this situation, you should have already engaged the centre diff. The name constant inplies that at any time, all four wheels are connected mechanicaly to drive. How it is shared amongst the wheels is down to the mechanical reaction in amongst the diffs and friction.


Layto....

[-Scott-]

if one wheel is in the air without the centre diff locked in and it sends all tourge to that 1 wheel then technically it's not a "constant" 4wd is it?

By the same logic, most conventional vehicles are 1wd, and unlocked "conventional" 4wd vehicles are only 2wd.

As Lay80n explained, while all wheels are turning they are all driving - it's a fundamental of the way diffs work.

If it helps, think about the power distribution.

• With open diffs, all wheels deliver the same power to the ground.
  Power = torque x revs.
  Zero revs (at any wheel) = zero power to the ground. Everywhere.

OK, that's a little simplistic, but I find it helps me.

[ROGQ]

cheers for your inputs...