Thread: 2009 Defender center diff lock fraser island trip

Hi Aulros,
Me and my mate are taking our defenders to fraser island next week for a trip, and I have read mixed views on here about using the centre diff lock.
Some say they never use it others wouldnt go off road without it due to if there is slip on the wheels can destroy the gear box?
Your feed back would be great
Cheers
Zapt

A brief explanation may change the way that yourself and many other drivers view the use of a CDL.

Simply put for the point of this explanation, an 'Open Differential', by their very design allow the wheel with the least traction to receive the most torque.(ignore some other factors for the simplicity of the explanation)

Your Defender with 'all wheel drive' an unlocked CDL, is simply a one wheel drive. When one wheel is spinning on a loose surface, the vehicle is effectively stuck. The CDL when locked turns this vehicle into a two wheel drive by distributing 50/50 torque distribution front and rear. Now you require one front wheel to spin and conversely the diagonally opposite rear wheel to also spin and you will once again be stuck.

Inter axle differential locks (think Air Lockers as an example) if fitted to the rear axle will turn your vehicle into a three wheel drive vehicle and if fitted to both front and real axles will be a four wheel drive.

Differentials can take into account the varying differences in wheel speed and distance as the inside wheel will travel a lesser distance than the outside wheel whilst turning a corner and also travel at a slower speed in the same situation. This applies equally to both front and rear differentials.

A centre differential has to take into account the difference in speed and distance between front and rear. Now do a simple drawing, Draw four wheels on a sheet of paper, looking from above, so that they resemble the four tyres on your vehicle. Now imagine these four wheels turning a corner and draw in the anticipated route that each wheel follows. Now you can see the difference between the distance that the inside front wheel has to take in relation to the outside front wheel and similarly the difference between the inside rear wheel and outside rear wheel


The right rear wheel in the diagram above has to travel considerably less distance than the front left wheel and at the same time also travel slower than the left rear wheel.

This large discrepancy in distance and speed front to rear in wheel speed and distance travelled is the cause of most CDL failures. (for the sake of this explanation, ignore other factors) Locking the CDL forces the front and rear prop shafts to turn at the same speed and therefore the front and rear differentials only have to take into account differences right to left which they can cope with.

There are other factors which also come into play, such as the fact that should you need to make an evasive manoeuvre, you have the front pulling as well as the rear pushing and can therefore get back 'on line' safely.

As has been noted by others earlier and in the video supplied. Always lock the CDL when on a loose surface, this can be done whilst the vehicle is moving but not whilst one wheel is spinning. Also if you are undertaking a tight turn on a firm surface such as a hard gravel road, then the CDL can simply be unlocked and locked again once the manoeuvre has been completed.