DA9009 - Automatic Torque Biasing Centre Differential by Ashcroft Transmission - For Defender Pre-1998, Discovery 1 Range Rover Classic LT230 Transfer Box

The centre diff is there to allow the props to turn at different speeds when cornering to stop drivetrain wind up. The speed difference is quite small and the centre diff gears are only designed to cope with these low speeds. If you are off-road on snow or ice and you get wheel spin from one front wheel, what will happen is the rear prop will not be moving, the front will thus be going double speed, this means the small centre diff gears will be spinning like fury and after a matter of only a few seconds the planet gears will friction weld to the cross pins and the gears will fail etc.

Of course in this situation the centre diff should be locked to avoid failure. There are instances when it’s not convenient to keep the diff locked or to constantly lock and unlock the diff as the available traction dictates, i.e,  when racing fast on a low traction surface, the vehicle will not handle well when locked but is likely to wheel spin when unlocked. Another example of where the ATB would help would be when rapidly changing from high to low traction surfaces,  i.e. when driving on snow or ice. In both of these examples the ATB will limit the amount the difference in propshaft speed and transfer torque to the axle with traction.

The two big advantages are increased traction when unlocked and eliminating the weakness of the stock unlocked centre diff. The ATB centre can still be locked like the stock unit when required, locking the diff is still advised when prolonged wheel spin is anticipated.

Note - Due to the nature of the ATB diff we do not recommend the vehicle is brake tested on rollers, ask for a decelerometer to be used instead.