Land Rover Diff Lock and High Low Gearbox

Most Land Rover models except the Freelander have a high – low transfer gearbox and a centre diff lock. Do you know what this does and when to use it?

From the very early Series models and Defenders, Land Rovers have been fitted with a main gearbox and a transfer gearbox. Everybody knows what the main gearstick is for but not everybody knows when to use the smaller gearstick.

The smaller gearstick operates the transfer or high – low gear box and if fitted the centre differential lock. On vehicles with permanent 4 wheel drive you need to have a centre differential that allows the front and rear wheels to turn at different speeds when cornering, this is great on road but when traction becomes tricky the centre differential will send all drive to the wheel(s) with least resistance and this is where you could get stuck.

Yes, even a 4WD Land Rover can get stuck! In reality a 4WD vehicle with open differentials on the axles and centre gearbox can become a 1 wheel drive vehicle as the drive will always divert to the wheel with least resistance. So if you have 3 wheels on hard ground and 1 wheel on slippery mud, ice, snow or loose gravel, it could be possible for all the drive to be transmitted to that 1 wheel with no traction.

Diff_Lock_and_High_Low_Gearbox

By operating the centre differential you can lock the drive to be split 50/50 between the front and rear axles. So your 4WD Land Rover now becomes a 2WD vehicle as the drive is split 50/50 to front and rear axles but each axle also has an open differential so the drive will again go to the wheel with least resistance. In most cases this is sufficient to get enough traction to get going again for all but the most extreme off-road conditions.

So when you are driving off road, stop the vehicle engage low ratio. This gives you a lower range of gears so that you can drive slower and have more control. You can pull away in Low 2nd and use Low 2nd and Low 3rd for most driving conditions. When descending hills, engage Low 1stto benefit from maximum engine breaking. When climbing hills, try to use a higher gear than you would descend, so try Low 2nd or even 3rd on more powerful models, this also helps prevent excess power resulting in wheel spin and loss of traction.

The centre differential or Diff Lock must not be used as a last resort, try and get into the habit of engaging the diff lock before an obstacle, that could be a climb or descent, mud, slippery grass, water crossing, or rough ground that could see you cross axled. Basically any situation that could see a loss in traction, engage the diff lock beforehand. It is safe to engage the diff lock whilst moving slowly but not when any wheels are spinning due to loos of traction, which could damage the gearbox.

With practice it is possible to shift from low to high whilst moving slowly, remember to use the clutch.

For more extreme off-roading, it is worth considering fitting axle diff locks, these can be operated by air, electric or automatically, these are called limited slip diffs, they sense when traction is lost and engage automatically. It is amazing how much extra traction locking axle diffs can give you, but be warned, you may end up even deeper in the mud before you do get hopelessly stuck!

On later modern Land Rovers locking diffs have been replaced or complimented with traction control. This clever system uses the ABS braking system to detect when a wheel is spinning and will apply the brake to that wheel, thus sending the power to another wheel with traction. This is a brilliant system and works incredibly well.

Posted in Hints & Tips

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