Ashcroft Limited Slip Diff ATB (Rover type)

For the occasional Green Laner or those driving frequently on low traction surfaces i.e. pulling a horsebox off a grass, the Limited Slip Differential is an ideal upgrade for your vehicle.

The Limited Slip operation differs from the Locking differential in that it is never 100% locked. It operates by applying load to the wheel with the least grip, i.e. spinning. This is the automatic torque biasing (ATB - gear type).

In operation the difference between the two is that the plate type begins to work immediately torque is applied to the diff centre and the more torque applied to the diff centre, the more the diff biases to a locked condition. In other words as soon as you start to drive the centre is operating and the more throttle applied the more the locking action functions. As soon as you back off the throttle the diff becomes free.

The ATB gear type limited slip relies on the internal friction generated by gear sets within the diff centre, these gear sets are unsupported and designed to be inefficient. In a normal situation, i.e. on road this diff will be totally transparent, you will not know it is fitted. Provided both wheels have grip no torque biasing takes place, on a bend or corner the faster outer wheel will try to bind up the internal gears but the inner slower wheel constantly unwinds the gears, so again on a corner no bias is felt. On low or no traction surfaces where one wheel has considerably less traction than the other and thus tends to spin. The gear action within the diff causes friction which in turn applies load to the wheel with traction. Bias ratios can be varied by different pre-loads and different gear profiles but the most common have a bias ratio of 2:1.

The advantage of a Limited Slip differential is totally automatic, no driver interaction and retains drive to both wheels at all times.

The disadvantage of ATB is that if one wheel is totally off the ground ,i.e. no drive then the other wheel similarly because the bias ratio is still 2:1 i.e. 2 x nothing is still nothing. Attempts at changing the preload or left foot braking can the fool the ATB into working or better still if the vehicle is fitted with ATC (automatic traction control) the ATB will enhance the action.

Key features of the Ashcroft ATB are:

- Fully automatic, needs no driver input

- Totally transparent on road, i.e, no unwanted adverse effects

- Only comes into play when one wheel looses traction, i.e, a difference in wheel speed

- Enhances the traction control as it multiplies the bias load created by the braking effect of the traction control

- Needs no special oils

- Needs no adjustment as the gears compensate for any wear that takes place

- Only with 24 spline side gears