ATB Torsen differential lock - Defender 90/110/130 front axle and Defender 90 rear axle

Differentials are among the most important and heavily used mechanical parts and can make a huge difference in performance, especially once you leave the asphalt behind. This much is undisputed, but then the first question usually is whether you need proper lockers on the axles or at least limited slip diffs?

Our answer: Unless you’re regularly punishing your Landy in heavy terrain and prefer it climbing over driving, a locker probably makes little sense for you. In ambitious everyday use, retro-fitting a Limited Slip Differential (LSD) like the Ashcroft ATB or the TrueTrac by Eaton will make a huge difference, though. For most drivers most of the time, limited slip diffs will be the best choice on-road, with varying surface and weather conditions, as well as off-road.

But first some basics: in contrast to real lockers, which lock up your axle either electronically or pneumatically, LSDs work in the background all the time and not only if you switch them on. Moreover, there is no need for external input. They neutralize the torque differential on one axle gradually or in increments, whereas a real locker has only two states: either completely off or on. This in turn means that the LSD supports the driver continuously and unnoticeably on loose or slippery surfaces and can even beat lockers in certain tricky situations. Every seasoned off-roader will know this one: the vehicle is tilted sideways on slippery ground and the lower rear wheel with most of the load on a locked axle will pull the back of the vehicle violently sideways and downhill when you step on the gas pedal. Moreover, the enormous forces working on locked axles usually require re-enforcements to the drive train, if you want to avoid costly damages in such situations.

The Ashcroft ATB LSD, available for Rover front axles (Defender 90/110/130) and rear (90) as well as for the P38 axle on 110/130, is of a Torsen Type 2 design, similar to the Eaton Truetrac, but with a slight difference. The engineers at Ashcroft are employing 6 instead of 3 pairs of helical gears parallel to the axle. The differential creates the necessary friction for torque compensation by pressing these helical gears to the sides of their pockets. Now, if you’re thinking metal on metal, there’s got to be loads of wear on these gears, you need not worry. Both the Ashcroft as well as the Eaton are designed to compensate for the wear and will be among the most long-lived movable parts in the car.

One drawback inherent in this particular design is the fact that at least one wheel per axle has to have a load on it for the diff to engage. Pre-load springs on the Ashcroft minimize the effect. If you have both wheels spinning, simply engaging brakes and throttle simultaneously will initialize the torque compensation again. In cars with traction control, this effect is achieved electronically, by the way. The ATB LSD otherwise supports the traction control by multiplying its effects. Because of these characteristics inherent in the design a vehicle fitted with Ashcroft ATBs should never be brake-tested on rollers.

The Ascroft ATB is reliable, quiet, supports traction control if fitted, needs little maintenance and improves both the driving characteristics and the power transmission, depending on your setup. It fits Rover and P38 axles (including fittings). 

ATB Torsen differential lock Salisbury is only suitable for Salisbury rear axles. For Salisbury axles, the Detroit Truetrac from Eaton is also recommended as an alternative.