Quaife 4 HA Locking (LSD) or Torque Biasing diff, specially altered & adapted by ourselves to fit  Aston Martin DB MkIII 4 HA axle, also fits Jaguar Mk2, 240 & 340 with solid axle.

This diff has most of the advantages of a plate LSD, it has the advantage of being quiet - instead of being noisy like a plate type diff, but if one rear wheel lifts fully of the ground the diff wont lock,

This is a Torsen Gleason gear type diff, which contain no noisy plates rubbing together, it also last a lot longer because of this, a description of which is below:

Quaife ATB Helical LSD differential sold by Four Ashes for Aston Martin models with live 4HA axle. A direct replacement for the standard Salisbury open differential, the Quaife ATB Helical LSD differential transforms your car’s performance.

Unlike a conventional plate-style limited slip differential, the Aston Martin Quaife ATB Helical LSD differential relies on gears rather than clutch plates for its operation. That means it is much smoother & quieter in operation.

The Four Ashes modified Quaife ATB Helical LSD differential never locks harshly with a set pre-load of wheel slip across the driven axle, like a conventional LSD. Rather, the  Quaife ATB Helical LSD differential automatically biases the torque away from the spinning wheel across the axle, to a constantly varying degree, and never locks.

The Quaife ATB Helical LSD differential has many benefits over a standard open differential, including maximising traction and minimizing wheelspin, eliminating torque steer and snatching in front wheel drive cars compared to conventional LSD units, and a maintenance-free design which retains the standard EP90 oil lubrication.