The cross section of the R14 gearbox shows the brake band operating mechanism arranged to function when compressed air is directed into the cylinder. Since the sunwheel is driven at all times the annulus is therefore rotating when in neutral gear, changing the annulus to rest with consequent wear of the brake band. For such an arrangement to be satisfactory, automatic adjustment for brake band wear is desirable and this is provided by the 'toggling' gear.
As each brake is applied, the adjuster mechanism swings towards the brake band (arrow A) bringing the adjuster ring into contact with the adjuster screw. The faces of these components in contact is shown; as the brake linings wear the adjuster ring is deflected when the brake is applied (arrow B) loosening the special spring formed round the adjuster nut.
When the brake is next released the spring tightens round the nut holding the adjuster ring in this position until the ring is partially rotated by striking the tail pin affixed to the gearcase.
This screws down the adjuster nut so shortening the effective length of the bolt by the correct amount and maintains the proper brake setting.
At times when the automatic adjuster cannot keep up with wear (resulting in slipping bands) the gearbox can be "toggled". To do this, with sufficient air pressure in the system, the engine is shut down and each gear is selected in turn repeatedly. This continually operates the automatic adjusters.