Spreading disc brakes for vehicles

A self-energising spreading disc brake comprising a housing having opposed spaced radial surfaces, friction discs within said housing provided with friction linings for engagement with said radial surfaces, stationary pilot lugs in said housing, pressure plates located between said friction discs and centered by said pilot lugs, a stop abutment in said housing, a radial projection on each said pressure plate, said pressure plates having adjacent faces provided with co-operating oppositely inclined recesses, and balls or rollers located in said recesses, wherein said brake is initiated by moving said pressure plates in opposite directions into engagement with said friction discs which, in turn, are urged into engagement with said radial surfaces whereafter said pressure plates are carried round angularly with said discs until one is arrested by said stop abutment and the continued angular movement of the other provides a servo-action, a cranked lever having a first end and a second end, a first connection pivotally connecting said cranked lever intermediate its ends to a radial projection on one of said pressure plates, a brake-applying pull-rod, a second connection pivotally connecting said first end of said lever to said pull-rod, and an automatic adjuster through which said second end of said lever acts directly to apply a thrust to the other of said pressure plates whereby movement of said pull-rod in a brake-applying direction urges said pressure plates angularly in opposite directions, said adjuster being operative automatically in response to movement of said lever to determine a relative angular position between said pressure plates at which braking clearances are maintained substantially at constant values, said adjuster comprising a screw-threaded strut acting at opposite ends between said lever and said radial projection on the other pressure plate and of which the effective length is adjustable to compensate for wear of said friction discs, a toothed wheel on said strut, a pawl pivotally mounted directly onto said strut and engageable at one end with said toothed wheel, said toothed wheel being rotatable to alter the effective length of said strut, and a spring adapted to hold said pawl in abutment with said lever during an adjustment stroke in which said pawl can rotate said wheel to increase the effective length of said strut until the force in said spring is overcome by the brake applying load, whereafter said pawl and said lever can move relatively away from each other to preclude further adjustment.