Automatic clearance adjustor device for a drum brake with two brake shoes

摘要

The adjustor device (50) comprises pressure blocks, (8, 9) engaging the shoes 2, 3 and carried by an internally threaded ratchet sleeve (10), a pawl lever (11) having a pawl (18) which projects through an aperture (20) in a housing (12) of the sleeve into engagement with ratchet teeth on the sleeve, the pawl lever (11) pivoted on the side of the housing (12) nearest the centre of a back plate (1), and a control lever (7) coupled to brake shoe (2) retracts the pawl lever in opposition to a tension spring (14) each time the brake is applied. If excessive brake shoe clearance is present, the spring (14) rotates the sleeve through one tooth pitch when the brake is next released. The spring anchorage (13) on housing (12) is nearer the drum circumference than the fulcrum (17) of the lever (11), and the spring (14) acts both to rotate the lever (11) in its own plane and to pivot the lever (11) down into resilient engagement with the ratchet teeth. One or both blocks (8, 9) may be threadedly connected in sleeve (10) - the pitches of the threads may be different. IMAGE