GB1490573A - Adjusting devices in internal shoe drum brakes - Google Patents

Abstract

1490573 Wear adjusters AUTOMOTIVE PRODUCTS Ltd 30 Jan 1975 [4 Feb 1974] 05030/74 Heading F2E An internal shoe drum brake with an automatic slack adjuster comprises a lever 28 which is pivoted to the web 22 of a shoe 17, 18, has limited free play relative to an abutment 32 secured to a back plate 10 or other fixed brake part and is restrained against free movement outwardly of the brake by a one-way locking device comprising a locking member 34 pivoted on the shoe and urged by a spring 37 into engagement with an edge 29 of the lever 28 and arranged so that outward pivotal movement of the lever 28 tends to urge the locking member more firmly against the lever, the lever 28 and abutment 32 together limiting inward movement of the brake shoe by the retractor springs 25, 26. The interengaging arcuate edge 29 centred at the pivot of the lever 28 and the straight edge 36 parallel to a straight line through the pivot 35 of the member 34 may both be smooth or one or both may be serrated or have ratchet teeth. In operation, when the brake lining 24 wears and on actuation of the brake the clearance between the stud 32 and the lever 28 is first taken up after which the lever pivots clockwise, Fig. 1, the locking member under the urging of the spring 37 permitting this movement but preventing the opposite movement of the lever 28. On release of the brakes the springs 25, 26 return the shoe until the clearance is again taken up between the lever in its new position and the abutment. In a modification of the above embodiment the lever 28 is mounted on the back plate side of the web 22, the end of the abutment pin 32 abuts the web 22 to space the shoe from the back plate and there is no need for an aperture 33 in the web for the abutment pin 32 to pass through. Reference has been directed by the Comptroller to Specification 992,873.