Drum brake

1. A thermal responsive adjuster for a drum brake wherein a hydraulic actuator engages a first web of a first brake shoe and a second web of a second brake shoe to move first and second friction pads into engagement with a drum to effect a brake application, an extendable strut member having a first end member connected to said first web and a second end member connected said second web with a shaft having a first end retained in the first end member and a second end that is connected through threads to the second end member to maintain a running clearance in a rest position between first and second friction pads on said first and second brake shoe and the drum, a lever arm that is mounted on said first web and engages a ratchet wheel on the shaft and a resilient member that extends between said lever arm to the second web to urge said first and second webs into engagement with the hydraulic actuator, said lever arm pivoting with respect to said first web during a brake application and on the occurrence of a predetermined maximum running clearance engaging a tooth on the ratchet wheel to rotate the shaft with respect to said second end member and extend the threaded connection there between and correspondingly a dimension between said first and second end members to re-establish a minimum width for the running clearance on return of said first and second webs to said rest position, said first and second friction pads on engagement with the drum generating thermal energy such that the drum expands and as a result said lever arm pivots on the first web as the first and second brake pads move into engagement with the drum, the improvement wherein said first end member is characterized by a cylindrical body having a having a first end and a second with an axial bore that extends from said first end toward said second end, said first end having first and second radial slots and said second end having third and fourth radial slots that extend from the axial bore, said first and second radial slots being received by the first web to locate said third and fourth radial slots in a vertical plane with respect to the first web, and wherein said third radial slot receives a first end of a coil strip of bi-metal material to locate a second end of the coil strip that is free to move along a tangent with respect to said cylindrical body and in a plane perpendicular to the lever arm, said coil strip responding to thermal energy generated during a brake application and to a predetermined temperature created by the thermal energy by uncoiling such that said second end is brought into engagement with the lever arm and thereafter moves the lever arm out of engagement with said ratchet wheel to prevent said lever arm from thereafter rotating said ratchet wheel during movement of the first web and second web to effect a brake application such that on termination of the brake application a same running clearance is maintained between the first and second brake shoes and the drum as prior to the development of the predetermined temperature.

2. The thermal responsive adjuster for a drum brake as recited in claim 1 wherein said ratchet wheel engages said second end of said first end member to retain said first end of said coil strip in said third slot without placing an axial restraint on said coil strip such that functional uncoiling of said coil strip in moving said lever arm is solely dependent on temperature change experienced by said drum brake.

3. The thermal responsive adjuster for a drum brake as recited in claim 2 wherein said coil strip of bi-material is selected such that a force resulting from a change in physical dimension only needs to move the lever arm and does not need to overcome any brake actuation force.