Expanding shoe drum brake

An improved cam actuated expanding shoe drum brake comprising:

• a spider member;
• a selectively displaceable brake actuation means fixed to said spider member, said actuation means comprising a rotatable cam,
• a pivot structure comprising a single anchor pin having a headed portion and a shank portion fixed to said spider member;
• a pair of generally arcuate radially outwardly movable brake shoes pivotably supported on said pivot structure, each of said brake shoes carrying a cam follower member at one end thereof engaged by said actuation cam for movement therewith, said actuation cam having a first position for allowing said shoes to be radially retracted and a second position for causing said shoes to be radially expanded;
• each of said brake shoes comprising a web structure comprising at least one web, said web structure defining a first and a second generally parallel opposed surfaces, and a table structure generally perpendicular to said web structure and carrying friction material on the radially outer surface thereof, each of said webs provided with a generally semiarcuate cavity at the other end thereof pivotably retained on the shank portion of said anchor pin;
• the improvement comprising means to locate said web structure on a predetermined plane relative to said spider in both the radially retracted and radially expanded positions thereof, said locating means comprising:
• first and second spaced generally flat guide surfaces fixed to said spider and directly slidably engageable with said first surface of said web structure, a fixed third generally flat guide surface defined by the shoulder between the headed and shank portions of said anchor pin, said third guide surface spaced from and parallel to said first and second guide surfaces, said third guide surface axially spaced from said first and second guide surfaces by a distance generally equal to spacing between said first and second surfaces on said web structure and directly slidably engageable with said second surface on said web structure, said third guide surface not being on a straight line drawn from said first to said second guide surface, and means resiliently engaging said second surface of said web structure and applying a resilient force on said web structure in the direction toward the first surface thereof, said resilient means engaging said second surface on the opposite side of said line drawn from said first to said second guide surface as said third guide surface and comprising with said guide surfaces the only guide means for said brake shoes whereby said web structure will be constantly resiliently urged into sliding engagement with said first, second and third guide surfaces.