Dual mode drum brake assembly

A drum brake assembly having a leading/trailing service brake and a duo-servo parking and emergency brake comprising:

• a backing plate;
• first and second opposed arcuate brake shoes supported relative to said backing plate and moveable outwardly into frictional engagement with an associated brake drum upon actuation of either the service brake or the parking and emergency brake, each of said first and second brake shoes including an arcuate table for supporting a friction pad and a web connected to said table;
• a hydraulic actuator secured relative to said backing plate and disposed between and engageable with a first pair of adjacent ends of said brake shoes for hydraulically actuating the service brake;
• a rotation preventing abutment secured relative to said backing plate and disposed between and engageable with a second pair of adjacent ends of said brake shoes;
• a pivot lever pivotally supported relative to said first brake shoe and operatively coupled to exert an outward force on said first brake shoe when the parking and emergency brake is mechanically actuated;
• first strut means disposed adjacent said hydraulic actuator and including one end coupled to said second brakes shoe and an opposite end coupled to one end of said pivot lever, said first strut means including an adjuster lever pivotally supported on said first brake shoe for automatically adjusting the effective length of said first strut means to compensate for wear of the brake shoes;
• second strut means disposed adjacent said rotation preventing abutment and including one end coupled to said second brake shoe and an opposite end coupled to an opposite end of said pivot lever;
• parking and emergency brake actuating means carried by said brake assembly for mechanically actuating said pivot lever to urge said first brake shoe outwardly into engagement with the brake drum and thereby initiate duo-servo actuation of the parking and emergency brake through one of said first and second strut means;
• and
• hold down means extending through said aperture of said first brake shoe for securing said first brake shoe to said backing plate;
• said pivot lever being pivotally supported on said first brake shoe generally intermediate said first and second strut means.