Abstract: A strong and lightweight adjustable slack adjuster is disclosed. The slack adjuster body portion includes, in one form thereof, an integral and a removable cover plate. In another form a pair of removable side cover plates are provided and are fixed to the slack body by deformation of a body rim over the cover plate edge. Other cover plate forms are deformable or resilient and include peripheral skirts which are expandable radially outwardly to fit within an annular groove in the body portion. Meshing worm gear and worm wheel means, which can be rotatably adjusted with respect to each other to thereby adjust the slack in a braking system, are positioned within the body. The worm wheel is supported by the body around its entire periphery to maximize the load carrying capacity of the slack while minimizing wear. The major portion of the worm gear is also supported by the body. Sealing means are positioned between the worm wheel and the cover plates to seal the worm gear and worm wheel from contaminants.