A slack adjuster (40) comprises a worm shaft (52) that is configured to drive a worm gear (42) adapted for coupling to a camshaft (14). An adjustment assembly receives slack adjustment input from a push rod (32) and is configured to automatically rotate the worm shaft when brake slack exceeds a predetermined limit. The slack adjuster includes a manual adjuster that is moveable between a non-adjustment position where the manual adjuster is de-coupled from the worm shaft and a manual adjustment position where the manual adjuster is coupled to the worm shaft such that a position of the worm shaft can be manually adjusted as needed.
