Abstract: An indicator for indicating a predetermined amount of wear of a brake lining comprising slack adjusting means operatively connected to an arrangement of brake shoes for automatically compensating for the wear occurring to the brake lining on the brake shoes, the automatic slack adjusting means includes a rotatable shaft means which rotatively moves in response to the wear of the lining on the brake shoe, the worm shaft has a threaded bore at one end thereof to receive a threaded member, electrical switching means disposed in the threaded member being operated by a plunger mechanism, the threaded member being restrained from rotation with respect to the rotatable shaft means by clamping means, the plunger being actuated by contacting a portion of the threaded bore of the worm shaft as the threaded member moves linearly with respect to the rotatable shaft means to activate the switch means to energize an indicating means electrically connected to the switch means and an electrical power means.