slipper-brake

from The Century Dictionary.

• noun A form of brake for railway-trains on steep gradients in which a block or shoe is pressed downward by a lever upon the surface of the rail to retard the motion. Since the block acts on the fixed surface of rails secured to the ground, and the abutment to its pressure is furnished by the weight of the car itself, these brakes can be very effective. Used on mountain roads as an emergency brake.