Abstract: The relatively complex and expensive "control valves", which are conventionally used in certain compression release engine brakes for such purposes as filling, isolating, and venting the high pressure portions of the hydraulic circuits in the engine brake, are eliminated and more direct means are provided for performing these functions. In brakes having a mechanism for resetting each slave piston, the high pressure portion of the circuit is filled through a selectively openable aperture in the slave piston. In brakes having a mechanism for automatically adjusting slave piston lash or for limiting ("clipping") the forward stroke of the slave piston, high pressure circuit fill is provided through a simple check valve. In systems in which hydraulic fluid is temporarily displaced from the high pressure circuit, a simple accumulator is provided to store hydraulic fluid for quick refill. A single such accumulator may replace multiple control valves.