A jaw crusher having a stationary jaw and a movable jaw which define a variable crushing gap (or closed side setting), a toggle beam, and a toggle between the toggle beam and the movable jaw, and a toggle seat between the toggle and each of the beam and movable jaw for seating the toggle against the beam and movable jaw. A double-acting hydraulic ram having a connection with the toggle beam for shifting the toggle beam toward and away from the fixed jaw. An abutment is supported by the housing and engageable by the toggle beam for defining an adjustably variable limit of shifting thereof. End caps provide a rigidly guided sliding toggle beam having a plurality of alternatively selectable positions of adjustment. An hydraulic circuit is connected to each end of the relief ram for extending and retracting thereof, a relief valve is provided for the ram for providing a quick discharge path for oil in the rams to vent the latter to substantially lower pressure to thereby provide a rapid overload release of the cylinder when uncrushable material is encountered in the crusher, and a double-acting toggle tension hydraulic ram in the circuit and pivotally connected between the toggle beam and the movable jaw to tension the toggle and its seats together. The jaw crusher and its hydraulic circuit enable the material between the jaws to be cleared when the machine has encountered an unscheduled stop due to, for example, an overload in the system, the failure of the electrical power system, the failure of the belt driving system, or any other unscheduled stops.