A braking system for a vehicle comprising: a cam coupled to a transmission shaft or a trailing wheel for rotation therewith; at least two hydraulic cylinder assemblies (126, 129), each assembly (126, 129) comprising a cylinder and a piston (125, 130) configured to reciprocate relative to one another and a cam follower attached to either the cylinder or the piston (125, 130) and arranged to contact the cam, whereby rotation of the cam causes the cam follower and the cylinder or the piston (125, 130) to which it is attached to reciprocate relative to the other of the piston (125, 130) or the cylinder; a first hydraulic circuit connecting the hydraulic cylinder assemblies (126, 129) together through which hydraulic fluid flows as the cylinder and piston (125, 130) of each assembly (126, 129) reciprocate relative to each other; a master brake valve configured to control the flow of fluid around the first hydraulic circuit; and an actuation system comprising a user input device configured to actuate the master brake valve; wherein actuation of the master brake valve obstructs the flow of the fluid in the first hydraulic circuit, such that the relative reciprocation of the cylinder and the piston (125, 130) of each assembly (126, 129), and reciprocation of each cam follower, is inhibited or prevented, whereby the cam followers thereby inhibit or prevent rotation of the cam; wherein each hydraulic cylinder assembly (126, 129) is movable between a first position in which the cam follower is maintained in contact with the cam and a second position in which the cam follower is disengaged from the cam, and further comprising an engagement and disengagement system (106, 115) configured to move each hydraulic cylinder assembly (126, 129) between the first position and the second position; and wherein the engagement and disengagement system (106, 115) comprises a single acting hydraulic cylinder (120, 136) with a single acting piston (119, 134) which is attached to each hydraulic cylinder assembly (126, 129) and a second hydraulic circuit connected to each single acting hydraulic cylinder (120, 136), wherein supply of hydraulic fluid to the single acting hydraulic cylinder (120, 136) moves the hydraulic cylinder assembly (126, 129) into the first position; wherein the engagement and disengagement system (106, 115) is coupled to the actuation system and is configured to move each hydraulic cylinder assembly (126, 129) into the first position upon actuation of the master brake valve and to lock each hydraulic cylinder assembly (126, 129) in the first position. a cam coupled to a transmission shaft or a trailing wheel for rotation therewith; at least two hydraulic cylinder assemblies (126, 129), each assembly (126, 129) comprising a cylinder and a piston (125, 130) configured to reciprocate relative to one another and a cam follower attached to either the cylinder or the piston (125, 130) and arranged to contact the cam, whereby rotation of the cam causes the cam follower and the cylinder or the piston (125, 130) to which it is attached to reciprocate relative to the other of the piston (125, 130) or the cylinder; a first hydraulic circuit connecting the hydraulic cylinder assemblies (126, 129) together through which hydraulic fluid flows as the cylinder and piston (125, 130) of each assembly (126, 129) reciprocate relative to each other; a master brake valve configured to control the flow of fluid around the first hydraulic circuit; and an actuation system comprising a user input device configured to actuate the master brake valve; wherein actuation of the master brake valve obstructs the flow of the fluid in the first hydraulic circuit, such that the relative reciprocation of the cylinder and the piston (125, 130) of each assembly (126, 129), and reciprocation of each cam follower, is inhibited or prevented, whereby the cam followers thereby inhibit or prevent rotation of the cam; wherein each hydraulic cylinder assembly (126, 129) is movable between a first position in which the cam follower is maintained in contact with the cam and a second position in which the cam follower is disengaged from the cam, and further comprising an engagement and disengagement system (106, 115) configured to move each hydraulic cylinder assembly (126, 129) between the first position and the second position; and wherein the engagement and disengagement system (106, 115) comprises a single acting hydraulic cylinder (120, 136) with a single acting piston (119, 134) which is attached to each hydraulic cylinder assembly (126, 129) and a second hydraulic circuit connected to each single acting hydraulic cylinder (120, 136), wherein supply of hydraulic fluid to the single acting hydraulic cylinder (120, 136) moves the hydraulic cylinder assembly (126, 129) into the first position; wherein the engagement and disengagement system (106, 115) is coupled to the actuation system and is configured to move each hydraulic cylinder assembly (126, 129) into the first position upon actuation of the master brake valve and to lock each hydraulic cylinder assembly (126, 129) in the first position.