Abstract: According to the present invention there is provided an exhaust brake of the sliding valve gate type comprising a piston cylinder device for operating the slidable valve gate to open or close the exhaust brake, an aperture through the valve gate for relieving manifold pressure, and control means for controlling the passage of exhaust gases through the aperture in the valve gate, wherein the control means is variably selectable to control venting of exhaust gases according to driving conditions of a vehicle as determined by the driver of the vehicle.