A rotary drilling system of the type having a drill string that rotates and drives a drill bit to provide directional control in the formation of a borehole, comprising: a bottom hole assembly that includes; a drive shaft driven by the drill string, said drive shaft having an axial bore therethrough to couple drilling fluid therethrough from the drill string to the drill bit; a steering collar having an axial bore therethrough through which said drive shaft extends, said steering collar having: at least one pressure relieved piston responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar; a first thrust pad that moves in response to the movement of said pressure relieved piston, said first pad for engaging a sidewall of the borehole; characterised by at least one non-pressure relieved piston (10, 11) responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar in a direction different from said pressure relieved piston; a second thrust pad that moves in response to the movement of said non-pressure relieved piston, said second pad for engaging a sidewall of the borehole; wherein the drive shaft is rotatable within said steering collar, and wherein said steering collar is lockable to said drive shaft, whereby the steering collar is configured to rotate with the drill string and drive shaft to position said steering collar at a desired angular location in the borehole; whereby when the drilling fluid is pumped down the drill string beyond a predetermined flow rate, said pressure relieved piston is forced against the sidewall of the borehole with less force than said non-pressure relieved piston (10, 11), thereby forcing said steering collar, said drive shaft and said drill bit in a lateral direction in said borehole to thereby deviate the direction of drilling the borehole. a drive shaft driven by the drill string, said drive shaft having an axial bore therethrough to couple drilling fluid therethrough from the drill string to the drill bit; a steering collar having an axial bore therethrough through which said drive shaft extends, said steering collar having: at least one pressure relieved piston responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar; a first thrust pad that moves in response to the movement of said pressure relieved piston, said first pad for engaging a sidewall of the borehole; characterised by at least one non-pressure relieved piston (10, 11) responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar in a direction different from said pressure relieved piston; a second thrust pad that moves in response to the movement of said non-pressure relieved piston, said second pad for engaging a sidewall of the borehole; wherein the drive shaft is rotatable within said steering collar, and wherein said steering collar is lockable to said drive shaft, whereby the steering collar is configured to rotate with the drill string and drive shaft to position said steering collar at a desired angular location in the borehole; whereby when the drilling fluid is pumped down the drill string beyond a predetermined flow rate, said pressure relieved piston is forced against the sidewall of the borehole with less force than said non-pressure relieved piston (10, 11), thereby forcing said steering collar, said drive shaft and said drill bit in a lateral direction in said borehole to thereby deviate the direction of drilling the borehole. at least one pressure relieved piston responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar; a first thrust pad that moves in response to the movement of said pressure relieved piston, said first pad for engaging a sidewall of the borehole; characterised by at least one non-pressure relieved piston (10, 11) responsive to the pressure of the drilling fluid for moving axially outwardly from said steering collar in a direction different from said pressure relieved piston; a second thrust pad that moves in response to the movement of said non-pressure relieved piston, said second pad for engaging a sidewall of the borehole; wherein the drive shaft is rotatable within said steering collar, and wherein said steering collar is lockable to said drive shaft, whereby the steering collar is configured to rotate with the drill string and drive shaft to position said steering collar at a desired angular location in the borehole; whereby when the drilling fluid is pumped down the drill string beyond a predetermined flow rate, said pressure relieved piston is forced against the sidewall of the borehole with less force than said non-pressure relieved piston (10, 11), thereby forcing said steering collar, said drive shaft and said drill bit in a lateral direction in said borehole to thereby deviate the direction of drilling the borehole.