What was found
WHILE WE WERE AWAITING TAKEOFF CLEARANCE WITH THE PARKING BRAKE SET, RECEIVED A MASTER CAUTION WITH A R HYD QTY EICAS MESSAGE FOLLOWED BY A R HYD PRIM PUMP EICAS MESSAGE. ACTIVATED THE STATUS PAGE AND WITNESSED THE RIGHT HYDRAULIC RESERVOIR QUANTITY DROP TO ZERO. ADVISED ATC AND CLEARED THE RUNWAY. COMPLIED WITH THE QRH, ADVISED GOC , RETURNED TO THE GATE. R & R SELF RESETING FUSE VALVE IAW AMM 32-42-02-4. RIGHT HYD SYS FILLED TO FULL IAW AMM 12-12-01-3 & PERFORMED HYD SYS PRESSURIZED ON ALL SYS IAW AMM 29-11-00-2 READ NORMAL WITH NO LEAK NOTED, PERFORMED RIGHT ENGINE RAN UP CHECK IAW JRH WITH ALL PARAMETER READ NORMAL IAW AMM 71-00-00-2-3. NO EICAS MESSAGE RELATED FOUND. ACFT OK FOR SERVICE.