A SF340 DEVELOPED A SEVERE YAW DURING THE TKOF ROLL. THE CAPT REJECTED THE TKOF.

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AFTER BEING CLRED FOR TKOF; I ADVANCED THE PWR LEVERS AND CALLED 'SET PWR.' THE PWR WAS SET AROUND THE SAME TIME WE REACHED A SPD THAT THE TILLER WAS NO LONGER NECESSARY (APPROX 60 KIAS). AT THAT MOMENT THE ACFT YAWED APPROX 20-30 DEGS TO THE R; WHILE I WAS TRYING TO MAINTAIN DIRECTIONAL CTL WITH THE RUDDER. THE RUDDER WAS INEFFECTIVE AT REALIGNING THE ACFT WITH THE RWY; HOWEVER; NO FURTHER YAW TO THE R OCCURRED WITH FULL L RUDDER. MY FO AND I IMMEDIATELY RECOGNIZED AN ABNORMAL SITUATION; I CALLED FOR AN ABORT AT APPROX 70 KIAS; AND WAS ABLE TO REALIGN THE ACFT WITH THE RWY CTRLINE USING THE TILLER. WE WERE ABLE TO EXIT THE RWY WITHOUT DRASTIC MEASURES OR EXCESSIVE BRAKING. THE MAX SPD NEVER GOT ABOVE 80 KTS. WHEN I REALIZED THE EVENT; I CALLED FOR AN ABORT; RETARDED THE PWR LEVERS TO GND IDLE (WHILE MAINTAINING FULL L RUDDER) AND REGAINED DIRECTIONAL CTL THROUGH THE TILLER. THE ACFT WAS MOVED OFF THE ACTIVE RWY AND AN AFTER LNDG CHKLIST WAS ACCOMPLISHED. AT THAT POINT; WE CONTACTED GND; TOLD THEM WE NEEDED TO RETURN TO THE GATE; NOTIFIED OPS ON THE FIELD OF THE EVENT AND WERE ASSIGNED A GATE. I AM UNSURE AS TO WHAT CAUSED THE ACFT TO YAW TO THE R. IT HAPPENED SO QUICKLY; AND WAS IDENTED AT SUCH A SLOW AIRSPD THAT THE ENTIRE EVENT ONLY LASTED A SECOND OR TWO. I REALLY HAD NO FORWARDING OR FORESIGHT THAT THIS EVENT WOULD OCCUR. I DON'T FEEL THAT MUCH CAN BE DONE BY A FLT CREW TO PREVENT THIS FROM HAPPENING AGAIN. I FEEL THAT IT WAS JUST A MECHANICAL IRREGULARITY THAT HAPPENED AT THAT MOMENT. I FEEL THAT OUR CREW'S EARLY RECOGNITION OF THE PROB AND AN IMMEDIATE DECISION TO ABORT THE TKOF VERY WELL MAY HAVE SAVED DAMAGE TO THE ACFT AND POSSIBLE INJURIES TO THOSE ABOARD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE ACFT REMAINED GNDED FOR SEVERAL HRS THAT DAY WHILE MAINT CREWS CHKED FOR FAULTS. THEY FOUND NOTHING WRONG AND THE ACFT WAS FLOWN LATER THAT DAY. THE RPTR SUSPECTS THAT A TRANSIENT FAULT OF SOME SORT DEVELOPED DURING THE TIME THAT STEERING CTL WAS XFERRED FROM THE TILLER TO THE RUDDER PEDALS. HE HAS NOT HEARD OF THIS PROB REDEVELOPING ON THIS OR OTHER ACFT.