AN ACR LTT CREW LOST A BOLT IN THEIR LNDG GEAR CAUSING A VIOLENT SHIMMY.

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I PERSONALLY CONDUCTED A THOROUGH PREFLT BEFORE WE FLEW THE AIRPLANE. AFTER A SMOOTH; UNEVENTFUL TOUCHDOWN ON RWY 1L AT DULLES INTL ARPT (IAD); THE AIRPLANE DECELERATED NORMALLY. UPON SLOWING TO APPROX 40-50 KTS; THE AIRPLANE SHOOK VIOLENTLY. WE WERE ABLE TO SLOW DOWN WHILE REMAINING ON THE RWY CTRLINE. WE THOUGHT THAT WE HAD POSSIBLY BLOWN A TIRE; SO A GENTLEMAN FROM ARPT OPS DROVE OUT TO LOOK AT OUR TIRES AFTER WE HAD TURNED ONTO THE TXWY. HE SAID THAT ALL OF OUR TIRES APPEARED TO BE INFLATED. WHILE TAXIING TO THE GATE; THE AIRPLANE SHOOK VIOLENTLY AGAIN -- VERY SIMILAR TO THE FIRST TIME. WE CALLED OUR MAINT OPS. THE MECH TOOK A QUICK LOOK. HE SAID HE DIDN'T SEE ANYTHING OBVIOUSLY WRONG WITH THE AIRPLANE OR LNDG GEAR. WE CALLED OUR MAINT DEPT AGAIN; AND THEY SAID TO SEE IF WE COULD MAKE IT HOME WITH THE AIRPLANE. WE WENT OUT TO THE AIRPLANE AND CONDUCTED ANOTHER THOROUGH PREFLT; AND NOTICED A PROB WITH THE R MAIN LNDG GEAR. A BOLT ON THE TORQUE KNEE HAD COME OUT; AND THE R LNDG GEAR HAD SPUN AROUND 180 DEGS. NEEDLESS TO SAY; THE AIRPLANE WAS UNABLE TO BE FLOWN. THE FOLLOWING DAY; 2 MECHS REPLACED THE LNDG GEAR; AND WE FLEW BACK TO OUR BASE.