What was found
AFTER TAKEOFF, RAISED GEAR HANDLE TO UP POSITION. NOSE GEAR POSITION LIGHT REMAINED ILLUMINATED GREEN. GEAR UNSAFE LIGHT ILLUMINATED RED, BOTH MAIN GEAR INDICATORS EXTINGUISHED. MAIN GEAR DID NOT SEEM TO RETRACT BY AUDIBLE & TACTILE CUES. PERFORMED GEAR SLOW CYCLE CHECK, FOUND GEAR WOULD NOT RETRACT FULLY, OR NOT AT ALL ON SEVERAL ATTEMPTS. ALSO NOTED NOSE WHEEL STEERING WOULD NOT CENTER WHEN GEAR WERE RETRACTED. REMOVED & REPLACED NWS ISOLATION VALVE, AND ACCUMULATOR ISOLATION VALVE. REMOVED & REPLACED NOSE WHEEL STEERING UNIT. PERFORMED OPS AND LEAK CHECK OF STEERING & GEAR, OPS CHECKED GOOD IAW MM 32-50-00.