What was found
AFTER TAKEOFF RETRACTED GEAR & BOTH RIGHT & LEFT MAIN GEAR REMAINED EXTENDED, ONLY NOSE GEAR RETRACTED. EICAS MESSAGE, GEAR DISAGREE, AFTER APPROXIMATELY 15 INCHES, BOTH MAINS RETRACTED. BACK WITH NORMAL EXTENSION. R & R MLG SELECTOR BYPASS VALVE IAW NR 4928011, 4928023 & 4928021 FOR WORK PERFORMED. OPERATIONS CHECKED GOOD AT THIS TIME.