What was found
GEAR HANDLE WOULD NOT MOVE TO THE GEAR UP POSITION AFTER TAKEOFF. ALL GEAR LIGHTS INDICATED THE GEAR WAS IN THE DOWN AND LOCKED POSITION AND THERE WAS NO UNSAFE LIGHT ILLUMINATED. JACKED ACFT AND FOUND NOSE STRUT CHAMBER PRESSURE WAS LESS THAN 5 PSI. REPLACED PACKINGS AND BACK-UP RINGS ON SCHRADER VALVE WITH NEW. SERVICED STRUT MM CH 12-10-38 TO PROPER PRESSURE. ACCOMPLISHED GEAR SWINGS IAW MM CH 32-00-01 & OPS CHECK GOOD, 5 TIMES. DOWNJACKED AND REJACKED ACFT AND PERFORMED GEAR SWINGS AGAIN - NO DEFECTS - DOWN JACKED ACFT.