A B757-200 RETURNED TO THE FIELD DUE TO UNSAFE INDICATION ON THE L MAIN LNDG GEAR CAUSED BY WIPE RAG INTERFERING WITH THE GEAR SENSOR.

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I AND ANOTHER EMPLOYEE INSPECTED AND LUBED ALL 3 LNDG GEAR ON ACFT X. IT HAD AN EMER LNDG FOR L-HAND MAIN LNDG GEAR DID NOT INDICATE DOWN AND LOCKED REF LOG PAGE #XXXXX. THE CAUSE OF THE PROB WAS FOUND TO BE A RAG HUNG UP IN THE SENSOR. I LUBE A GEAR STARTING AT THE TOP AND WORK DOWN; THAT WAY I DON'T MISS ANYTHING AND CLEAN AS I MOVE DOWN THE GEAR. I NEVER LEAVE TOOLS OR RAGS ON THE ACFT WHEN NOT USING THEM. THEY REMAIN ON TOP OF THE LADDER AND WITH ME. I HAVE BEEN USING THIS METHOD FOR THE LAST 10 YRS. AFTER THE GEAR IS LUBED; WE CLEAN UP THE AREA; REMOVE LADDERS AND ANY GREASE THAT MAY HAVE HIT THE FLOOR. THERE WERE 2 OF US LUBING ALL 3 GEAR AND 2 SETS OF EYES CHKING EVERYTHING FOR PROBS AND FOD. WE FINISHED THE GEAR AROUND XA00 HRS AND MOVED ON TO THE NOSE GEAR. AFTER WE LEFT THE GEAR; WE DIDN'T RETURN TO WORK IN THAT AREA AGAIN THAT NIGHT. IT WAS LUBED AND INSPECTED AND THE AREA CLEAN. ON THESE 'A' CHKS; THERE ARE SEVERAL CARDS THAT HAVE MANY MECHS WORKING IN COMMON AREAS. THE TRAILING EDGE WING LUBE WAS ALSO DONE THAT NIGHT; THE INBOARD FLAP XMISSION IS IN THE L-HAND WHEEL WELL ALSO. THERE WAS A WORK CARD FOR GENERAL VISUAL INSPECTIONS -- ALSO THAT CARD HAS YOU INSPECT THE DELTA 'P' INDICATORS ON THE HYD FILTERS LOCATED IN THE WHEEL WELL ALSO. ALSO; PRESSURE IS RELEASED FOR THE HYD IN THE WHEEL WELL; NORMALLY DONE WITH A RAG TO KEEP YOUR EYES FROM BURNING FROM THE VAPORS. WE CLEANED UP OUR AREA AND LEFT. I DIDN'T SEE ANY RAGS IN THE GEAR AT THAT TIME. I DON'T KNOW IF SOMEONE ELSE LEFT A RAG IN THE AREA LATER OR IF IT WAS LEFT IN THE WHEEL WELL AREA IN A SPOT AWAY FROM THE GEAR AND BLOWN AROUND ON TKOF AND ENDED UP ON THE GEAR OR IF IT WAS PICKED UP ON THE TAXI TO THE GATE. I TALKED TO THE GUYS WHO TAXIED THE ACFT TO THE GATE AND THEY SAID THEY DID A WALKAROUND ALSO BEFORE TAXI AND SAW NO RAGS OR FOD IN THE GEAR OR ENGS.