AFTER ABORTING DUE TO AN UNSAFE TKOF WARNING HORN; THE FO DID NOT WANT TO TKOF AGAIN UNTIL COMPANY MAINT SIGNED OFF THEIR SYS FOR ANOTHER FLT RELEASE. FLC DISCOVERED THAT THE CAUSE WAS DUE TO THE SPD BRAKE HANDLE NOT BEING FULLY STOWED. HOWEVER; THE CAPT INSISTED THAT IT WAS 'OK' TO TKOF WITHOUT MAINT CHK OR REDISPATCHING.

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WE HAD COMPLETED ALL CHKLISTS PROPERLY. IT WAS MY TKOF. AS I BROUGHT UP THE THRUST LEVERS; WE GOT THE 'UNSAFE TKOF WARNING' HORN. WE REJECTED THE TKOF AT ABOUT 10 KTS AND EXITED RWY. I TOLD THE CAPT WE MIGHT WANT TO RETURN TO GATE. HE SAID LET'S FIND THE PROB FIRST. WE DOUBLECHKED ALL POSSIBLE ITEMS BUT STILL GOT HORN. THEN I NOTICED THE SPD BRAKE HANDLE WAS IN THE 'DOWN DETENT' POS AS IT SHOULD BE; BUT THE LITTLE METAL TAB THAT LOCKS IT IN PLACE HAD ABOUT 1/8 INCH MORE TO GO TO HIT THE PHYSICAL BOTTOM. I GAVE IT A LIGHT TAP AND THAT TOOK CARE OF PROB. WE WERE BOTH SATISFIED THAT WAS THE PROB. I SAID WE STILL NEEDED TO GO BACK TO THE GATE AND HAVE MAINT SIGN IT OFF AS BEING OK. CAPT ASKED ME IF I WAS SATISFIED THAT IT WAS SAFE TO GO. I SAID I WAS 100 PERCENT CERTAIN WE WERE SAFE BUT STILL NEEDED TO RETURN TO GATE. THE REASON I GAVE WAS THAT IF WE GOT A 'TKOF WARNING HORN' WE EITHER HAD MECHANICAL PROB OR WE DID NOT DO OUR CHKLIST PROPERLY. IF WE DON'T RETURN TO THE GATE; WE ARE SAYING BY DEFAULT THAT THE AIRPLANE IS OK THEN THE PROB WAS IMPROPER CHKLIST PROCS BY CREW. I TOLD CAPT THERE HAD BEEN PROBS WITH THE FAA SEVERAL YRS AGO CONCERNING THIS MATTER. HE NOTED MY DESIRE TO RETURN TO THE GATE; BUT TOOK CAPT AUTH AND SAID WE WOULD NOT RETURN TO THE GATE. WE TOOK OFF AND PROCEEDED NORMALLY. I HAD NO PROB WITH THIS FROM A SAFETY STANDPOINT; BUT I AM VERY CONCERNED THAT THE FAA WILL COME AFTER US.