REINITIATING PUSHBACK FROM THE GATE AT DTW; GND CREW BREAKS TOW BAR DUE TO COM FAILURE WITH FLT CREW TO RELEASE BRAKES.

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ON PUSHBACK FROM THE GATE IN DTW; WE WERE ASKED TO CONFIGURE FOR DEICING. AFTER PUSHING BACK 10 FT; WE SET THE BRAKE; AND I TURNED OFF THE APU BLEED VALVE AND PACK SWITCHES. THE ACFT WAS DEICED; AND WE WERE TOLD THAT WE WOULD BE PUSHING BACK THE REMAINING DISTANCE. SINCE I DID NOT HAVE MY FLT INTERPHONE SWITCH VOLUME TURNED UP (SOP); I DID NOT HEAR THE CONVERSATION BTWN THE CAPT AND THE TUG DRIVER. THE NEXT THING I FELT WAS THE ACFT MOVING BACK AND THEN A LARGE JOLT. IT FELT LIKE AN IMPACT SOMEWHERE ON THE FUSELAGE. IT WAS THEN I TURNED UP MY INTERPHONE VOLUME AND HEARD THE MECH TELL THE CAPT THAT THE TOW BAR HAD BROKEN. I THEN LOOKED DOWN AND SAW THAT THE BRAKE WAS STILL SET. THE MECH TOLD US THAT HE WAS GOING TO GET A NEW TOWBAR AND THE ENSUING PUSHBACK WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 573683: TO THE BEST OF MY RECOLLECTION; THE MECH INSTRUCTED US TO SET THE BRAKES. 10 MINS LATER; THE MECH TOLD US WE WOULD BE CONTINUING THE PUSHBACK. THE FO AND I WERE RECONFIGURING AFTER DEICING WHEN WE FELT A LARGE LURCH. THE TUG CREW ATTEMPTED TO MOVE THE ACFT WITH THE PARKING BRAKE STILL SET. COM CONFLICTS BTWN THE TUG CREW AND US UP IN THE COCKPIT INCLUDED THE FACT THAT THE TUG DRIVER WAS NOT TALKING WITH US -- IT WAS A 2 PERSON PUSHBACK. ALSO; WHILE WE DID NOT HEAR THE PUSH CREW ASK FOR 'BRAKES OFF' PRIOR TO ATTEMPTING TO RESTART THE PUSH; WE WERE BUSY RE-ESTABLISHING ACFT HEAT AFTER DEICING.