I'm not too familiar with how mechanical brakes work in parallel with an ESC. Do you use a Y connector?
You can use a Y connector for the ESC and brake or you can just use the 3rd channel of your tx/rx and mix throttle and brake. This is how I set up my revo conversion because I don't like using a Y connector.
Castle Neu 1520 on 6S LiPo Powered Gmaxx (Nitro Killer)
Predator with OS .21TM
Supermaxx with Mach .26
Revo with OS .18TZ
Kyosho ST-RR Conversion
Ofna CR with Tekin ESC/Motor (2)