I have the Park 400 Eflite with the Gearbox 6.6x1 ratio and I have crashed several time wide open and it just pushed the spur gear off of the splines on the prop shaft I just pushed it back on the splines and it worked great, and for setting up the gear mesh I just put a piece of thin grocery bag plastic into the gears(this is how Eflite/Horizon says set it up) and just pushed them TIGHT together and they are great never had a problem after about 50 flights and I put a dab of white lithium grease on the spur gear about every 5 flights and I have been nothing but pleased with the gearbox set up,,,,