I also have a reddy heater 115000 btu fan spins freely until I put the plate on the back of the motor back on. It then instantly tightens the fan so it won't spin. The black circle on the back of the motor is what causes the drag. How do I stop it from slipping back?

Make sure the all the fins (4 of them) are in the right way. I think they are longer on one side than the other. You may need to remove the black rotor and make sure the plastic insert isn't broken and check for build up on the plate behind it and the plate that you have already removed. Do not loosen the metal ring around it unless you have some feeler guages to reset the gap between the ring and the black rotor.The only thing that holds the black rotor on the shaft is the plastic insert. There also isn't very much clearance between the black rotor and the plates that is sandwiched between so it doesn't take much build up on either surface to cause a problem. One more thing, do you have the foam input filter air installed. Without it, the compressor will **** in dust, dirt or what have you and that will cause buildup around the rotor. It will also cause the rotor to break if it gets tight enough.