Most likely the axle moved slightly and the brake shoes are rubbing the rotor. or the axle is moving slightly and allow the shoes to rub the rotor. If you are using locking collars make sure they are not too tight . In other words make sure you did not do anything to make things touch or bind. Check the alignment of sprockets on clutch and axle. If the axle is pinned through the bearing set screw, is the bearing exactly the same size and the hole in the exact location. Last but not least , do the bearing themselves turn freely. Were they either oiled or greased.