Today on a ride my girlfriend's 63 Schwinn Hornet ran into problems. A little over an hour into the ride the hub began giving problems. She complained that the hub became harder to pedal. She had the hub serviced recently by a local bike mechanic who repaired the bearings and added some fresh grease. She'd said at the start that the hub seemed tougher to push along than it was before slightly, but right at the end of the short ride she had a failure of the hub because the rear wheel began to struggle. Apparently there was more friction than there was before and the bike became very difficult to pedal. I looked some info on this problem up and one site suggested that it was old grease. I'm not totally convinced it's this because the hub suddenly became significantly more difficult only at the end of the ride. Any ideas?