Stripped down for cleaning.The next day,there I was,lying as near prone along the bike as I could,coming down the A74 dual carriagewayalmost 20 miles downhill,at nigh on 100 miles an hour,I could feel a knocking sensation through the bike.So,reluctantly,I slowed down.Convinced it was the footrests I'd taken off to clean,the day before,I didn't use the back brake,in case the footrest fell off.So,a mile or so later I came to a halt.There was nothing wrong with the footrests;the rear brake linkage had come adrift,and the knocking sensation,was the brake arm(drum brake) bouncing off of the road.The hexagonal locking nut had worn flat.Ouch!