I have a problem with my drivechain at the moment as it has the tendancy to lock out when I apply a large force to the pedals. It simply wont rotate forwards at all but will spin when 'back pedalling'.
Some of the components are fairly old (Jockey Wheels are 6yrs old!) but a new chain and a clean/degrease/regrease has had no effect. All of the components are Shimano and have given me no problems in the past.
Any ideas on what might be causing this or is it just a case that old components need to be replaced?