I found this on another forum and thought it might help.....Turn the chair over on its side ( the side opposite the handle). Now be carefull of the springs under there.. Work the handle.. YOu need to get the foot rest all the way up, then you will see a small spring which holds a little rod in an L shaped channel. When the rest is all the way up, the spring should pull the pin into the other part of the L. Play with it a little.. As they wear, this is where it wears and catches...
: If you see a burr on the metal, that is keeping it from sliding in... once you get it freed up and know how it is working... you can file off the burr to get it working smooth again. Add some grease to the L shaped channel for good measure.
Rich, December 2006