0jtobakoBest Answer 10 years ago ReplyUpvoteSounds like the cup gasket wore out. Assuming that it's built to be repaired, unscrew the top of the pump tube and pull the handle and rod out. On the end of the rod is going to be a piston with a rubber or leather ring around it and a nut and washer holding the gasket on. If you unscrew the nut and take off the washer you should end up with a (probably ripped or worn out) bowl shaped piece of leather or rubber. The trick is to find or make a replacement : ) Oh, and make sure you remember which way the cup goes on or it won't work : ) A newer pump might have an o-ring and a one way valve. Either one might be worn out, broken or have something stuck in them.