This is a Sunbeam LeChef food processor, Catalog # 14-11. We
inherited it from my wife's mother. It's at least 20 years old. It
sat unused for about 15 years until we developed a need for it about 9
months ago. Since then we have used it many times. It has always
worked properly.

Our dog has no teeth so we use it to grind kibble into a powder. It
has worked great for this, week in and week out. A few nights ago
when we started to grind our regular three cups of kibble the cutter
blade rose on it's support post until it reached the lid. This was
high enough that it came off the center post, began to wobble and made
a disturbing bumping sound.

We tried to grind the same batch about five or six times. It runs for
a short time, then repeats the behavior. By the end it had gotten to
the powder stage and the blade quit rising. To test it I ran it with
nothing in the bowl and again with water -- it will run properly
apparently forever this way.

Anybody know what's causing this?