Repeatedly Clogged Printrbot Simple Extruder
I had a similar issue on my Printrbot Simple Metal. I believe my problem was initially caused by clogged nozzle which I replaced, however the jamming persisted. I can't say for sure that it was acting exactly as you describe but I think it may have been similar. I noticed that the little red insulating sleeve was pushed up higher than it was when I got it from Printrbot. When I lowered this my problem seemed to go away.