there should be a small clip which goes under the knurled knob. pull it back and arm should pull off. it sounds like you are messing with the spring that supplies pressure to the wiper against the winshield. the spring clip that holds the arm on is very small and just runs down along and under the knurled knob. I think -- I'm 270 miles from our truck and can't run down and look.
unbroke


Can U believe it? My wife says: "I want an old pickup truck" so I HAD to buy it!!
'50 Chevy 3100 5 window.