The paper jams in the bottom because the leading edge hasn't reached the correct sensor in time, thus causing a jam message. Do a sensor test on the front panel of the printer before replacing any parts. Go into Diagnostics/Sensor test and you will see the letters across the top follwed by numbers below. Then you want to toggle the sensors located through out the paper path-usually black plastic hanging done into the tray areas. Up in output tray has black plastic hanging down-sensors. lift top cover and you can see the sensors on the left side of the top a black horseshoe shape is a sensor. This will help with the correct parts needed to be replaced.