spray all around the seam where it comes apart with WD_40 & leave it soak over night..... or use a strong thin screw driver to push the tabs in & pry it open carefully not to brake it.
Gmanrocksteady: my question was asked 3 weeks, 4 days ago. If I had waited for an answer, with all the rain we have had, my grass would have been up to my ears.
Wal-mart wouldn’t replace it since it was a seasonal item and had only a 30 day replacement guarantee.
I figured, “what the heck, it works or breaks” it wasn’t doing me any good without line anyway.
I tried your solution before I asked the question, and it did not work. I removed the lower part of the weed eater shaft by loosing the clamp in the middle of the shaft, depressing the lock button and pulling down. I got help, and we inserted a screw driver into the slot where the lower cable connects with the upper cable, (make sure the screw driver is large enough to fit flush in the cable slot so there is no slippage, you don't want to damage the linking slot) one held onto the screw driver while the other turned the bump knob counter clock wise. After a lot of muscle was applied, the bump knob finally gave and screwed off. I replaced the shaft, put trimmer line on and it works perfect. The bump knob had got too tight for some reason to remove. I really like this weed eater, it's light and with the curved handle I can maneuver it any way I need to do the job.
use a flat head screwdriver and stick it in between the knob and the casing, this will put pressure on the bolt inside if it is stripped, then turn counter clockwise. It should come loose.