I have a Stihl FS 36 which I was given. I was using it today and tried to bump the knob to let out some string but none came out. I tried to disassemble the spool to remove what I presume is a tangled mess.

I have one slight problem, the bump knob is not budging. I tried for a while by hand and then I brought out a vice grip and I still couldn't get it to budge.

Does anyone have any ideas on how to screw off the bump knob?

Here is a forum post that has the same spool set up as mine in case anyone wonders exactly what it looks like.

  • Just a guess but on some string trimmers the screw is a left-handed thread, so it unscrews clockwise. Did you check the manual? – Jim Garrison Jul 2 '16 at 5:13
  • 1
    @JimGarrison Most curved-shaft trimmers have a right-hand-threaded knob, while most straight-shafts have left-handed. It's because the straight-shaft trimmers have a right-angle-bend gear cluster which reverses the spin of the spool. – Ross Patterson Jul 2 '16 at 13:16
  • Just checked mine Ross is right .+ – Ed Beal Jul 2 '16 at 14:36
  • The bump knob assembly doesn't last forever. It may need replacement. They're sold separately. How to get a jammed one off -- force. – Tyson Jul 2 '16 at 22:52
  • There was A LOT of force needed to get it to come off. I needed vice grips and a second pair of hands, but we finally got it. The head needed to be replaced or something. I ended up buying a new straight shaft weed eater. – DrZoo Aug 24 '17 at 17:47

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