I have been using my bosch drill to power a small wood turning lathe. Now the drill is always in hammer drill mode even though it is not switched to hammer drill. I opened the drill up but it looks like a bit of a maze in there. Can anyone point me in the right direction here before i dump the drill. What I should be looking for etc. Id love to repair this myself if possible.

  • "Hammer Drill Mode"? Is it possible that you are referring to the torque setting? It would help if we knew the model number.
    – Zach
    Apr 15, 2014 at 23:21
  • @Zach my DeWalt drills both have modes for hammer drilling and regular drilling. My cordless also has a collar to adjust the clutch for screwing in screws. The hammer drill mode chews through batteries on my cordless, which is why I bought a corded hammer drill. It sounds like the asker may want to figure out how to turn off hammer drill mode when not needed to conserve power.
    – user4302
    Apr 16, 2014 at 2:30
  • there is a switch on the top of the drill to have it as a hammer drill (for drilling masonry) or a normal drill( for drilling wood etc). The drill is permanently running as a hammer drill no matter what way the switch is.Its a bosch PSB 900 RES
    – Fergal
    Apr 17, 2014 at 21:06

1 Answer 1


Really old question, but here goes.

Inside the drill, this is the gear that will make the Hammer action (an un-related example) enter image description here As the drill turns, the ratchet action of caused from the teeth sliding against each other creates the hammer action you feel in Impact Drills.

The Switch to activate this is obviously failing in your drill.

The Complicated image below describes your problem.

The Drills drive shaft (#3) in the pic, either makes heavy contact with the ratchet (2) or not. depending on its vertical position (how left or right the shaft sits on in the casing) That position is determined by the shifter knob (point #1 /A) as you turn that knob, the plastic resses is either deep or shallow and makes the shaft either engage the impact driver or not.

There is a spring (at point B) which applies constant pressure on the shaft, making it always want to be in a certain state (either hammer or not depending on drill)

Essentially, you need to push the drive shaft (3) out of hammer drill.. check if the knob (A) is somehow broken, or if the Spring (B) has collapsed and not giving any push.

Alternatively, if you are feeling brave, you could try to remove one of the sides of the impact driver, thereby disabling the hammer action completely.

enter image description here

  • Are both sides of the gear/ratchet with teeth rotating? (Gear/ratchet = 1st image = part 2 in other image) I expect one to be slower or blocked.
    – simohe
    Nov 15, 2021 at 13:01

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