Dewalt Impact driver DCF840 Teardown

ID: 157490

Description: Dewalt 1/4" Impact driver and battery teardown.

Steps:

1. This guide covers the complete tool and battery.

2. Remove the 8 screws holding the two halves together.

3. Battery Contacts
4. Potted Circuit
5. Brushless Motor
6. Impact Gearbox

7. With the Gearbox removed we are left with the motor on one side and the light ring on the other.

8. Neutral: Trigger Locked
9. Forward
10. Reverse
11. When selector is neutral this tab keeps the trigger from being depressed

12. Gear box fits into housing as a press fit with two clips. Releasing the two clips allows the gear box to be freed from its housing.

13. Planetary gear set: reduce motor speed and increase torque
14. Splines to gear box case
15. Internal teeth for planetary gear set
16. Spring (hard to see) for impact function: base spins and strikes output drive labeled with blue arrow in last picture

17. 20V battery at full charge
18. Nominally around 18.5V

19. Remove four screws to open battery
20. Spring for latch to lock battery into tool

21. 5 cells nominally 3.7V in series.
22. 0V (GND)
23. 12V (likely for LED light ring)
24. 3.7V (not connected to tool)
25. 18.5V
26. 18.5V (main output)