If a drill chuck stops turning under load, it is often due to a slipping spindle pulley caused by worn or smooth surfaces between the pulley and drive sleeve. To fix this, remove the left-hand thread pulley nut by turning clockwise, then remove the spindle pulley using a rubber mallet. Lightly roughen the inner diameter of the pulley and the outer diameter of the drive sleeve with fine-grit sandpaper to improve grip. Reinstall the pulley and tighten the nut counterclockwise. If issues persist, further inspection or replacement may be needed.
If your drill chuck stops turning under load, the most common cause is a slipping spindle pulley, the pulley located directly above the chuck.
Over time, the connection between the spindle pulley and the drive sleeve can become worn or smooth, causing the pulley to lose grip. This results in the chuck stopping even though the motor continues to run.
🛠️ How to Fix a Slipping Spindle Pulley
Remove the (LH) Pulley Nut
This is a left-hand thread nut; turn it clockwise to loosen.
Remove the Spindle Pulley
Use a rubber mallet or dead blow hammer to gently tap the sides of the pulley while pulling it upward.
Once it pops loose, set it aside.
Access the Oscillating Mechanism (if needed)
With the pulley off, you'll also be able to reach the screws holding the oscillating mechanism.
Improve Surface Grip
Use fine-grit sandpaper or emery cloth to lightly roughen:
The inner diameter (I.D.) of the pulley
The outer diameter (O.D.) of the drive sleeve
This helps the pulley grip more securely when reinstalled.
Reinstall the Pulley
Press the pulley back onto the drive sleeve.
Tap gently with the mallet to seat it fully.
Reattach the (LH) Pulley Nut
Tighten it securely (left-hand thread, turn counterclockwise to tighten).
If the problem persists after this repair, there may be additional wear on the spindle or drive sleeve that requires inspection or replacement.