DIAGNOSIS The chuck's internal jaws are worn or the spindle it mounts to is bent. Wear from heavy side pressure or dropping the tool is the most common cause.
FIX Replace the chuck. It's a direct job.
- Open the chuck fully.
- Look inside for a left-hand threaded screw (turns clockwise to loosen).
- Secure that screw, then use a large Allen key or chuck key in the jaws to unscrew the entire chuck (standard right-hand threads).
- Screw the new chuck on hand-tight, then tighten the left-hand screw inside.
IF THAT DIDN'T WORK If a new chuck still wobbles, the spindle shaft itself is bent. This requires replacing the entire transmission assembly, as the spindle is part of it.
HEADS UP When installing the new chuck, do NOT use an impact wrench. Hand-tighten with the Allen key. Over-torquing can strip the spindle threads, forcing a full transmission replacement.