It sounds like your inner shaft may have come loose from the
motor. The inner set screw at the top of the shaft where it
attaches to the motor has a screw that can either wear out or
come loose. This part rotates inside the housing between the
motor and the black outer sheath.
If the motor is able to run you don’t have a motor problem. If
the motor slows when drilling it could be that you need new
brushes in the motor. I have never replaced any of these brushes
on any of my motors so I don’t think it may be that.
The inner shaft inside the spring of the shaft is the probable
cause. At the top of you shaft see if you can free it from the
motor, You may have a set screw on the outside of the housing. On
the unit I have the there is a small set screw close to the black
rubber outer sleeve. Unscrew that screw. This will remove the
outer black sheath. If the inner shaft and spring is the problem
it may come off the motor now. It should not.
The housing directly below the motor has a bolt shape built
right into it. Take your whole motor to a vise and clamp the bolt
part in the vise. Turn the motor counter clock wise. This will
expose the shaft part that bolts onto the motor. I would bet this
is the problem. Sometimes you can just tighten this set screw on
the motors shaft. Tighten it and see if you problem goes away.
If the spring come out of this screw housing that bolts to the
motor shaft you need a new part. If you need to replace the part
you need to get a new inner shaft & spring. I think they sell
inner shafts and springs together. I don’t think they are
outrageously priced. Your supplier should carry these parts. If
not any of the major tool suppliers have them. Just make sure to
tell them your model number.
TR the Teacher & student