Cordless Drill: No Variable Speed

The brushes provide the electrical current to the armature by riding on the commutator. If these brushes become worn down too much, it can impact the drills ability to work at different speeds, as they will not be able to supply the correct voltage to run the motor.
To check the condition of these brushes, begin by removing the battery. Take out the screws on the end cap and remove from the drill. Locate the spade connectors and remove them with pliers. Insert a small screwdriver in the access hole, close to the center of the housing, and gently pry out the brush.
On some drill models, you will have to remove the case on the housing and remove the two screws securing the transmission to the drill on the same side that the cover is located on. Then remove the cover. One brush will be in the cover and other under the motor. Take out the hold-down bracket on the motor to access the second brush. Check for wear – severe brush wear is a major culprit. If detected, replace.
Insert back in the housing and reinstall the spade connectors. Tighten the motor back in the housing and with the hold-down bracket. Reinstall the cover on the housing and reattach the two screws that secure the transmission to the drill. Reattach the end cap and test the drill.

The speed selector switch allows you to choose what speed you want to operate the drill at. If you find this switch has stopped working, then you will need to replace it. Remove the end cap and separate the case from the cover. Take out the two transmission screws on the same side the cover is located on and remove. Lift all the components out of the casing, including the motor, gear assembly, trigger assembly and chuck. Using tweezers, grab the metal leg on either side of the switch and lift it outwards from the case. Remove the other leg manually – it should easily come out. Clean out any debris inside the holes where the metal leg inserts into. Install the new switch and reinstall the motor, gear assembly, trigger assembly and chuck back in the housing. Now, reattach the cover and secure it tight. Reinstall the two transmission screws and the end cap.