I recently noticed that my power drill was not functioning properly. When tilted or when performing heavy load tasks like sanding with a wire wheel the motor would stop and the on/off switch would stop functioning. Moving the drill around would cause the switch to work again.

I took the drill apart to see what may be happening. The brushes looks fine. I noticed that one of the housings for a brush was not attached to the case. It easily popped out of its encasing. I suspected that this was the cause of the problem. For example when the drill was upside down the housing would come out to cause the brush to no longer make contact with the commutator and stop the electrical flow.  The diagram below shows where the problem was. This drill is a Craftsman model 315.101230. I simply used Crazy Glue to attach the loose part and put the drill back together. This fix worked and the problem went away.

craftsman 3/8 drill

A note to anyone who may have this problem and wishes to do this repair. This drill seemed hard to take apart and put back together as it required some dexterity. This seems to be a lower end model and does not appear to be designed for servicing. On the other hand the drill seems to be build solidly so with possible brush change in the future it should last for many more years.