Cars House

My starter on my '84 CJ-7 seems to be dragging when trying to start it sometimes. What causes this and how can I fix it?
First thing I do is clean all the battery cables at both ends with special attention paid to the starter solenoid on the fender. Then if it is still dragging, I remove it and check the brushes. Lots of times they are just gummed up with mud and can be cleaned with lots of WD40. They also can be replaced easily if worn.