I have a 87 ranger 2.9. My alternator light came on the other day. Had the battery check. They said it was good. Took the alternator to advance. And it was putting out 13 volts. They want around $100 for a rebuilt one. But could order the brushes for a little under $5. So, my question. Can you rebuild the alternator? And do you special tooks to do the job? This is the factory alternator it has been a good one.

 

Usually it just requires a new regulator when it's the built in kind. The regulator itself is probably good but it also has the carbon slip-ring brushes as part of it. Those wear out and account for most alternator "wear outs".

If the shafts and bearings are still reasonably tight, you just need to replace the onboard regulator if it's a 2G or 3G, I do believe. I've done this before for other people.