Confirm my diagnosis?

Long story short.
Been having intermittent charging probs on my 97 grand cherokee 4.0 with stock nippon alt.

When alt stops charging i pop the hood and tap on the back of the alt case with a pair of pliers (light taps do it)and it starts charging.

Park the jeep and start it and alt not charging so i tap it and it charges...

Sticky brushes and or slip ring needs polished up?
Would hate to drop $100 if $15 brushes will get me more miles down the road....
TIA

Worn/sticky brushes is the likely cause.

Thanks for the input.
Since brushes arent available at parts stores around here (that i know of)

Ill grab some good ones at the pick n pull tomorrow and report back with results for future search purposes.

Ok just an update.
Looks like worn and sticky brushes were the issue.
Inner brush was almost gone and was gunked up with worn brush dust.(was the reason why it started charging when i tapped on the back of the case with pliers)
Slip ring was fouled with carbon arching so i used scotchbrite to clean it back to shiney.
All seems well

So the lesson here is if you are having an issue with your alternator charging fine but stops after you shut engine off try tapping on the back of the case with it running.

If it starts charging then you can be almost certain worn/gunked up brushes and or carbon traces from brushes making intermittent contact with the slip ring is the likely prob.

Nippon denso alts are super easy to take apart to get to the brushes so i highly recommend this procedure before you drop money on a new alt.

Hope this helps someone in the future.

Check this out

http://www.naxja.org/forum/showthread.php?t=1113950&highlight=alternator+brush

Typically if the dashboard gauge shows 9 volts there is an alternator issue, usually worn brushes. If the dashboard gauge shows 19 volts, there is usually a connectivity issue with the battery clamps, or corroded battery wires. Both examples assume the battery is good.

Yea ive definitely learned alot from this experience.And learned a lot more trouble shooting skills.

In my situation i chased my tail on this because my brushes started flaking out the day after i had the pcm opened to resolder pins on the board that caused an intermitten stalling issue.

So i said well the pcm regulation driver didnt like what i did while i was in there (not knowing that the brushes decided to start failing)

I then proceeded to do th external regulator mod that had me chasing my tail for another week because the external regs would start off working fine then after a couple days stop.

Finally after having the battery replaced (under warranty)and having the alt test good 3x on the bench even during the last one i wacked on it.

I hooked it back up to stock reg through pcm and all was well for a week then one night after work i went to leave and bam no charge.

That made me pissed so i got under the hood and beat the shit out of the pcm (no charge)
Then beat the alt. And here we are....bad brushes the entire time!!
I feel a bit wee todd id.
Oh well live and learn.