Fluctuating Voltage

[nodaksn3]

I've had my '99 hundy for almost two years and really like how it drives etc., but it's been "nickel and diming" me to death, if $100 is a nickel and $1000 is a dime. Yesterday evening we went for a drive to meet friends, and I suddenly noticed the red "battery" light on the instrument panel came on. I switched my scangauge to volts, and saw that the voltage reading was fluctuating from 9 to 13 volts. I'm away from my garage and tools, so I took it to my local mechanic (misspelling intentional) to get it checked out, and after putting his reader on it, he told me that it was the alternator, and to replace it with a rebuilt one would be $500, including the part of course.
I trust the guy, but am wondering if maybe just replacing the diodes like I did on my 80 would fix the problem? Does anybody have any ideas? Might this simply be a diode problem?
I'm wondering about this hundy because my 80 (with 300,000 + miles) has never been this finicky and troublesome. On the 80 I replaced the diodes at around 250,000 miles simply because I was worried about them, and not that they gave any trouble, same with the waterpump, etc. I'm surprised that at 180,000 the hundy's alternator has apparently s*** the bed.
Is this a one banana, or two or three banana job? Can I just replace the diodes? The bearing aren't noisy or anything else to indicate any other issues with the alternator.
Thanks, Ned

 

[Supra88]

The alternator on my Hundy went bad for the previous owner with less than 100,000 miles on it.


...via IH8MUD app

 

[Sandroad]

I've not messed with alternator myself, but I was interested in the diode question. Not much on MUD from a search, but I did find this from a 2012 post:

"You can have the alternator serviced at an alternator/starter rebuilding shop. The rectifier can be replaced if it's faulty and if the alternator is open already, change the bearings and brushes as well. Most rebuilds will cost around $100 and the rectifier costs about $30 to $50 depending on the mark-up. If you rebuild it, make sure they test it to verify the alternator has a problem. They may test it and find it's perfectly fine and the problem is in the connections and/or grounding of the alternator. If you don't want to repair the alternator, you can always replace it for a couple hundred bucks."

Also, 180,000 miles is over 7 times around the world and if you don't know the history your '99 (which is 15 years old), it may be perfectly reasonable to replace a hard-working part like the alternator.

 

[re_guderian]

Alternator failures are few and far between here. If the original lasted 180K, just spend the $200 and put in a new one, good until 360K, right? Why risk failure in the boonies? Land Cruisers (all models) will eat you alive financially if you can't do your own work. An alternator failure at 180K is not too shabby...

 

[mobi-arc]

Likely the carbon brushes are worn and a new brush pack would resolve the issue. You might grab the original and replace the bearings and brushes and use it as a back-up.