[flucus]

I was thinking that my alternator was failing so I put a voltmeter across it while idling-it came up at 12.7v. I am not a mechanic but do as much of my own work as possible. What would be the feasibility of me rebuilding my own alternator? What would it be-brushes and rectifier?
Thanks.

 

[arthurgoboom]

First off, what do you get when the engine is off? Same voltage, or more or less?

You may need to change your voltage regulator. As for alternator rebuild, I don't know much about that, sorry.

 

[Mr_Roboto]

Back in the 80's you could get rebuild kits that would replace some of the commonly failed parts. Now that the market is flooded with cheap Chinese rebuilds it hardly makes sense to DIY. Either throw on a cheap reman or have a electric rebuilder do the work.

You should see somewhere between 13 - 14 volts with the engine running. Normally when you lose "partial" voltage it is due to shorted diodes.

 

[flucus]

There was minimal difference between the battery and the alternator, 12.65v and 12.75v respectively, at idle, drops down to 12.5v when off. Thanks for the advice about the rebuild, I am just a tight bugger and tinkerer at heart and spending $20.00 for parts sounds nicer to me than $60.00 for the reman.
I am not sure exactly what the current output is supposed to be on the one that is in there but it isn't problematic to go from a 60 to 70 amp output is it?
Thanks for your wisdom.
BTW-what should my dash gauge be doing? It just sits there right in the middle.

 

[cdnsarguy]

Check the small yellow/white wire for continuity, it has a fusible link... power goes thru that wire to activate the alternator for charging.....

 

[arthurgoboom]

The dash charge gauges seldom do much, at least mine didn't. I replaced it with an aftermarket voltmeter. It sounds like you are charging a little bit, like Roboto said maybe a shorted diode. I'm not sure how to go about changing them, but if you can buy the parts go for it. You'll probably want to have your local electrical rebuilder test it after you're done to make sure it's working right. I would be leery of going to an auto parts store, one of their test machines lied to me.

 

[LMJD]

Multimeter or test light to test your diode plate, front and rear bearing, set of brushes, fine crocus cloth to clean up the brush rings and it's overhauled good as new. If you don't want to do it yourself, an auto electric shop won't charge too much and you'll get a better job than an "over the counter" rebuilt.
Before you take it off, you can disconnect the reg, jump a hot wire to the alt. field terminal, run the engine, if it puts out high voltage, you're diodes are OK.

 

[icanfixall]

I remember something about putting a steel screwdriver on the back of the alternator where the bearing is found. If while the motor is running you find it magnitized then the alternator is good. I'm not really sure about this but something seems correct about what I have posted.

 

[jaluhn]

Most of the time the brushes wear out in my experince, just speperate the case halfs, pull them out and go to the hardware store. I've had decent luck finding brushes for other alternators there. Might need a bit of adaptation to make the work.
~John

 

[flucus]

So here is the latest. Took out the alt and took it to my local big chain auto parts dealer and had him test it side by side with a reman that I was going to purchase. Both passed. So, I went home with a regulator instead. After tugging at some of my wires with fusible links and not getting any play in them I proceeded to exchange the regulators. Installed the regulator first, plugged in the regulator, and then proceeded to reinstall my alternator. Started it up and still only got 12.75v across the battery terminals on idle, it went down to 12.62 with the lights on. I guess I will pull out the manual and try to trace out the problem.
Is there a problem with just chopping out the fusible links and trying to replace them with fuse holders?
Something I forgot to do was disconnect my batterys when reinstalling the alternator, I got a few sparks. With my regulator grounded to the body I wouldn't think that would be a concern. Am I right? Is there a way to test the regulator in place with the trusty multi-meter? Thanks a lot-I sure like working on this truck.

 

[flucus]

05/16
So, here's an update that I would enjoy your perspective on. I had felt after everything last night that there was a failure somewhere yet to be determined. About five miles into my commute this morning out of the corner of my eye I see the charge gauge on the dash start to 'tick', for lack of a better word. By the time I get the remaining two miles to work the gauge is steady on the mark that would seem to indicate that the system is fully functional and charging. It now varies a bit, by how many rpms I am operating on and load, but I am absolutely intrigued. Perspective? My wife thinks I'm a genius because I saved us hundreds of dollars-I'm not going to tell her any different.

 

[arthurgoboom]

Check the batteries again with your multimeter, see if it's showing you over 13 volts now. If so...I would say you have a loose connection somewhere.

 

[JGRockwell]

Though it's obvious that the problem is outside the alternator, the next time you check one with a voltmeter, you also want to check for AC VOLTS.

The alternator produces alternating current (that's the difference between an alternator and an older-type generator). The diodes in the alternator rectify it to direct current. If you get ANY voltage reading on AC, you have a shorted diode.

 

[flucus]

5/24-It keeps getting better. I replaced the regulator and kept the alternator because it bench tested just fine side by side with a brand new one. I charge the battery and it would start but over night it would completely discharge leaving me with a dead truck in the morning. I used a mechanic friends tester and determined that there was a draw on my battery with the rig just sitting there on the charger. In poking around with a temp gun found that the new regulator was almost too hot to touch and that the alternator was much warmer than ambient as well. I purchased an alternator and regulator and replaced the regulator only, again, and thought that I had it licked. This morning it was discharged again. I am going to replace the alternator.
Does it make sense that the battery could discharge through a intermittent problem with the alternator to the regulator?

 

[94_turbo]

if it discharges overnight--youve got a shorted to ground diode---try this--remove the heavy hot wire off the alt when shut down for the night--reconnect it in the morning--if it goes--shorted diode---replace alt--or the diode plate--they are cheap-- i have a few extra---as dont do many old alts anymore--

 

[HiVoltage]

I'm having the same problem,and when I disconnected the alt for the night I finally located my drain.Question for 94,can the diode pack be changed out without removing alt? By the way its the bottom one of duals.TIA