So as a diy kind of guy i dont want to just replace the alternator on my car. I want to repair my current one. I have a spare one that has a bad diode so i want to use it as a parts part. The thing i need to know is why my current one ownt charge. I mean i know its bad but i want to know what part of it is bad. Any ideas? Massey im looking at you!

 

Look at the back side of the alternator. You should see a shiny metal part inside there, just adjacent to the plug. That's the voltage regulator that the wires plug into. With the engine running, take a small screwdriver and poke it through one of the openings in the back of the case, touching both the voltage regulator and the case at the same time. Don't be skeered, it won't bite you! Doing that grounds the voltage regulator, and puts the alternator into a full charge state (you should hear the alternator whistle). If the alternator does go into charge mode while doing this test, the voltage regulator is bad (which is a common thing to go bad btw).

 

Wow neat trick.

 

It is a neat trick, I've done it numerous times. It can also save you a trip to town having to get the alternator tested, providing it is the voltage regulator that's bad. I did mean to mention that while testing the regulator, if the alternator still doesn't charge, you have something else wrong, instead of or in addition to it being the regulator.

 

I am a DIY guy too but there are some things that are just better bought new so you dont have to worry any more and the warranty is a great piece of piece of mind... say that 5 times fast...

Massey

 

That's fine and dandy, and I spose it also depends on one's ability. I've rebuilt a few alternators. And me, I'd rather replace a $15 voltage regulator, re-grease the bearings, and dress down the arm myself, as opposed to buying a new/rebuilt $125~$150 alternator. You do realize that a "rebuilt" alternator retains the used internal parts (the bearings and brushes do get replaced), unless they were bad and needed a replacement right? It's not rocket science, but yeah, some people might feel more comfortable spending their hard earned money on a new alternator instead.

 

Every remanufacturing line I have seen replaces the Brushs and bearings. The bearings would need to be noise tested to be sure they where good. That testing would cost, in time, more that a set of mass produced bearings.

I was not aware the new alternators could be repaired. Back before computers forced the a major redesign of the classic GM alernator we use to rebuild them all the time. It cost about 15 bucks in parts. Starts too. Just about everything could be tested with a volt meter. When GM came out with the 4 wire alternator it became exchange only. Nice to know they are back to repairing them.

 

Right, I did say the bearings and brushes automatically get replaced on a rebuilt unit. When doing it the DIY way, those can be a margin call when you're in there. Of the ones I've rebuilt, none of them had badly worn down brushes (still had plenty of meat left), and the bearings were still good too. If and when the bearings go, it's usually from running dry. Often times, a good cleaning and greasing makes the bearings happy again, provided you get to them before they get toasted. What needs fixing all depends on just what put the alternator out of commission.

 

The Cheaper of the rebuilds are just a test and reuse type of rebuild similar to what you would be doing in your garage. The line of Ultima Remanned that is sold by O'Reilly are 100% new electrically and reused case, pulley (some times) and the armeture is rewound and new comms installed. Yea it is about $125 or so for that level of a rebuild.

I used to rebuild the 70's and 80's GM alternators all the time too. I have access to a metal lathe where I can turn the comm nice and true, and the internals of that alternator are so simple it is nearly impossible to mess them up. The newer ones are not as rubust and if you dont get the case off right things break inside. Careful here goes a long way. Personally I just find it simpler to buy the lifetime remanned and not worry about it. The old ones, sure I will play with them and not worry. Another thing to look at is some of the parts to rebuild the new style Delphi alternator will cost you almost as much as the remanned one will. Last time I looked up the kit for a customer the kit was only $50 less than the lifetime reman. Yes the kit for the 70's style and the CS style is still cheap enough to make it worth it.

Massey

 

ok so im a lil confused on the trick you should me but will this test kicks it into charge mode then the voltage regulator is bad and thats why its undercharging? Im getting only like 13.0-13.3 volts when running.