What questions do I ask alternator rebuilder at pick up to confirm alternator works

[911SCfanatic]

Background: I'm in the middle of a total restoration project started in 2004 and (hopefully) finished in 2007. When I bought the car, which was in terrible disrepair, the alternator light was always on and the PO complained about a slow drain that killed the battery when parked after a few days. The wiring was a complete rat's nest with splices and stripped wires scattered everywhere.

Now: Took the alternator to a place today to be tested. The shop has been in town for 30 years (run by the same guy) and all they do is alternator and starters. They are very respected by the local muscle guys, Shelby owners and other generally high end, American iron. Also, there's no guys in town that do just VW/Porsche etc. so I figured I'm as well off with these guys than with some onesie, twosie European alternator rebuilder. I hope my premise isn't way out of whack.

The young, tatooed kid at the counter couldn't figure out what to do with it since it didn't have a pulley, but the old guy just popped out the key and was able to bench test it just fine. The old guy tells me the alternator is dead and he tells me it has an internal v/r, so I now know its not the original alternator. Other than that, I don't have a clue about this alternator, and quite frankly, didn't really know what else I should know. I told him not to lose the nut because IIRC replacements where hard to find. He's rebuilding it for $150 and giving me a 2 year warranty.

When I pick it up, what do I need to ask/know to make sure it works? I won't be installing it for another 6-8 months. What kind of voltage should it put out on the bench--13.5V at any particular speed (alternator shaft speed)? I assume I should get a current rating from him?

[scottb]

If it's a reputable shop, you don't need to ask anything. They'll have gone thru the alternator and repaired or replaced what was necessary. Of course, if you can speak to the person who actually did the work, you might ask what was done. The bottom line, from my perspective, is that a business wouldn't survive for 30 years under the same ownership if they did shoddy work. I'm sure you'll get a quality rebuilt unit that will work fine.

[EarlyPorsche]

Really an alternator is an alternator. If he has been doing if to 30 years he probably uses non made in china components and most importantly bearings. Bad bearings cause tolerances to go out of whack and quickly kill alternators. The bearings are usually why cheap rebuilds go bad in a month or two.

[304065]

Bill, your caution is appropriate. As a former Birmingham resident myself, I saw all kinds of butchery done to electrical parts for my 1975 2002 when I tried to use vendors who were accustomed to working with Detroit stuff.

So here are some questions for the "old guy." If he gets in your face about the answers, well, that's an answer too.

1. What kind of alternator is it? Bosch? Motorola/Marchal? Paris-Rhone? Valeo? How many amps?

2. What parts were replaced when this particular alternator was rebuilt? A good rebuild, particularly for $150, will include new ball bearings for the rotor shaft. Were any diodes replaced? If so, what type? Bosch 10mm diodes are pretty common. Were any of the "trio" diodes replaced? If it's an old Motorola, which it sounds like it's not because of the internal VR, then there are no "trio" diodes, there is a single "isolation" diode.

3. If diodes were replaced, how were they attached to the wires? Soldered or crimped?

4. How did the rotor and stator windings look? Were they in good condition?

5. Was there any sign of the alternator overheating in the past?

6. What internal voltage regulator was used? OEM, or one from a supplier like Huco or Transpo?

7. Big question: What is the "set-point" of the internal voltage regulator? What output voltage, measured at the alternator B+ terminal, should you expect when the alternator is installed.

This is about a five minute conversation, a good rebuilder will value these questions and teach you something.

Good luck!

[911SCfanatic]

Thanks, John...just the type of answer I was looking for.