I really need the forum's help on this one because I'm stumped. The alternator on my 89 went out in June, so bought an AC Delco 334-2368A with lifetime warranty. Two weeks ago it stopped charging so I got a replacement unit under warranty. The replacement unit stopped working after only a week.

So got another unit under warranty and installed it. Fired up the Vette and everything looked fine for about 5 seconds. The in-dash voltage meter showed 13.5 but then began dropping - from 13.5 down to 13.1, to 12.7, etc until I shut off the car when it hit 11.5.

Installed yet another unit on Saturday but when turning on the car for the first time, the voltage meter stays in the high 11's and never shows the alternator to be charging.

I have used my battery charger to fully charge the battery each time before starting the car with each new alternator. According to the FSM, with the key in the RUN position, if I unhook the alternator harness and the charging system indicator light goes out then the alternator is bad. I've done that test each time, and it always indicates that the alternator is bad.

The company I bought this from has no warranty history on this particular AC Delco model number (other than their histroy with me). However, the sales guy did look up their warranty history on the previous model 334-2368 (without an "A" at the end) and said it had about a 50% return rate under warranty.

So my question is this - is it possible that I've gotten 3 defective alternators in a row (i.e. this is the worst unit AC Delco has ever made), or is there something else I need to check on my car that would keep the alternator from charging?

I don't think there's an electrical issue causing the alternator to fail because on the unit that lasted a week, I think the bearings may have gone out. When I removed it, I noticed that if I hand-spun the pulley, it would spin freely for 2-3 revolutions but then I'd start hearing a scraping sound for a second or two before the pulley would abruptly stop. That's why I don't think there's an electrical issue causing the alternator failures, but at this point I'm at my wit's end.

 

Years ago when I had an 84 there was a stretch there when I would go through an ALT one a year for about 7 years.I finally put a regulator in the last one I had and didnt have anymore problems.

 

The alternator is supposed to put out 14.7 volts across the battery cold and this drops to 13.7 volts when it gets to its operating temperature. The dash voltmeter reads 0.3 volts low due to the voltage drop on the ign sw contacts. The voltmeter reads the voltage after the ign sw, so your dash voltmeter on a good alternator should read 14.4 volts cold and 13.4 volts hot. Anything below 13 volts, you have a defective alternator, even if it is the 16th one in a row from the parts place. I have bought AC rebuilts from a local chevy dealer parts dept. and have had good luck with them. You might ask the parts place if they have a better quality alternator and if they will credit the cost of the AC rebuilt you keep having to replace. Good parts stores will usually do this to keep a customer. Also, if the next alternator isn't a lifetime guarantee, when it goes bad have it rebuilt at a local auto electrical place, they usually do a much better job with higher quality parts than the big assembly line rebuilders do.

 

No expert here, but I wonder if terminals 1 and 2 have the correct input voltages. My FSM says that with 1 and 2 removed from alt, #1 should have 2-4 volts (key in "run") and #2 should have full battery voltage(always hot).

 

I've heard rumors that most alternators you get on warranty replacement are rebuilds that have ONLY the defective part rebuilt! Everything else in the whole unit is left as is regardless of wear. You'll get the best chance of a quality and reliable rebuild if you take your old one to a local electric motor rebuild shop. They will usually go through the whole unit (alt or starter) and replace brushes, diodes and resurface the commutator. Plus you will probably get a better warranty you won't have to use because it won't fail for a long, long time. Plus you help a local buisness instead of some offshore sweatshop.