Alternator overvoltage -- '78

[FastWoman]

Hi all,

My alternator had been cranking out marginally high voltage since I've bought it -- high 14's. It's now putting out slightly higher. I discovered the problem (no thanks to my largely inaccurate dashboard volt meter) when my stereo was freaking out from the high-ish voltage. Anyway, I obviously need to address the problem now.

I looked in the FSM, and I see this sort of problem can happen when the internal voltage regulator isn't well grounded. Thinking back, I had rewired all of my grounds (making them much better) when I did my conversion from fusible links to maxi fuses. In the process, I took loose the ground wire from the back of the alternator, which was only barely tight. When I went to attach the new wire to the ground lug, I found that the threads had previously been stripped (the reason for the loose connection). As the ground seemed to me just to the shell, I simply grounded to a different screw on the shell. In hindsight, I'm wondering whether this same ground screw ran internally to ground the voltage regulator. Is that how it's built?

So now I'm considering my options. My first option is to try pulling the alternator apart and fixing the voltage regulator's ground connection (if that's the problem). From the FSM, it looks as though I have to go pulling bearings apart and such. I don't have the special tools for that. Can the alternator be pulled apart and reassembled without the special tools?

My other option is a rebuilt alternator for $55 -- a Duralast lifetime warranted unit from AutoZone. Is this the better route?

Thanks for any input!

Peace,

Sarah

[sblake01]

Buying a new/rebuilt one is likely your best bet. Not necessarily better but easier. Years ago, I used to be able to get the parts to rebuild alternators from a friend that has a shop. Even though, I used to have to borrow tools from him to disassemble/reassamble it.

[FastWoman]

A rebuilt one it shall be! Thanks.

[FastWoman]

Quick questions, though:

1. Is the "E" terminal ground simply a ground to the case? Would any other ground to the case be equivalent?

2. There are two nylon plug-in type connectors on the back of the alternator. One is the 2-conductor connector for the L and S terminals. The B and E terminals are screw/nut type. I can't account for the remaining nylon connector, which is single-conductor. Is it for the F terminal, and if so, what is its purpose? Would it connect to an ammeter if I had one? Currently the terminal is not connected, and there are no dangling wires in the vicinity. As far as I can tell, it's not used in my car. Would that be correct?

Thanks again!

[sblake01]

What I recall about my 78 280Z and the 810 was the E terminal which was a ground, the battery terminal, and the two terminal plug. I don't recall seeing the other terminal you describe on either car.

[FastWoman]

Maybe a ZX thing? Anyway, if it's not present on a properly wired '78, I'm sure it should be N/C on mine. Thanks.

As I think about this problem more, I'm pretty sure it's a case of semiconductor breakdown (undoubtedly the zener diode), rather than a lifted ground. That's because the alternator regulates quite steadily at 16.25V. The regulator is doing its job, but at the wrong reference voltage.

Anyway, the alternator is on order. All will be better tomorrow.

[FastWoman]

Fixed. A nice, steady 14.3V. I'm much happier now, as is my stereo.

FAIW, the Duralast alternator appears to be a nice rebuild (pretty, anyway), albeit of Mexican origin. The prior alternator appeared to be rebuilt in Japan (by the sticker) but only lasted 2.5 years before the semiconductors broke down.