GM one wire alternator problem

Here's whats happening. Start the car and the volt meter shows approx 14 volts. Drive about 2 miles and the voltage starts dropping. Goes down to 12 then continues a slow drop to 8 and finally car doesn't run. I assume it just running on the battery at this point. Is this caused by the internal regulator going bad or some other problem. If you let the car sit about an hour and restart it with a jump the volt meter shows 14 volts again but after about five minutes starts dropping again. Maybe a heat problem in the internal regulator? Thanks to all who reply.

 

sounds like the alternator isn't working. Could be the regulator, brushes, diodes, windings, etc

 

stick a volt meter on it if you dont have one place a screw driver near the back of alt center boss where shaft is you should fell magnetic pull if not its the alt...then its prob diode in alt

 

Had one of those on my wife's 61 ranchero. It did the same thing. If it is only putting out minimal voltage it doesn't take long to run the battery down. Quicker if you are running radio heater and lights at night. Took it back to the parts house traded it in for a new one and problem solved

 

Try swapping out the little solid state regulator in the back. They're relatively cheap and not a horrid job to change out.

Flatman

 

Sounds like a bad diode.I'd just replace the altertnator ....Ole Pork

 

I recomend before you go and start swaping parts to trouble shoot and pinpoint where the problem is, if you ran youre battery down to where youre coil could not energize and keep youre engine running chances are you have a sulfated battery.
the reason its at 14 volts when you jump start it is couse the current is only filling the battery with a surface charge and as you use youre loads its going throu it fast.
take youre battery and youre alternator to a parts house that can test em also check youre battery cables for voltage drops.
and be sure that youre battery can hanle the load if you have a 600cca rated battery and youre starter draws 300 amps to start youre engine and youre alternater only puts out 50 amps its gonna take a long time to catch up.

 

A one wire alternator is nothing more than a battery charger, plain and simple. But it will not charge unless the alternator RPM's (not the engine rpm's) reach a certain speed.
The internal regulator will not excite (kick on) and produce voltage until this happens.

Try starting the car and take a reading. Positive to the big BATT terminal on the back, negative to ground. See what the reading is. Rev the motor pretty good a couple of times to kick in the regulator, then take a reading.
If the alternator is working properly, it will show 14.4-14.8 volts off the BATT terminal.
If revving the motor doesn't help, then the alternator may be turning too slow to kick in, and the remedey is going to a smaller pulley to speed it up.

If your alternator has a space for a 2 terminal plug on the top somewhere, then chances are you can make it a 3 wire. Run the white wire from the plug (sold at most auto parts stores) to the ignition switch, with a small idiot light ($2.00 light from the parts store) in series to prevent backfeed. The red wire gets looped to the BATT terminal. This provides constant voltage. The white wire uses the battery voltage to excite the regulator to produce output immediately upon start-up.

The idiot light will light when you turn the key, and go out when the alternator starts producing voltage. It's also handy to have because it will light up when something happens to the belt when you're driving.
Hope this helps...

 

reading his voltage at high med or low rpm's isnt going to tell him if his alternator is working or not.
he needs to find out what his alternator is rated at, put a(current) load on it and measure what its outputting.
and all the talk about diodes all a diode is, is a one way check valve with three of them being wired in three differnt arangements converting a non true alternating current to a dc output.

 

Taking Your Altenator To You Local Parts Store Should
Be Your Fastest Route.they Should Have A Machine They
Can Run It On,and Tell You Exactly What Your Problem Is.
The Same For The Battery.

 

Thanks guys for all the tips and information. Took the alternator to a shop and had it tested and everything seems to be OK. Am going to have the battery tested today and I think that has to be the problem. Thanks for the suggestion about the idiot light, I think I will take advantage of that too.

 

Are you saying to run the white wire to postive on the ign terminal on the key switch.

 

That is correct.

 

3 wire conversion is a good idea, if regulator turns out to be wonky...there is a way shown in GM manuals to eliminate regulator for a test--you just stick a screwdriver through proper hole in back, and regulator is full fielded or whatever and voltage should go right up to 14. It's been a long time, but I think it's a little D shaped hole.

 

Had the same problem on my 40 chev .had a fire in the wiring rewired the car . I was looking for bad parts or wire problems ,the alt. belt was tight , but it was ran off my water pump and my water pump was ran off my A.C. My A.C. belt was loose which caused all the trouble. Sometimes the more you know ,you may not look at the simple problem .