Bad Alternator?

Posted By: Got2Gnow

Bad Alternator? - 11/24/14 09:40 PM

I've got my Dart "stored", up on jack stands, for the winter. While "stored" I start/run the vehicle for about 30-45 minutes (running through the gears (A904) putting about 2 1/2 miles on the odometer).

Yesterday I started/ran the vehicle as usual. While watching my volt gauge it never left the 10-12V range. Normally as the RPMs increase the volt gauge will increase up to the 12-14V range.

The battery is/was fully charged (battery tender in use) and was replaced in June (2014).

I did the AMP gauge bypass (MAD Electrical) several years ago. All connections are clean and tight.

The alternator has been on the vehicle as long as I've owned the car (~11 years).

What do you guys think?

Posted By: Supercuda

Re: Bad Alternator? - 11/24/14 10:05 PM

Several things are needed for a charging system to work.

Voltage regulator needs to work.

Alternator needs to work.

Wiring needs to be correct and working.

Since you do not say what year your Dart is there are two possible charging system designs that are possible. 70 and up or 69 and earlier.

On the early system the field gets a switched 12v supplied to it from the alternator. If that voltage is there then the wiring and voltage regulator is good. If not then you need to look that way. As a test of the alternator you can jumper 12v to the field terminal on the alternator and it should charge if the alternator is good. Do not let it run like that for long.

On the late system the alternator gets a constant 12v on one field terminal and a variable ground on the other terminal, if you use a meter to read the voltage on that terminal you will see a voltage there less than 12v, the less it is the harder it is charging, the closer to 12v the less it is charging.

Posted By: RapidRobert

Re: Bad Alternator? - 11/24/14 10:53 PM

'70 & up "late" system I will guess. (2 field terminal alt/flat reg with triangle connector). (1) turn the key on & see if you have voltage at both alt field terminals and at the blue/green wire female terminals in the reg triangle connector. (2) replace the triangle connector back on the reg & start it to a fast idle & pull the green wire connector off of it's alt field terminal & with a jumper wire with alligator clips ground the male alt nub (not the female connector/wire you removed from it) for 5 seconds max & have a helper in the dr seat holler if the voltage jumps up & you can hear if the alt kicking in (if it is good) pulls the RPM down a hair (not much but you can feel/hear it). If so the alt is good. (3) if alt is good unbolt the reg & clean it's backside/firewall & reinstall to confirm continuity to ground (4) if the alt is bad pull/check the 2 brushes/brush holders & if they are OK then replace the alt (an 85 M body 78 amper is the best OE one). (5) if the alt is good & cleaning the reg ground does not fix it then replace the reg. You might recheck the voltages at the reg connector/alt field terminals (4 terminals) when running but if they are hot with eng off/key on they should still be hot with eng running. Holler back

Posted By: Got2Gnow

Re: Bad Alternator? - 11/24/14 11:01 PM

Sorry, it is a 1971 Swinger with a 318, auto, A/C, PS, manual brakes (was 4 drum, now front disc/rear drum).

I was told to turn the key ON (engine OFF) and hold a screwdriver in front of the pulley and feel for a magnetic pull to the pulley. I tried with NO magnetic pull. I then started the engine (volt gauge ~10-11V) and tried the screwdriver magnetic pull test again. I felt NO magnetic pull (front or rear).

Looks like I need an alternator. I see there is a 65A or a 50A unit available for my car. I assume the 65A unit is what I need (because of the A/C)?

Posted By: RapidRobert

Re: Bad Alternator? - 11/24/14 11:15 PM

pull the green wire female connector off of the field terminal & ground the male field terminal for 5 seconds (fast idle)/lights/acc off & see if you have magnetic pull or the voltmeter rises. If so the alt is good. If not, check the brushes/brush holders & if they look OK then yes the alt is bad. Get a 78 amp alt for an 85 M body (perfect fit/better alt), price should be similar & even if higher I would still go with it. If the alt IS good holler back & we'll continue on. EDIT the screwdriver test is at the rear center & has to be running as the alt ain't charging when not rotating even if it has field current to it (key on/not running). MORE EDIT My parts house just quoted me $42.75 out the door exchange for a rebuilt 78 amper for an 85 Chrysler

Posted By: 383man

Re: Bad Alternator? - 11/25/14 03:43 AM

Just because its not charging does not mean its a bad alt. Do what "RapidRobert" says and let us know and we can go from there. Heck you could have a wireing problem or a bad regulator just to start that will keep it from charging. Ron

Posted By: denfireguy

Re: Bad Alternator? - 11/25/14 05:15 AM

Quote:

I've got my Dart "stored", up on jack stands, for the winter. While "stored" I start/run the vehicle for about 30-45 minutes (running through the gears (A904) putting about 2 1/2 miles on the odometer).

Yesterday I started/ran the vehicle as usual. While watching my volt gauge it never left the 10-12V range. Normally as the RPMs increase the volt gauge will increase up to the 12-14V range.

The battery is/was fully charged (battery tender in use) and was replaced in June (2014).

I did the AMP gauge bypass (MAD Electrical) several years ago. All connections are clean and tight.

The alternator has been on the vehicle as long as I've owned the car (~11 years).

What do you guys think?

I would say your battery probably has a short. One cell is gone. If you had an ammeter, you would see that it is not taking a charge.
Craig

Posted By: DAYCLONA

Re: Bad Alternator? - 11/25/14 12:34 PM

Quote:

Sorry, it is a 1971 Swinger with a 318, auto, A/C, PS, manual brakes (was 4 drum, now front disc/rear drum).

I was told to turn the key ON (engine OFF) and hold a screwdriver in front of the pulley and feel for a magnetic pull to the pulley. I tried with NO magnetic pull. I then started the engine (volt gauge ~10-11V) and tried the screwdriver magnetic pull test again. I felt NO magnetic pull (front or rear).

The "poor man's" alternator test is to put a screwdriver to the rear bearing located in the center of the alt in the rear case, WHILE THE VEHICLE IS RUNNING, if you have a magnetic pull enough to slightly hold the screwdriver in place then your system is making a complete charging circuit,...you need a meter to properly evaluate each component in the system for proper troubleshooting

Posted By: Got2Gnow

Re: Bad Alternator? - 11/25/14 06:25 PM

Quote:

'70 & up "late" system I will guess. (2 field terminal alt/flat reg with triangle connector). (1) turn the key on & see if you have voltage at both alt field terminals and at the blue/green wire female terminals in the reg triangle connector. (2) replace the triangle connector back on the reg & start it to a fast idle & pull the green wire connector off of it's alt field terminal & with a jumper wire with alligator clips ground the male alt nub (not the female connector/wire you removed from it) for 5 seconds max & have a helper in the dr seat holler if the voltage jumps up & you can hear if the alt kicking in (if it is good) pulls the RPM down a hair (not much but you can feel/hear it). If so the alt is good. (3) if alt is good unbolt the reg & clean it's backside/firewall & reinstall to confirm continuity to ground (4) if the alt is bad pull/check the 2 brushes/brush holders & if they are OK then replace the alt (an 85 M body 78 amper is the best OE one). (5) if the alt is good & cleaning the reg ground does not fix it then replace the reg. You might recheck the voltages at the reg connector/alt field terminals (4 terminals) when running but if they are hot with eng off/key on they should still be hot with eng running. Holler back

RapidRobert,

I performed the tests above as you suggested. Everything checked out OK until I unscrewed the Voltage Regulator from the firewall. Check out the photo:

Attached picture 8341626-Back.jpg

Posted By: RapidRobert

Re: Bad Alternator? - 11/25/14 10:50 PM

Good thing it opened as opposed to full fielded

Posted By: burdar

Re: Bad Alternator? - 11/25/14 10:56 PM

nasty!