Can you ID this alternator?

[7T Swinger]

Gents,

Numbers on it:
3874271
2095191
R795

Thanks for your time

Graham

 

[Dana67Dart]

Is there a reason that you need to know about that particular alternator?

Also

1. what car?
2. What year?
3. What electrical modifications?
4. Which type of voltage regulator?

 

[65 Dartman]

Well, for sure it’s a square back

 

[67Dart273]

Is there a reason that you need to know about that particular alternator?

Also

1. what car?
2. What year?
3. What electrical modifications?
4. Which type of voltage regulator?

I'm thinking this plus

What does it matter? Corroded, "looks like a core." Maybe already been rebuilt once. The one FIELD TERMINAL is either broken off or modified to be GROUNDED

That was originally a "square back" AKA somewhere around 73 and later. It has/ had isolated field (two field terminals, incorrectly called "dual field") and one is broken or modified.

So the question "what regulator" are you running is somewhat important, because if you replace that with a similar --later model-- and--isolated field unit--and if-- you have the older 69/ earlier regulator, you will have to ground one field terminal to get it to work

 

[7T Swinger]

It’s shot and I’m looking to replace it. I was hoping the numbers on it meant something. From what I’ve seen on here, it’s a 72 up square back.

 

[67Dart273]

It’s shot and I’m looking to replace it. I was hoping the numbers on it meant something. From what I’ve seen on here, it’s a 72 up square back.

Well you still have not explained anything. Which regulator are you using? If you replace this one with a like one, you need to ground one field IF you are using the older regulator. IF you are using the 70/ later regulator you need BOTH field terminals functional and you need to be sure the "new" on does not have one field GROUNDED. THAT is a common problem with rebuilts Just ask for one for "about" a 73/ later vehicle. I would not get anything more than 50-55 A if you have not upgraded the factory wiring.

 

[pishta]

Just pick up a few brushes and bearings and see if $12 will make it come around.

 

[Dana67Dart]

It’s shot and I’m looking to replace it

The numbers are useful but do not tell the whole story.

There are 3 to 4 alternators

Single field wire "round back" uses old style 2 connector voltage regulator

2 field wire (isolated field) "round back" used "V" shaped connector voltage regulator

2 field wire (isolated field) "square back" used "V" shaped connector voltage regulator

A modified 2 field wire (isolated field) "square back" one field wire is grounded and uses the old style 2 connector voltage regulator

So as you can see the answers to the questions are very important to you getting a functional replacement

BTW, the reason the number may be irrelevant is if it is a rebuild or was modified to run with a single wire VR

• What year?

• What electrical modifications?

• Which type of voltage regulator

 

[cudamark]

If you clean off that large flat rectangle pad on the rear housing, there should be some other numbers there that will show the year and output of that alternator.

 

[Demonic]

Looks like one field grounded? Hard to make out, but an ohm meter would tell the tale.

 

[cudamark]

The insulator and hardware for the battery post is missing too.

 

[7T Swinger]

Well you still have not explained anything. Which regulator are you using? If you replace this one with a like one, you need to ground one field IF you are using the older regulator. IF you are using the 70/ later regulator you need BOTH field terminals functional and you need to be sure the "new" on does not have one field GROUNDED. THAT is a common problem with rebuilts Just ask for one for "about" a 73/ later vehicle. I would not get anything more than 50-55 A if you have not upgraded the factory wiring.

It’s a 1967 barracuda with a 1970 318 installed. The wiring in the car is original. I think I found my problem. When the car is running, I took readings at my old style voltage regulator. I have ~11v at the IGN terminal and only ~2v at the FLD terminal. Safe to say the VR is faulty? The car is simply running off the battery at this point.

 

[Dana67Dart]

Dang you have a corrosive environment.

Ok
If you buy an alternator for your car model and year.

You will most likely get a square back alt that has one of the field terminals snipped off. It is internally grounded to work with your 67 style voltage regulator. Single field wire round back rebuilt alternators are few and far between.

As for what's at fault...

Since the alt is out might as well have it tested.

The 11 volts into the VR is low unless that is battery voltage as well.

The 2v out probably is not right, but without the load of the field I could not say for sure.

I would work on your grounds, with that much corrosion you might just have a bad ground issue.

 

[7T Swinger]

Dang you have a corrosive environment.

Ok
If you buy an alternator for your car model and year.

You will most likely get a square back alt that has one of the field terminals snipped off. It is internally grounded to work with your 67 style voltage regulator. Single field wire round back rebuilt alternators are few and far between.

As for what's at fault...

Since the alt is out might as well have it tested.

The 11 volts into the VR is low unless that is battery voltage as well.

The 2v out probably is not right, but without the load of the field I could not say for sure.

I would work on your grounds, with that much corrosion you might just have a bad ground issue.

The voltage readings were taken after I installed a new alternator yesterday and temporarily grounded the second FLD terminal. I spent half an hour cleaning the firewall beneath the VR to ensure a good ground.

 

[Dana67Dart]

The 11 volts in to the VR 0is still a potential issue...
67dart273 will pointout that the voltage drop into the VR will result in an increase of voltage out possibly over charging the battery

Was the engine running when you took your measurements?



Has the battery been charged by a external charger?

If the battery is really discharged the alternator will try to charge it and pass a lot of current through the bulkhead connectors ( A body weak spot )

The alt in your photo seems to be a 2 field wire (isolated field ) alt. Grounding one field perminatly will work just fine.

I would double check with an ohm meter and both field terminals disconnected, that there is no continuity between either field terminal and the housing of the alt.

Also the cracks in the green (field) wire insulation could have broken wire strands under it. Fewer strands increases resistance which causes all kinds of problems

 

[7T Swinger]

The 11 volts in to the VR 0is still a potential issue...
67dart273 will pointout that the voltage drop into the VR will result in an increase of voltage out possibly over charging the battery

Was the engine running when you took your measurements?



Has the battery been charged by a external charger?

If the battery is really discharged the alternator will try to charge it and pass a lot of current through the bulkhead connectors ( A body weak spot )

The alt in your photo seems to be a 2 field wire (isolated field ) alt. Grounding one field perminatly will work just fine.

I would double check with an ohm meter and both field terminals disconnected, that there is no continuity between either field terminal and the housing of the alt.

Also the cracks in the green (field) wire insulation could have broken wire strands under it. Fewer strands increases resistance which causes all kinds of problems

The battery was fully charged ( via battery charger ) and the voltage readings were taken with the engine running. I checked the green wire that runs from the VR to the alternator with an ohmmeter and it’s ok.

I’m stumped, unless of course it’s just a bad VR.

 

[Dana67Dart]

Know anyone with a same type vr you can try before you spend money?

Also you can temporarily apply 12v directly to the field terminal that the green field wire attached to (remove the field wire first) this will cause the alternator to go to max charging. But that will only prove the alternator and wiring and terminals between it and the battery are ok.




Ohm meter on a wire with broken strands will show good. Put current in the wire and it can't handle the the load. Think about a fuse, it is a tiny wire as compared to the wire it is protecting.

Voltage drop from one end to the other under load is the only to really measure it.

Visually you might be able to determin if it's ok or not.

 

[Mattax]

Please read this. Identifying Chrysler Alternators (1960-1976)
The numbers in post 1 are most likely the casting numbers.

The battery was fully charged ( via battery charger ) and the voltage readings were taken with the engine running.

It’s a 1967 barracuda with a 1970 318 installed. The wiring in the car is original. I think I found my problem. When the car is running, I took readings at my old style voltage regulator. I have ~11v at the IGN terminal and only ~2v at the FLD terminal. Safe to say the VR is faulty?

Not sure what is going on but it might simply need adjustment. At voltage lower than setpoint it should switch rapidly between full field (no resistor) and feeding through one resistor. If its really below setpoint, then yes it should full field (no resistance) and votlage on both sides should be the same. I'd call 11 volts really low.

The car is simply running off the battery at this point.

The way to verify that is to look at the ammeter.
If the ammeter is pointing toward discharge while the engine is running. Then yes.

Verify by comparing voltage while current is flowing.
a. Observe the ammeter for how much current is flowing out of the battery. The meter reads 40 amps discharge to 40 amps charge, zero in center. Estimate from that.
b. Measure the voltage at the battery and the voltage at the alternator output terminal. They should be the same if current demands are low (under 5 amps) and may show some slight difference if demands are high.
c. Then compare with voltage in the ignition run circuit at a couple locations. Backprobe at the ballast resistor as well as at the regulator as you did. Voltage at both locations should be the same, and be very close to the same as measured at alternator stud.

Quick test of the regulator vs. alternator.
Jumper the regulator allowing the alternator's rotor to draw as much current as it wants.
Output voltage should immediately increase. Slightly increasing the rpm should increase the output voltage. Do not rev the engine as the voltage will follow. This will result in everything from the battery to the ignition will draw more current with increasing voltage and can be quickly damaged.
Also be careful with the jumper and do not let it contact ground. This will result a short and wirs will get damaged.

 

[Mattax]

If there is voltage drop between the main splice and the ballast resistor, backprobe cavity N.

PS. I agree the green field wire (R3) looks terrible. It may not be the immediate issue but fix it.

For repair, depending on what is damaged, you may find these threads useful:
Open barrel crimpers and Chryser terminals, wire strippers. Sources for Chrysler type wire terminals
Splice connectors and shrink tubing. Inline wiring splice clips........from the Dodge RAM service manual
Deoxit and other cleaning supplies. What do y'all use to clean the metal connectors that go into the bulkhead on either side of the fw?
Adhesive free harness tape in couple widths. Vendor needed for cloth / fabric tape non adhesive type

 

[7T Swinger]

Darn, I thought the 2v at the VR meant it was the problem. I’ll check things further as suggested. Thanks to all for your help.

Graham

 

[Mattax]

Darn, I thought the 2v at the VR meant it was the problem. I’ll check things further as suggested. Thanks to all for your help.

Graham

It may be. jumping the regulator will be a quick test. It may not be the only issue, but will be a quick check. mechanical regulators can be opened to see what has happened.

 

[7T Swinger]

Update:

I discovered a crappy connection at the bulkhead connector where the fusible link goes into the firewall and a wire blown apart in the VR. A new one arrives next week and hopefully I’ll be up and running again.

Thanks to all for the replies.

Graham

 

[Mattax]

a wire blown apart in the VR

That wire is also a fusible link. The regulator has two fusible links. Depending on which one, or both, melted will indicate where the short occurred.
A short to ground in the regulator's output any place before the rotor's windings would result in high current draw.

There's a fuse wire for the upper contact and another for the lower.
My first guess would be a short to ground.
If the upper points got welded together then it was trying for maximum power for long period of time. probably because it had low voltage readings.

from 1969 Dodge Service Chassis Manual

Normal operation
When system voltage is lower than set point, not much current flows through the regulator's electromagnetic coil.
The spring pulls the upper contacts together.
Current flows directly through the regulator to the alternator's rotor.
The only resistance in the circuit is the alternator's rotor windings. (This draws a current of 2 or 3 amps, although later alternators and many replacements draw 5 amps or more).

Short to Ground in the Field Circuit
If the output wire contacts ground, then there is no resistance and current flow becomes excessive.

Then the fusible link melts and there's no flow.

These illustrations and a full explanation can be found in the 1966 Chrysler Master Technicians Conference.
Available online here: Browse MTSC by Model Year – 1966 – MyMopar

 

[Dana67Dart]

@7T Swinger

What part of the country are you in?

You have corosion inside the semi sealed VR.

was the car under water at some point?

I would be tempted to go through every connection with some terminal cleaner and a tooth brush.

 

[Mattax]

a crappy connection at the bulkhead connector where the fusible link goes into the firewall

That connection (cavity Z in '67) can be overheated by excessively high battery charging or a short in an unprotected circuit. Depending on how bad it is you can clean it up. One thing to make sure of is the metal terminals are locked into the plastic housings. If the lock tabs are not holding, the terminals back out when the connectors are assembled, resulting in a poor connection.
This post shows the locking tabs.
Often the foam seals need replacing. DMT makes and sells those.

If the terminals at Z looks bad, then its worth checking out P (alternator output) and N (ignition run).

P because if the battery was charging at high rate, then the alternator was supplying that!
N because any resistance in the run circuit will also cause the regulator to read system voltage and correct for it.


PS This should be a direct link to the 67 Barracuda Supplement which has the fastback and rally dash wiring diagram.
http://www.mymopar.com/downloads/servicemanuals/1967_Plymouth_Service_Manual_Supplement.zip