some one else have openions of the smaller pully?

 

Recheck the alternator output, if it is still okay, you probably have a bad diode trio inside the alternator, also referred to as the light minder diode.  It's not that hard to replace.  I have posted the procedure twice, but if you can't find it, I will post it again if you need it.

Would like the trio post, I hear they go bad quiet often.  Will have the terminal installator change out as well.

 

Thanks guys.

 

 

 

To inspect and replace the alternator diodes.

 

This applies to the 1974 and newer alternators with the internal regulator.

 

Once the alternator is off the car, place it with the pulley down.  You will see four bolts around the outer diameter of the case.  Remove the bolts.

Now the back half of the alternator case can be lifted off of the other sections.  You will see a thin center section between the alternator halves.  Make sure this part stays with the back half of the case (opposite side from the pulley).  As you lift, you will hear a light snap.  This is the alternator brushes dropping out of place.  Two springs may fall out.  These springs will look like a spring in a ball point pen.

 

Inside the back half you just removed you will see the brushes hanging by a ceramic holding fixture.  Looking at the outside, you will see a small hole that lines up with holes in the ceramic brush holder.  Place the springs back in the section where they were in the holder, and where the brushes slide in place.  Now line up the brushes and slide them back in place.  Insert a piece of wire, toothpick etc, into the hole from the outside of the housing, and into the hole in the brush holder.  Push the brushes backing far enough that your pin will hold the brushes back in place.  Insert the pin far enough to go through the top hole on the brush holder.  This the only way to hold the brushes back in place when reassembling the alternator later.  If the brushes are worn get a new set.   They will come installed in a new holder.

 

Now look down in the alternator back half.  You will see the center section is bunch of wires in a wound bunch.  This is the alternator stator.  You will see three wires from the stator held in place with three nuts.  Remove the nuts and lift the stator out of the case.  Use an ohm meter and make sure all three wires in the stator have contact with each other.  If not, replace the stator.

 

Where you removed the nuts you will see three taps going to a rectangle block with another tab going to the regulator and brush holder.  The same screws hold the regulator as the brush holder.  There are three of them.  Two of the three have insulators under the screw heads.  Don’t mix them up.   Remove the screw holding the last tab on the block and lift the block out of the alternator.  This block is the light minder diode, also known as the diode trio.

 

Use an ohm meter set to diode check.  Touch one lead to the single tab on the trio, and touch the other meter lead to each of the other three tabs, one at a time.  Read the meter.  Now reverse the leads and check all three again.  One combination of the leads will show an open circuit on all three of the other tabs.  When reversed you should read an almost equal reading at all three.  If it fails either way, replace the diode trio.

 

Now back down inside the case. And back to where you first removed the three nuts.  They are located in the rectifier bridge.  This contains six more diodes.  These affect the charging rate, and control changing the three phase A/C into D/C current.  Rotate the case so the rectifier bridge is at the top of the case.  This is just for reference and description.  With the case in this position, you will see cooling fins on both the bottom and top side of the bridge.  Connect your ohm meter lead to the bottom set of fins, and check the three lugs where the nuts were.  Now reverse the leads, just like you did with the trio, and take another set of readings.  Again, there should be an open circuit one direction, and a constant even reading with the leads reversed.   This checks three of the six diodes.

Now put one of the meter leads on the top set of fins, and repeat the checks to test the other three diodes.   If any of the diodes flow both ways, or are open both ways, you will need to replace the rectifier bridge.   It is held in place with a screw into the case on the right side, and by the nut holding the terminal on the battery connection on the outside of the case.  Remove those and the wire from the condenser and the bridge lifts out.  Be sure to reinstall the insulator on the battery terminal, or the electrical system will short out, and blow a fusible link by the starter.  If all test were good but the alternator does not charge, replace the voltage regulator.

 

Before reassembling the alternator, look at the two copper rings on the alternator rotor in the front half of the case.  If they are rough and burned gently sand them to a smoother surface.  Don't sand too much or you will need a new rotor.  You can't put the copper back.  It's best to hold the rotor upright, and wrap a piece of very fine sandpaper around it, and pull back and forth like Chubby Checker doing the twist.  This way you don't create low spots. Use your ohm meter again, and make sure there is a connection between the two copper rings.  If not, you will need a rotor.  This is fairly rare.

 

Be sure to remove the pin, toothpick, etc after assembling the alternator.  If you forget, the brushes won’t make contact and the alternator won’t charge.

 

I have drawings, but they are copywrited, so I can’t post them.  But I can e-mail them if you need to see them.

 

Once the alternator is off the car I can do all of this in about 10 minutes.  It's not that tough. Your first time will take quite a bit longer.  Just take your time.

http://www.4wheelnoffroad.com/alter.html  

John