200amp alternator not charging

[joshuaS]

Hello,

My rig is a 2006 M1165. It has a 200amp alt. The other day it quit on me. RPM gauge doesn't work and the voltage gauge is in the yellow. I have gone through the Niemoff trouble shooting procedure and with the engine off my ohm reading is 2.5. That reading indicates that the alternator is bad.

My specific question has to do with the free spinning of the alternator. With the engine off I can spin the the nut on the front of the alternator and it will spin freely. When the truck is running, the alternator spins but, with just a little bit of pressure on the back of the unit where the fan is, I can stop the alternator from spinning. Is this normal?

Thank you,

Josh

 

[Mogman]

Sounds like the overrunning clutch on the front of the alternator (pulley) is bad, you should be able to turn it one direction but not the other with motor off.
Unfortunately that is a relatively high dollar item..

 

[Mogman]

What reading are you seeing 2.5 ohms and what does the guide call for?

 

[Retiredwarhorses]

Your clutch pulley is faulty…..not uncommon.

 

[joshuaS]

Your clutch pulley is faulty…..not uncommon.

If I can fix that do you suppose the generator will function properly? Any guidance in much appreciated. Is the fix to get a new pulley?

 

[Retiredwarhorses]

If I can fix that do you suppose the generator will function properly? Any guidance in much appreciated. Is the fix to get a new pulley?

if the pulley is free wheeling in both direction, yes…the first course of action it to replace the pulley assy and TS from there.

 

[joshuaS]

What reading are you seeing 2.5 ohms and what does the guide call for?

The guide states, with key off, engine off check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator harness plug. Connect black lead to B+ terminal on alternator, Does meter show 1.8 to 2.2 ohms? If the answer is no then the arrow points to "alternator is defective."

It does seem that my pully clutch is not working.

 

[Coug]

Part of your ohm reading may be the wires and meter itself. 2.5 ohms is close enough to the 1.8-2.2 that I would personally not be all that concerned about it, unless I was using a stupid expensive meter that was truly accurate at those levels.

One thing you can do is connect your meter leads together and see what it reads. On one of my fluke meters it's usually 0.5-0.7 ohms resistance with just the meter leads, on a cheaper meter I see about 0.9-1 ohm resistance.

 

[Mogman]

The guide states, with key off, engine off check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator harness plug. Connect black lead to B+ terminal on alternator, Does meter show 1.8 to 2.2 ohms? If the answer is no then the arrow points to "alternator is defective."

It does seem that my pully clutch is not working.

As Coug said, probably meter error, not far enough off to worry..

 

[joshuaS]

if the pulley is free wheeling in both direction, yes…the first course of action it to replace the pulley assy and TS from there.

So, the clutch pulley is bad. I pulled it off and in doing so it re-engaged. I replaced everything and now everything works.

I will have to get another clutch pulley soon, as I’m sure it will fail again. I very happy I asked questions and that I didn‘t drop $1600 or more on a new generator and regulator.

Thank you all for the help and this wealth of information the site provides.

 

[joshuaS]

Sounds like the overrunning clutch on the front of the alternator (pulley) is bad, you should be able to turn it one direction but not the other with motor off.
Unfortunately that is a relatively high dollar item..

Thank you and yes that was the problem.