M939 Alternator

[Clayshootr]

I was trucking down the road the other day in my M931 to pick up a John Deere 4430 tractor that I had purchased and all of a sudden it started to stink something terrible in the cab. I looked down at the gages and noticed the alternator needle was up in the red zone. I looked under the seat and the batteries were boiling over. I did not have the correct tools to remove the belts so I just cut them off. I hated to cook $500 in batteries.

My question is do these things have a internal voltage regulator in the alternator or one located somewhere remotely? I assume that is the problem??

Thanks for any insight!

 

[juanprado]

The prestolite voltage regulator is an external small box bolted to the outside of the alt.

 

[jonesal]

Not if it's stock. Standard 60 amp alt. has the VR on the back of the unit. Use search for lots of info.

It sounds like the alt. ran wide open to boil the batteries over. That means the brushes grounded out to do that. Pull the unit, then the VR and decide if its fixable. The VR is serviceable in the vehicle but I suspect you might have more problems than that.

Al Jones
84 M923

 

[91W350]

We have plenty if you need one. I have one tested and ready to ship, next week I will get some more checked out. Are you close to Reb87? He may have a loaner until you can source one, I would be glad to replace his for him if he does. I owe him a few favors. Glen