charging falling off to the red

[steve6x6x6]

The charging on my M35A3 was in the green , then over time fell into the yellow and now it is on the edge of red. The truck starts right up but very concerned about this. Not sure if it is the alternator or voltage regulator? Did a search but no info on deuce, all CUCV.

 

[scootertrs]

Check the voltage coming out of it. If it isn't 27+ you are in trouble. I just went through that with my deuce fire truck. She would start well and showed borderline green, but during a night response to a fire with all of the spots running as well as the emergency lights, even at a high idle, they got dimmer and dimmer until my battery voltage was under 18 Volts. Truck kept running... gotta love a deuce and the mechanical fuel shutoff... if it had been a 5 ton, I am afraid I would have been dead in the middle of the ordeal. Afterwards, I Took it off and while looking inside, the alternator looked like someone had placed an IED inside the regulator back.

I am curious though, is it worthwhile to have a spare regulator backup for an alternator or usually when the alternator goes south, all of it needs rebuilding. I am going to try posting as a new thread to see if it merits having a spare regulator.

Good luck

Raul

 

[goodguyzy]

Mine voltage was low and then not to long after that it smoked, had to replace the whole thing with a SAW Eriks.

 

[kimbilly]

Under the cover where the wires attach there is an allen screw. You can turn that to adjust the voltage.

 

[M35A2-AZ]

I think it is the allen screw plug not under the cover. Remove the allen screw plug and the use an allen wrench to adjust.
Check it at the gen. with the lights on.

 

[kimbilly]

That is correct. The allen is next to the cover. Once allen plug is removed a phillips head driver can turn the adjustment.

 

[steve6x6x6]

Thanks guys, i will check into that.

 

[135gmc]

If the voltage gradually drops off, start by checking belt tension, then cleaning and tightening all the alternator output connections, also the battery cable terminals - then check the voltage adjustment screw. If the voltage suddenly drops off, you probably lost a rectifier. You can buy a new rectifier bridge a lot cheaper than a new alternator---

 

[steve6x6x6]

If the voltage gradually drops off, start by checking belt tension, then cleaning and tightening all the alternator output connections, also the battery cable terminals - then check the voltage adjustment screw. If the voltage suddenly drops off, you probably lost a rectifier. You can buy a new rectifier bridge a lot cheaper than a new alternator---

I do not think it is the serpentine belt slipping, i will look into the other things.

 

[wilfreeman]

Hey guys. I am also having charging (not charging) problems. I bought the deuce last week knowing that it wasn't charging. Drove the truck home (about 40 miles) at night - lights were still bright when we got there. 2 days later the batteries weren't strong enough to start the truck. Anyway, I took the alternator off and took it to an alternator/starter shop - he said the rotor(?) was bad and didn't know where to get one. I found a used alternator that was guaranteed, so I bought it. I put it on and get the same thing - no charge. I have been reading all the posts I can find and am trying all of the suggestions. So far I have: 1)Checked the exciter wire - 24v, 2)Checked my ground wire, and 3)Removed the #2 wire and checked the voltage at the post on the alternator @ 1200rpm - 22.8v. I turned the voltage adjustment screw under the allen plug about 2 turns and it didn't change - 22.8v. So, what am I doing wrong and what else can I test. Or is my replacement alternator crap too? Thanks

 

[wilfreeman]

I found a used alternator that was guaranteed, so I bought it. I put it on and get the same thing - no charge. I have been reading all the posts I can find and am trying all of the suggestions. So far I have: 1)Checked the exciter wire - 24v, 2)Checked my ground wire, and 3)Removed the #2 wire and checked the voltage at the post on the alternator @ 1200rpm - 22.8v. I turned the voltage adjustment screw under the allen plug about 2 turns and it didn't change - 22.8v. So, what am I doing wrong and what else can I test. Or is my replacement alternator crap too? Thanks

OK, it looks like the original post is dead, since the OP never followed up with the solution to his problem. Since this is sortof related to my problem, I am going to hijack this thread - unless that is a problem.

With that said, I will continue with my troubleshooting progress and continue to ask for suggestions. After the above steps resulted in no progress, I removed the alternator and popped the back cover off. And there was the problem! Looked like a grenade blew up in there! That was 2 weeks ago.

Fast forward to today. Today, the dealer that sold me the alternator was making a delivery in Columbia, SC. Fortunately, he was travelling I77, which passes close to my house. I met him at the off ramp and exchanged my alternator - easy enough - good man! I took it home, installed the pulley, and installed the alternator. I double checked everything then hooked up the batteries. I fired her up and the voltage gauge was in the yellow - STILL. I turned on the headlights and raised the rpms to ~1300 - no change. I turned the voltage adjustment screw - no change. I measured exciter wire voltage - 24.4. I measured output voltage at the alternator - 24.4. I measured the batteries - 24.5!

I went inside and turned off the accessory switch and turned it back on - the volt gauge jumped over to the RED. I switched it back off and decided to turn the voltage adjustment back to where it was when I installed the alternator. I turned the switch back on and it went to the red again. switched off and adjusted the voltage screw again - still in the red. I shut the engine down and measured the voltage at the batteries - 26.2v.

That's when I decided to come inside for lunch and post my new (over charging now) problems before I screwed this alternator up!

Question: Why (when I start the engine up) does the alternator NOT charge, then when I switch the accessory switch off then back on, it DOES charge (overcharge)?
Question 2: Why is the voltage adjustment not changing the output?

I am doing all of this stuff by myself, so it is kindof a pain to keep climbing up and down to the engine compartment and back and forth to the cabin. Has anyone run into this problem?

 

[Jeepsinker]

Just an idea... Check/ replace master power switch. No experience with that on a deuce so take that into consideration, but I have seen faulty ignition switches in other vehicles start them up and run all of the accessories but cause the alt not to charge sometimes or unless you wiggle the key/cylinder. Also check just the connections on the back of the master switch. This will at least give you something to rule out. At 26.6 volts you are not overcharging. It's good up to 28 volts or so. I wouldn't be concerned with almost 30.

 

[wilfreeman]

Thanks for the idea jeepsinker. I went back out and made sure the wires were solidly attached to the switch, but I don't have a spare switch to test with. I did fire the truck up to see if it changed anything after I played with the wires though - no change. Had to cut it off and back on - then the volt gauge went over in the red. I ran out and checked the battery voltage and it read 35.6. I ran back and switched it off. I then played with the adjusting screw some more, switching it off and back on between adjustments - no change. And yes, I did remove the allen plug and am adjusting the Phillips screw inside.

One new question: How much would I have to turn the screw to affect the output from 36 down to 28? I don't know if I am turning too much with each try or what (I am turning about 1/8 - 1/4 turn each time).

I am seriously considering ditching the original alternator and doing the Delco conversion. Although I hate to lose the $175 I spent on this used one, it is becoming a PITA - I can't get anything else done to the truck until I get the charging problem ironed out, but REALLY don't want to drop $300 - 400 on an NOS alternator!

Thanks for the info!

 

[Jeepsinker]

I would say do 1/8 of a turn at a time because small rheostats like that are usually sensitive in a very small part of their range and do nothing at all on the other 90% of their range of motion. I would suggest a last try with the truck running and a volt/ohm meter hooked up with alligator clips right beside you where you can see it while you make adjustments. Take your time. A few minutes charging like that isn't going to blow the batteries, but don't screw around too long either or you may. Bear in mind that I have done this with other vehicles, not a deuce. These statements are FWIW.

 

[wilfreeman]

So you can't run the alternator while it's not hooked to the batteries? That would be nice! I was wondering how long I could run it with it overcharging like that.

 

[Jeepsinker]

You can on a normal vehicle, but I seem to remember reading somewhere specifically not to disconnect battery cables with the truck running because it damages the alt?

 

[wilfreeman]

Thanks again for the info. I guess I'll try adjusting while running now that I know I should have a couple of minutes to play around with it! I also have a reason to buy a new multimeter since mine doesn't have alligator clips. I know I could just buy new leads or the clips, but then I wouldn't be upgrading my tools, would I? HeHe. I'll give this a try tomorrow and report back. In the meantime, if anybody has anything to add, shout out!

 

[steve6x6x6]

I installed a new volt gauge, that was the problem.

 

[Jeepsinker]

Yeah but he already verified that the voltage is off with a multimeter.

 

[wilfreeman]

Yep, I'm getting 35.6v at the batteries. I was hoping the volt gauge was the problem, but that's not the way my luck runs - this truck is fighting me every step of the way so far! Not a good start for me with the "Big Trucks", but I'm still hopeful that she will become my bestest friend, LOL!