M925 Voltage Fluctuation Problem, Time for an Alternator?

[Piper Cub]

My truck starts and runs great but occasionally when I start it the voltage is fluctuating enough to make the gauges go crazy. Once I get on the throttle it stabilizes and everything is fine until I let off the throttle. After driving it and warming up the engine it doesn't happen anymore even at idle. I'm thinking it's the voltage regulator in the alternator going out but don't want to spend a bunch of money to replace the alternator (either with stock or an aftermarket if I can figure out what would fit) if that's not it. Video should be attached to show what the gauges were doing earlier today. Anyone had a similar problem in their truck?

https://youtu.be/V56QCbUWPsQ

 

[NDT]

Pull the little excite wire loose from the alt and see if it still does it. If not, well your alt is throwing pvc's as they say in the hospital.

 

[Piper Cub]

Thanks, I'll give that a try in a couple days. If I do need an alternator I'm having trouble finding what an ideal aftermarket replacement would be. Any ideas on a part number/ source?

 

[74M35A2]

It may be a loose connection somewhere that is vibrating at idle (ground)? But, when running, it does not seem like you are charging anyway? If you are still running the stock alternator, tweak the voltage adjustment screw just a pinch up and see if your problem goes away. Sometimes they can get flaky staying in the same position for decades, and a single movement either way will clean the potentiometer within the regulator and make it behave. Not promising, but a free try.

 

[pjwest03]

Wolverine Technologies has a kit for M923/M925 to put a modern Delco alternator on it. He used to have a Steel Soldiers price. Give him a call.

http://www.wolverinetechnologiesllc.com/M925Alternator.html

 

[Piper Cub]

Thanks guys, I'll tinker with it a little and see if I can get it to work right without buying anything. It still charges fine once the engine's warmed up. Hopefully just something simple like your suggestions.

 

[Cape Coastie]

Hey Piper, when I first got my truck voltage reading was showing low. In the TM there is a good instruction on adjusting the voltage. All that is needed is an Allen wrench to remove the plug and a small flat head screwdriver to turn the screw inside. Use a good volt meter to make sure you set it right as the truck gauges are not very accurate. If you need the TM number give me a little bit to find it and attach as I am traveling.

 

[SLOrazorsedge]

Adjusting the voltage screw up and down with my Fluke meter monitoring cleared up similar issues I was having with my M936A1. It would intermittently peg into the red.

 

[Russ58]

HI piper .. yea it maybe a ground or cable loose

 

[Tinstar]

Replace your old Alternator before it goes out and takes other components with it.
Mine took out the PCB, ABS controller, and CTIS controller when it spiked and literally fried itself. Worst smelling smoke ever!


I installed a brand new (not reman) Delco-Remy 33si 100A unit.
Best thing I ever did for the truck.
Batterys much happier and stronger now.
The correct factory Cummins alternator bracket makes install a breeze.

SS member 74M35A2 has best prices period!

 

[74M35A2]

Thanks. I really didn't want to blow my own horn.

A lot of people think the stock military alternator must be the best one, because that is what it came with. But in this case, it is not. They are junk, and have about 4 different commonly seen failure modes, some of which are the pulley interface, and when that fails, you'd better have your walking shoes on if the belt drives your water pump. As TS mentioned, an over-volt, of which can happen whenever the stock unit wants, or if the truck is shut down in the wrong switch order (how stupid of a design), can/will wipe out the ABS module, and sometimes CTIS module, PCB, etc...

In this case, as hard as it may be to believe, civilian units are much further ahead. Even the Delco clone units. As a friendly reminder, a brand new "genuine" Delco alternator is about $390 just for the alternator, so if you are paying less than that, it is likely a Chinese Delco clone. Yet, these have been testing to hold up surprisingly well, and are about 30 years newer in design than the stock mil unit. They are single wire connection, and will not over-volt on usual circumstances (shutdown switch order, etc..). They are available to fit LDT/S 465, NHC 250, and 6CTA8.3, at a very reasonable price.

 

[Gary Anderson]

Thanks. I really didn't want to blow my own horn.

A lot of people think the stock military alternator must be the best one, because that is what it came with. But in this case, it is not. They are junk, and have about 4 different commonly seen failure modes, some of which are the pulley interface, and when that fails, you'd better have your walking shoes on if the belt drives your water pump. As TS mentioned, an over-volt, of which can happen whenever the stock unit wants, or if the truck is shut down in the wrong switch order (how stupid of a design), can/will wipe out the ABS module, and sometimes CTIS module, PCB, etc...

In this case, as hard as it may be to believe, civilian units are much further ahead. Even the Delco clone units. As a friendly reminder, a brand new "genuine" Delco alternator is about $390 just for the alternator, so if you are paying less than that, it is likely a Chinese Delco clone. Yet, these have been testing to hold up surprisingly well, and are about 30 years newer in design than the stock mil unit. They are single wire connection, and will not over-volt on usual circumstances (shutdown switch order, etc..). They are available to fit LDT/S 465, NHC 250, and 6CTA8.3, at a very reasonable price.

Hey 74m35a2,
I have an 84 m925 with the nhc250, having the same voltage fluctuations as described in this link. Interested in a new alternator. How to proceed? I read alot of posts but this is my 1st and don't want to break any rules by listing contact info or doing something to be court marshaled for.....Please advise proper procedures.....Thxs, Hlfd18

 

[74M35A2]

Do you know how to send a “PM”? Click my name and hit “Start Conversation”, and away we go.

Basically it will be to click my name, send $, install your alt, and done. 3 step process.