M925A2 Delco Style Alternator

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74M35A2

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eBay of full of nice ones spun from solid barstock, in both 8 groove serpentine and double V groove. 21Si and clone are 7/8" shaft diameter. Serpentine pulley is about $14 delivered, and double V groove about $18. Both may include a keyway broached into it, simply ignore this, it is designed to work with both key type and keyless (slip-fit) shafts. Make sure you use either a lock washer and conventional nut, or flange head lock nut (impact install) on the shaft, the alternator will come with the shaft nut.
 

dmerrell89

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Just did my conversion with a Delco Remy 110 amp 28si alternator and it works perfectly. We have fried 2 of the factory alternators and were ready for something different. I used the cummins bracket so it all fit nicely. If anyone wants the part numbers feel free to email me. Thank you to 74M32A2 for all of this information.

dustin@removesediment.com
 

tobyS

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The M931A2 I sold is experiencing some alternator problems and has fried the first rebuild. I like the idea of simplifying and making it so the shut down sequence is irrelevant. The lower cost unit, 70a, seems fine if it holds up....which apparently it does. .
 

74M35A2

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Trying to keep the radar on for failure cases of them, but don’t see much. Many people using them. May even be better than the genuine thing, the voltage regulator quit in the genuine Delco I was benchmarking, in my avatar pic, less than 1 year old of hobby use. Soldered a replacement in, and has been fine. Yoi can get the Chinese Delco clone for $66 delivered, including 1 year warranty, sans pulley. The stock military alternator will not fit it.
 

sdflatfender

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Big Thanks to Tractors0130 for starting this thread back in 2012, and to all the contributors along the way, and Especially!! to 74M35A2. It's been a good read from the beginning filled with all the info I need to fix my junk. I'm currently looking at a toasty generator that also fried my engine temp gauge. The gauge literally blew up, and the outer ring, lens, and faceplate of the gauge went flying across the cab, AND the truck horn went on full blast by itself. It literally scared the **** out of me as was outside closing the hood. Anyways, I jumped into the cab and noticed the voltage gauge was pegged past the red as I turned the rig off. Goodtimes!
My rig is an M932A2 so it's the 8.3 and has the longer cummins bracket.
No clue what else has fried like what happenined to TinStar. ABS, or PCB, or the CTIS controller, or my horn :(.
I'll post back when I figure out which route I'm gonna go but I do like the 130Amp option and thinking 74M knows his stuff and has taken the time to put a kit together that bolts right in.
Thanks again ALL!!
 

Katavic918

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Same thing happened to my hmmwv. I started smelling battery while driving and saw my gauge was pegged. Shut it off quick. Nothing was damaged, hopefully the same for you. I replaced with delco 21 clones on both the hmmwv and m35a2. So far so good.
 

74M35A2

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Glad everybody is having fun. I don’t have or sell the 130’s anymore. The 24v 70 amp Delco 21Si clones can be had off the internet for $70-$100 delivered including 1 year warranty. They appear to be more reliable than the genuine ones, actually. The correct 8.3L Cummins bracket is $100 from any Cummins dealer. I do sell a kit with these parts together for those that don’t want to do the legwork, and I make $100 for the legwork, include an adjustable belt arm, all the fasteners, and technical support/guidance. Some very much find this worth it, vs 7 trips to a hardware store 45 minutes away for them. This is for any M939a2 (8.3L). For the 250 engine, no bracket purchase, you basically just space it correctly with long bolts, a spacer tube, and washers.

So, 2 paths to go for one wanting this. You can bottom dollar it and be changed over for under $200 (under $200 for 250 engine), or have it all land on your porch in a single box for $300. Either way is a great deal to prevent electrical damage to your truck. It also enables anybody to shut the truck down in any switch order with zero over-volt risk.
 

Jbulach

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I just want to know what battery smells like? All I keep smelling is burning feathers...

BEVERS AND DUCKS!!!
 

sdflatfender

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74M ... Thanks ... You're awesome ... I'm down and I'll send you a PM now.
Regarding the other items, before I get "Betsy" up & running again I'll do some reading up on the PCB to understand what to look for to know whether it's toast or not. Same for the ABS, and CTIS.
Now onto finding a replacement Eng Temp Gauge.
PEACE!
 

74M35A2

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It was more of an info post rather than a classified, for those that want to save $ and do it themselves. If you are interested in purchasing from me, PM we and we can go from there. 1 week lead time, nothing kept in stock.
 

TexAndy

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Sorry to beat a dead horse, but I'm about to do the changeover to a chinese 21SI clone on my 923a2. I know multiple people have said don't use wires 566 and 568 for anything on this alternator.

However, the -10 says

CIRCUIT 566 - Controls a relay in the protective control box that prevents the starter from reactivating while
the engine is running.
CIRCUIT 568 - Senses system voltage and excites the alternator field.


So I guess I understand that 568 won't do anything for the 21SI because of it's internal design, but by leaving 566 disconnected, does this mean one could technically engage the starter while they're driving? I know it's not a big deal and has practically 0.0 percent chance of happening with that springloaded start/run switch. Just asking for my own personal education.
 

74M35A2

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Livonia, MI
Correct on your #568. This is also why the civilian unit is a much superior unit. Some of the modern civilian ones can use an external remote sense, but if nothing is detected on this wire they default to the internal setpoint. The military one would instead just go full field because it thought system voltage was super low.

On #566, you would only be able to do a running re-engagement in park or neutral. Even by not using this wire, you will (should) not be able to crank the starter in any driving gear, only in neutral, due to the neutral safety switch integrated into the shift tower. The starter design itself would not prevent a running re-engagement attempt. The pinion would not engage, but it would try pretty hard to as it is being forced against the moving face of the ring gear teeth.

#566 is typically connected before the diodes inside the alternator, so it is sensing an AC output, since that is what alternators make, prior to the current being rectified into DC through the diode bridges. Therefore, it is easy to see an AC voltage sine wave and judge the engine is running. Not as easy to do with DC. AC alternator connectivity is a thing of the past, but it was used for double-start protection, a frequency signal to run a tachometer, and/or an hour meter. Some modern units still offer this AC terminal, but only got be able to back-service older vehicles.
 
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Corn

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Asher, Oklahoma
Hello,
New to the site, this being my first post. I am running into the same problems as everyone else on this thread with the generator not charging the batteries properly. I have decided to convert to the 21SI alternator and by reading through this thread I have determined I will need a new 7/8" shaft V belt pulley to go in this new alternator. I see there is a new bottom bracket that comes from Cummins that bolts on the bottom for the 6 CTA 8.3 engines. However, I have an NHC-250 engine. Does this still require the bottom bracket or will the new alternator bolt right on? After reading the thread I am still confused about this.
Thanks!
 
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