M-38 24 Volt charging system

[1948willyman]

Just lost charging amps on my jeep today. Has two new batteries purchased last few weeks. Looked down at amp gauge and showed 0 Turned lights on and went to discharge. Always kicked up right after engine started and backed off to close to zero shortly. Always stayed on charge side even with lights on. Checked with engine running AND SHOWED 24.5 volts which I assume was battery voltage. Used to always show 28 volts running. Do not know if that was too much or not. Checked all wiring I think was connected with charging system and did not find any issues. What else should I check before removing I guess voltage regulator and or generator. Always done fine until today? Anyone have any ideas what to go to next? Did not know if system goes through circuit breaker or not ?
Many Thanks for input on this.

[OKCM38CDN]

Sounds like you lost the voltage regulator...
_________________
Hal, KB1ZQ
TSGT, USAF (Ret)
1952 M-38 CDN CAR 52-31313
1952 M-100 Strick #104
1951 Willys Wagon (For Sale)
1954 Willys M38A1 201001205
Tornado Alley
Del City, OK

[wesk]

Have you followed the steps in your M38's operating handbook TM 9-8012 Troubleshooting Generating System pages 84 & 85? If yes then to isolate the Generator and regulator to determine which is the culprit you simply perform a full field test on the generator.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[1948willyman]

Done the steps on page 84-85 of TM9-8012 and did not find any issues. Completed the full field test as Wesk stated from Generator Testing Subject Posted on Friday May 14 2021 for full fielding test. When completed as stated the generator quickly went up to 34 Volts just a little off idle speed, So I shut down and assume the problem does not lay with generator. I guess my next step is checking regulator ? Maybe checking wiring and grounds again first although previously did not see anything. To remove lid on regulator, Should I just remove from vehicle and then try to inspect inside for any issues? I guess I could try cleaning the contacts if do not see anything burned or melted. Have a regulator that came off M-170 but do not know if correct one for this jeep or if it is even good? Looked at some of the testing pages on these but looks to be very complicated. Any ideas for an easier check to see if it is the problem or have to bite the bullet and purchase another one.

[Kendall]

If you decide to remove the cover of your regulator in place remember to disconnect the battery cable FIRST!
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1951 M38
1952 M38
1952 M38A1
1942 Dodge WC-55
1951 M100 trailer
1942 Ben Hur trailer

[wesk]

The full field test takes quick care of which of the two is the problem. The quick and easy "Is it really the regulator???" is a simple substitution of the regulator. What is the part number/model # of the your 170 regulator?
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[1948willyman]

ID TAG shows to be a Prestolite
PART # VBC or C could be O ? 4004 UT
SERIAL # 72 or 2 could be Z 1426
25 AMP
SPEC. No MIL-R 10265

[wesk]

The VBC4002UT and VBC4003UT were used on the M38 and M38A1. The VBC4004UT was introduced about 59 or 60 with the M151 jeep. There are a few subtle differences between the early 4002/4003 vs the 4004. Review these papers carefully before deciding what to use and how to adjust it to what spec.



















The large size copy of these illustrations are in my photo album main URL http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Go to sub album "M Series Electric" http://www.willysmjeeps.com/v2/modules.php?set_albumName=album173&op=modload&name=gallery&file=index&include=view_album.php

Go to sub-sub album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album758&op=modload&name=gallery&file=index&include=view_album.php

Then go to: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album759&op=modload&name=gallery&file=index&include=view_album.php

Take NOTE: the post WWII edition of the Autolite/Prestolite Service manual TM 9-1825B dated 1952 only covers servicing VBC4002UT. 4003 came out in late 52 and 4004 late 59. However most common items in this manual still apply to the 4004 and the important items are found on the sheets already illustrated.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[1948willyman]

Thanks Wesk for the great info on this as always.
Will look into these sheets of info and try to see what to do. Did remove the regulator yesterday and removed the cover. Did not see any thing that looked burned, melted, or had been hot? Will keep you informed.

Thanks Again

[wesk]

If you now have the cover off that regulator you should have several pubs on you work bench:

They are all found here in bold:

[1948willyman]

I can see why you must remove battery cable before messing with voltage regulator according to Kendall That info was not put on the lid for nothing ,
That is for sure close as everything is.

[1948willyman]

Did place the m-170 voltage regulator on my jeep and it is charging as normal now . Just as the old regulator did,when working. I figured out, that the original one would charge if you manually held contacts together on the cut out relay. Looking at the service manuals that Wesk placed on site to try and figure out what is going on, that the contacts will not pull together when generator puts out 26 Volts . It appears the winding on the cut out relay must be shorted or burned in two somewhere ? Trying to do some ohm tests to confirm. Would like to repair if possible, but most likely be hard to ever find any parts for it, Always like to keep a spare when possible as I have a good extra generator also. Thanks again for Wesk placing these manuals on here to look at, as this is a dying art in these days. Maybe I could learn how to re-wind a defective cut out to work, as I did in my younger days at school in electrical class, though could not get mine to work like it should have. Went to old school alt/ gen/ starter repair shop locally, but said no experience on this type unit and also was first he had ever seen being almost eighty years old and repairing over 50 years

[wesk]

Look for shops with old X-GI's on their staff and/or public service vehicle experience since many were and are 24V as well as heavy trucks and equipment.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php