Is a Regulator VBC4004UT interchangeable with VBC4002UT

keats · Post by **keats** » Fri Feb 18, 2022 5:17 pm

is a voltage Regulator VBC4004UT interchangeable with VBC4002UT?

the vbc4004ut has metal mounting feet. Internals look very similar.

Post by **wesk** » Sat Feb 19, 2022 3:40 am

There are a few differences: http://www.willysmjeeps.com/v2/modules. ... _album.php

keats · Post by **keats** » Sat Feb 19, 2022 8:46 am

Adjustment and configuration differences aside, will the 4004ut work as a replacement? It would still regulate 24 volt system, no?

Post by **wesk** » Sat Feb 19, 2022 7:20 pm

Can't say. Voltage and Amperage regulation in any 24 V system must be configured (ie wired) precisely and regulated accurately. This is a test process you will need to have the fire bottle standing by for!

4x4M38 · Post by **4x4M38** » Sun Feb 20, 2022 7:20 am

I guess the question is one a replacement for the other, I.e., listed in the Ord 9?

Post by **wesk** » Sun Feb 20, 2022 12:16 pm

The M38 ORD 9 only offered the VBC4002UT. The M38 ORD 8 Jun 56 offers VBC4002UT and an alternate VBC4003UT. The M38A1 ORD 9 and much later TM 9-2320-208-20P offers the VBC4003UT as an approved sub. None of the M38/M38A1 parts manual list a VBC4004UT! The late M38A1 TM 9-2320-208-20P also offers the Leese-Neville transistorized regulator used on the M151 as a sub for the VBC4003UT.

keats · Post by **keats** » Sun Feb 20, 2022 8:14 pm

4002.4003,4004. seems like a simple progression in a series of
vr's. all 25 amp, and 24 volt. I did see references where m151's used the 4004.

I just can't see why the 4004 is not an improved version of the previous VR's.

the 4004 obviously produced after m38 and m38a1 production.

If a m151 ord 9 exists, it might be there.

I wish I could remember where I got these. most likely takeouts. Never had a m151 available for takeouts however.

2920013076875 NSN still available?

Post by **wesk** » Mon Feb 21, 2022 12:44 pm

If a m151 ord 9 exists, it might be there.

I have never found an ORD 9 or ORD 7 or ORD 8 for the M151 series. There are several issues of TM 9-2320-218-20P (Organization Parts List) and several issues of TM 9-2320-218-34P (Depot Level parts list). The -20P's offer up the 25 amp transistor type regulator only. Both -20P & -34P offer up the 24V / 25A generator but neither show a conventional VBC-400_UT series regulator.

2920013076875 NSN still available?

I googled it and got quite a few hits.

keats · Post by **keats** » Sat Feb 26, 2022 5:51 pm

interesting find in the 1966 TM 9-2320-208-20-P manual for the m38a1,m38a1c, and m170.

though there is no mention of the vbc 4004ut in the parts lists, there is a photo of a voltage regulator in the manual on page 41. Also, on (the visual guide to parts0 section at the front of the manual, there is a drawing labeled regulator and stating it as a vbc4004ut. i have inclosed photos.

when enlarged, the vbc4004ut can be seen clearly!!!!!

proved the VR existed at that time (1966). With m38a1 production into 1971, and the m151 starting production in 1960, ,its quite possible the vbc4004ut was utilized.

RonD2 · Post by **RonD2** » Sat Feb 26, 2022 6:05 pm

All three VBC-4002, 4003, and 4004 have data plates that say 24 Volts and 25 Amps.
All three have identical cable connections to the vehicle.

I see no reason why they're not equally interchangeable.

If the Army didn't want it that way, they typically do something to make it "Soldier proof" to prevent it.

Just my 2-cents....

Post by **wesk** » Sat Feb 26, 2022 8:43 pm

Ron, did you read the Yellow Autolite manual pages specs? The 4004 is noticeably different internally on specs.

Keats,

As Don said all three regulators look identical from the outside except for numbers. The Army's Tech Order folks have used many photos and illustrations of a item to simply show it's shape and appearance in those manuals which were not the specific intended part number. So it is not odd to see the faximalty of a basic VR40XX series reg in a IPL illustration and not see that particular samples part number in the text.

As I stated above there are subtle internal differences in specs that may or may not have ill effects if they are used in place of the the other two. It's quite clear you are getting no assurances or guarantees the 4004 will work from our membership. It is a "Your option to trying it!" deal.

keats · Post by **keats** » Sun Feb 27, 2022 10:35 am

solid state VR's are very different yet they seem to work with a volt meter instead of a amp gauge. Will continue search for more info.

Post by **wesk** » Sun Feb 27, 2022 12:42 pm

Good point. The Army switched to the Solid State regulators almost completely across the board for all the 24V 25A systems in the late 50's. However we are still unable to find a documented approval for substitution of a 4004 for a 4002 unit.

lilm38 · Post by **lilm38** » Sun Mar 05, 2023 3:11 pm

I have a NOS 4004 and the mounting configuration for an M38 is totally different in these pictures. The various manuals and resto books have different mounting brackets for both M38 and M38A1.
One shows a M38 with a splash plate mounted to the two welded to frame brackets and the regulator mounts on that I guess.
The M38 manual shows just the frame brackets and two aluminum brackets attached to the regulator which then gets mounted to the frame brackets bolted to the 4 rubber cushion/ground straps attached.
The m3A1 drawing shown in this thread shows the 4004 regulator mounted with the two aluminum brackets (which isnt possible because there are no threaded holes to screw into)
and the these long C shaped brackets that mount it to the frame brackets.
Are the C shaped brackets still available? Ive never seen them anywhere.
I will post pics of what I am poorly describing asap.

Post by **wesk** » Sun Mar 05, 2023 4:40 pm

The M38 & M38A1 have many clear and detailed photos of their regulator mounts thru-out this web site and their TM's and Parts Manuals. The problem is there is no official Army pub showing the actually listing the 4004 unit as a legitimate sub for the 4002 & 4003 units they do list.

Bottom line are the Autolite Spec sheets. You will be at risk of damaging your system since the specs are a bit different.

Here's the M38 regulator mount from an M38 manual:

Here's the M38A1 regulator installation from TM 9-8014

Here's the Autolite Spec sheet set for the 4000 series regulators discussed here:

When the M151 came out in 59/60 and introduced the 4004 unit they also published a very detailed set of setup sheets for it. If you absolutely insist on experimenting with 4004 unit in early model vehicles I would suggest you get very familiar with these sheets as well.

If you prefer larger file sizes of these pages just follow them to my photo album and download the larger file size: http://www.willysmjeeps.com/v2/modules. ... _album.php

You should also be using the proper TM for the Autolite accessories TM 9-1825B dated 1952 or newer. The Army abandoned this manual in the 70's and started opening new individual unit repair and parts manuals.