willysmjeeps.com

Haines Auto Electric in Twin Falls ID. A buddy of mine recommended them to me about 15yrs ago. I walked in with a genny, reggy, starter and the gentleman knew exactly what I had, Said he was a military contractor in the '60s for electrical rebuilds. They're still in biz.

Don, I've got more than one untested VR gathering dust on the shelf but somewhat reluctant to ship (given my current shipping record).

The one pic above shows “Prestolite 1 67” which is all I could find on the wires. I will double check.

I have been trying to trace back the fried section and found a spot where two of the wires had touched with a partial burn through of the outer coverings.

The strands of the badly burned wires were fused and showed a lot of corrosion but the corrosion could have come after the burn. There is also a board attachment rivet with corrosion on the underside.

I need to add some pics of the coils.

Rick.... very good info.
Hey, those parts may show up yet

Wes gave us some good clues and a treasure map in his above posts.
I am distilling the Prestolite Info pages down to my VR model.

If anyone finds the other resources mentioned in the post, maybe jump into the conversation.

Think PRESTOLITE “VBC-4004UT” ..... our VR flavor of the month.

This thread is in Draft form; subject to examination, corrections and additions by people who know a lot more than me.

Wes gave us the VBC Regulator & Relay Prestolite Service Info Sheet (above), which also appears in a NGBB from 1967 (below), but not in the exact same wording.

Wes also pointed out a Rosetta Stone clue that lets us pick info that pertains to my VBC-4004UT target subject.
Not all VBS-4004UT VR's are the same.

"That 3Z serial puts your regulatory as listed on page 2 of the Prestolite spec sheet in the 12X to 6Y group."Wes.
Without that nugget our research data here and to come would be tainted.

I have tried to combine info from the two sources and present it in an easier to manipulate text format. Please evaluate my efforts and point out any errors, misleading typos and omissions. Thanks, Don
****************************************

From National Guard Bureau Bulletin. Vol. 18. No. 20 67

VOL. XVIII , NO. 20 , 67 3 . TRUCK , 1/4 TON , M151, M151A1.

Several States have reported difficulty with the Voltage Regulators on the subject series vehicle . As an interim measure , the following tentative Prestolite service manual specifications may be used as guidance in checking out and adjusting the vehicle voltage regulators .

VOLTS 24

GROUND POLARITY Negative

RESISTORS See tabulation ( R1-4?)

CONDENSER CAPACITY 2.0 to 2.7 Microfarads

CIRCUIT BREAKER
Resistance of Voltage Winding 214.7 to 237.3 Ohms
Armature Core Gap .066 " to .070 "
Contact Point Gap .047 " Minimum
Contacts Close 25.0 to 27.0 Volts
Contacts Open
5.0-10.0 amp discharge at 25v after charge of 10 amp min.(My 4004UT only)

VOLTAGE REGULATOR
Resistance of Winding 154.8 to 171.2 Ohms.
Armature Core Gap
.057" to .060" (My VBC-4004UT only. Code Dated 12X or later)

Contacts should be closed with the high limit gauge in place on the contact side and next to the armature stop pin .

Pressure of Contact Points
7-8 ounces except VBC-4004UT
(So what is the value for my VBC-4004UT ?)

Gap Between Contact Spring and Armature Stop
.010 " to .016 " Except VBC- 4004UT
(So what is the valve for my VBC-4004UT ?)

Clean contacts using number 6 Swiss file, then clean with paper.

Operating Amps 25.0 +/- 2.5 Amps

Operating Voltages
Figures for a unit in normal operation while charging at 1/2 maximum output. Use Test B for my VBC-4004UT : (28 +/- 1.0 volts)

28.0V @ 50deg. / 27.85V @80deg. / 27.6V @110deg. / 27.3V @ 140deg.
Tolerance = +/- .5 Volts

VBC-4004UT (Units 12X- 6Y)
Test/B R1/575 R2/60 R3/40 R4/200 Fig.2 (R= Resistor #)

CURRENT REGULATOR
Armature Core Gap
.057 " to .060 " (My VBC-4004UT Unit 12X & Later)

Contacts should be closed with high limit gauge in place and open with the low limit gauge in place on the contact side and next to the armature stop .


*Notes #1-3 apply only to VBC-4004UT before 12X... not mine. (I think)
*Notes from NGBB and Prestolite Service Info Sheet are not the same.
*Note #4 may apply to all units (I think)

NOTE 1 (From NGBB) - (May not apply to my VR unit.)
On voltage regulator , temporarily remove spring and loosen stationary contact and check float of the armature . Bend each hinge ear to establish an .052" to .056 " core gap . Reassemble spring and adjust stationary contact to provide an armature core gap of .052 " to .056 " . Mount the regulator in the same position as it will be used on the vehicle . Do not connect the battery to the regulator . Start the generator and increase the speed to 5000 rpm. Ad just the voltage to 28.0 + .2 volt . Voltmeter needle should not fluctuate more than + 0.5 volts from the set value . If fluctuation is more than this , stop the generator and clean or replace contacts . Connect a battery and operate for 20 minutes at 12 to 13 amperes load . Stop the generator , remove the load and restart the generator , increasing speed to When a 0 to 4 ampere charge to the battery is reached , stop and restart the generator five times . The voltage should be within 0.5 volt from the set value with 12 to 13 amperes load . 5000 rpm. NOTE 2 Adjust circuit breaker by inserting correct size wire gauge between armature air gap and core on contact side and next to brass pin in core . Gap should be .066 to .070 inch . Ad just gap by bending armature stop

NOTE 1 (From Prestolite Service Info Sheet) - To be added later.


NOTE 2 (From NGBB) (May not apply to my VR unit.)
Adjust circuit breaker by inserting correct size wire gauge between armature air gap and core on contact side and next to brass pin in core . Gap should be .066 to .070 inch . Ad just gap by bending armature stop .

Mount regulator on test stand in same position that it is mounted on vehicle . If this position is unknown , mount with base vertical and terminals pointing down . Use GHA generator and mount on test stand . Connect battery for 24 volts and negative polarity . Connect regulator , generator , battery and meters . (Figure 3 ) Polarize generator to prevent burning regulator contacts . Το polarize , first remove generator field lead from variable resistance then close test stand battery switch and touch field lead to regulator battery terminal for not longer than one second . Connect field lead to variable resistance Adjust variable resistance to insert all resistance in field circuit . Start generator and operate at 1,000 to 2,000 rpm . Decrease field resistance until ammeter shows a charge of one half current value stamped on regulator name - plate . Now increase resistance slowly. Note amperage discharge just before contacts open and ammeter reading drops to zero . Adjust closing voltage to 25.7-26.7 by turning adjusting nut on lower end of armature spring . Check closing voltage after each adjustment . Ad just opening discharge current to 7.0-11.0 by raising or lowering stationary contacts . Open test stand battery switch to prevent shorting . Bend stationary contact bracket to increase or decrease gap . Increasing contact gap increases opening discharge amperes . Keep contacts aligned for full face contact and adjust both sets of contacts so they operate simultaneously . Do not adjust gap between contacts to less than 0.025 inches . Open test stand battery switch

NOTE 2 (From Prestolite Service Info Sheet) - To be added later.

NOTE 3 (From NGBB) (May not apply to my VR unit.)
Adjust current regulator by changing connections to those shown for voltage and current limiter test as shown in Figure 4 . The load rheostat may consist of a carbon pile or lamp bank .

On units that have been completely repaired , close test stand battery switch and operate generator at 2,500 to 3,000 rpm . Test current limiter by pressing lightly on back of voltage limiter armature to hold contacts closed . Read ammeter . If reading is 24.5-26 , do not ad just . If current setting is within two amperes , turn adjusting nut on lower end of armature spring . Release voltage limiter arma ture. To test voltage limiter , stop generator , then start and bring speed up to 2,500 to 3,000 rpm . Ad just current to one- half the value stamped on the regulator name- plate by changing carbon pile rheostat or lamp bank . Read voltmeter . If reading is within 0.4 volt of correct operating voltage , do not adjust . If voltage is not within 0.4 volt of specific voltage ( Page 4 ) , turn adjusting nut on lower end of arma ture spring . Stop generator and open test stand battery switch .

Install cover gasket and cover on regulator. .. close test stand battery switch and operate generator at 2,500 to 3,000 rpm . Adjust load rheostat or lamp bank so ammeter reads one-half current regulator operating amperage . Operate at this current for 30 minutes to bring regulator up to operating temperatures .

Place thermometer near regulator to ascertain air temp around unit . Thermometer must not touch regulator. Stop generator , then immediately start and bring it up to 2,500 to 3,000 rpm. Ad just current to one- half current limiter operating current ( Page 4) . Read voltmeter and thermometer . Voltage must be within limits specified for voltage regulator for temperature specified ( Page 4) . If voltage is not within limits , stop generator , open test stand battery switch and remove generator cover . close switch and start generator . Turn adjust ing nut on lower end of voltage limiter arma ture spring until voltmeter reading is within limits . Check this setting by first stopping generator , then operating generator at 2,500 to ad just and check voltage limiter if not within operating limits .

and read ammeter . Reading must be within limits specified for current limit operating amperage ( Page 4 ) . If current is not within limits, stop generator and remove regulator cover . Start generator and adjust current setting by turning adjusting nut on lower end of armature spring .

Stop generator and open battery switch . Secure all screws on regulator and tighten lock nuts . Install regulator " O " ring and cover . close test stand battery switch and operate generator at one half current regulator setting for five minutes . Check voltage and current setting as above . Make any necessary adjustments and finish with final five minute run and check to be sure generator regulator is now in operating condition and ready for sealing .

NOTE 3 (From Prestolite Service Info Sheet) To be added later.

Note 4 Found only on Prestolite Info Sheet. (I think.)
When (2) nuts are provided on adjusting screws, the upper nut is for locking and should be tightened after each adjustment.

Only Fig. #2 below goes with VBC-4004UT (I think.)

In the handful of manuals I found for the M37, M35, and M151, I found no mention of the VBC4004UT voltage regulator. They either show the VBC-4002UT, the VBC-4003UT, or the solid state (transistorized) regulator.

It's certainly not clear why no Army manual for the 5 vehicles that could possibly use it don't mention it, but considering that the wires in Don's VBC-4004UT and the National Guard Bulletin are dated 1967, it seems possible that this mechanical regulator might have been the last of it's kind, and was right at the edge of the Army adopting the solid state transistorized model instead? I believe a lot of stuff military and civilian in the mid-to-late 1960's was becoming transistorized.

Just a SWAG on my part.

I hope your VR only needs some new wire, cleaning, and simple adjustment to get working again. Except for RickG's stash, finding repair parts or carcasses to scavenge from might get thin pretty fast.

As always, I say good luck!

Don, I think you will be more successful with your fishing expedition if you first provide a clean, undisturbed/un-edited copy of this Nat. Guard Bulletin for us to make the suggested corrections and additions. Folks can see the Prestolite data at anytime they wish in my post and my photo album "M Electrics".

The entire NGBB document is many hundreds of pages long, does not produce a clean copy/paste without extensive reworking and is a mostly dispiriting reminder that every munition discharged in battle requires an encyclopedia of bureaucratic bean counting that I suspect goes mostly unread. Here are a few pages that may be useful. I closely double checked the doc. but there could be errors in my conversion to a simple text format.

I hope to compile info from several sources, producing a clearer path to repair of my particular VR.
********************************

National Guard Bureau Bulletin
Vol. 20. 67 Pages 4-8.

VOL. XVIII , NO. 20 , 67 3 . TRUCK , 1/4 TON , M151, M151A1.

Several States have reported difficulty with the Voltage Regulators on the subject series vehicle . As an interim measure , the following tentative Prestolite service manual specifications may be used as guidance in checking out and adjusting the vehicle voltage regulators .

VOLTS 24
GROUND POLARITY Negative
RESISTORS 2.0 to 2.7 Microfarads

CIRCUIT BREAKER
Resistance of Voltage Winding 214.7 to 237.3 Ohms
Armature Core Gap .066 " to .070 "
Contact Point Gap .047 " minimum
Contacts Close 25.0 to 27.0 Volts
Contacts Open
(A11 except VBC- 4004UT) 7.0 to 27.0 volts
amperes discharge at 25.6 volts after a charge of 25.0 amperes .
(VBC- 4004UT) 5.0-10.0 amperes discharge at 25 volts after a charge of 10 amps min.

VOLTAGE REGULATOR
Resistance of Winding 154.8 to 171.2 Ohms
Armature Core Gap.
.040 " to .042 " ( except VBC- 4004UT)
.052" to .056 " (VBC- 4004UT)

Contacts should be closed with the high limit gauge in place on the contact side and next to the armature stop pin .

Pressure of Contact Points ( Except VBC-4004UT ) 7-8 ounces

Gap Between Contact Spring and Armature Stop
( Except VBC- 4004UT) .010 " to .016 "

Operating Voltages
Figures are for a unit in normal operation while charging at 1/2 maximum output .

Test A
28.45V @50deg. 28.25V @80deg. 28.05V @110deg. 27.85V @140deg.
Tolerance +/- .4

Test B
28.0V @50deg. 27.85V @80deg. 27.6V @110deg. 27.3V @140deg.
Tolerance +/- .5


CURRENT REGULATOR
Armature Core Gap
.047 " to .049" ( except VBC-4004UT)
.052 " to .056 " (VBC- 4004UT)

Contacts should be closed with high limit gauge in place and open with the low limit gauge in place on the contact side and next to the armature stop .

Pressure of Contact Points
( Except VBC- 4004UT) 7-8 ounces

Clean contacts using number 6 Swiss file , then clean with paper .

Gap Between Contact Spring and Armature Stop
( Except VBC- 4004UT) .010 " to .016 "

Operating Amperes 25.0

VBC- 4002UT / Voltage Test A / R1=400 / R2=15 / R3= ---- / Fig.1

VBC - 4003UT , -5 , -9 / Voltage Test A / R1=400 / R2=15 / R3=100 / Fig.1

VBC -4004UT / Voltage Test B / R1=400 / R2=60 / R3=200 / Fig.2
See notes 1,2,3.


NOTE 1 - On voltage regulator , temporarily remove spring and loosen stationary contact and check float of the armature . Bend each hinge ear to establish an .052" to .056 " core gap . Reassemble spring and adjust stationary contact to provide an armature core gap of .052 " to .056 " . Mount the regulator in the same position as it will be used on the vehicle . Do not connect the battery to the regulator . Start the generator and increase the speed to 5000 rpm. Ad just the voltage to 28.0 + .2 volt . Voltmeter needle should not fluctuate more than + 0.5 volts from the set value . If fluctuation is more than this , stop the generator and clean or replace contacts . Connect a battery and operate for 20 minutes at 12 to 13 amperes load . Stop the generator , remove the load and restart the generator , increasing speed to When a 0 to 4 ampere charge to the battery is reached , stop and restart the generator five times . The voltage should be within 0.5 volt from the set value with 12 to 13 amperes load .

NOTE 2 Adjust circuit breaker by inserting correct size wire gauge between armature air gap and core on contact side and next to brass pin in core . Gap should be .066 to .070 inch . Ad just gap by bending armature stop .Mount regulator on test stand in same position that it is mounted on vehicle . If this position is unknown , mount with base vertical and terminals pointing down . Use GHA generator and mount on test stand . Connect battery for 24 volts and negative polarity . Connect regulator , generator , battery and meters . (Figure 3 ) Polarize generator to prevent burning regulator contacts . Το polarize , first remove generator field lead from variable resistance then close test stand battery switch and touch field lead to regulator battery terminal for not longer than one second . Connect field lead to variable resistance . Ad just variable resistance to insert all resistance in field circuit . Start generator and operate at 1,000 to 2,000 rpm . Decrease field resistance until ammeter shows a charge of one half current value stamped on regulator name - plate . Now increase resistance slowly . Note amperage discharge just before contacts open and ammeter reading drops to zero . Adjust closing voltage to 25.7-26.7 by turning adjusting nut on lower end of armature spring . Check closing voltage after each adjustment . Ad just opening discharge current to 7.0-11.0 by raising or lowering stationary contacts . Open test stand battery switch to prevent shorting . Bend stationary contact bracket to increase or decrease gap . Increasing contact gap increases opening discharge amperes . Keep contacts aligned for full face contact and adjust both sets of contacts so they operate simultaneously . Do not adjust gap between contacts to less than 0.025 inches . Open test stand battery switch.

NOTE 3 Adjust current regulator by changing connections to those shown for voltage and current limiter test as shown in Figure 4 . The load rheostat may consist of a carbon pile or lamp bank .

On units that have been completely repaired , close test stand battery switch and operate generator at 2,500 to 3,000 rpm . Test current limiter by pressing lightly on back of voltage limiter armature to hold contacts closed . Read ammeter . If reading is 24.5-26 , do not ad just . If current setting is within two amperes , turn adjusting nut on lower end of armature spring . Release voltage limiter arma ture. To test voltage limiter , stop generator , then start and bring speed up to 2,500 to 3,000 rpm . Ad just current to one- half the value stamped on the regulator name- plate by changing carbon pile rheostat or lamp bank . Read voltmeter . If reading is within 0.4 volt of correct operating voltage , do not adjust . If voltage is not within 0.4 volt of specific voltage ( Page 4 ) , turn adjusting nut on lower end of arma ture spring . Stop generator and open test stand battery switch . ! 1 : Install cover gasket and cover on regulator . close test stand battery switch and operate generator at 2,500 to 3,000 rpm . Adjust load rheostat or lamp bank so ammeter reads one-half current regulator operating amperage . Operate at this current for 30 minutes to bring regulator up to oper ating temperatures . Place thermometer near regulator to ascertain temperature air around unit . Thermometer must not touch regulator. Stop generator , then immediately start and bring it up to 2,500 to 3,000 rpm . Ad just current to one- half current limiter operating current ( Page 4) . Read voltmeter and thermometer . Voltage must be within limits specified for voltage regulator for temperature specified ( Page 4) . If voltage is not within limits , stop generator , open test stand battery switch and remove generator cover . close switch and start generator . Turn adjust ing nut on lower end of voltage limiter arma ture spring until voltmeter reading is within limits . Check this setting by first stopping generator , then operating generator at 2,500 to 3,000 rpm at one- half maximum current . Read voltmeter and again ad just and check voltage limiter if not within operating limits . Ad just load rheostat or lamp bank so voltmeter reads 24 volts and read ammeter . Reading must be within limits specified for current limit operating amperage ( Page 4 ) . If current is not within limits, stop generator and remove regulator cover . Start generator and adjust current setting by turning adjusting nut on lower end of armature spring . Stop generator and open battery switch . Secure all screws on regulator and tighten lock nuts . Install regulator " O " ring and cover . close test stand battery switch and operate generator at one half current regulator setting for five minutes . Check voltage and current setting as above . Make any necessary adjustments and finish with final five minute run and check to be sure generator regulator is now in operating condition and ready for sealing .

Don,
Assuming you found it on the interweb, can you post the link to the NGBB?

Good point Ron. If Don found it, he should be able to share it with this web site. This web site has always been a sharing site. No reason to change that spirit now.

Don,

I will not be able to answer your questions above without having an equal opportunity to read and digest whatever it was you read and digested.

Here is the eBooks link to the entire document.
It’s a big ‘ol Idaho Moose of a thing.
Probably thousands of these leviathans swimming in cyber-space.

https://books.google.com/books?id=H6xfh ... &q&f=false

Yup. Just caught another fish.
Is this one already be in the Downloads?

https://books.google.com/books?id=0gAYA ... ut&f=false

Don,
How in the Wide Wide World of Sports did you ever come across something so obscure as an archive of National Guard Bureau Bulletins?
Especially one out of probably thousands that happens to have technical info on your VR?
Awesome. Frightening, but awesome.

Don,

Take a look at my earlier post on the first page of this thread. I added the copies of your preliminary/tentative 1967 Prestolite spec sheet (5 pages) from your 729 page Nat. Guard report from 1967. I posted them alongside my 4 pages of the Prestolite 1978 edition of the same spec sheet. It would have saved me an hour of paging thru that report if you had just separated pages 266, 267, 268, 269 & 270 from your copy of that 729 page report and posted them here. At any rate with your 1967 issue placed alongside the 1978 issue it should be obvious which one is to be followed!

“It would have saved me an hour of paging thru that report if you had just separated pages 266, 267, 268, 269 & 270 from your copy of that 729 page report and posted them here.” Wes

I apologize for the search. The noodles between my ears are wired strangely and do not contain much info. on voltage regulators..... but here was what I was thinking.

Realizing folks wanted the VR info. directly from the NGBB I sent the link for the entire document, knowing the thing was huge but also thinking that locating the specific VBC-4004UT data would be straight forward.

In my summary of the document I had titled the important stuff as :
National Guard Bureau Bulletin /. Vol. 20. 67 Pages 4-8 which points the way.

Also, if “VBC-4004UT” is placed in the document Search Box on the left of the page it takes one directly to that article..... and any other articles on that subject.

“At any rate with your 1967 issue placed alongside the 1978 issue it should be obvious which one is to be followed!” Wes.

Almost nothing here is obvious to me. Maybe paint it yellow with flashing lights.

I do see as you have pointed out, there are variations within the VBC- 4004UT units .... before 12X/ after 12X etc

Another thing... it looks like the “See Notes 1,2,3” directions refer to different VR versions in the two documents. I will go back and take another look.

I am trying to translate the info into a “Don, do this for your particular VBC- 4004UT.”
Or at least know what to show/tell the guys at the shop.

Don and Wes,

I do see Don's confusion on what to do. I looked through some of the documentation on the pages Don specified and it seems I would need more training on electrical to even attempt the testing.

Not to mention all the VR numbers referenced, etc. it starts to get cumbersome. I kept falling asleep trying to follow along when reading through last night - I am just glad I didn't get any drool on my computer keyboard!

It only took me a few minutes to find the pertinent pages once I realized the NGBB's were aggregated in Volume number order.
I don't think I'd throw out the NGBB information, but it seems clear to me.

The NGBB was published in 1967 and opens with words like "interim measure" and "tentative Prestolite service manual specifications may be used as guidance..."

-or-

use the actual Prestolite Service Bulletin published by the manufacturer and dated 11 years later in 1978.

As for diving into testing (including building test rigs), servicing, and repairing rare, expensive, and impossible to find repair parts for 60-70 year old military vehicle 24V electro-mechanical components that have only limited technical data, and without any training or experience?

The answer to that also seems clear to me.