Zenith Mechanovac Governor

[JDToumanian]

Hi Group,
My Studebaker V-18A/MTQ Earth Borer - Pole Setter has a Zenith Mechanovac Auxiliary Governor on it. This is a constant speed governor (to keep the engine RPM constant while operating the pole-setting mechanism or rear winch) that is totally separate from the governor that is integral with the Holley 885-FFG carburetor / governor (which only controls max. RPM).... It's a "sandwich style" governor with it's own throttle body stacked between the heat riser and the carburetor.

It is in need of overhaul. Both sections, the centrifugal speed sensing unit as well as the diaphragm and throttle control unit. Searches here and on Google have turned up nothing useful.

I have TM 9-8647 (Carburetors and Governors - Holley) and TM 9-1826C (Carburetors and Governors - Zenith) and NEITHER of them cover this auxiliary governor! None of the manuals specific to the V-18A/MTQ (that I own, anyway) cover this auxiliary governor. In fact, the only mention of it at all is removal / installation / adjustment instructions in TM 9-8022.

I am looking for an overhaul manual - even knowing the TM number would be helpful - and I need overhaul kits for both sections of the unit.... The diaphragm is cracked and the gaskets are all crumbly. See pics.....

Regards,
Jon

 

[jatonka]

Jon, I will look through my manuals this weekend and see what I may have to help you, we V18A-MTQ people must stick together. I also have a source for carb and fuel pump parts for very old vehicles, PM me and I will guide you on. JT Out

 

[scooter01922]

I would be very interested in this info as well. I seem to recall reading of a secondary gov on the 108 for crane use to keep the rpm constant. What are the odds they made a bunch of aux govs for the gasser??? I bet its the same.

 

[Stretch44875]

FYI, I just checked the carb on the gasser M108 engine, and it also has the same governor. It is also not working.

 

[DDoyle]

Jon,
Do you have a TM9-1819B (not 1819A)? From memory, this is the book that covers this. I loaned mine out a few years ago and haven't seen it since - so I can't check my memory for you.

Best wishes,
David

 

[JDToumanian]

Thanks for the help guys! Yes there are lots of other trucks that use these governors, including M49, M49C, M50, M60, and M108. That's why I'm surprised I haven't easily found the appropriate TM and repair kits.

Do you have a TM9-1819B (not 1819A)? From memory, this is the book that covers this.

David, yes I have that manual but it's not in there.... One of my other manuals referred me to TM 9-1826C for "Detailled information on the overhaul of Zenith auxiliary governors", which is why I bought it, but that manual contains nothing about them either. I suspect maybe it's in TM 9-8023-3, 9-8023-4, or 9-8023-5 (TM 9-1819C, 9-1819D, or 9-1819E) which are for the M34, M49/M50, and M108, respectively.

I did make some progress today, by looking in TM 9-2805-222-35P (parts manual for the OA-331 engine). The NSN for the repair kits are:

2990-00-040-2069 (Auxiliary Governor Drive Unit)
2990-00-563-5497 (Auxiliary Governor Slave Unit)

Googling these numbers turned up a few suppliers to the government, including ISO-Parts. After a little poking around I discovered that "Zenith Fuel Systems" is still in business and listed as the supplier. I sent them an e-mail.

Obtaining the correct TM is important, but the information will be of little use without repair parts... Hopefully Zenith can help or point me in the right direction. I'll post as soon as I hear back from them...

Oh, BTW - there is a drive unit for a Zenith Mechanovac Auxiliary Governor on eBay right now if anyone needs it. It's located in Vietnam, but the seller has 5,000+ positive feedback. It says NOS and it's got a tag on it, but looks pretty dirty. I don't need a drive unit, mine just needs cleaning, lube, and a few gaskets which I can make if I have to.... it's the slave unit that is really bad on mine, the diaphragm has crumbled.

Jon

 

[cranetruck]

FWIW, the governor for the multifuel is covered in the C1 section of the -20 TM.

 

[Crazyguyla]

Jon,

TM 9-2805-222-35P dated April 1962 (OA 331 parts manual) has the parts listing for the aux governor. Maybe 9-2805-222-35 has the overhaul procedure.

Marcus

 

[DDoyle]

I suspect maybe it's in TM 9-8023-3, 9-8023-4, or 9-8023-5 (TM 9-1819C, 9-1819D, or 9-1819E) which are for the M34, M49/M50, and M108, respectively.

Jon

I have all those. I'll take a look later today and see if the info you need is there.

Regards,
David

 

[JDToumanian]

Oh, BTW - there is a drive unit for a Zenith Mechanovac Auxiliary Governor on eBay right now if anyone needs it.

Too late, I bought it as a spare.

Zenith responded to my initial e-mail by asking for more information, I gave them what they requested and have not heard back.... I prodded them gently this morning.

Another interesting discovery - The diaphragm from the Mechanovac governor and the diaphragm from the Holley 885FFG carburetor appear to be the same! To what and how they are attached is different but the rubber piece itself is identical. On the zenith, the diaphragm can be easily removed by unscrewing a jam nut and the rubber part is sandwiched between two washers. On the Holley, the washers are crimped to the shaft but I will get it apart.

So basically I can overhaul the unit without a rebuild kit if necessary, by cutting new gaskets, cleaning parts, greasing the bearings, and replacing the diaphragm with one from a Holley which is readily available.

Assembly instructions are still needed, because there is supposed to be tension on the diaphragm when the housing screws are tightened, and some other things that should be adjusted on assembly, which information would be contained in the appropriate TM that I do not have or know the number of...

Jon

 

[JDToumanian]

Hi Group,
Zenith never got back to me and stopped responding to my e-mail. Oh well, I doubted they were going to be able to help much but I'd prefer not to be left hanging.

My NOS Mechanovac Speed Unit arrived safely from Vietnam today.... Awesome! It's in brand new condition and has a tag on it that says to fill it with 2oz of 30wt. motor oil. I thought the plugs on the top and bottom of these units might be oil fill and drain plugs, but this information is not in the LO manual and the one from my truck that I took apart was dry inside. I think I'll oil this new one.

So, all I have to do now is put the Slave Unit w/ Throttle Body back together. I got a diaphragm for it (it's the same as a Holley 885FFG diaphragm) and there's only a couple gaskets, so I'll just cut my own for those, but I do still need the TM.....

My OA331 engine overhaul manual from 1957 says to refer to TM 9-1826C, but my 1952 copy of that manual does not contain the information. I discovered that there is a 25-page supplement..... CH-1826C. Does anyone have that manual?

Jon

 

[cranetruck]

Jon, is there a patent number anywhere on the unit? If so, do a patent search and get all the info you you'll need.

 

[Crazyguyla]

Jon,

Don't know if you ever found the info for adjusting the aux govenor, but here is a link for TM 9-2320-209-35 C6, p 131, para 192. Adjusting Auxilary Governor. it's on Google Books

Chassis, truck, M44, M44A1, M44A2 ... - Google Books

Marcus

 

[JDToumanian]

Hey Marcus!

I hadn't noticed you had posted to my old thread, thanks for the help. I have that manual.... The problem isn't really adjusting it, it's that the slave unit / throttle body portion of the governor is seized up. It looks like there are ball bearings on both ends of the butterfly shaft, but they are crimped into the unit and there doesn't appear to be any way to take it apart....

I've pretty much given up on finding repair information, and I plan to re-manufacture the unit myself. I'll cut off the bearing housings on both ends and machine them to take screw-on caps.... Blind on one end and with an o-ring equipped hole for the throttle shaft on the other. Anyway, I was afraid that the manual would say something like, "The slave unit throttle assembly is a sealed unit, do not attempt repair. Discard and obtain a new unit."

Jon

 

[JDToumanian]

Finally some progress!

After leaving the governor slave assembly to sit a while, I recently decided to try to take it apart.... I was pleasantly surprised to find that it came apart easily. I simply took the two valve plates out of the valve body and then put pressure on the shaft with my press. The "crimped-on" cover popped right off, and I was able to remove some snap rings and take the whole thing apart. I ordered new bearings from McMaster-Carr, cleaned it all up and put it back together....

Pic 1 - The new and cleaned up slave unit parts ready for assembly.

Pic 2 - My inner teenager laughed at these new ball bearings, and I thought of gimpy...

Pic 3 - Inner snap ring is installed, bearing goes on next, outer snap ring, then retainer and press-in cover.

Pic 4 & 5 - Close up of the Holley 885FFG carburetor governor diaphragm which turned out to be identical to the Zenith Mechanovac diaphragm... Same bolt hole and vent hole pattern and same material, all that needed to be done is remove the crimped on Holley shaft, enlarge the center hole in the diaphragm, and install it on the two-piece hub of the Zenith.

Pic 6 - Finished governor assemblies, the speed sensing unit is on the lower left, then the control cable, and the slave valve body unit on the upper right.

 

[JDToumanian]

Here's a few more pics of the diaphragm in the slave unit...

Pic 1 - Shows the brittle old Zenith diaphragm on the left and the new Holley on the right. I have already removed the Holley pull rod and enlarged the center hole, it's ready to install.

Pic 2 - This is the way the Holley diaphragms look before the pull rod is removed.

Pic 3 - Here the Holley diaphragm is installed on the Zenith Mechanovac Governor's hub.

 

[JDToumanian]

A few more...

Pic 1 - This is the front of the label that came attached to my NOS Governor speed sensing unit I got on eBay from Vietnam.

Pic 2 - Here's the back side with instructions.

Pic 3 - Here's the NOS Zenith Mechanovac speed sensing unit from Vietnam. The connector on the left side goes to the power divider via a long speedometer cable. The connector on the right connects to the throttle body slave unit via a pull cable.

Pic 4 - The completed Carburetor and governor assemblies ready to re-install in the truck.

I struggled quite a bit with this project... I was unable to find the correct military TMs even after several years of diligent searching, and there is little to no information on these governors anywhere on the internet. It seems that most people who have these trucks (V-18A/MTQ pole setters and M108 cranes) do not have operational governors, but that was unacceptable to me. Hopefully this will help others get their governors working.... Feel free to contact me if any further information is needed. I'll revive this thread after I get the truck back together to report on the governor's performance.

Regards,
Jon

 

[steelypip]

I had forgotten about those! I worked on a church (school) bus that had one on the IH gasser engine back in the '90s. The bus dated from the early '70s as I vaguely remember. Fun times. I haven't seen a gasoline powered school bus in years, but they all had these governors on them as well. Not sure if better documentation would be available via that avenue.

 

[JDToumanian]

FYI.... eBay seller '2003viperkillingcobra' regularly has rebuild kits for the Zenith Mechanovac governor speed sensing unit. Look up his seller name or just search for "mechanovac". With that kit and a Holley kit for an 885FFG carburetor (to cannibalize for the diaphragm) you have everything you need except for the ball bearings, if they even need replacing.