The Stovebolt Site Forums The Parking Lot Big Bolts Vacuum switch rebuild for late '55 6400 2-speed rear?

I'm going through all the mechanicals on the 2nd series '55 6400 I bought a couple years ago and the vacuum switch on the shifter (push/pull knob) is not working in a responsible manner! The diaphragm has been rebuilt on the diff and seems to work properly. I isolated the vacuum lines from the brake vacuum unit. The switch seems to work sometimes, not others. Can it be torn down, cleaned, and repaired? Is there a website that discusses this? Or is there a known good (easy) electrical replacement for it? I've searched about everywhere and am not finding info on the vacuum switch.

If it were mine, I would get an electric 2 speed switch to put on the stick and then use an air solenoid to switch the vacuum. Something like a Horton 993281 switch would work fine. There is a guy on eBay that I have bought a lot of stuff from has the Horton switches for $75. Item No. 231549326443 A Cole Hersee switch can be bought for under $16 eBay 281406325825

That's the exact info I was looking for! Thanks! I'll be ordering parts yet today.

Here is some more info that may be useful.
https://www.flickr.com/photos/advance-design_parts_co/albums/72157632724599711

I hope I don't end up needing ALL that info, but thanks for posting. My truck has 47K on the odometer, one owner until last year. I just want to use it to service my hops field, and to be able to drive to the gas station.

Today I received the parts listed above - an electric air solenoid and switch. Now for the theoretical questions:
I'm going to replace all air lines and install these components. Do I run the factory size line (5/16") or a smaller more responsive line size? Do I install the valve near the diff or near the engine? What will activate the diaphragm at the diff in the fastest manner? I know small vac lines offer a faster signal, but the large diaphragm needs a large volume of air to be removed so it will shift. I assume the small ports in the solenoid will be the limiting factor.

The valve being for air and with small passage in it might be the limiting factor when used in your vacuum system. If it is quite restrictive you might not notice any difference if the valve is in the cab or on at the axle.

Large line to rear and solenoid at the rear should be most responsive. Suppose could have a vacuum reservoir (with check valve) located at the rear between engine and solenoid valve, then the vacuum line size running to the rear is of little concern.

So here's how I ran the system:
3/8" brake line from the intake midway back down the frame. Then I used an old fire extinguisher bottle as a vacuum canister. I tied in a Tee back to the rear crossmember, just before the axle. On the axle I mounted the electric solenoid, so there would be the largest vacuum signal to feed it. A short hose jumpered from a short piece of tubing in the solenoid to the axle. The solenoid was powered from a spare fuse at the panel, switch mounted at the shift knob. The solenoid works instantly, the shift happens in the time you lazily push in the clutch and release it. I'm not even sure if you need to push in the clutch to shift?
My speedometer doesn't work, so I didn't bother reattaching the (leaking) vacuum line to accommodate for the shifts. Some day when I work on that, I'll investigate further.