The Stovebolt Site Forums The Parking Lot Big Bolts Vacuum to electric 2 speed?

Hi all;
Been a longtime since I've checked in,but I have a question about vacuum 2 speed axles. The axle in my 54 GMC is vacuum, (I think it's a 1350),and I was told there used to be a vacuum to electric conversion kit available for it. Anyone know about this? My axle shifts up very well,but shifting down almost takes help from God to accomplish. It's caused some very tense moments already. I've searched for vacuum leaks and everything I can find shows no leaks. Typically I'd use the axle and main box up to 4th and High,then use the main box and the Brownie Direct and Over to reach road speed. As often as I use the 2 speed,it'd really be great if it'd downshift when I need it to. Any ideas that won't cost me a truckload of $$$?
Thanks for any info you might have.
Speed

Honestly, I love that you asked this question as I was wondering the same thing. I have a 6400 and that's on my "what am I going to do about that" list. I want to say I saw something about a conversion kit somewhere along the way. You can certainly get an electronic solenoid switch to make the change but I seem to recall that I read there is also a gearing change that has to be made with the speedo when you shift the rear end. The vacuum system does that for you but if you change, you have to make that speedo adjust manually somehow...

Disclaimer: NOT an expert at all but trying to recall what I read.

Definitely following this, as I would like to make this change myself. Not worried about the speedo gearing as it doesn't work anyway.

I am hoping that I have fixed/avoided vacuum leaks on my 54/55 GMC 350. There was originally an o-ring at each vacuum-line compression fitting - I replaced/added new rings.

I'll get around to testing the vacuum-operated devices (including the clever vacuum-operated speedometer-range/gear switch) within a few months (I hope).

Your plunger may be sticking. Chock the wheels. Loosen the two hoses at the pumpkin. Remove the three 9/16 bolts.Now you may remove the 2-speed unit. There is a lever,similar to a fuel pump,that actuates the 2-speed switch in the differential. Block one of the hoses with a correct size bolt.hold your thumb over the end of the other hose,as you push the lever up and down. You should feel compression,if your diaphragm is air-tight. If not,then you'll need to replace it. Simple. Remove all of the screws that hold the two halves together. Now you can see te diaphragm. It's rubber,about the same thickness as an inner tube. I replaced mine from a truck "boot",I got for Free,at a truck tire shop.they're a little thicker than an inner tube,but still flex well.cut the diaphragm material slightly larger than the original-it doesn't need to look pretty. Cut a Tiny X in the center,where the plunger will pass through. push the plunger through,and "Permatex" the bottom of the washer to the rubber,before you tighten down the nut.Lube the plunger with motor oil,before re-installation. "Permatex" both halves of the diaphragm housing. Put the two halves back together.With an awl,punch holes at 12:00,3;00,6:00,and 9:00. Start the screws,to secure the diaphragm. Install and tighten the rest of the screws. Now you may trim the excess "boot" with a utility knife.Make sure the lever is contacting the switch before you "Button it up". I had fun rebuilding mine,and it took less than an hour. Cheaper,and less headache,than going electric. Hope this helps.