The Stovebolt Site Forums The Parking Lot Big Bolts Tow speed actuator

What is the best choice to replace my badly neglected vacuum two speed rear end actuator? Should I stay vacuum or go electric? Where do I find it? Period correctness is not as important on this project as cost and reliability.
Thanks,
Mark

I'm not sure what you are working on, but vacuum became obsolete in the mid 50's and no one has supported it in many years. If you have an Eaton 2 speed, an electric shift will probably work and they are vendor item. A Chev, Ford or anything will be the same. 6 volt motors are getting rare, 12 volt are pretty plentiful. There is a new and old style. You would want the old style which has a 3 bolt motor with holes evenly spaced. The later ones have 3 bolts also, but they are staggered. The new style has electronics. Any truck with a 2 speed from the mid 50's through the 80's should work. You will need a switch and a speedo switching gear if you care about the speedo.

Thank you. I am going to use a new elecronic speedo calibrated for high range. This is a 1950(ish) two speed on a GMC 2 ton. I will start looking for elecric shifters. What is the bolt spacing about?
Mark

If you switch from vacuum to electric it's changing the vacuum diaphragm and mechanism on the differential and replacing it with an electric motor version, obviously the bolt spacing needs to be the same between the two different actuators.
I wonder if there is an electric replacement/upgrade for that axle?
If so I'd check trucks just new enough to have electric shift two speed, and hope that it interchanges.

Grigg

I don't know when they stopped using vacuum shift I have how ever found them in trucks into the mid seventies. My 56 and 64 even have the same rear ends. The vacuum switch however is different, the 56 uses vacuum to shift both the rear-end and the speedo, the 64 is vacuum for the rear but eclectic for the speedo.
I have found a degree of difficulty in finding vacuum shift parts and am thinking about updating the axles in my 64.If I do this I will most likely use both the front and rear axles from a mid to late seventies gas powered truck with the regular 11 inch 10 lug bud pattern. I would also like to do this with the 56 how ever that takes narrowing a front axle but thanx to Grigg I know that it can be done . If this is a truck you use on a regular bases and need the reliability I would recommend the change to something with better parts support even new truck brake and down time can be a killer if you are waiting forever for parts.

I have a 53 GMC with vacuum shift and a 55 GMC with electric shift. I will try to see if they interchange this weekend. I lean toward thinking that they do because I remember a lot of GM trucks being retrofitted with electric shift off of International and Ford. Exchanging the entire rear is not difficult either because by then the 96" tread width on dive axles and 34" frame was standard.

Thanks. I look forward to hearing what you find this weekend. I hope I can use this rearend, but I agree that exchanging it wouldn't be the end of the world.

I couldn't view your '64 for some reason, but I love your '56! Great inspiration!
After all of the advice, I am convinced that I will use electric. Now I need to find one. I hope to use the original switch because it looks cool. I am putting a '33 cab on this so originality has gone out the window! How is your big block engine swap going?

Thanks Grigg. I will look for electric that will bolt up. How is your diesel coming? Do you have new photos to share?
Mark

I looked at my 53 with a vacuum shift and my 55 with an electric shift and there is no resemblance between the two. I remember a lot of vacuum shifts were scrapped in favor of electric shift. I don't know how they did it. All we ever had were electric shifts to begin with. There is a good chance they changed the whole rear end because salvage yards were full of trucks with electric 2 speeds. I bought a 53 with a vacuum 2 speed a couple of years ago, but I never drove it out on the highway because of no brakes. I have it in the shop right now putting brakes on it. Once I get that done, I will try it and see if it works. If not, I will decide as to whether I want to try to fix it or if I just want to drive it in high range. It's a GMC with a 270 and I don't haul anything with it.

Mark,
Wasn't implying that there is an electric shifter for your axle, just what to look for and where I'd start if there really is such a thing.
And by the sounds of it there may not be one.

My diesel project is really slow, haven't done anything in months, to much other stuff to do and not much money left after the morgage...
Feel like I really need to get it done soon though, more and more lately I miss not having a truck of my own.

If you scroll down on this thread it shows a common air valve that was used on a 2 speed apparently as original equipment. http://oldgmctrucks.infopop.cc/eve/forums/a/tpc/f/993000056/m/694101484 I think this is the route I will go instead of trying to fix the complicated valve on the firewall. This is a common valve that is still available. The one pictured has a plate that is identical to air valves. The screws go through the plate and screw into the valve.

If you scroll down on this thread it shows a common air valve that was used on a 2 speed apparently as original equipment. http://oldgmctrucks.infopop.cc/eve/forums/a/tpc/f/993000056/m/694101484 I think this is the route I will go instead of trying to fix the complicated valve on the firewall. This is a common valve that is still available. The one pictured has a plate that is identical to air valves. The screws go through the plate and screw into the valve.