The Stovebolt Site Forums The Shop Area Driveline Question re Master Cyl for 1/2 ton FrankenTruck

I purchased this project as a 1940 KC ½ ton pickup. It turned out that it is a ’40 cab on a later chassis (’46-’47?).

I have been reading up on Huck brakes and have ordered the Herbrand 188 tool to make it easier to work with the springs and not get too frustrated. While I wait for the tool to be delivered, I inspected the brake lines and they do seem to be true to the “story” that came with the project - that the brakes had been redone. (The lines I have inspected so far appear to be unused!)

I went through my stash of parts and put my hands on the master cylinder I purchased from the Barry Weeks auction. I believe that it is probably an appropriate unit for this ½ ton truck, but if someone could confirm that from the casting or part number on the unit, I would really appreciate it! (This unit does appear to have been rather freshly rebuilt.) The casting number on the unit is 5450256-15-R, there is a “Model” stamped into the end of the unit, “Model No. 325-J” (I do find the casting number 5450256 (with no following dash numbers listed in the ’29-’50 Master Parts catalog for 1936-’37 with a note, “(does not have 11/32 hole thru cyl. wall)”. It is also listed for 1938-’46 All ½ ton Comm, with a note, “(has 11/32 thd’d. hole thru cyl. wall”). Does anyone know what the 11/32 hole was for? I have not located it in the drawings, so I don’t know where to look to see if it exists in the unit that I have.

I was disappointed to see that there are parts missing from the master cylinder. I am new to this, but it appears that I am missing a spring, a valve, a valve seat and probably a gasket for the end plug. Is there a source for these parts or will I have to locate a rebuilt master cylinder? Included in the lot from the auction were a bunch of brake parts, including a couple of springs…but I don’t know if they are the correct springs for this master cylinder.

The master cylinder does seem to bolt correctly to where it should.

Again, I am learning as I go along, having not dealt with this sort of thing in 59 years when building a hot rod as a young guy. So the gaps in my knowledge and experience are huge!