The Stovebolt Site Forums The Shop Area Engine Shop Diff between 1940 frame mount master cylinder and 47-54

I have a 1940 3/4 ton that I'm looking to upgrade to dual master cylinder.

I see these master cylinders on e-bay for the 47-54.

On the 40 3/4 ton the MC mounts to the frame. Does anyone know if the 47-54 mount was the same? I'd like to bolt this right in place.

Greg,

I took the brake pedal setup off your 1 1/2 ton, and am planning to do the same thing... Put a dual master for disc brakes in my 1940. If I am not mistaken, on your 1940 the brake pedal pulls a rod and a clevis to another lever that is mounted to the frame. From that lever there is a shorter rod and clevis that attaches to the MC which is basically turned around. The pulling motion on the frame mounted lever ends up pushing the MC. There is force multiplication happening twice in that setup. You have the pedal ratio, and the lever ratio.

I think a standard frame mount master cylinder bracket would work in your case. You would look for a 1 inch bore MC if you are not using a booster. The beautiful part about that linkage is that you could lengthen or shorten the rod(s) to keep your MC accessable.

Your 1940 3/4 ton differs from most of the prewar and decco trucks in that you did not have the transmission mounted MC which is typical on most the light duty trucks I have seen.

Good Luck
John

Just looked at the ebay link... I don't think that setup will work if you are planning to keep a manual transmission. You should look for a simple "L Bracket" that has been bored for a MC, and use your stock pedal, lever, and rods. If you want the booster... just lengthen the rods and remount the lever so that the MC sits where it is accessable. It might not be necessary because you could always pull off the entire floor pan to gain access.

It was a dumb question as I forgot the brake pedal mounts to the bell housing so a universal mount would never work.

The problem with our setup is that since it's turn around the frame mount is on the wrong side.

Maybe I could go with something like this MC and fabricate a bracket to mount it in the right spot.

If you figure it out first let me know.

Also, did you mount an NV4500 onto your existing bell housing? I was going to give a call to Buffalo Enterprise and see if they make an adapter plate.

Greg

I did mount an NV4500 to my existing bellhousing... but that was with my 1959 GMC 1/2 ton. I had an adapter plate cut out of 1 inch thick alluminum made locally for my 1940 gmc. It was expensive. When I called Buffalo... Steve was familiar with our bellhousings, and had that pattern. He didn't have the pattern for the NV4500.

Advance Adapter may be able to come up with something also, but I am not to thrilled with them. I got the adapter for my 59 gmc through them. 1947 through about 1967 or 8 bellhousings had an index of 4.686 inches. Later bellhousings had an index of 5.125 inches. The adapter plate was indexed for the larger 5.125 bore (there's a lip that slides into the bellhousing to center the transmission) I had to machine the lip on the adapter plate down to properly index on the smaller 4.686 bellhousing. The instructions mentioned it was for the 5.125 bellhousings only, but the sales staff didn't mention that when I ordered.

Short story Long... I am driving my 59 with the NV4500 and it is far superior to the tired sm420 that was in there when I got the truck. I still have to work out some driveline vibrations though.