Re: Drum is stuck
 

The threaded fitting sizes are the same on the drum-drum master cylinder and the disc-drum master cylinder. On both types of master cylinders the threaded part of the front port is smaller and the flare cone and hole that passes fluid are the same size with no difference between front and rear ports. For the drum-drum setup, the brake line going through the fittings are the same size for front and rear, and those 2 lines go to the drum-drum distribution block. The new Inline Tube brake lines that I have that will be going to the 71-72 combination valve have a smaller tube size for the front reservoir, but the threaded fitting is the same size used on the drum-drum master cylinder. So I believe I will not need any adapter if I use my disc-drum master cylinder on my 4-drum truck.

I don't have the option to trade the new disc-drum master cylinder in as it came from a different store, and I would like to keep my complete pile of disc-drum parts ready for the swap. I have everything I need ready to go except some of the expertise.

Re: Drum is stuck
 

That's good then, you should be good to go. I would suspect dirt and debris in that combination valve if your reusing the original, might be prudent clean it out as well. I have a nylon lock that traps the combo-valve open for bleeding, it screws in where the electrical switch is located once the switch is removed. https://www.jegs.com/i/JEGS/555/63200/10002/-1 Both of my 72 C/10's have MC's with 3/16" lines in the front port and 1/4" lines in the rear port. 1/2" wrench fits the front and a 9/16" wrench fits the rear. Kinda weird because everywhere else the 3/16" lines are used the fittings use a 3/8" wrench except where they connect to the hose fittings which are 7/16"...I've been in the process of replacing all the lines in one of my trucks because I couldn't get the rear wheel cylinders to bleed. I wound up replacing everything from the booster down including the MC and combo-valve to the wheel cylinders. I had the rear brakes disconnected for like three years for burnout contests. And in that time the lines and rear reservoir had rusted so badly that the rust was clogging the system rendering everything useless when I went to refill the rehook the rear circuit.