So, I am at the point on my rebuild were I am installing the plumbing. I did not replace the original single bowl master cylinder with another. A double bowl MC is installed. Should there be a check valve and a proportioning valve?
Hy 87GN, I am going to assume that you are working on a 1955.1 3600, by your pictures and your signature line, please remember to give us that information when you ask questions. What was the master cylinder you installed originally intended for? Are you going to have drum brakes all around or will you be doing a disk brake conversion?
If you are doing drums all the way around no extra valves are required. 🛠
I agree, but may I add a couple of possible exceptions he might want to be aware of?
If the master cylinder is lower than the wheel cylinders you would need an inline check valve to prevent backflow. I also think there would be a little quicker brake response with 10-lb inline residual pressure valves front and rear to offset drum brake spring tension.
Yes, all 4 of the drum brakes will be reinstalled completely new. The dual bowl MC is mounted in the original location except for the mounting bracket that came in the kit. The wheel cylinders are below the MC as it sits on level ground but they would not be below the MC on a hill. The double bowl MC intention was to provide a second chance to stop if a failure accrued in one of the lines. I know it's not original and I had to make that hard decision to make this alteration to the master cylinder.
The original master cylinder and some replacements already have residual pressure valves built in. Find out what you have before adding other things.
A check valve is a bad idea, unless you want your brakes engaged always.
The residual pressure valves are a type of check valve but only hold the listed pressure, freely return excess pressure. The brake shoe return springs should be able to provide more pressure than the valve is rated for.
I went to a double mc and stayed with drums and had to add 10lbs residual check valves. I added one to the front line and one to the rearclose to the mc. I was told to add 2 on the front line after the split and then add a proportion valve but I didn’t go that route. They work great now, before the check valves I couldn’t get any pressure from the pedal. Now it’s good and firm.