1935 Ford Panel Delivery installed rear disc brakes. Had the normal br*** proportional valve when I had disc/drum brake system. Rear discs has the external emergency brake. I adjusted them by the instructions. What I can't get is a brake pedal, installed Wilwood proportioning valve towards the rear with the 2 lb. check valves. For the disc/disc combo, bleeding brakes with the vacuum type of one-person tool or should I get a buddy to pump the brake pedal. Pedal seems like it's getting firm but as soon as I start the truck, pedal goes to the floor. Where am I going wrong.
Did you bench bleed the master cylinder? Shouldn't the proportioning valve be up close to the master cylinder? Could be air trapped in that thing. Have someone operate the brake pedal and crack open any line connection fitting to see if you can get any bubbles. That might help you locate any trap points. Don't open the fittings, 1/4 turn will do it. Just crack them and immediately tighten them.
For those that can answer(I don’t know) they will probably want more information. Front and rear caliper piston diameters, type of calipers, MC specs as well. Maybe even pedal ratio. Best of luck and a bump!
Never changed MC, been on truck 500-700 miles, bleed when installed then. Valve is 12" or so from MC in rear line. Had disc/drum for about 1000 miles worked OK but just wanted a little more braking.
Built in residual valves are usually installed in drum masters. Disc masters usually have larger reservoirs for both circuits. Master piston size and stroke is important, as well as pedal ratio to making things work together.
A front disc, rear drum master may not have enough capacity be able to deliver enough fluid to a rear disc brake caliper to properly apply the rear disc brakes. One needs to compare the amount of fluid it takes for the wheel cylinders to fully function that have been replaced to the amount of fluid it takes for the disc brake calipers to fully function. I suspect a single stroke on the drum rear brake master cylinder can't provide as much fluid as needed to make the disc caliper function fully.
Bore size of master cylinder needs to be increased to push enough fluid to the larger capacity disc brake calipers... Plus Disc brakes don’t need a check ball as required by a wheel cylinder...discs have O-Rings...Wheel Cylinders have cups, which require that 2lbs. of pressure to keep wheel cylinders from leaking out.
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