I have a 36 ford with 40 brake drums. I have a mid 60s mustang mastercylinder on the frame with 10 psi residual valves. I can either get the brakes to work but they will stick until I crack a bleeder to release the pressure or have the master cylinder rod backed off so the don’t stick but I won’t have brakes until I pump them a few times there is not happy medium. I changed mastercylinders but that didn’t do anything to help I’m lost on what to try next. Has anyone had this problem
a common cause is swelling inside the brake hoses. the hydraulics can push past the restriction and push the shoes out but the return springs arent strong enough to force brake fluid back to the master
Everything is new. Should I jack the car up spin the front and back once they are stuck if it’s the hoses the back wheels would still spin
what is the bore size of the master? it may need to be bigger. the 1940 cylinders should be 1 1/4" bore. depending on your pedal ratio the master may not be moving enough fluid.
There is a hose for the rear brakes as well, someplace between the rear axle and the body. If you didn't know it was there, you probably haven't replaced it, might be a good starting point. But finding out if all the brakes are dragging, or just the front or rear would be the place to start, rather then just throwing money at it. Dragging front brakes could still be caused by a bad new brake hose, unfortunately, a part being new doesn't always mean the part is good. It could also be caused by a master cylinder rod that is still applying pressure to the system. Dragging rear brakes could be caused by a bad hoses, or emergency brakes hanging up. If all the brakes are dragging, I might suspect the problem may be the brake pedal rod does not have enough free play. I have also seen where a brake light switch was improperly adjusted and was applying pressure to the brake pedal. The master cylinder has to be able to retract the piston completely, or it may still be applying the brakes. I have also seen drum brakes that don't release because the flat pads the brake shoes sit against have grooves worn in them the shoe gets trapped in, and the shoes can't back away from the drums.
if it wasn’t moving enough fluid I wouldn’t have much of a pedal. This I can get a really hard pedal but then it just doesn’t release the pressure and my brakes lock up
when the rod is adjusted correctly, 1/8" of play , do the brakes work? I thought from what you wrote they would not work unless they were pumped which could be caused but too small of a master cylinder bore or too short of a pedal throw. adjusting the rod too far in would not allow the fluid to return causing a sticking brake.
if I remove the residual valve that then I would know that’s not the issue. I’ve thought about mounting a brake pedal to the fire wall to get rid of all that and hope it fixes my problems
Did the car have 10 lb residual valves when it was new? Just wondering why they are installed. Did original master cylinders have a residual valve built in? Find out which end has the sticking brake or brakes. Then start unhooking lines till you find where there the pressure is. It may take a few joints, so keep pumping the brakes up between tests.
Is the pushrod touching the piston in the MC? If you adjust the brake pushrod too tight it won’t allow the pressure to release. There needs to be the slightest gap between the brake pushrod and the MC piston.
My truck <----- doesn't have residual valves, master is on the frame rail with disk up front and drums in the rear. It doesn't need pedal pumped up or anything weird, it works like any other brake system. Again, just wondering why they are always installed when the cars didn't come with any.
I’m not even adjusting the rod that much before they go from needing to pump them up to having a hard pedal and the brakes sticking. The mastercylinder is from a mid 60s mustang
65-66 mustang master is 7/8" bore. 40 ford wheel cylinders are 1 1/8 bore my guess is it is not pushing enough fluid. put the PROPER adjustment on the rod and don't touch it. if it needs to be pumped to get a pedal it either needs to be bled or it is not moving enough fluid.
I always saw you need them when your mastercylinder is lower than the wheel cylinders. I changed out master cylinders from the original single bowl to a dual bowl
A 1" bore '67 Mustang drum/drum master cylinder usually works with Ford Lockheed brakes as long as they are properly adjusted. Most of the times these come with built in residual check valve; but it is a good idea to check for sure. If you gently poke inside the port with a paper clip or something similar and there is a check valve you will feel the spring loaded disc. If no valve use a 10 psi external valve on each port. The reason you didn't see residual valves on original cars is because it was built into the master cylinder.
Thanks for the explanation, I have a Ford Master cylinder, so probably it has the internal valve and I never knew it.
If there is an internal residual valve, and you add another in the line, it is not detrimental. They don’t add together. I read this on the ECI website years ago.
You can get away without residual valves if you drive the car/truck every day or at least several times a week and never let it set for two or three weeks at a time. I drove my 48 with a dual master cylinder for 20 years that way but if I let it set for three weeks I had to bleed the brakes because they had lost their residual pressure. The drum brake dual master cylinders have a check valve behind he seat for the brake line . I'd have to go out and dig out a 40 style backing plate to check but are there wear points on the backing plate where the shoes slide that they and especially new shoes might hang up? That is common on Bendix style brakes but I don't know the nitty gritty about it on the 40 style.
If you’re not sure if your MC has built in residual valves or not, open up a paper clip and gently stick it in the port, if it stops it has residual valves. If it goes all the way in, it does not. I also used a 60s Mustang MC in my 40 Ford and it did have built in residual valves. What I’d do is put a little slack in the brake rod, then adjust the shoes tight against the drums and if you have a good pedal, then you know it was the adjustment, then back them off to slight drag. If you still have to pump them, keep bleeding, there’s air somewhere.
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