| smbryansr | -- 01-14-2012 @ 4:22 PM |
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I have a stock 1949 Ford F-1 that has had no issues for the last 9 years since I put it on the road. About 3 weeks ago, I was driving it and noticed that the brake pedal got higher and higher until there was no play and noticed the brakes were dragging. I bled one of the bleeder screws and all 4 wheels released. I returned home, but again, every time I braked the pedal got higher and higher. I removed the master cylinder to check it and it looked like new inside. I ordered a kit anyway, installed it and bled the brakes only to have the same thing happen again. The pressure is so high in the system that with the truck sitting, the brake light switch is engaged and the brake lights will not go off unless I bleed one of the wheel cylinders. Before I change out any more parts, does anyone have an idea what might be going on? All the lines are stainless and were installed 9 years ago, all the wheel cylinders were new 9 years ago, as was the master cylinder. Thanks, SMB
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| flatheadman | -- 01-14-2012 @ 5:19 PM |
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I had that happen on a 1946 sedan. The body mounts had settled enough that the pedal didn't come all the way back up and covered the return port. The vibration thus pumped up the brakes.Check that the pedal is returning. You perhaps can adjust it.
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| alanwoodieman | -- 01-15-2012 @ 4:57 AM |
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your master cylinder pedal is not allowing the cylinder piston to return to allow the brake fluid back into the resevoir-adjust the pedal free play-do you have a return spring to hold the pedal up so it does not put pressure on the master cylinder? you need one inch of free play with no weight on the pedal rod to master cylinder piston.
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| trjford8 | -- 01-15-2012 @ 7:40 AM |
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You indicate that you have stainless steel brake lines. Did you make any other modifications to the system at the time? (disc brakes,inline residual valves, proportioning valve?). If no other modification then check the pedal free play. As others have indicated you need 1 inch of free play. Check the linkage, especailly the MC push rod. There is a lock nut on the push rod. If that came loose it will allow the push rod to spin and slowly reduce the free play to the pedal. If all this checks out then you need to look at the wheel cylinders. They may be hanging up.
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| smbryansr | -- 01-16-2012 @ 6:00 AM |
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First, as I said, it is a stock as built system, there have been no modifications. There is no blockage in the lines as I have run close to 1/2 gallon of brake fluid through the system while bleeding it 3 times now. Second, the pushrod is 1/8" off of the piston in the master cylinder and has not crept tighter, piston is all the way back against the retainer, I pulled the boot back and checked while the cylinder was still installed. Return spring is as original and it does keep the pedal tight against the rubber stop, it doesn't sag. I've been working on automobiles for close to 35 years and have not run into anything like this before. Any other ideas?
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| trjford8 | -- 01-16-2012 @ 7:20 AM |
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I know you said you put a new kit in the master cylinder. Did the kit include a new residual valve? That valve at the rear of the master cylinder keeps a certain amount of pressure on the brakes at all times. I had the exact same problem you describe on a car with disc brakes. It had an inline 2lb residual valve to the front brakes. The valve malfunctioned and would not allow fluid to return to the master cylinder. After changing the valve I was back to normal braking.
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| TomO | -- 01-18-2012 @ 7:59 AM |
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The piston in the master cylinder is not returning all the way covering the bypass port or there is debris plugging the bypass port. Try increasing the pedal free play to between 3/4" and 1" measured at the pedal. If this does not cure the problem, you will have to replace the master cylinder as the bypass port is blocked. Tom
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| smbryansr | -- 01-22-2012 @ 3:47 PM |
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There is nothing outside of the master cylinder other than a 3 way splitting block that one line goes to the front right, one to the front left and one to the rear axle (and a brake light switch in the end of the hollow bolt). The kit did have the new residual valve that goes in the output end of the inside cylinder and it was installed.
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| smbryansr | -- 01-22-2012 @ 3:55 PM |
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The piston in the master cylinder IS returning all the way and is NOT covering the one hole in the cylinder between the resivoir and the cylinder. The Brake pedal plunger is NOT making positive contact with the piston, there is about 1/4" of play between the shaft and the contact surface of the piston, which is actually more than the original Ford shop manual recommends. I can look down through the resivoir at the hole between it and the cylinder and see the edge of the piston just at the edge of the hole with open area of at least 80% of the hole. When I apply brakes looking down in the resivoir and then let them off, some fluid is returning to the resivoir (there is a small plume of fluid caused by the returning pressure) but with each additional braking action, the pedal gets higher and higher until there is no pedal and the system is fully pressured, enough to keep the brake lights on without the pedal being pressed. Any OTHER ideas?
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| smbryansr | -- 01-22-2012 @ 3:57 PM |
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I also tried pulling the plunger attached to the brake clevis while the system was pressured up and it did not affect the system, to those that think the adjustment is an issue. IN that state, the piston would have nothing touching it fromt he brake pedal.
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| smbryansr | -- 01-22-2012 @ 4:01 PM |
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Put the truck on jack stand this weekend also, pulled all 4 tires while the system was fully pressured up and none of the wheels turning. Couldn't pull the brake drums the shoes were so tight. loosened the right rear bleeder screw on the slave cylinder and all 4 wheels released allowing all 4 brake drums to be removed. Wheel cylinders are all working fine and none are locked up.
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| flatheadman | -- 01-22-2012 @ 5:09 PM |
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About the only thing left is a bad residual check valve.
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| trjford8 | -- 01-23-2012 @ 6:59 AM |
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I agree with flatheadfan. I think even though the residual valve is new it may be defective. The residual valve has a very small orfice in it(to allow some fluid return) and maybe a small piece of dirt or other foreign matter may be blocking the orfice.
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