Classic Mustangs (Tech)Technical discussions about the Mustangs of yester-year.
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I have a 1968 gt with disc and drum.
pump the brakes
brake shoes increased
front brake hoses rebuild
The circuit is free and clean and are not bleeding. We can not bleed the system would seem to take that every time you brake air somewhere.
Can you help me?
Roma - Italia
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You brake system has a line cut-off valve on the driver firewall. This valve is to stop fluid from leaking out completely incase of a line being ruptured. It has one side connected to the front brakes and the other connected to the rear brakes. Inside is a piston which, when centered allows brake fluid from one part of the master cylinder to go to the front brakes and fluid from the other to go the the rear bakes. The pressure must be equal on both sides of the piston. Should the pressure fall in one circuit the plunger moves to block that circuit and only the the non-broken circuit will get fluid. This maintains at least some braking.
If you open a bleeder and push the brake pedal down quickly you will cause the piston to move and block the circuit. On the second push, you only pressurize the other circuit and the one with the bleeder open will be blocked keeping it from bleeding.
You need to insure that the plunger is centered. The plunger not only blocks a leaking circuit, it has switch contacts that light the light on the dash saying one circuit has failed. You need to open a bleed valve on the unblocked circuit, with the blocked circuit bleed closed and depress the brake pedal until the light goes out. Push too far and the piston move the other way and the light comes on again. Only push until the light goes out. Then close the bleeder. This will center the piston. Now go back to bleeding the brakes but only open the bleeder a little bit and push the pedal down slowly so the safety plunger does not move.
Remember this when changing brake pads . When new pads are installed there is some space between them and the disk. Slowly push the pedal down and never all the way to the floor or you will probably throw the safety piston.
I guess because I am new, I can't post attachments so I can send a picture. It should be just below the master cylinder with a white and purple wire going to it. Follow the lines from the brake master cylinder to it. It also serves in many cases as the proportioning valve. Normally the line from the rear of the master cylinder goes to the top front of the valve. The front brakes come out as two separate lines left front brake out front of valve, right front brake out bottom. The Front of the master cylinder goes to the back top of the valve and a line comes out the back bottom and goes to the rear brakes. There is a hydraulic plug on the back under which is the proportioning valve to keep the rears from locking during braking as the weight is transferred to the front of the car.
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