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  • Brakes locked

    I had my car with disc brakes. During a trip in the alps last year where I used a lot the brakes, they seized. I noticed that when slowing down almost to a stop the car was braked. After a few pedal strokes it releases. I removed the Wheels but saw nothing wrong. Where shall I look?
    Attached Files

  • #2
    Locking brakes can be caused by two problems. Did ALL your wheels lock? If so, your brake pedal and booster need to be adjusted because the master cylinder is not returning all the way when you release the brake pedal. This procedure is covered in your Shop Manual.

    Another cause usually comes up after a car was sitting for long periods of time. That is, disc pistons rust if they are not made of stainless steel. Corvette had this problem in the early days. People would put their car in the garage for the winter then the first time they stepped on the brake pedal the brakes would lock up. It took a tow truck to drag the car out in order to work on it. Chevrolet solved this problem by replacing the caliper pistons. Corvette has dual-piston calipers.
    My latest project:
    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan

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    • #3
      Both front wheels are locked but not the rear. Rears are drum brakes; Front are discs.
      It started last year in the alps. I did not had the problem until I run on mountain roads (and slopes)
      Now the car sat for the winter (and spring and summer) and it locks. So this may be rust now, but not before.
      It seems to me that heavy use started the thing.
      Last edited by Eric S; September 20th, 2019, 03:17 AM.

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      • #4
        If you loosen either front caliper bleeder screw and your front wheels turn freely, the problem is caused by your master cylinder adjustment. If one or both front wheels still stick after hydraulic pressure is removed, you have a rust problem.

        Front discs have no return springs but they do back off just enough to free the wheel when hydraulic pressure is removed. If the master cylinder is not allowed to return all the way, fluid cannot go back to the reservoir and it is trapped in the lines. If your front brakes are partially grabbing they create heat that warms your brake fluid. Warm brake fluid expands which puts even MORE pressure on the caliper pistons which makes the brakes grab harder, until the fluid cools (or you remove hydraulic pressure).

        There are two adjustments. One at the brake pedal bolt which pushes the brake rod into the booster. The other is at the OUTPUT end of your booster. The master cylinder must be disconnected to access this adjustment. The hydraulic lines DO NOT need to be removed, but simply pushed out of the way when the master cylinder's mounting bolts are removed. There is a 'jack screw and a jam nut' inside the booster. If you have a helper push the brake pedal, this jack screw comes out for easy access. Again, this procedure is covered in the Shop Manual. Take this adjustment in small steps. If you back off the jack screw, only try 1/2-turn at a time, then put the master cylinder back on and try it. - Dave
        My latest project:
        CLICK HERE to see my custom hydraulic roller 390 FE build.

        "We've got to pause and ask ourselves: How much clean air do we need?"
        --Lee Iacocca

        From: Royal Oak, Michigan

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        • #5
          Can I have a drawing for the brake pedal (only illustrated in the manual with clutch pedal)
          I need to see the set up as I guess there is a return spring on the pedal which I don't remember having seen when I removed the pedal earlier this year. I will have to see that on the car over the week-end.

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          • #6
            Here you go. I don't believe there's a return spring on power brake cars. Only on manual brakes. I'm not sure what system you have so I posted both diagrams. It's the same whether there's a clutch or not.

            John

            59 brakes.jpg60 brakes.jpg
            Last edited by jopizz; September 20th, 2019, 03:32 PM.
            John Pizzi - Squarebirds Administrator

            Thunderbird Registry #36223
            jopizz@squarebirds.org 856-779-9695

            https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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            • #7
              Hi Eric...EASY check for proper M/cyl to Booster/pedal rod distance...Remove M/cyl cover..Check fluid level is good in both reservoirs, look into reservoirs and note the 2 holes in the bottom of each reservoir...One is the compensation port...Have a helper gently push/release the pedal, fluid should erupt from the comp port in both reservoirs, as the piston moves back...this allows pressure to escape from the system...if the comp port does not uncover, as soon as the fluid heats up it WILL APPLY the brakes and hold them on..if no fluid eruption at EITHER FRONT BRAKE OR REAR BRAKE COMP PORT {of course the large res is for the front discs}.......you can loosen m/cyl to booster nuts, and pull master out away from booster, all you need is a little clearance...retry the fluid eruption thing...if both ports now show fluid movement, you know that you must shorten rod between booster and m/cyl. as there is not enough clearance between booster and M/Cyl push rod..so adjust rod as required..... ..Check on line fore " front disc brakes coming on with out pedal being pushed or similar words..there are many other causes as already noted in the other posts, but, ...this is a very common prob in custom brake additions...Hope this helps CHEERS TERRY
              Last edited by BEVS BIRD; September 20th, 2019, 12:56 PM.

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              • #8
                I have a retracting spring in the 60 manual!?
                Attached Files

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                • #9
                  I have a single reservoir in the master cylinder.
                  The forward compensating port is not drilled through. 1st picture taken with a lamp in the reservoir.
                  Made a rough jig and the rod protrusion is within specs.
                  Do I have to replace the gasket on the end of the MC or just putting the damaged part up will be fine?
                  On the drawing I made one can see where the parts ends in relation to the port. (I know spring needs to be reversed with valve forward). I am concerned that the rubber cup does not comes back past the port??
                  Do we need a paper gasket between MC and the booster ?
                  Pedal checked and seems fine. No spring on it.
                  Any thought here as I don't see what can be wrong.
                  Attached Files
                  Last edited by Eric S; September 22nd, 2019, 02:06 AM.

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                  • #10
                    Originally posted by Eric S View Post
                    I have a retracting spring in the 60 manual!?
                    As I pointed out manual brake cars had the return spring. The diagram you posted is for manual brakes. If that's what you have you should have the spring. If you have the under dash or under hood booster then refer to the diagrams I posted.

                    John
                    John Pizzi - Squarebirds Administrator

                    Thunderbird Registry #36223
                    jopizz@squarebirds.org 856-779-9695

                    https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                    • #11
                      John

                      the diagram I posted is for a manual gear box with a spring on the clutch pedal. One of those you posted is also for a manual (2 pedals) and has no spring on the brake pedal. Only on the clutch pedal and different than mine.

                      My car is an auto anyway and I have no spring.

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                      • #12
                        Sorry just noticed you modified your text and understood you're talking manual brakes not gear box.

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                        • #13
                          Hi Eric How about some pix of your set up..you really don't show or say much about the set up in this post..Single reservoir m/cyl??, excuse my dumbness, is this the orig 58/60 m/cyl? are you using a combination valve? Have you checked pressures at the calipers , are they releasing fully? Is you brake pedal fully retracted? again my dumbness may be showing...Is there a residual valve built into the m/cyl if it was for 4 wheel drum brakes? CHEERS TERRY

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                          • #14
                            Terry brings up a good point. You should have at least an 8" two stage booster with a dual disk/drum master cylinder if you have discs in the front. When you say you have a single reservoir I hope it's not a single master cylinder.

                            John
                            John Pizzi - Squarebirds Administrator

                            Thunderbird Registry #36223
                            jopizz@squarebirds.org 856-779-9695

                            https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                            • #15
                              Here is the picture. I did not included it earlier as it matches the manuel so yes I guess it's the OEM.
                              I dont know what is a combination valve or a residual valve. I don't see anything that may be it.
                              Did not checked pressure at calipers but they do not retract fully, hence my original post. The expanding fluid when heating and not going through the compensating port is/was appealing to me.
                              Pedal seems to behave correctly.
                              John I am not sure about a 2 stage booster but it looks like a single master cylinder to me.
                              Except front wheels being braked sligthly after a while (heated?) I had no braking issues.
                              Attached Files

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