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Thread: Brake Pedal sticking

  1. #1
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    Brake Pedal sticking

    Hi from Germany! My 79 Riviera S-Type has this problem: Sometimes (engine on) the brake pedal sticks after hard braking and comes loose again after a few meters of driving. Brake booster and master brake cylinder are new. I did the brake booster test (engine off, some steps on pedal until hard, engine on, pedal goes down a few inches) and this was ok.

    When the pedal is stuck (at idle) and when I remove the valve from the brake booster the pedal comes up! There is a lot of vacuum on the hose and the valve is ok. I exclude problems with calipers, brake hoses, because when I use the brake with the brake booster valve disengaged everything is ok (with the exception of course that I need much force to brake).

    I would very much appreciate every hint what I can do next and how to solve the problem.

    Cheers
    Michael

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    I would lean toward the booster being the problem. If it is a rebuilt unit there may be a fault in it. You must also check the actuating shaft that goes through the firewall. Insure that the shaft itself is not binding. If it is that could mean the booster is not in proper alignment with the shaft or it is incorrect for your application. A sticking caliper should never affect the pedal.
    Next time it sticks try pulling up from under it with your left foot. That may give you an indication as to where the bind is. - Bill

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    Hi,

    thank you very much for your comment! When the pedal sticks it is nearly very hard or even impossible to pull it up with my left foot. So what does that that mean?

    I want to mention that during "normal" driving and breaking everything seems ok and sometimes after some hard breaking nothing unusual happens.

    Cheers

    Michael

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    Tool question

    Hi, which tool do I need to loosen/tighten this brake caliper bolt? In all my tool boxes (with German measures) there is nothing that fits !

    Thanks for your help

    Michael
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  5. #5
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    Michael I'm still thinking you have a booster problem. It sounds like under certain conditions the vacuum is not releasing. There is a possibility the small valve that makes the 90 degree turn from the vacuum hose that actually plugs into the booster is failing. That should cut off the vacuum while its engaged, if it doesn't the pedal can stay down until you reduce the vacuum to it by opening the throttle plates which sounds like your problem.

    Welcome to the world of American cars! The Allen key you need is the American/SAE type. It is an inch fraction head, nothing metric will work. The size your looking for is 5/16 of an inch. On some larger vehicles it would be 3/8 of an inch. Your 1979 is just before American car makers started to transition to metric fasteners. Throughout the 1980's-90's car makers changed over slowly with both being used making a full tool box a necessity! By the 2000's all cars made here had a full complement of metric fasteners.

    As you may or may not know several metric and inch fraction fastener heads are the same with 13mm and 1/2 inch being the first coming to mind. If you are going to be working on this car I strongly recommend that you find yourself a full set of SAE inch fraction tools, including Allen keys, open and boxed wrenches and socket wrenches. - Bill

  6. #6
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    Hi Bill, thank you so much for your advice ! I changed to the old valve, still the same! At idle I press the pedal 3 times, it comes back, the 4th time it sticks. Engine stops, pedal comes back. Your idea about some fault in the vacuum seems very logical to me, because when I pull out the valve I can hear the vacuum escape... When I blow into the valve (engine side) air goes thru, when I suck it blocks.
    Cheers
    Michael

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    Yes it's a one-way valve Michael so it sounds like its working properly. Its designed to only pull toward the vacuum source. From what you've told me I am now lead to believe the booster itself is the problem. If you purchased it locally bring it back, explain your problem and request an exchange for another. If purchased on-line you may be stuck with it and should try and find another. You should also check the pivot pin for the brake pedal as well. If you can disconnect it and check that it moves freely at all heights. On very high mileage vehicles it can wear and create a flat spot that can also cause a sticking condition. However I doubt that is your problem. I've only seen this condition on heavily used service vehicles.
    Good luck figuring this out, it's not a condition that seems safe to drive with. - Bill

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    Hi again! A neighbour, who is a car mechanic, meant that the cause of the problem might be air in the brake master cylinder. Is that possible?

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    I can see that giving you a low pedal and brakes that are not very effective but not causing the pedal to get stuck down unless the system is nearly empty. When you use the brakes do they seem to be working properly other than the pedal sticking? When you did the master cylinder installation was the system blead properly? Did you use the correct brake fluid for that system? Was the fluid fresh from a new unopened container? When you open the cover of the master cylinder is the fluid at the proper level? It is hard to figure out a problem like this from over 5,000 miles away without being able to see it in person. Did your friend drive the car or is he giving you a second hand guess like I am? - Bill

  10. #10
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    Normally in daily traffic the brakes work properly. I blead with new DOT 3 fluid and the level in the master cylinder is correct. Nevertheless we will bleed again next week with the "pedal method". When I installed the new master cylinder I didn't yet have the special tool for master cylinder bleeding which I have now, maybe we will try this as well. In the meanwhile I've ordered a new booster.
    Thanks again for your help, Bill!

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