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    Combination brake valve

    Hi I have a 1967 coupe and my brake light stays on on the dash. I know the light comes on because of the differential valve being across one side detecting a loss in pressure and therefore operates a switch telling you you have a problem with the brakes. But does that valve stop brake fluid going to the problem or is it just a warning light? Thanks

    #2
    I am not absolutely sure of the valve design but the general principle is that the act of the shuttle moving over to lock off the faulty side of the brake circuit then moves a contact up to put your light on. I would not drive the car until you have sorted this. Basically check the brake pipes, connections and rear/front wheel cylinders. If you have discs on the front I have never known the seals to leak badly in the caliper pistons, its usually pistons seizing in the bores with calipers and that wont put the light on.
    Allan

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      #3
      Thanks Allan for the advice. Yes it is discs up front and the light was disconnected when I bought the car. I plugged it in and the light came on! I will get the brakes checked out. I have heard that the valve can stick over one side. I presume that means thatís the first thing to be fixed if it restricts the flow. Cheers Colin

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        #4
        ok I understand. Something doesn't sound quite right. Can you not take it to an Mot garage and try it on the roller brake tester to see how the front and back brakes are working. It could be a faulty valve and the brakes are fine, which is why someone might have pulled the connection.
        Allan

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          #5
          This is very common on these cars. They are duel circuit brakes which are linked only at that shuttle valve. If one circuit develops a leak there is a pressure loss in that circuit and the pressure from the other circuit pushes the shuttle across thereby activating the light switch. This pressure loss of course also occurs temporarily when the brakes are bled and once the shuttle has moved it wonít return of its own accord.

          First thing to do is check around the entire brake system for leaks. If there are none, turn the ignition on so the light comes on and get someone to press the brake pedal gently while you open a bleed nipple first on the front circuit and then the rear. As the pressure drops on the open circuit the shuttle will move back to the centre position and the light will go out.

          Don't press the pedal too hard or fast as that will cause the shuttle to go past centre and the light will come back on. If this happens simply repeat the procedure whilst opening the bleed nipple on the other circuit.

          Hope that hat makes sense

          David

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            #6
            Originally posted by skidado View Post
            First thing to do is check around the entire brake system for leaks. If there are none, turn the ignition on so the light comes on and get someone to press the brake pedal gently while you open a bleed nipple first on the front circuit and then the rear. As the pressure drops on the open circuit the shuttle will move back to the centre position and the light will go out.

            Don't press the pedal too hard or fast as that will cause the shuttle to go past centre and the light will come back on. If this happens simply repeat the procedure whilst opening the bleed nipple on the other circuit.
            Is this the "official" way of centreing these valves? I remember with the Mk1 Granada's that one undid a littl cap on the valve and inserted a screwdriver shaped tool to hold the shuttle central whilst bleeding the brakes.
            Allan

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              #7
              Not official but it works

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                #8
                Thanks guys for the advice. I will definitely try the bleeding trick to get it to move one way or another. I had the brakes checked out and they were ok, most parts were new or had been replaced so no leeks etc. But the hand brake mechanism and cable was loose and everything was flopping about. They were on full adjustment and seemed to no where to adjust the cable. My hand brake is one you pull out from under the dash. Have you any knowledge about this problem? Cheers

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                  #9
                  It sounds like the handbrake mechanism needs to be adjusted up. The main adjustment for the cables is under the car by the gearbox. Before you get to that though I would check that the rear brake shoes are adjusted up properly and the handbrake mechanism inside the brake drum is all present and correctly fitted. If it is all working ok in the drum then I adjust the rear brake shoes by putting a screw driver in the slot in the bottom of the brake back plate and cranking the adjuster ratchet wheel around until the shoes are beginning to make the drum drag a bit. I would then go to the adjuster on the equalising rod at the gearbox and tighten that up until the brake lever puls up about 5-6 clicks before applying the brake. Another thing that happens is the rear brake cables get stuck in their outer sheathes. If this has happened its probably best to replace them.
                  Allan

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                    #10
                    Looks like Iím gona be busy sorting out the brakes this weekend, thatís if the rain stops. Thanks again for the advice guys.

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