Dim and flickering hydraulic warning light
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Thread: Dim and flickering hydraulic warning light

  1. #1
    Fellow Frogger! ds21bvh's Avatar
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    Default Dim and flickering hydraulic warning light

    Another minor issue I have.
    The hydraulic warning light is always on dimly and itís flickering as I change gears.
    The hydraulic system is perfect with plenty of reserve pressure, could this just be gremlins from sitting? Trapped air? Or could the priority valve a bit sticky? Or an earthing or electrical issue?
    The bit Iím concerned about is itís on dimly, i would expect it to be bright when on or completely off.
    Any ideas?
    Kind regards
    Mark

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    Flickering? Obvious one - but do you have the right amount of fluid in the reservoir? Eliminate that as a possibility and move on:

    I'm sure you know, but the default light/ switch position is 'on', and it is the rising hydraulic pressure that makes it go 'off'. If pressure drops while you're driving, the warning light comes on again. Simple. I think the operating switch is part of the brake pedal mechanism? Is that right? Could city be that the switch needs cleaning or adjusting (or both) so that it stays off when the system is up to pressure?
    1968 DS21bvh Pallas in Gris Palladium

    Restoration blog: https://ds-restoration.blogspot.co.uk

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    Fellow Frogger! citroenthusiast's Avatar
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    It would help to know the model year we are talking about. Early cars have a mano contact switch. Later cars have a hydraulic pressure switch at the bottom of the priority/security valve. These sometimes gets plugged with debris because of the orientation. If you have one of these, unscrew it from the valve and flush any debris from the sensor port. That may take care of it.
    Cheers,
    John T.

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    Fellow Frogger! ds21bvh's Avatar
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    Sorry guys itís a 71 DS21. I also thought it was part of the priority valve also.... My question is why is it dim? Iíd have thought if it was faulty it would be fully on? Also can air get trapped there - it could also be the issue if that is the case?
    Many thanks for the replies
    Mark


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    Default Dim and flickering hydraulic warning light

    For a DS the switch lives down at the brake pedal. Itís job is to measure the amount of pressure available to the breaking circuit not so much total system pressure. I think Dspecials and IDs have it at the security valve and itís a different switch.

    IMG_1549868728.269061.jpg

    The switch is the bent copper tube in my hand, itís usually covered by a black plastic cap. It works by deflecting to copper tube away from a small brass screw. Now back to your question, it could be dim because the contacts are dirty or because the contacts are just barely touching. Itís easily adjusted with a screwdriver. Ideally it should turn off somewhere around 1250psi if memory serves but double check with a manual:
    Last edited by faulksy; 12th February 2019 at 07:38 PM.
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    Quote Originally Posted by faulksy View Post
    For a DS the switch lives down at the break pedal. It’s job is to measure the amount of pressure available to the breaking circuit not so much total system pressure. I think Dspecials and IDs have it at the security valve and it’s a different switch.

    IMG_1549868728.269061.jpg

    The switch is the bent copper tube in my hand, it’s usually covered by a black plastic cap. It works by deflecting to copper tube away from a small brass screw. Now back to your question, it could be dim because the contacts are dirty or because the contacts are just barely touching. It’s easily adjusted with a screwdriver. Ideally it should turn off somewhere around 1250psi if memory serves but double check with a manual:
    Is it really as simple as that! Simply that hydraulic pressure tries to 'un-curl' a bent pipe, breaking an electrical contact? I knew they adjusted, but what is the adjustable part? the brass screw that touches the copper pipe?
    1968 DS21bvh Pallas in Gris Palladium

    Restoration blog: https://ds-restoration.blogspot.co.uk

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    Too many posts! JohnW's Avatar
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    Quote Originally Posted by Budge View Post
    Is it really as simple as that! Simply that hydraulic pressure tries to 'un-curl' a bent pipe, breaking an electrical contact? I knew they adjusted, but what is the adjustable part? the brass screw that touches the copper pipe?
    That's how a standard "Bourdon" pressure gauge works, with suitable gearing attached in some way to the curved tube, as far as I understand it. I've always been amazed that they don't crack with all the flexing but I've had such an oil pressure gauge in my Renault R8 since 1974 and it is fine.
    JohnW

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    Fellow Frogger! ds21bvh's Avatar
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    That is interesting! You always seem to learn something new about these cars even after decades of ownership. Could it be related to air in the front or rear brake circuits at all? Do you need to disassemble the pedal mounting plates to adjust or is there a strategic hole somewhere?
    Many thanks for the post.
    Kind regards
    Mark


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    Hello, my 1972 Safari had been stored for over 25 years. The hydraulic warning light would dim but not go out even though fully pressurised. I took out the switch under the brake pedal, even with the points manually separated, it still didn't go open circuit. I solved it by using a hot air gun to completely dry out the switch (even though it was dry to the touch). I got it really quite hot. Once re-fitted it worked properly.
    Maybe a coincidence, maybe not, but it worked.

    Peter

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    Default Dim and flickering hydraulic warning light

    Your only two options for adjusting the switch are to crawl into the drivers footwell or take the whole pedal assembly out. Itís a bit hard to picture till youíre there but the switch is buried under the accelerator pedal linkage. Doing it on the car does let you fine tune the point it goes out.

    Air can indeed get trapped there as itís a dead end on the system. Bleeding requires filling the pipe with lhm from where the pipes connect onto the brake pedal.

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    I am not familiar with the model you have, but Xantias & a lot of others have a fluid level switch as well as the loss of pressure switch, this can go dicky with age. If it has a level switch it will be at the top of the reservoir & will have a plug & 2 wires to it, the light goes out when the level is high enough. To check if it is a problem, pull the plug out & the light should go off completely. Took me ages to twig to this as I thought the "stop" light only came on with a loss of pressure, the light kept coming on even though there was no trace of any problem with the hydraulics, once I realised that it had a level switch it was easy to fault find & fix. Check if yours is similar as the level switch is much easier to deal with!Regardsagd123

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    Maybe a bit left field, but I assume you have verified that the flickering is not from that nasty little engine oil pressure switch that loves to leak under the inlet manifold ?

    Richard

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    Here's a closeup of the unit. The small brass screw is what you adjust, here it has been wound out far to far and should actually be touching the bent tube when no hydraulic pressure is present. It earths through the copper plate to the brake pedal assembly.

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    The cars are just a strange and magical genius of there own arenít they! So many wonderful ideas


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    Quote Originally Posted by faulksy View Post
    Here's a closeup of the unit. The small brass screw is what you adjust, here it has been wound out far to far and should actually be touching the bent tube when no hydraulic pressure is present. It earths through the copper plate to the brake pedal assembly.

    That photos a 'keeper'. Great bit of reference material. Thanks for sharing it.
    1968 DS21bvh Pallas in Gris Palladium

    Restoration blog: https://ds-restoration.blogspot.co.uk

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