DS Brake control valve
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  1. #1
    Fellow Frogger! CorneSoutAfrica's Avatar
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    Default DS Brake control valve

    Hi everyone

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    It has been such a long while since I posted on here I actually feel ashamed!! Between work and family sometimes the things we want to take part in get left behind!!

    First of all I remember guys asking for LHS sphere diaphraghms, well I have got 2 good ones, not new but they still had a fair amount of pressure inside when I got the spheres. I couldn't test thm because I don't have an LHS test bench. if someone want them pm me. I don't know if it is worth it but you never know!!

    Now I have a question. My DS21 BVH. I always had a stop light on the dash that would come on almost immediately after I shut off the car. I overhauled the brake accumilator, new ballbearing and spring. but my old brake accumilator was still ok. Main accumilator still good. I suspected my brake switch and replaced it with another second hand unit, I would ideally like to fit a new unit but our currency state caused that idea to die in the thinking stage, after replacing the stop light will come on almost whilst driving along or under hard braking, so before I start the replacing procedure the best bet would be to check the system with guages, I aquired a test bench a while back so I think that would be the best way to go.

    After checking my manuals (manual 814 and 814-2) They show in great detail how to adjust brake pedal pressure distribution and checking the pressure switch which I will check the latter tomorrow, but to check the brake control valve of the "DX" vehicle is no where to be found only the "DV - DT" vehicle, and the brake control valve on these cars are by the looks of it much easier to check than the "DX" vehicle brake control valve. Which manual do you guys suggest I have a look in?

    Is this becoming a common problem? I think it is just my cars because in all the cars I've seen before the stop light doesn't come on for weeks whilst the car is stationary. mine loses pressure whilst driving

    I will keep you guys posted
    thanks
    Corne
    1968 ID21 break
    1971 DS21 IE BVH Rouge de grenade (Madamoiselle Rouge)
    1974 DS Pallas Sable metalisse My first restoration (Edith) Now BVH
    1973 DS pallas Metallic red. "Rusty"

    1947 Traction Avant

    Modern

    2006 C4 VTS 180 Coupe

    What would life be if we had no courage to attempt anything?
    - Vincent van Gogh

  2. #2
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    Hi Corne,

    If I am wrong about this I am sure someone will chime in pronto . Being a non US car that light, IIRC, is actually the main pressure warning light for the car. Drove me nuts the first time I ran into one over here. What I think it is telling you is that you just are losing overall hydraulic pressure after the engine is shut off. With USA models the factory moved the hydraulic system pressure indicator to the security valve mounted behind the LH wheel well's dust shield. With non USA cars (the rest of the world) that pressure indicating switch was mounted on the brake control valve.

    What kind of cycle time do you have?. If short - in the 6 to 10 second range - the most likely culprit, being a BVH car, is the centrifugal regulator. That one is easy to check by just pulling off the units return hose from the top of the reservoir and seeing how much fluid is pouring out at idle. A good one will only show a few drops per second. The second source is the steering rack. Specifically the rotating union. You can get some good internal leaks between the hp input port and the other ports inside the union with no outside seepage or leaking. The only way to check is to isolate the steering from the rest of the car by either using a blocking plate at the fluid connection flange or a plug in the 4-way (in your case) union mounted on the frame.

    If you still suspect the brake control valve the simplest way to check it - though a bit of a fiddle - is to remove the units return line that runs back to the bottom of the main reservoir. You can remove it with out fear of losing fluid as the return tubes inside the reservoir are designed to stick above the fluid level even with the car depressurized. A good control unit will show virtually no fluid flow - worn ones will have fluid running out at various rates back to the reservoir.

    Steve

  3. #3
    Fellow Frogger! CorneSoutAfrica's Avatar
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    Hi Steve

    I recently tested a car with cood hydraulics the car lost main accumilator pressure (loosened bleed screw) and the light only came on after exhausting the brake circuit by operating the footswitch so I am thinking due to the different position of the stop light switch it shows different characteristics? I am not sure so I may aswell be wrong.

    I forgot to mention I overhauled an HP pump aswell before fitting the new brake switch and my cycle time increased from a lousy 3 seconds to a sort of better 15 second cycle time. Centrifugal regulator is a newly overhauled unit, not even a drip from the return hose, ok just a drip now and then Steering I am not certain at this moment but at full lock there is no increase or decrease in cycle time at all.

    I will follow the return hose from the brake pipes to the resovoir and report back!

    Thanks!!
    Corne
    1968 ID21 break
    1971 DS21 IE BVH Rouge de grenade (Madamoiselle Rouge)
    1974 DS Pallas Sable metalisse My first restoration (Edith) Now BVH
    1973 DS pallas Metallic red. "Rusty"

    1947 Traction Avant

    Modern

    2006 C4 VTS 180 Coupe

    What would life be if we had no courage to attempt anything?
    - Vincent van Gogh

  4. #4
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    If it were genuinely losing pressure as soon as you switch off, would it not instantly drop to the ground? Isn't the stop light meant to light when any or all of several conditions are met, including when there is no engine oil pressure with the ignition is on? Maybe, the other car you tested did not have the wire from the ending oil pressure switch hooked up to the harness? It has a foot long wire that plugs into a connector near the rear of the battery box, at least on cars with the battery on the left side. The wiring diagram confirms the 'Stop' light is lit by any or all of engine oil switch, coolant temperature too high and the LHM pressure, but only when the ignition is on.
    Last edited by David S; 15th February 2014 at 09:58 PM.

  5. #5
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    Hi Corne,

    The front brake unit can be a major source of pressure loss. Not all that common, but have heard from Lon Price and a couple of others (Dave Burnham being one) that when all else failed to pan out, the brake controller proved to be the culprit . The steering not changing the cycle time at full lock does not mean much, frankly. It will only do so under some quite specific internal leakage conditions in the rack. Not having it change times does not rule out the rack .

    Steve

  6. #6
    Fellow Frogger! CorneSoutAfrica's Avatar
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    David S

    The stop light illuminates when one of three things go wrong. Overheat, low on hydraulic oil pressure and no engine oil pressure. The stop light will come on when either one of these go wrong. I am not sure if a DS should immediately lose all pressure in suspension because whilst on normal height I loosened the main accumilator screw but no drop in any of my DS' s suspension.

    Steve.
    I didn't check the steering by blanking it off but I pulled the return hose from the brake unit off. It had a stream of oil going back to the resovoir, with both units I have.... it seems like in the near future I will have to import a newly overhauled one

    I am still unsure if the stop light switch is connected to total system pressure or to brake pressure. I always presumed it was brake pressure but now after what you described I am not sure anymore.

    Cheers

    Via the aussiefrogs App
    1968 ID21 break
    1971 DS21 IE BVH Rouge de grenade (Madamoiselle Rouge)
    1974 DS Pallas Sable metalisse My first restoration (Edith) Now BVH
    1973 DS pallas Metallic red. "Rusty"

    1947 Traction Avant

    Modern

    2006 C4 VTS 180 Coupe

    What would life be if we had no courage to attempt anything?
    - Vincent van Gogh

  7. #7
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    Quote Originally Posted by CorneSoutAfrica View Post
    David S

    The stop light illuminates when one of three things go wrong. Overheat, low on hydraulic oil pressure and no engine oil pressure. The stop light will come on when either one of these go wrong. I am not sure if a DS should immediately lose all pressure in suspension because whilst on normal height I loosened the main accumilator screw but no drop in any of my DS' s suspension.

    Steve.
    I didn't check the steering by blanking it off but I pulled the return hose from the brake unit off. It had a stream of oil going back to the resovoir, with both units I have.... it seems like in the near future I will have to import a newly overhauled one

    I am still unsure if the stop light switch is connected to total system pressure or to brake pressure. I always presumed it was brake pressure but now after what you described I am not sure anymore.

    Cheers

    Via the aussiefrogs App
    Corne,

    A D's suspenison does not lose pressure via the main accumulator - typically. It can if the non-return valve in the pressure regulator is faulty or if one or more of the 7 little sealing discs in the pump are corroded or grooved (happens occasionally). Typical loss of pressure - can be quite slow or fairly fast - is via the steering/BVH components/brakes if the slide valve in the priority valve is worn. Until 12/67 cars had a positive acting pressure valve (ball and seat) that was a bit more effective is preventing reverse pressure flow from the suspension back to the 3 or 4 way feed union mounted on the fire wall. The other source of pressure loss is through the Teflon wear strips or rubber lip seal on early (pre 66) cars.

    On Euro spec D's the system pressure switch is mounted on the front brake controller. Prior to 3/73 that switch should turn 'off', IOW the hydraulic warning light is extinguished at a pressure in the area of 1300 psi or greater. On NA (USA and Canada) cars that switch is located on the priority valve. Reason is that on our cars an additional component was added to the brake controller - known as the 'leak' finder. Makes our car really had to bleed the front/rear brakes properly. As the brake controller is always at system pressure that switch is telling you the same thing as the one on my cars. The difference being that on the Euro spec cars, if the brake controller is tight that light will stay 'off' a lot longer than on NA cars because of the non-return valve in the brake accumulator on cars so equipped.

    Steve

  8. #8
    Fellow Frogger! CorneSoutAfrica's Avatar
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    Thanks for the info Steve. I would think that in a case of a catastrophic lhm leak the 'leak finder' would be much quicker at telling you there is pressure loss than the euro spec unit due to the position and sensitivity of the unit. But that is probably the intention of the unit

    I haven't yet had time to get to the root of my car's problem but hopefully this weekend.

    I will keep you updated
    Cheers
    Corne

    Via the aussiefrogs App
    1968 ID21 break
    1971 DS21 IE BVH Rouge de grenade (Madamoiselle Rouge)
    1974 DS Pallas Sable metalisse My first restoration (Edith) Now BVH
    1973 DS pallas Metallic red. "Rusty"

    1947 Traction Avant

    Modern

    2006 C4 VTS 180 Coupe

    What would life be if we had no courage to attempt anything?
    - Vincent van Gogh

  9. #9
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    Quote Originally Posted by CorneSoutAfrica View Post
    Thanks for the info Steve. I would think that in a case of a catastrophic lhm leak the 'leak finder' would be much quicker at telling you there is pressure loss than the euro spec unit due to the position and sensitivity of the unit. But that is probably the intention of the unit

    I haven't yet had time to get to the root of my car's problem but hopefully this weekend.

    I will keep you updated
    Cheers
    Corne

    Via the aussiefrogs App

    Hi Corne,

    Well, yes, in a way - In a case where there is a pressure leak (does not take much) down stream of that bloody valve what happens is - you HAVE no brakes at all. It will let you know there is a problem - in WTF way. Chalk another one up to the idiots at the US DOT. The reason they required Cit to install that so-called 'safety' device was that with the LHM based cars, the fluid (LHM) was not on the DOT's 'approved' list of brake fluids. Now the fact that every commercial and military jet air craft (including Air Force 1 - the plane used by the President of the USA) had the same fluid in its hydraulic system (just colored red instead of green) made no difference to those pencil pushers.

    Steve

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