Interesting brake observation.
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Thread: Interesting brake observation.

  1. #1
    WRB
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    Default Interesting brake observation.

    When the engine on the XM is stopped, there is still some braking power in reserve. When the engine in the CX is stopped, there are no brakes at all. Anyone have an explanation for this?

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    Quote Originally Posted by WRB View Post
    When the engine on the XM is stopped, there is still some braking power in reserve. When the engine in the CX is stopped, there are no brakes at all. Anyone have an explanation for this?
    Uhm, that does not sound good. There should still be brakes on a CX after the engine stops, if I understand what you are describing correctly. They are supplied by stored pressure in the regulator accumulator, brake acculator and I think perhaps also the suspension spheres via a valve.

    Does the suspension drop immediately when the engine switches off?

    Driving - '90 XM, '85 CX IE Auto, 406 Coupe, 405 srdt wagon, '78 dyane, Resting (or Rusting): '73 Birotor '82 CX Presitige, '81 CX Break IE, GS X2, GS1015 Wagon, GS 1300 5sp Wagon, '76 GS 1220 Wagon, '75 GS Wagon, '58 2CV, '58 Vauxhall Velox

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    Quote Originally Posted by WRB View Post
    When the engine on the XM is stopped, there is still some braking power in reserve. When the engine in the CX is stopped, there are no brakes at all. Anyone have an explanation for this?
    SIMPLES !!! dead brake accumulator (s).
    Anticipate more advice. Those with more knowledge and experience are sure to oblige with tales of IMMINENT necessity to resolve that situation.

    There are complications with bleeding too from memory. Once the accumulators are restored ( and therefore able to keep stored pressure made by the engine's high pressure pump ) and the circuitry has been "opened' the bleeding procedure must be done in the correct sequence.

    Is there stored pressure for steering after switching off the engine ?? It may be a good time to consider THAT accumulator as well. In the scheme of thing accumulator spheres are not that expensive, and are vital to the safety of the entire brake AND steering system. It is the access to the buried spheres that is the major obstacle. Remember CX Diravi steering uses LOTS of stored pressure when parking when demand is high and engine speed and therefore supply, is low.
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    1000+ Posts Greg C's Avatar
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    i would say dead spheres all round. the rear suspension supplies pressure for the rear brakes, main accumulator/brake accumulator for the front. The other thing to check is the rear brake pads. You may have early pads in later calliper which have pad material outside the disc area
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    WRB
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    I have replaced the accumulator sphere along with the all of the suspension spheres and it takes all night to sink. car doesn't have a brake accumulator as it has manual steering. The accumulator is stuffed as it is running every second or so, so I need to send this off to Pleiadies ASAP

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    ?? I thought all except the early model CX without Diravi (5) have at least 6 spheres. One at each wheel and the main accumulator up in the engine bay and the brake accumulator low down in front of the engine to the left and under the battery. Mine has 7 as do most Australian sold models but regardless there should be a brake accumulator low down in front of the engine somewhere.?
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    Real cars have hydraulics DoubleChevron's Avatar
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    It needs new accumulators. You should also have very limited braking from the rear while there is height in the rear suspension. I'd suggest a couple of house bricks is the best way to ensure a CX is still where you left it parked

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    According to the w/shop manual the early manual steering cars only have five spheres. There is no dedicated brake accumulator. The front and rear brakes are fed from the main accumulator via the priority valve. OP MA 390 page 13.
    Cheers Gerry

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    WRB
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    Yeah, I went looking for the brake accumulator when I bought it and, it wasn't in the usual spot down low on the left side and I couldn't find it anywhere else so, checked the manual and discovered it only had 5. as all of the spheres are new, I suspect the accumulator as it goes off every second or so. how long should it go between squirts?

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    PS, I doubt if the priority valve is stuffed as the suspension would drop fairly quickly

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    1000+ Posts gerrypro's Avatar
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    It is possible that the accumulator was low in pressure even though new! It may have been on the shelf a while??
    Do you have the single piston pump or is it a seven piston pump?
    The regulator may have a problem and be by-passing fluid back to the reservoir before system pressure is at the optimum!
    I would be looking for a cycle time of between 30 and 49 seconds.
    Unlikely to be the priority valve!
    Cheers Gerry

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    Single piston pump - I cannot count to 5 before the regulator cycles so - it can't really be anything else.

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    Quote Originally Posted by WRB View Post
    Single piston pump - I cannot count to 5 before the regulator cycles so - it can't really be anything else.
    The fact that it cycles and lifts on the suspension suggests that the pump is working and the regular is cutting in and out. So a flat accumulator or bleeding back somewhere else.
    On the XM I can get the hydraulic pump to run more frequently after sustained braking. Looks like the brake valve will bleed off pressure if it is in just the right spot. This can be fixed by a sharp stab at the brake pedal.

    So perhaps it could be the brake valve?

    First step is to vary the pressure on the brake pedal and see if the regularity of pump cycle changes. Next would be to disconnect the hydraulic return line to the brake valve and see if fluid is constantly flowing past (with the car safely supported of course!)

    Good luck...Cheers, Andrew

    Driving - '90 XM, '85 CX IE Auto, 406 Coupe, 405 srdt wagon, '78 dyane, Resting (or Rusting): '73 Birotor '82 CX Presitige, '81 CX Break IE, GS X2, GS1015 Wagon, GS 1300 5sp Wagon, '76 GS 1220 Wagon, '75 GS Wagon, '58 2CV, '58 Vauxhall Velox

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    Thanks Andrew, I will give it a go when I can tie my son down to help (VCE exams)

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