XM anti-sink not working
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  1. #1
    Member ajm212's Avatar
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    Default XM anti-sink not working

    A few weeks ago, I had the rear spheres replaced on the car formerly known as XM 2000: suspension much better but the anti-sink is now failing intermittently. It's pretty all-or-none: when it stays up, it does so for days and days, but when it decides to sink it does so quickly, certainly within an hour, perhaps quicker and it goes right down on its stops.

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    I took it back a week or so ago and the system was bled for air which seemed to fix it but today after not having been driven for a week, the problem is just the same.

    The rear has had other work done over the years - new anti-sink sphere, one replacement suspension cylinder and, possibly some work (a clean-out?) of the anti-sink valve.

    Not really looking forward to multiple trips back to try and track down intermittent problem. Any ideas of what to look for myself?

    Andrew

  2. #2
    1000+ Posts George 1/8th's Avatar
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    Hi Andrew,
    I'd be thinking you have possibly fitted a faulty anti - sink sphere, just because a new one was fitted, that's no guarantee that there is still no fault. It's easily removed and pressure tested. I'd also be removing the rear height corrector and dismantling and cleaning it, and re- fitting it. I will have to do mine soon. I hope this helps.

  3. #3
    Real cars have hydraulics DoubleChevron's Avatar
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    I'm not sure where the anti-sink valve is. Apparently it's a simple differential valve. Changing spheres etc... should have no impact on it's operation. The sphere everyone refers to as "anti-sink" is a rear brake accumulator for the models with the 6&2 hydraulic pump. That's my understanding anyway. Much like the local CX2400's where everyone refered to the extra sphere on the aussie models as a "power steering accumulator". It's not, it's an addition brake accumulator.

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/citro%EBn-forum/90325-best-project-car-you-have-ever-seen.html
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  4. #4
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Wot happens with anti sink if the brake valve is faulty? My CX sinks at the rear within half an hour because of this.

  5. #5
    Member Chimbu's Avatar
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    XM anti-sink not working-private-cars-book-2-2001.jpg

    Introduced for the XM for retaining a constant ride height in 1995 for Series 2 XU10J4R and DK5ATE models only. Progressively to all XM's from this date.

    "SC/MAC is a system (direct quote here) which limits the settling of the vehicle at rest, with the engine switched off. The system reduces the rising time of the vehicle.
    Two valves, one at the front and one at the back, isolate hydraulically the suspension units...
    There exist two valve types."

    As with all things Citroen it would be a brave person to say exactly which models are fitted with what.

    My 1995 Series 2 for example has 7 spheres:-
    Four suspension; one main; one front hydractive; one rear hydractive.
    No antistink.

  6. #6
    Contented Peugeot Driver addo's Avatar
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    The antisink wears out IMO. It probably wears faster if the car is run protractedly with inadequate pressure in the regulator and rear spheres to maintain equilibrium.

    First step is to make sure all spheres test at correct pressure; rectify if needed. Newness or allegedly recent refilling are no guarantee; as one person noted a seller can represent something as "new" for quite some while after the fact - it's in their mind. If this step makes no difference then the antisink needs replacing with new. An Hydractive antisink is likely to be the same as for Hydractive Xantia.

    P/N 5293.02 front and rear for Hydractive cars, just over $250 each here or €210 the pair posted from France.

  7. #7
    1000+ Posts Greg C's Avatar
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    It would be very unlikely the anti sink valve is worn, they don't do much. Their main job is to isolate the brake valve from the suspension system and as we all know the brake valve gets the most work because the driver is always stomping on it so it wears more than any other on the system. Get the sphere pressures checked
    Mine

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    In the family

    Xantia SX

  8. #8
    Contented Peugeot Driver addo's Avatar
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    I reckon they do wear. They shuttle back and forth a small amount and they are also supposed to be a fluid-tight seal.

    Doseurs wear, and my experience with the later type (Xantia) is resealing them does bugger-all to stop internal fluid leakback.

  9. #9
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by Chimbu View Post
    Click image for larger version. 

Name:	PRIVATE CARS BOOK 2 - 2001.jpg 
Views:	683 
Size:	62.6 KB 
ID:	36955

    Introduced for the XM for retaining a constant ride height in 1995 for Series 2 XU10J4R and DK5ATE models only. Progressively to all XM's from this date.

    "SC/MAC is a system (direct quote here) which limits the settling of the vehicle at rest, with the engine switched off. The system reduces the rising time of the vehicle.
    Two valves, one at the front and one at the back, isolate hydraulically the suspension units...
    There exist two valve types."

    As with all things Citroen it would be a brave person to say exactly which models are fitted with what.

    My 1995 Series 2 for example has 7 spheres:-
    Four suspension; one main; one front hydractive; one rear hydractive.
    No antistink.
    It's easy to tell. If you have a "6&2" pump, you will have anti-sink. The only reason they did this was with two piddly little pistons dedicated to the proper high pressure hydraulics it takes a bloody eternity for them to raise from "flat". The other 6 put aside for the shit low pressure poogoe steering rack (through a simple blow off valve like normal power assisted steering). PSA constantly goes backwards. several decades of amazing fully hydraulic fully powered steering, to the crappy low pressure "assisted" as opposed to "powered" racks for the modern stuff.

    Imagine if the XM had a daravi rack with one 1.5turns lock to lock. It would absolutely transform it

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  10. #10
    Member ajm212's Avatar
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    Hi George,

    The anti-sink sphere was replaced a while ago. It was the two regular spheres that were changed recently. The key things are that the anti-sink was working perfectly before the two new spheres and that sinking is intermittent and quick. I started it briefly around lunchtime and let it rise - 3 hours later it's still up.

    Is the intermittentment and speed of sinking consistent with a malfunctioning/dirty height corrector?

    Andrew

  11. #11
    Contented Peugeot Driver addo's Avatar
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    Unlikely.

    An out-of-adjustment regulator can also cause problems as it may not hold enough residual pressure at rest, to correct a slight leakback.

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