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Thread: Self-levelling Air Suspension System

  1. #1
    Senior Member Ice Cube's Avatar
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    Self-levelling Air Suspension System

    The car has been sitting on the drive for several days now, and I'm puzzled by how much the car is tilting down at the rear offside. I know that the drive is not even, but these cars are supposed to wake up every 24 hours and level themselves. But what does 'levelling' mean - do they have a weight inside a component somewhere that tells the car what its angular lateral and longitudinal attitude is? I've measured from ground up to wheel arch top on all 4 corners, and the front arches are the same at 68 cm, despite it sitting on a lateral slope.

    Does the car think it is doing its stuff by equalising the suspension across the front, even though it results in a lateral tilt, and having equalised the front, does it just give up on the rear arch heights, which are 6 cm different?
    2008 XJR + sun roof + soft leather + ACC + retrofit: burr walnut interior trim
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    2007 X-Type 3.0 SP Auto + retrofit: walnut dash & gear knob + rear sill protectors + mudflaps + Al powerwash crucifers + memory powerfolds

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    Senior Member redfox666's Avatar
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    The car can only go down when it's off, I don't think the rear should be sagging though. Park it somewhere level for a while to check if you can.
    Previous: 2006 X-Type 2.2d S- EBC Turbo Groove & Red Stuff
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    Senior Member FastEddie's Avatar
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    My car has sat for over a week for the first time ever , due to poorly turbo.

    I unlocked the car today for the first time , the rear suspension was low and didn't move.

    I sat in the boot catch area as I do to play with the suspension , up she went without power.

    As I got off , moments later she dumped a bit of air and lowered a little bit.

    I have to say it wasn't really low to start with , just lower than with daily use that I noticed.

    The rear articulation is pretty good to be fair , no exact science to the behaviours though.

    If I put one rear wheel up a kerb , this tucks in the arch and the other side goes monster truck.

    Same again on the other side too and soon sorts itself again on the flat ........
    2009 X358 XJ LWB 2.7 Tdvi , Liquid Silver , 100k+ and going strong.
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    Waking up to level itself, does not include running the air compressor - so in effect the car tries to level to the lowest wheel

  5. #5
    Senior Member Ice Cube's Avatar
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    . . . It hasn't levelled down after a whole week, so something seems wrong with either a wheel height sensor or whatever senses the overall level of the car. I'll give it a run on saturday.
    2008 XJR + sun roof + soft leather + ACC + retrofit: burr walnut interior trim
    ++++++++++++++++++++++++++++++++++++++++++++++++++
    2007 X-Type 3.0 SP Auto + retrofit: walnut dash & gear knob + rear sill protectors + mudflaps + Al powerwash crucifers + memory powerfolds

    "Life's too short for touchscreens - give me lots of nice buttons to press"

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    I thought that later models only have one front sensor, so they can't tell if the fronts are different heights.
    If true it doesn't seem like a logical design change to me.

  7. #7
    Senior Member Jimbov8's Avatar
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    Have you plugged in a reader to see if the car is saying something is wrong? It may give you a clue as to where to start tracking the fault down.
    Last edited by Jimbov8; 09-08-18 at 19:44.
    Jim.
    2009 XK 5.0L PortfolioPast:-87'XJS 3.6L, 93'XJ40 3.2L gold, 95'XJ6 4.0L sport, 00'XJ8 3.2L sport, 2005 XK8 4.2L coupe in that order and enjoyed all of 'em.

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    Quote Originally Posted by dieselnutjob View Post
    I thought that later models only have one front sensor, so they can't tell if the fronts are different heights.
    If true it doesn't seem like a logical design change to me.
    The front end doesn't suffer loading changes, which is the main driver for self-levelling suspension - maintaining a level ride height irrespective of the number of passengers, luggage and fuel

  9. #9
    Senior Member Ice Cube's Avatar
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    @Jimbov8: I don't have access to a code reader.

    I had a read of the Technical Specification last night. In answer to one of my original questions, the system does not appear to incorporate a 'true level' sensor, so the car doesn't know if it's on sloping ground, and cannot compensate for it. The front axle is levelled as a unit, which is presumably why my front wheel arches are equidistant from the ground. The rear axle is load compemsating, and must also compensate for unlevel ground, so that the chassis isn't in a state of torsion. So as I read it, my visible rear axle tilt is simply the car levelling relative to the front axle on an uneven surface. That in a nutshell is what the self-levelling suspension does - forget any notions of it trying to keep the passengers upright, it follows the road camber.
    2008 XJR + sun roof + soft leather + ACC + retrofit: burr walnut interior trim
    ++++++++++++++++++++++++++++++++++++++++++++++++++
    2007 X-Type 3.0 SP Auto + retrofit: walnut dash & gear knob + rear sill protectors + mudflaps + Al powerwash crucifers + memory powerfolds

    "Life's too short for touchscreens - give me lots of nice buttons to press"

  10. #10
    Member scrubber's Avatar
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    Quote Originally Posted by Ice Cube View Post
    @Jimbov8: I don't have access to a code reader.

    I had a read of the Technical Specification last night. In answer to one of my original questions, the system does not appear to incorporate a 'true level' sensor, so the car doesn't know if it's on sloping ground, and cannot compensate for it. The front axle is levelled as a unit, which is presumably why my front wheel arches are equidistant from the ground. The rear axle is load compemsating, and must also compensate for unlevel ground, so that the chassis isn't in a state of torsion. So as I read it, my visible rear axle tilt is simply the car levelling relative to the front axle on an uneven surface. That in a nutshell is what the self-levelling suspension does - forget any notions of it trying to keep the passengers upright, it follows the road camber.
    Agreed, the car does not try and level itself, it merely serves to maintain a particular ride height regardless of load, if I park mine half on half of the kerb it stays at an angle as one would expect, I believe once on the move it only performs a level check occasionally otherwise it would constantly try and compensate for road imperfections I also believe the car lowers itself at speed, but how fast and how much I have no idea.
    2003 X350 3.5SE

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