Uprading DS suspension
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Thread: Uprading DS suspension

  1. #1
    GGR
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    Default Uprading DS suspension

    Hi All,

    I'm looking at options to upgrade the suspension of my '67 DS to improve handling.

    Fitting smaller spheres would correspond to fitting stiffer springs on a conventional suspension I guess. Changing leaf valves would also correspond to stiffer shock absorbers. What is the experience of forum members in this regard? Spheres and leaf valves from what cars?

    Are there bigger diameter sway bars I can fit on my '67 21? Are station wagon sway bars bigger? What about the SM ones? can they be fitted on a DS?

    Finally, I guess I can drop the car by one inch or two by adjusting the height. Any negative side effect to be expected from this?

    Thanks!

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    UFO
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    Leave it alone. Tinkering with the original design always leads to failure. Driven properly a DS will handle just as well as any modern car with the same available power.

    Deliberately running the car at a lower height serves no purpose, will make it uncomfortable and also lead to premature wear of components such as bump stops and in severe cases it could lead to damage to the front brake discs or engine sump as the car bottoms out in a dip.

    Also, don't be tempted to try to "upgrade" the cooling system. That also ends in frustration and tears.
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    Craig K
    2009 C5 HDi Exclusive

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    Hello, as UFO said, leave it alone.

    Have you driven the car fast around all types of bends? I often drive like a hooligan, I leave following cars for dead. The car always feel sure-footed and planted to the road, even if my wife ends up on my side of the car.

    If you change one thing, reckon on having to change seven other things. And then seven more. Until you put it back to standard.
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    GGR
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    Thank you for your insight.

    I've been driving DS since I'm 18, long years as my sole daily driver, and I'm over 50 now.

    I may give a bit more details on my project. I will be reproducing a CX turbo2 engine mixing DS and CX parts. The transmission will also be longer legged by combining the "long" ID transmission with a C35 diff. The objective is a long distance comfortable travel car, not a racing car. A car that would be equal to a Jaguar XJ6 or a Mercedes W109 3.5.

    Experience with previous such kind projects tought me that homegenity among systems is more important than all out performance in each one of them. A more powerful engine usually requires upgrading transmission and diff ratios, suspension, brakes etc.

    The DS has good brakes and suspension, and I may leave them alone, at least at the beginning, to see how they cope with the added power. But I am still trying to gather some knowledge from other's experience, just to see what my options are.

    Any information and experience on various spheres, leaf valves, sway bars etc. is welcome.

    In the end I may leave it stock. But I'm still interested in hearing from other's experimentations.

    Here is another project I did:

    https://www.sl113.org/forums/index.php?topic=15521.0

    English is not my mother tongue, so please bear with me.

    Thanks.

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    About 20 years ago there was a chap in the U.K. who took his DS on the Inca Trail rally through South America and he fitted a thicker roll bar to the rear. From memory it was a square section bar. Stiffening the rear to reduce roll is a good idea if belting around corners, even more important than the front I think, but it won’t help ride comfort. The car itself is still around, it had a BX steering rack, repositioned BVH brain, flat radiator and was replumbed with flexible hydraulic hoses to the gearbox Rally Prepared Citroen DS 23 PALLAS For Sale Hampshire, United Kingdom | AutoMotoClassicSale.com . Changing the rear roll bar looks like a very simple option, if you can size it by working out the torsional stiffness that you want relative to the standard one.

    Another option worth considering is fitting an XM hydractive valve, front and rear, to stop the crosswise flow of LHM when the car starts to roll. I did that many years ago on the front of my Safari and it made a huge difference limiting the roll angle - there’s a description about halfway through this thread here Special DS23 Safari for sale . It doesn’t impact ride comfort.

    Many people run with CX spheres - GTi Turbo ones on the front will help limit roll because they have a smaller centre hole than standard CX ones, but it won’t help comfort.
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

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    GGR
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    Thanks Marc.

    That's very interesting input. I may fit the CX GTI Turbo spheres first, as it looks the simplest and is easily reversible.

    I really like the hydractive valve idea, well in the spirit of the DS. In the other thread, you seem to say that the system could do without the 5th sphere. Could you elaborate on that? What is the use for that 5th sphere then?

    You also mention the SM has less roll than the DS. Why is that? Do they have thicker sway bars? Would they fit in the DS?

    A bigger sway bar in the back would introduce a bias towards oversteering. Nice on a track or in a rally race, not so much for normal road use.

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    Inside the hydractive valve is a simple ball valve which blocks fluid transfer left/right and right/left during roll, thatís what gives the anti roll benefit. However, the hole where the XM centre (accumulator) sphere screws in needs to be plugged to prevent fluid leakage, the simplest option being to fit a sphere or make a plug screw. Some people have done the latter, because the sphere takes up a lot of space especially if youíre looking to fit one at the rear.

    Now thereís no electrics involved or sensors/computer like on the XM to bring the centre sphere in and out of the hydraulic circuit, which makes things simple. To me thatís what makes it attractive. Alternatively you could try to copy the XM and energise the electrovalve when the car is travelling straight (soft mode) and switch it off when cornering (hard mode), in which case XM spheres could be fitted on the front suspension cylinders. These have very small centre holes so the suspension is a lot firmer when cornering, while in a straight line the XM soft mode is very comfortable because all three spheres are in circuit. Iím not sure if someone has tried that yet on a DS - it would need some form of steering wheel movement sensor like on the XM and something to give the electrovalve the right voltage (itís some PWM signal not 12V).

    The SM front arms are leading so to speak, not lagging like on the DS. My understanding is Citroen figured out some time after the DS was launched that the SM layout had less dive and roll characteristic, so adopted it on the SM. Someone knowledgeable about suspension geometries would be able to explain why the SM layout is better.
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

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    GGR
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    That's brillant. I had started looking into it when you first mentioned it to me in our email exchanges, but I got scared by all the complication of the XM system. I hadn't realised one could bypass most of it to end up with such a simple set up. Do you think such hydractive valve could also be fitted between the front and rear suspension to counter brake diving? How would it interact with the height correctors?

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    UFO
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    Then I suggest you contact Harry Martens Limmen in Holland. What he would know about making a DS faster and handle better and the ability of components to handle it - is priceless. Harry is on here occasionally so he may see your post.
    Craig K
    2009 C5 HDi Exclusive

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    GGR
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    I found this:

    http://www.citroen-ds-id.com/xm/Hydractive2.pdf

    The hydractive hardware wouldn't seem to be that difficult to fit on a DS. I would do without the ECU and sensors, which I would replace by a switch powering the electrovalve. So one would have a choice between "comfort" mode, and "sports" mode at a flick of a switch.

    Powering the valve would put the car in "comfort" mode. As put in the document I put the link for above, "the valve resistance is 4 ohms andthe nominal voltage, for continuous duty is 2.6V. However, due to the inductance of the winding, the ECUuses pulse width modulation to achieve a constant current through the winding". I'm no electronician. Would that be difficult to achieve, and what would it take?

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    The Hydractive system only works really well if there is a center sphere. On a car with conventional springs, the springs support the weight of the car, but they also contribute to the roll stiffness of the car. Not so with hydropneumatic suspension, because the common line between the two front spheres and the two rear spheres means the spheres support the weight of the car, but contribute zero to roll stiffness since the fluid can slosh (under pressure of course) from side to side. The hydractive system isolates left from right so the spheres now contribute to roll stiffness, but the roll stiffness contribution is only as substantial as the spring rate of the spheres, which in a Citroen DS is very, very low for the sake of comfort. To get any kind of significant roll stiffness contribution from the spheres, the spheres themselves have to be substantially undercharged (or under sized) so that the volume of gas in the sphere is relatively small. As anyone who has driven on undercharged spheres knows, this will give the car a very harsh ride. Hence, you need a third, relatively large sphere in communication with both suspension spheres to restore the soft ride. Without it, you will either have a reasonable ride with very little improvement in roll stiffness or a harsh ride with improved roll stiffness...
    Cheers,
    John T.

    54 TAV Legere; 61DS19 LHM BVH (son's); 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  12. #12
    GGR
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    Yes, fitting the hydractive system on the DS would also require fitting all the XM spheres, including the middle ones.

    BTW: Does the XM have a sway bar, or is all the antiroll work done by the hydractive system?

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    Hi GGR
    You are interested in playing so information to "chew on" is what you want. My two cents worth !
    I believe all the Citroen spheres are the same volume, but not sure if the saucer spheres, late models, are somewhat smaller ?? But with any spheres if they are charged with gas to a lower initial pressure they are stiffer because there is less gas to compress. The same thing happens as they loose their gas over time(or failure). However they can be recharged with special equipment or even by fitting special charging valves and having a nitrogen cylinder. So you could charge them to what ever pressure you like and try different pressures if you want.
    It is incorrect to say there is just harsh or soft options as far as the pressure goes. There is a complete range to be tried IMHO. Usually people do not notice the pressure has been lost till all the gas is gone and the 'spring' left is just the rubber diaphram being compressed and the ride is HARSH
    The idea of the totally mechanical ball valve to control the displacement of the oil on roll seem ideal to me. Why have an electronic fancy valve if you can avoid it. If you put a constant voltage on a valve which normally needs PWM signals it risks burning it out IMHO.
    There is no displacement of fluid between the front and the rear under brakes. The D has no anti dive in the front suspension but does have anti lift at the rear. The SM possibly has anti dive built into the front geometry. That is hard to change.
    Good luck Jaahn
    Last edited by jaahn; 22nd October 2018 at 08:01 AM.
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  14. #14
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    There are small DC motor speed controllers that take 12V input and put out a lower PWM voltage, which could power the electro valve. I think the electro valve needs a brief kick at 12V to get it to move, then reduced to 2.6V to stop it burning out, which would need a bit more electronics. Then what youíll need is some sort of sensor to switch it off immediately when turning the steering wheel more than a few degrees away from straight ahead.

    If that works then you could try running with XM hydractive spheres for each wheel and the big 500cc accumulator on the central HA valves - if memory serves me right, I think itís 70bar for the front centre sphere and 50bar for the rear on the XM. Each corner sphere will then access 50% of the capacity of the centre sphere when the electro valve is energised, which provides the comfort, and only run on the corner spheres alone when the car is subject to roll.

    The principles behind the XM hydractive system are well proven with several sensors and maps controlling when the centre spheres get cut out of circuit, but a simplified version would be interesting for the DS. Someone on AF with some electronics ability might be able to advise.....Iíll just stick with the HA valve and no electronics myself



    Quote Originally Posted by GGR View Post
    I found this:

    http://www.citroen-ds-id.com/xm/Hydractive2.pdf

    The hydractive hardware wouldn't seem to be that difficult to fit on a DS. I would do without the ECU and sensors, which I would replace by a switch powering the electrovalve. So one would have a choice between "comfort" mode, and "sports" mode at a flick of a switch.

    Powering the valve would put the car in "comfort" mode. As put in the document I put the link for above, "the valve resistance is 4 ohms andthe nominal voltage, for continuous duty is 2.6V. However, due to the inductance of the winding, the ECUuses pulse width modulation to achieve a constant current through the winding". I'm no electronician. Would that be difficult to achieve, and what would it take?
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

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