Citroen hydraulics - Khamsin, Bora, early Merak, late Indy

Discussion in 'Maserati' started by thecarnut, Jan 11, 2009.

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  1. staatsof

    staatsof Five Time F1 World Champ
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    Mar 13, 2005
    52,509
    Hiddin' in da garden
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    Boo
    OK, well I heard all the giggles ... speaks volumes about the general perception and extreme ignorance. Especially when he talks about a mechanic having it for 2 years not fixing then it sits in you garage for years and a shark, er ah I'm sorry a GUY like Wayne comes along buys and fixes it in about a day. Yah sure Wayne ... :rolleyes: I've met Wayne a few times at small gatherings and he's nice guy in those surroundings. He genuinely knows quite a bit about a lot of cars just not this one. I think he was falling in love with his own voice and felt like he had to perform as expert for the audience so he improvised. Others on the panel made lots of snarky remarks and the audience laughed. You'd never get away with this for a Ferrari. I wish one of us had been there. It's might have been satisfying for the sake of the car to rip him a new one, in a polite and informative way, for being so ignorant. Someone should have prepped him with the right script.

    It does make one wonder about so much of the wisdom being imparted by automotive experts does it not?

    But I think you need to contact Haggarty about this and just have them delete the Bora segment. There's no fixing it IMHO. It belongs on the bloopers reel of automotive collecting, Wayne and the segment, not the car! :)
     
  2. thecarnut

    thecarnut Formula 3
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    Apr 22, 2006
    2,131
    Atlanta
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    The Car Nut
    I recently repaired two of the Bosch hydraulic cylinders and one switch on a Khamsin. These are used for headlight lift, seat height adjustment and pedal adjustment (on the Bora). Although the leaks were not severe they really bugged me since LHM is very slippery on a concrete floor.

    I decided to write a DYI article as it might help others, and help myself when I try to do this years from now and won't remember :)

    It is posted here on my website: http://thecarnut.com/Manuals/Hydraulic_cylinder_port_seal_replacement.pdf

    Ivan
     
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  3. highwaybora

    highwaybora Karting

    Jun 18, 2013
    112
    SoCal
    Bravo!

    Good call...

    Thanks for objective description, photos, et al
     
  4. Froggie

    Froggie Rookie

    Sep 27, 2017
    47
    Belgium
    I have a question regarding fading resistance of hydraulic brakes using LHM.
    Such a system has the reputation of providing greatly improved braking power also during strong/repeated braking.
    I am not sure of the rationale of such a good fading resistance even when the rotors/pads are submitted to very high temperatures, if it is due to the very high pressure of the hydraulic fluid in the circuit avoiding its boiling, or because it would counteract pads outgassing pressure.
    Does anyone know what happens in case of extreme use bringing the rotors to red, such as e.g. during repeated strong brakings on a long and stiff downhill or during track use?
     
  5. staatsof

    staatsof Five Time F1 World Champ
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    Mar 13, 2005
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    OK well I can help with this one a bit as I've race open road in a Bora though not a lot of braking with that but also I've done the tri oval at Pocono in mine and have seen one other guy drive his harder than I did there.

    He destroyed a set of junky aftermarket pads, they're Pantera pads and we drove to my house that evening and picked up my backup set of OEM pads which he used the next day and it was fine.
    I never had brake fade, pad issues or rotor problems on that track with my Bora.

    Can't speak to the outgassing issue but yes I suppose the higher pressure might inhibit boiling. But I also think you need to look into the characteristics of original LHM more and see what it's boiling point is. I do know that it's far less hygroscopic than brake fluid
    and have often wondered why all of braking systems done use this? That alone will raise it's boiling point in practical usage situations. When I disassembled my braking system after being in a museum for it's 1st 10 year of life I found zero evidence of moisture or corrosion. It's even better than silicone brake fluid.

    The Group 4 Thepenier Boras originally had the LHM brakes on them and one has since been converted to a standard braking system.

    At speed on the track the braking feel under such loads is much better than it is on normal streets at ration speeds! :)

    My opinion on the system is that you need to bleed it more often which I beleive is due to nitrogen microscopy over time leaking into the system through the accumulators bladders. If you don't the brakes get a bit grabby and can pull right or left until the nitrogen is fully compressed. That's an opinion based upon experience I have not scientifically proven it.

    Bob S.
     
  6. Froggie

    Froggie Rookie

    Sep 27, 2017
    47
    Belgium
    Thank you Bob, very helpful comments.

    In the meantime I have found extensive info on the use of LHM and its physical/chemical properties.
    Unfortunately, most of that info is in French, because of the Citroen origin and main users.
    I attach however two interesting links with tables (you may go deeper by using the usual translators).
    http://www.hd19.net/technique/hydraulique/etude_liquides_hydrauliques.html
    http://arnaud.meunier.chez-alice.fr/fr/theo/2cv/tr-roul/frein.htm

    Basically the LHM does have a slightly higher boiling point (265°C instead of 260 °C for DOT 4 or 5) but such properties remain very stable because of the inherent chemical stability and low affinity of LHM to water, contrarily to DOT 5 and DOT 4 respectively.

    Add to that the high pressure in the hydraulic circuit and you get indeed a master combination for braking.
    Also worth noting is the fact that the LHM use was abandoned because of an European regulation on the years 2000's obliging to separate the fluid circuit for braking, which would have obliged Peugeot/Citroen to make additional R&D to optimise the previous hydraulic systems used for braking/suspension/steering.
    Pity...
    So let's preserve our LHM braking, it's a worthwile historical piece of well designed technology!
     
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  8. highwaybora

    highwaybora Karting

    Jun 18, 2013
    112
    SoCal
    Hi, Ivan..

    Always interested in your observations, appreciative of your knowledge and website... Thanks!

    The LHM /Bosch component related resources of long back are not really now current--
    wondering if you can re-publish any/all updated inf0' ??

    Or, is there some part of your website that is LHM-specialized (or could be?)

    All the best,
    Ned Evans
    Bora '626



     

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