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Thread: Dee Diaphrams

  1. #1
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    Default Dee Diaphrams

    Just driving the D Spec home today,I got a ruptured diaphram on one of my front sheres,the LHM resy sounded as though it was boiling,but no harm done(other than the sphere)I notice that, there are 2 types of diaphram available,the original type black ones and some translucent white ones,any observations are welcome.
    Woody

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    Fellow Frogger! CorneSoutAfrica's Avatar
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    Brian

    Get the translucent ones, they are much better and last longer, the lhm seems not to attack the rubber as much as the black ones

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    Corne
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    Quote Originally Posted by CorneSoutAfrica View Post
    Brian

    Get the translucent ones, they are much better and last longer, the lhm seems not to attack the rubber as much as the black ones

    Cheers
    Corne
    Hi Corne and Brian,

    The black LHM compatible diaphragms, if made correctly, are molded from a Nitrile rubber compound. The translucent diaphragms are molded from a thermoplastic, Desmopan, made by Bayer Chemical. Neither compound is attacked by LHM or any other mineral oil based fluid. The principal differences are mechanical strength and gas permeability. The advantage of good rubber diaphragms is that they 'leak' gas pressure at a much slower rate than thermoplastic ones. OTOH the Desmopan molded ones are stronger mechanically. Either will work fine - the real trick is getting quality ones. The Desmopan diaphragms are made, I believe, by IFHS and are of excellent quality. The rubber ones, frankly, seem to be a hit and miss affair - not sure who is making them and if they are coming from one source or several.

    Steve

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    UFO
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    Richo has been using Desmopan diaphrams with great results, as have many others.
    Craig K
    2009 C5 HDi Exclusive

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    Quote Originally Posted by UFO View Post
    Richo has been using Desmopan diaphrams with great results, as have many others.
    Hi Craig,

    I have been using them since they became available. All of the welded ones, AFAIK, also use a type of Desmopan - of which Bayer makes a boat load of versions. OTOH I have a set of replaceable shock body units on my 72 with rubber diaphragms that have been there for coming onto 80,000 miles and have not had to 'top' them up since installed 7 years ago. However when I do up spheres for customers and they are LHM cars, I use the Desmopan also. I just warn people that they need to look after the pressure in the units every 24 to 36 months. So long as they are kept at the proper pressures, they will last a long time. The same holds true for good quality rubber ones, though those are getting a lot harder to source these days.

    The real problem we all have, and have been in contact with Andre, Richo and others, is sourcing decent LHS compatible diaphragms. Those have detoured to that part of the Periodical Table where the material known as "Unobtainium" is listed .

    Steve

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    Contented Peugeot Driver addo's Avatar
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    I'd been under the impression those Desmopan diaphragms were reasonably tolerant of LHS. You probably saved me a misadventure by saying they aren't.

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    Quote Originally Posted by addo View Post
    I'd been under the impression those Desmopan diaphragms were reasonably tolerant of LHS. You probably saved me a misadventure by saying they aren't.
    Andre and I had a long discussion about this in Saratoga Springs, NY over June 15th weekend at the Rendezvous held there. He has been experimenting with them - IIRC he has them in one car. The problem with urethane based plastics and glycol based fluids is that material attack can be quite temperature dependent. IOW at moderate temperatures - say in the 20 to 30 C range - it may appear to have OK resistance. Move the temps up to the to 60 to 80 C range (as found under hood in LA or Sydney during the summer season) and the materials can quickly be compromised.

    Attached is data from Bayer Chemical with testing they did on Desmopan 453 and Texin resins. Note the loss of tensile strength, tear strength and softening in Brake Fluid compared to the results for oils (which LHM would fall under).

    Steve

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    Contented Peugeot Driver addo's Avatar
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    Thanks for that.

    Writing's on the wall, it seems. Bummer; I had wanted to keep the car in question on LHS, although this was at least in part simply cussedness.

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    I'm a desmopan fan for LHM. 2 year guarantee from me rebuilding a sphere with Desmopan diaphragm.
    No guarantee from any supplier.

    Rubber diaphragms available for those who would prefer them, but my 2 year guarantee is not applicable.

    I do have some reservation as to whether the diaphragms are Desmopan 453 or another Desmopan formulation. I have seen and used a couple of different types, identified by their colour.
    No source of the diaphragms is knowing their formulation or have had the type disclosed, despite requests.

    Re LHS: "Houston we have a problem".

    Nobody, currently, is making anything I would guarantee.

    This is something which I have discussed personally with a number of peers, including Steve Hammond, Andre Pohl and others in both Europe and the UK.

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    I now feel most enlightened,can someone tellme the best scource of the Desmo diaphrams.
    Woody

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    Quote Originally Posted by richo View Post
    I'm a desmopan fan for LHM. 2 year guarantee from me rebuilding a sphere with Desmopan diaphragm.
    No guarantee from any supplier.

    Rubber diaphragms available for those who would prefer them, but my 2 year guarantee is not applicable.

    I do have some reservation as to whether the diaphragms are Desmopan 453 or another Desmopan formulation. I have seen and used a couple of different types, identified by their colour.
    No source of the diaphragms is knowing their formulation or have had the type disclosed, despite requests.

    Re LHS: "Houston we have a problem".

    Nobody, currently, is making anything I would guarantee.

    This is something which I have discussed personally with a number of peers, including Steve Hammond, Andre Pohl and others in both Europe and the UK.

    Richo,

    Some years ago - maybe 7 or 8 on the Bayer site - they had a reference to 481 being used for automotive suspension diaphragms. Some time later I went back and that reference was gone. With the original webpage they also stated that the resin could be had in a number of different colors as well as translucent.

    Steve

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    Quote Originally Posted by brian woodcock View Post
    I now feel most enlightened,can someone tellme the best scource of the Desmo diaphrams.
    Woody

    Woody,

    Personally I get mine via Citroworld (Geert Bukkems) - but Andre Pohl, Chris Brownhill and others also carry them.

    Steve

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    I just love AussieFrogs. It encompasses the whole gamut from French letters to D Diaphragms.

    No wonder current Citroens bare no resemblance to the old classic Citroens. We've stopped breeding them. Too much contraception.

    John

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    Default Sticky rubber.

    I had to replace some diaphrams recently (Ian Steele at Maleny) When we got the rear spheres apart there were some patches where the rubber had stuck to the steel, and torn when the oil was pumped in (car had sat for several years) It had, in the past, had Dexron in the hydraulic system, but it isn't known if this was the reason the rubber diaphrams stuck to the steel.

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    Unless you knew how long the spheres had been on the car, whether they were charged and at what pressure, how long the Dexron had been in the system, age of the fluids, oxygenation, if the two liquids LHM and Dexron had been mixed together along with the origin of the diaphragms, there could be no subjective, definitive or educated answer.

    Too many variables and unknown conditions.

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    Quote Originally Posted by Bruce Llewellyn View Post
    I had to replace some diaphrams recently (Ian Steele at Maleny) When we got the rear spheres apart there were some patches where the rubber had stuck to the steel, and torn when the oil was pumped in (car had sat for several years) It had, in the past, had Dexron in the hydraulic system, but it isn't known if this was the reason the rubber diaphrams stuck to the steel.
    If the diaphragms were LHM ones of good quality - the Dexron would not have caused the rubber to stick to the steel. Have seen this in the past with both LHM and Dexron cars where the spheres were devoid of gas and cars sitting for along period of time.

    Steve

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    Default Sticky rubber.

    Quote Originally Posted by Citroenfan View Post
    If the diaphragms were LHM ones of good quality - the Dexron would not have caused the rubber to stick to the steel. Have seen this in the past with both LHM and Dexron cars where the spheres were devoid of gas and cars sitting for along period of time.

    Steve
    That means my spheres died of sheer cussedness!

  18. #18
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    Default Perversity.

    Quote Originally Posted by richo View Post
    Unless you knew how long the spheres had been on the car, whether they were charged and at what pressure, how long the Dexron had been in the system, age of the fluids, oxygenation, if the two liquids LHM and Dexron had been mixed together along with the origin of the diaphragms, there could be no subjective, definitive or educated answer.

    Too many variables and unknown conditions.
    The car sat with dextron in it for 12 years. Spheres were re-gassed. Car was run as a daily for several years with LHM and then sat again. Diphrams tore on the next pump up. There is an age factor, as with most elastomers here too.

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