2CV brake failure.
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Thread: 2CV brake failure.

  1. #1
    1000+ Posts Bad Bertie's Avatar
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    Default 2CV brake failure.

    Driving my 2CV van today, I noticed that the brakes suddenly felt different.
    Not braking as efficiently, I turned into a quiet street and the braking felt like fading I once experienced driving a semi trailer. (Over heating). Anyway, I slowed down to about ten kms, and used the hand brake to stop. I donít remember the pedal going down at all, she just wasnít stopping.I checked for leaks, and none to be found. The NRMA towed me home. Putting it onto the tow truck, miraculously the brakes worked again! Later this evening I pressed the pedal for a while and she is not going down. This 73 model van has the disc brakes, and the LHM reservoir has not lost any fluid. Master cylinder is nice and dry, and so are all the wheel cylinders. Any suggestions would be welcome 🤷🏼*♂️

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  2. #2
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    Bertie, I believe that you answered the question when you said "felt like fading I once experienced driving a semi trailer. (Over heating)"

    The symptoms of no drop in fluid, no leaks and it worked OK when it cooled down, are all consistent with overheated brakes. I guess you would have pushed really hard on the pedal with no retardation. Can happen when you work fresh pads too hard before they have been bedded. Will also happen with old pads if you ride the brakes, left foot braking or forget you have a big load on the trailer going down hill. What were you doing differently when the symptoms occurred ?
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    I'm betting on an intermittent or partial blockage in the master cylinder or main brake line.

    Cheers

    Alec
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  4. #4
    1000+ Posts Bad Bertie's Avatar
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    Quote Originally Posted by Bustamif View Post
    Bertie, I believe that you answered the question when you said "felt like fading I once experienced driving a semi trailer. (Over heating)"

    The symptoms of no drop in fluid, no leaks and it worked OK when it cooled down, are all consistent with overheated brakes. I guess you would have pushed really hard on the pedal with no retardation. Can happen when you work fresh pads too hard before they have been bedded. Will also happen with old pads if you ride the brakes, left foot braking or forget you have a big load on the trailer going down hill. What were you doing differently when the symptoms occurred ?
    . I did drive it a bit more briskly than normal I suspect , as I was trying out the new carby I just put on. I would have used the brakes more often as I was in a hilly part of Sydney. I don’t know the history of the brake pads , but I will take them out and replace them with new ones. I know wonder how do people cope coming down mountain passes in other parts of the world? Braking on the gears , sure, but using the pedal a lot also. Scary!

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    Quote Originally Posted by Armidillo View Post
    I'm betting on an intermittent or partial blockage in the master cylinder or main brake line.

    Cheers

    Alec
    Or, or - just thought - check the vacuum line to your brake booster. If you have disk brakes, you must have a booster, right?

    Had this happen to me in a Sigma (yes don't judge me ) - brake pedal used to get really hard on a trip - always seemed fine after it cooled down. There was a leak in the vacuum line - such a simple fix, and so potentially dangerous.

    Cheers

    Alec

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    The brisk drive involving hills will do it. If you put new pads in you need to bed them properly, most mechanics don't these days. bedding properly involves first driving normally and gently to settle them into the disk, then you gt them really hot, almost to the point of fading, them let them cool completely.

    New standard pads will do exactly what the old ones did if they are not bedded. You may possibly be able to get some hard or competition pads which are good to much higher temps. Some are pre-bedded. Hard or competition pads will sometimes have little or no grip when cold, requiring considerable pedal effort until they get really hot.

    Also worth adding new fluid and bleeding the brakes, that will also indicate if you have any blockage etc.

  7. #7
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    if the pedal is solid and won't move.... the master cylinder is wedging. I'd be more than a little concerned about driving it without replacing the master cylinder "just in case". I doubt it is a blockage as doesn't it have two circuits out fo the master cylinder? I would expect one circuit to continue to work!

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    Some good advice here....best to act on it, just in case ! It is so embarrassing to rear-end someone....and expensive.

    Vacuum line to booster is a good thing to replace if it never has been.

    Wedging ? Could you please explain that phenomenon, Shane ?

    The pedal should feel the same as it used to, with a small amount of movement....otherwise don't even think of driving it...

    The only way the pedal will go down is if the master cylinder is no longer reliable. Nothing else will produce this effect.
    Apart from perhaps a ballooning flexible hose, and that will not then miraculously fix itself.

    I reckon some kind of crap has gotten into the master and temporarily stayed between the wall and seals.

    Bottom line is....take apart master and check carefully.

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    Don't miss the point that the brakes stopped working after a spirited drive and then came back when they cooled off. Based on that history and without further info, I stand by my original diagnosis.
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    Bertie, if you overused and overheated your 2CV brakes, that would probably indicate temporary fade because of vapour. But it was only a bit spirited and then braking down hills.

    When you were putting it on the tow truck, I am guessing that you did not have the engine going. So the brake booster was not operating. Start the engine later and see how the pedal level is. You may find it's down.....as the booster is now helping it go down.

    Bertie, do 2CVs have a twin circuit master cylinder with two pipes coming out ? Because if it only has a single circuit then if the master fails, you will get total brake failure suddenly, which is frightening. I had it in an early 504.

    If it is twin circuit and the brakes felt different with lower pedal then you have most likely had one circuit in the master cylinder fail (or partially, anyway).....you will have only front or rear braking now.
    Last edited by Beano; 23rd November 2018 at 06:34 PM.

  11. #11
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    I suspect that vacuum line failure is unlikely to be the problem in a 2CV.
    Maybe it is overheating. If so, do you have the cooling ducts in place?
    Apparently they are almost essential on a disc brake 2CV.

    Otherwise check the basics, are the rear drums still working efficiently - they are often ignored,
    check the disks are in good condition, consider replacing the pads and fluid.

    Let us know how you go.

    Ian S
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  12. #12
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    Bertie, your 2CV disc brake system DOESN'T have vacuum assist like normal "power assisted" disc brakes on cars, so that is not your problem.
    I suspect your problem is over heating. The inboard placement of disc brakes on any car puts the discs very close to the gearbox and engine, which is the main reason most discs are out near the wheels and away from the heat. Generally on normal cars, they have some ducting to force the airstream to blow on the discs to keep them cool.

    Surprisingly, on the 2CV there are two curved metal V shaped ducts that are mounted at the bottom of the discs. At the front of each duct, there should be a concertina rubber tube that extends to the bottom rear of the metal fan housing. As the fans spins, some air is deflected into the rubber tubes to the cooling ducts and that cool air is blown onto the disc. This keeps the discs cool.

    Check that you have both the metal ducts and the rubber tubes. The ducts do have a metal flange that is bolted onto the side of the gearbox. They are prone to rust, crack and break off. Australian motor mechanics think the ducts are shaped like boomerangs so they throw them to see if they return. They don't, so they leave them off.

    If you ever experience brake failure, just double clutch down through the gears to slow yourself down. If you are really good, you can get 1st and use the handbrake.

    John

  13. #13
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    Quote Originally Posted by Armidillo View Post
    Or, or - just thought - check the vacuum line to your brake booster. If you have disk brakes, you must have a booster, right?

    Had this happen to me in a Sigma (yes don't judge me ) - brake pedal used to get really hard on a trip - always seemed fine after it cooled down. There was a leak in the vacuum line - such a simple fix, and so potentially dangerous.

    Cheers

    Alec
    I don’t think the 2CV has a booster.

  14. #14
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    Quote Originally Posted by Ian S View Post
    I suspect that vacuum line failure is unlikely to be the problem in a 2CV.
    Maybe it is overheating. If so, do you have the cooling ducts in place?
    Apparently they are almost essential on a disc brake 2CV.

    Otherwise check the basics, are the rear drums still working efficiently - they are often ignored,
    check the disks are in good condition, consider replacing the pads and fluid.

    Let us know how you go.

    Ian S
    The 2CV has cooling ducts? I will check!

  15. #15
    1000+ Posts Bad Bertie's Avatar
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    Thank you all for your input and advice. I checked the pads this morning, and there seems to be sufficient meat on it.
    The pedal felt fine and how it should be. I took it for a similar length of time test run, but without out the hills.
    Being cautious, I did brake on the gears a lot ( we all should). All went fine. ����*♂️

  16. #16
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    Quote Originally Posted by JBN View Post
    Bertie, your 2CV disc brake system DOESN'T have vacuum assist like normal "power assisted" disc brakes on cars, so that is not your problem.
    I suspect your problem is over heating. The inboard placement of disc brakes on any car puts the discs very close to the gearbox and engine, which is the main reason most discs are out near the wheels and away from the heat. Generally on normal cars, they have some ducting to force the airstream to blow on the discs to keep them cool.

    Surprisingly, on the 2CV there are two curved metal V shaped ducts that are mounted at the bottom of the discs. At the front of each duct, there should be a concertina rubber tube that extends to the bottom rear of the metal fan housing. As the fans spins, some air is deflected into the rubber tubes to the cooling ducts and that cool air is blown onto the disc. This keeps the discs cool.

    Check that you have both the metal ducts and the rubber tubes. The ducts do have a metal flange that is bolted onto the side of the gearbox. They are prone to rust, crack and break off. Australian motor mechanics think the ducts are shaped like boomerangs so they throw them to see if they return. They don't, so they leave them off.

    If you ever experience brake failure, just double clutch down through the gears to slow yourself down. If you are really good, you can get 1st and use the handbrake.

    John
    Thanks you John. I will check if it has air ducts!

  17. #17
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    Quote Originally Posted by Bad Bertie View Post
    Thanks you John. I will check if it has air ducts!
    I am happy to report that there is nothing that looks remotely like ducts. Nothing! So, now we know the cause, over heating and causing brake fading.

  18. #18
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    Great result Bertie, we all learnt something about 2CV engineering and confirmed that brake ducts will reduce potential brake fade.
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    Bertie et alia, just want to throw a cat or two among the pigeons.

    I admit my experience with 2CVs is limited, but I can't imagine any of them have ever been fitted with a brake booster.

    Assuming the car in question uses LHM in the braking system then fade through boiling of the fluid is highly unlikely since this fluid is totally non-hygroscopic and has a boiling point (according to the relevant MSDS documents) at least as high if not higher than the DOT series of fluids. The boiling point of these latter types is severely lowered by absorption of water, hence fade happens in DOT based systems.

    Yes, the manufacturer fitted ducts to use cooling air to waft onto the discs, a nice touch. However, they omitted to make these robust enough to survive a few pad changes, hence they often fall off, or are simply discarded. I have a set of these ready to install, but haven't got around to it. (and probably won't)

    I have yet to experience ANY loss of brakes in Gaston, even over 6500km around some of the steeper roads of NZ earlier in the year, and certainly not on any of the winding roads I've explored since. And yes, I've been driving enthusiastically.

    There have been issues with replacement master cylinders. The new one I installed is (so far) fine.

    All that being said, I believe others have experienced fade in their LHM systems under adverse conditions so maybe I'm just lucky so far.

    Cheers, Pottsy.
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    Fade is not only when the fluid boils, fade can also present itself when the brakes get really hot, the pedal does not go spongy, it feels like you are pushing on a solid brick, not a brake pedal. There is no grip in the pad material so there is no retardation no matter how hard you push that pedal. It does no go spongy. When they cool down all is fine again. No blockage, no booster involved, no jammed master cylinder, just really hot pads that don't have any grip.
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    Hi
    Yes as Bustamif said also, there are two types of fade the pad(shoe) material becoming too hot and loosing friction grip and the fluid boiling and causing the fluid to loose the ability to apply pressure. Or both together of course if you really try. Only happened to me in a Holden ute driven quickly though the suburbs. The boss had the brakes relined and almost killed me. He took it back and had them redo the job with quality parts after I complained and he tested them for the same result !! Scarey !!!
    Jaahn
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  22. #22
    1000+ Posts Bad Bertie's Avatar
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    Thank you all again for your suggestions and advice. I have also put my feelers out on a Dutch forum , and was told that in the Netherlands at least, cooling ducts are often removed as they are not needed, and presumably in the way, when working on them.
    Last edited by Bad Bertie; 1st December 2018 at 09:17 PM.

  23. #23
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    Sorry but 2CV's donot have a brake booster on their disc brakes. Bertie I am pretty sure you just had brake fade. I have experienced this myself. Most 2CV's have lost their cooling ducts and it is probably a good idea to refit them for a van which is heavier than a sedan. Also using you gears to downshift when going down hills is a wise precaution in any 2CV.
    We lost our brakes once on the Mountain Raid in the Snowy Mountains and it is scarey. Hawk ( Ted Cross )

  24. #24
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    Quote Originally Posted by Bad Bertie View Post
    Thank you all again for your suggestions and advice. I have also put my feelers out on a Dutch forum , and was told that in the Netherlands at least, cooling ducts are often removed as they are not needed, and presumably in the way, when working on them.
    Not too hilly in Holland, I'd observe. But I do struggle with the concept of brake fade in a 2CV, especially with disc brakes instead of drums. But people say it happens, so...Ö.. Are the pistons really freely moving in the callipers?
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  25. #25
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    It happens, even when the pistons are moving as free as can be.
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