4cv brakes
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Thread: 4cv brakes

  1. #1
    Tadpole
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    Default 4cv brakes

    Gidday all
    I seem to be having continuing problems with the brakes. Didn't have much before but now have less. Fitted reconditioned wheel cylinders & relined shoes. Had a bit more then but master cylinder was not returning properly so had it rebuilt & have not been able to bleed the brakes since. Have had a good mechanic go through the process of trying to bleed them including pressure bleed but no go. Some pedal there but brakes feel like a rock just off the floor but no retardation. Any hints? How hard would it be to fit other types of brakes off say a Floride or Caravelle? I would like to retain the spider wheel if possible.
    Hope you may be able to help.
    Phill

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  2. #2
    VIP Sponsor 59 Floride's Avatar
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    Quote Originally Posted by hometurn View Post
    Gidday all
    I seem to be having continuing problems with the brakes. Didn't have much before but now have less. Fitted reconditioned wheel cylinders & relined shoes. Had a bit more then but master cylinder was not returning properly so had it rebuilt & have not been able to bleed the brakes since. Have had a good mechanic go through the process of trying to bleed them including pressure bleed but no go. Some pedal there but brakes feel like a rock just off the floor but no retardation. Any hints? How hard would it be to fit other types of brakes off say a Floride or Caravelle? I would like to retain the spider wheel if possible.
    Hope you may be able to help.
    Phill
    The problem will be with the new piston rubber in the master cylinder being a tad too fat. It will be blocking the fluid return hole which is tiny as it is. I think this is a common problem with the Lockheed master cylinders and the solution seems to be to drill the fluid return hole a little larger or find the correct piston rubber (good luck with that).

    Even if you do manage to bleed the brakes they will overheat and bind as the fluid can't return to the reservoir and so won't let the brakes release due to fluid expansion.

    I'd be taking the master cylinder back to a brake shop for a redrill..
    Last edited by 59 Floride; 6th October 2014 at 06:41 PM. Reason: t
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  3. #3
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    Default Thems the breaks :(

    Hi hometurn,
    It sounds to me like there is a mismatch on the stroke of the master cylinder. 59 floride has made a suggestion and that could be an answer but it sounds like more to me.

    Assuming the master cylinder is working as it should out of the car then it must be fitted correctly so that it works properly fitted. The retracted position should be checked and that the port is open as said above. Slacken the push rod so it is visably loose. Then it should be able to be bled OK. If not then something is blocked. The lines or hoses should be blown through to check and a visual check of them end to end also. Perhaps a fluid retention valve is fitted incorrectly in the end of the master cylinder.

    What diameter was the master cylinder bored to, and how does this compare to the original. A very much larger size will give a hard pedal and not much stopping. The brakes worked OK originally when it was built so while they may be a bit under 2014 specs they were OK by my memory on the day.
    Cheers jaahn

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    Bit of a side issue to your problem but modern innings are often too hard for brakes with out power boosters. You need to specify soft linings if you can get them. I had a tractor with drum brakes relined and they were worse than before. The brake guy claimed that the lining was too hard with out asbestos, but all he could get these days. I am about to use new old stock linings on my 4 CV riveted on too.
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  5. #5
    1000+ Posts Frans's Avatar
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    59F I think that if he managed to pressure bleed them the bleed hole will be open. Being drum brakes, is the little check valve there in front and is it facing the right way. It needs to keep a little pressure on the wheel side. That is if they had check valves at all in the 4CVs.
    Frans
    Old enough to know better
    Young enough to do it anyway.

  6. #6
    Tadpole
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    Thanks guys
    Don't know what the original size was or the new size as I assumed the "Brake specialist" would know what he was doing. But it was done over 12 months ago. New wheel hoses have been fitted & a new hose from the fluid bottle too. The linings are light grey so could be a later type bonded to the shoes. Will try to bed them in on the road.
    Many thanks
    Phill

  7. #7
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    Yes, the check valve has probably been left out when the cylinder was recoed.
    These aren't used with disc brake systems so the rebuilder probably didn't know what it was for.



    Quote Originally Posted by Frans View Post
    59F I think that if he managed to pressure bleed them the bleed hole will be open. Being drum brakes, is the little check valve there in front and is it facing the right way. It needs to keep a little pressure on the wheel side. That is if they had check valves at all in the 4CVs.
    Frans

  8. #8
    Too many posts! JohnW's Avatar
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    They came mostly with 19 or 22 mm master cylinders, with some at 20.4 mm or something odd. I have the larger 22 mm variety on my 4CV and it is fine although you do have to push hard with standard drums.

    It is a bit confusing as both disc and drum braked cars use essentially the same master cylinder but the disc braked ones have a different type of check valve from the drum braked ones. Both types have a brass and rubber "check" valve that fits under the spring inside the master cylinder, but they are quite different in design and function.

    If the cylinder rubber seal is too large it may bind in the master cylinder, as the internal spring isn't particularly strong.

    So you need to be quite sure you have the right type of check valve first up.

    I've never needed to drill out the entry hole, but the comment does make sense. You need a tiny bit of free play (say 0.5 mm) at the rod that enters the master cylinder, again as commented. The service manual gives the exact clearance.

    For the spider wheel cars, you can greatly improve the braking by fitting Dauphine brakes, which a few Australian owners have done. The early Dauphines had spider wheels too, but much bigger drums and they are a fairly easy fit as everything bolts together basically. Discs may be better but they are light cars with modest performance unless you get a bit excited in the engine department.

    Jean-Pierre Delaunoy in Paris (Web Pièces Rétro : pièces rétro, pièces de voitures anciennes renault 4cv Dauphine) has 1063 brakes and they are excellent on his 4CV. I got some of the spider wheel Dauphine brake parts from him.

    Good luck.
    JohnW

    Renault 4CV 1951
    Renault R8 1965
    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Renault Scenic 2006 (daughter's)
    Citroën CX Pallas 1980

    National Co-ordinator, Renault 4CV Register of Australia

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