MasterCylinder Input Hose Fittings Question

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This topic contains 9 replies, has 4 voices, and was last updated by  royal 2 weeks, 4 days ago.

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  • #304311

    newkitman
    Participant

    @newkitman

    The brake master cylinder in my TD is a new MC and it leaks at the two input fittings from the reservoir. I have change these fittings and they still leak around the rubber stopper portion of the fittings. I would like to tap these two bosses so I can screw in brass fittings and connect the hoses. Has any VW guru come across any type of screw-in fitting for the master cylinders? If so please let me know. Thanks and Happy Thanksgiving to everyone!

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #304319

    billnparts
    Participant

    @billnparts

    What master cylinder are you using?

    Bill Ascheman
    Fiberfab Ford
    Modified 5.0, 5sp., 4:11
    Autocross & Hillclimb
    "Drive Happy"

    #304321

    edsnova
    Participant

    @edsnova

    Seems like overkill. And this is me talking.

    #304323

    newkitman
    Participant

    @newkitman

    The master cylinder I have is the stock VW dual Master Cylinder. It is leaking from the front fitting rubber seal around the base of the seal. This is the second time I’ve replaced the fittings and seals. I’m thinking of installing threaded input fittings on my other new master cylinder. Getting tired of servicing the break system every 4 months.

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #304324

    edsnova
    Participant

    @edsnova

    If it’s leaking I guess it’s due for some R&R, but I’ve not heard of this particular issue before. Is the hose the right size? Did you try just putting a hose clamp? Does the hose have that outside braid like it’s supposed to? I guess you already know that not just any kind of hose is brake fluid safe.

    If it’s not the little hose and you already changed the plastic and rubber(?) gravity fittings then the only other possible culprit is the master cylinder itself. I suppose it’s possible that one of the bores on top is too large or maybe has some kind of groove in it or is out-of-round. If that’s the case—and I think it’s unlikely that they’d be so wrong they’d leak past a rubber stopper with no pressure in the line like you have—then drilling and tapping for the next size up pipe thread is an option. But…

    You’ll have to remove the MC to do it, and you’ll have to devise a good way to get all the chips out of it from the drilling and the tapping, and unless you have the taps and dies and good fittings handy on your bench already, the price of this procedure in time and treasure will far exceed the cost of a new Brazilian MC, which is like $50 or something.

    #304336

    newkitman
    Participant

    @newkitman

    All my hoses are the correct braided hoses and secured as they should be. I may take my new brake master cylinder and mount it with reservoir in the shed, service the reservoir and let it sit in the shed for a month and see if this one leaks. If it leaks I’ll have to head to a salvage yard and get a master cylinder from a 71 beetle. If it doesn’t leak I’ll install it.

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #304338

    edsnova
    Participant

    @edsnova

    Good luck & keep us posted.

    So I had one other thought which is probably off-base but, just spit-ballin’: Is there any kind of residual pressure valve in your system that might (?) somehow create pressure inside the reservoir? I don’t even think it’s possible but I’m trying to see all the angles here.

     

    #304339

    royal
    Participant

    @royal

    Allen, you might want to check and make sure that the reservoir is vented and the hole in the fill cap is clear.

    #304340

    newkitman
    Participant

    @newkitman

    Two good suggestions to check.

    Ed. No pressure valve that I’m aware of but I’ll check again tomorrow. There may be one internal to the master cylinder. Let you know tomorrow.

    Roy. I’ve removed and installed the reservoir cap numerous times. Each time I’ve noticed the vent in the cap but have never checked it. I’ll check it tomorrow.

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #304341

    royal
    Participant

    @royal

    Allen, there is no design check valve in a braking system on any car that I am aware of.  The entire system needs to be at atmospheric pressure (when not actually braking) as this allows the brakes to relieve when you take your foot off the pedal.

    If your pedal is incorrectly setup such that the rod between the pedal and the master cylinder is too long, then the piston inside the master cylinder does not return to it’s “at rest” position.  When “at rest” then and only then the system is vented to atmos.  When you first step on the brakes, the MC piston closes off the reservoir and applies pressure to the lines and to the slave cylinders.

    It is important to check the vent on the filler cap is open.

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