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Thread: Clutch Master Cylinder Leak

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  1. #1
    Jedi Warrior Drone Dog's Avatar
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    Clutch Master Cylinder Leak

    i have a leak at my master cylinder. it is a slow leak but it leaks. it looks to be coming from around the fitting, from the reservoir. either that or i have a porous casting. most likely the fitting.

    the master cylinder is new but the pipe is original. No problem with the brake one, just the clutch. And no leaks at the pedal box.

    tomorrow i plan to take it out and put something on the threads. any suggestions here on what to use? it will be easier to use something other than tape since it is so hard to get both hands in there to wrap any tape on it.

    i am using DOT5 fluid.

    Thanks
    Last edited by Editor_Reid; 02-06-2020 at 01:24 AM. Reason: No need to thank me. My caps key still works.

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    Yoda John Turney's Avatar
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    Re: leak at clutch master cylinder

    The flair on the pipe may have hardened and cracked, or the nut may not be tight enough, or the conical surface on the MC may be contaminated, or .... The sealing surface is the flair against a conical surface in the cylinder. Putting anything on the threads won't help. If the nut is tight enough and the surfaces are not contaminated with debris, and if you have a bit of slack in the pipe, you might cut the flair off and re-flair.
    John, BN4

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    Jedi Warrior Drone Dog's Avatar
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    Re: leak at clutch master cylinder

    John
    Deep down, i figured it would not be something i could just fix with some sealant. never that simple right?

    going to pull the line out tomorrow. hopefully it is just something not letting it seat. but probably not.

    thanks

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    Re: leak at clutch master cylinder

    To seal threads on gas or oil line fittings I use plumbers paste with PFTE. Might work with brake fluid as well.

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    Yoda steveg's Avatar
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    Re: leak at clutch master cylinder

    Quote Originally Posted by John Turney View Post
    .... The sealing surface is the flair against a conical surface in the cylinder....
    I second this. There is no sealing on the threads - all of it is between the flare and the curved seat in the master cylinder.

    If the line is stock plain steel or cunifer (copper alloy) you may be able to anneal the flare and get it to re-seat. If it's stainless, forget it.

    If you have the dies to re-flare it, might as well buy some pipe and do it new.

    Otherwise you'll need a new pipe, which Moss sells.
    Steve Gerow
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    Obi Wan RAC68's Avatar
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    Re: Clutch Master Cylinder Leak

    Hi Drone Dog,

    I don't mean to expand your issue but have you identified the location of the leak specifically within the reservoir-MC line? If not, I would suggest you look under the dash and pull back the rubber cup over the clutch rod. I use silicone brake fluid and, although it does not absorb moisture, is sometimes a little more prone to leaking. When my Healey sits for a significant period, my first push on the clutch meets little resistance. However, the second push is back to normal and all those pushes that follow. I have experienced this a few times over a 10-year period and, although I have considered rebuilding the master, never felt the urgency based upon the number of repetitive happenings. One of these days I will climb under the dash and replace the Clutch MC rubber and eliminate this small leak.

    Just my thoughts,
    Ray(64BJ8P1)

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    Jedi Warrior Drone Dog's Avatar
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    Re: Clutch Master Cylinder Leak

    Ray
    Thanks for the reply. pretty sure where the leak is.

    when i was driving the car more, in the summer, i would usually check the reservoir probably every couple of hundred miles with all the other fluids. i could see it would be down a little each time. not a lot but a little. both in the brake side and the clutch. i checked all around, including at the pedal box, for leaks. could not find anything anywhere. i kept watching it and adding a little back each time. again very little. after a while i assumed maybe it was leaking at the cap while i was driving. always looked a little wet around the cap. i made a new gasket for the cap with that in mind. Still no other leaks showed after drives or in the shop while the car was sitting.

    once in the fall i had started the car to move it over to the other side of the shop so i could work on another car. i don't like to start cars up and run them just a few minutes so i let the car run for a while until i was sure it was warmed up. the whole time it was sitting in the driveway. later in the driveway i could see a small puddle of what i thought was a little oil. usually do not get this but figured i would keep an eye out. next few drives, no drips or puddles.

    during my cold air box test the other day, i started the car and let it sit running until it warmed up to do the test. when i moved the lift blocks i saw fluid again. this time i could tell it was coming from the front left of the car. Odd place for oil... took it for a ride and came back. let the car sit, no more fluid. shut it off, let it sit and started it again, no fluid. shut the car down and put it back up on the lift. No more drips. Hmmmm.

    here is what i think was happening: i have exhaust wrap on my down tubes from the manifold to just above where the pipes turn to the muffler. (so the wrap can't be seen) the hydraulic fluid was dripping down in to the wrap which soaked it up. there is a hole there in the frame brace so it did not drip on any surface i could see. when i ran the car and the pipes got hot, the fluid i guess got thinned enough it would all run out... or boiled out. once all had dripped out, it did not drip anymore. And would not until enough fluid leaked out to soak the wrap again. (after sitting for days, weeks?) then the whole process started over.

    in the summer, i did not let the car sit long before i would drive off. So that fluid probably just got released on the road somewhere. then the wrap was dry and no drips. So i never saw it or knew where to look. i would not have known this time except i did not move the car during my test. the only thing above the wrap are the master cylinders. feeling under each one, i found the clutch MC was wet under it. SO i wiped it off and left a paper towel under it to catch any drip. sure enough, after sitting overnight, there was a spot on the paper towel. i tried loosening the fitting and tightening again but same thing. not a big leak. just a little bit.

    I may have gotten lucky though. i took the fitting out today and checked the flair. it looked ok. it was gritty and a bit nasty there. So i took some sand paper and cleaned it up. wiped it all down and cleaned it with some brake clean. i also lightly sanded the bottom of the flair. cleaned it up and put it all back together. put some fluid in the tank and loosened the fitting until i got some fluid coming out of it. figured this might push out any air in there. tightened it up and checked it thru out the afternoon. Pumped the clutch a number of times. No leak. Letting it sit overnight and going to check it tomorrow. if it is still dry, going to assume i have it.

    if not, i am just going to buy new pipes and replace the brake one as well. those two pipes are the only ones i have not replaced.

    fingers crossed...

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    Jedi Knight Rob Glasgow's Avatar
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    Re: Clutch Master Cylinder Leak

    Ray, if you're talking about replacing the large rubber dust cover that attaches to the back of the MC and has the rod through the center, I don't think that will stop the leak. The leak is coming from the seal inside the MC and I don't believe it can be replaced while the MC is in the car.
    Rob Glasgow

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    Obi Wan RAC68's Avatar
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    Re: Clutch Master Cylinder Leak

    Hi Rob,

    No. I am talking about changing all the rubber in the clutch master cylinder (i.e. rebuilding). I always understood you had to take the MC out of the car to perform the rubber exchange. A friend indicated that it can be done from the inside, maybe twisting yourself into a pretzel to do, but you eliminate the hassle of having to remove it from the car.

    Hope my understanding is correct,
    Ray(64BJ8P1)

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    Luke Skywalker Roger's Avatar
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    Re: Clutch Master Cylinder Leak

    Drone dog, if you had fluid in your exhaust wrap, then when the exhaust got hot it would smoke like crazy.
    Oh, and while you may be talented and have a real creative flair, what you have on your pipe is a flare.
    Roger
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    Jedi Knight Rob Glasgow's Avatar
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    Re: Clutch Master Cylinder Leak

    Ray, I considered rebuilding the MC from inside the car and I think it's possible but in the end, I decided to replace with a new unit so I have never tried it. It would take some major twisting and contortions I would think.
    Rob Glasgow

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    Re: Clutch Master Cylinder Leak

    Roger
    with the car sitting this last time and the hood up, i could see some smoke. not a lot but there was some. guess when it smoked this summer i was rolling down the road so i did not notice.

    Ha, flare... sorry. when i get on a roll typing anything may come out of my computer. Sadly i don't have much creative "flair" either as this points out.

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    Obi Wan RAC68's Avatar
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    Re: Clutch Master Cylinder Leak

    Drone Dog,

    If the leak was relatively light, it may have been slowed by the engine heat expanding the connection. However this would not be as probable if the opening was in the pipe created by corrosion caused by moisture in absorbed in traditional brake fluid (the reason I have use silicone brake fluid since 1989 after my rebuild).

    Rob:
    Absolutely would required substantial body manipulation, discomfort, and some working upside down. A good friend has just successfully completed the replacement of MC clutch rubber from inside his BJ8, so I know it can be done. Before that, I did not know it could be done in that way. It is limited to only the replacement of rubber but in many cases that is the only thing needed to renew the MC's operational function. I will try the rebuild form inside the cabin and, if I run into too much discomfort or difficulty (not as nimble as I used to be), I will just go back to removing the MC the old way.

    Ray(64BJ8P1)

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    Yoda
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    Re: Clutch Master Cylinder Leak

    In the car--not sure if it's possible--or on the bench, you'll need to carefully inspect the bore for pitting and/or scoring. Those are what usually cause the rubber parts to deteriorate. A soft pedal, temporarily cured with a couple pumps, can be caused by a bad foot valve, which closes off the line to the reservoir when the clutch is applied.

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    Jedi Warrior Drone Dog's Avatar
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    Re: Clutch Master Cylinder Leak

    no leaks today either. So whatever the reason, i hope i got it.

    you know for the price of a new MC, (25 bucks?) i would just replace it. the real pain is in the bleeding to me and that will have to be done either way.

    back in the day on my old TR6, we would hone the cylinder and put the old seal back in. but put a spark plug washer in when we put it back together. we uased the washer to help expand the seal even tighter. it would last quite a while. ahhh the days of no money....

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    Obi Wan RAC68's Avatar
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    Re: Clutch Master Cylinder Leak

    Hi Drone,

    First, isn't it nice when a fix works that doesn't require a replacement. I like your TR6-fix and will consider using it before ordering new parts.

    Good work,
    Ray(64BJ8P1)

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    Jedi Warrior Drone Dog's Avatar
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    Re: Clutch Master Cylinder Leak

    yes it is. the project i am on now does not seem to be going as well...

    keep in mind that TR6 fix was in the old days of no money... And actually parts weren't as easy to get in this neck of the woods as they are now. Another great thing about the internet. can't recall how long it actually lasted. but it held for a while.

    i can also remember using rubber cement to glue the seals in those ZS carbs. ahh the old days. i drove home, about 40 miles thru 5 towns, with no clutch at all once. that was fun. And the time i drove up in to mid-PA, and back, with a broken valve spring. the old girl always made it home though.

    Now my wife won't hardly ride to the next town for fear she may have to walk. this car is in 10 times better shape than what she rode in then. And she can't talk. She drove a piece-of-crap Vega. We literally gave that thing away.

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    Obi Wan RAC68's Avatar
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    Re: Clutch Master Cylinder Leak

    Drone,

    I hate to correct you but they were the Good YOUNG Days and these are the Good Old Days...at least as I see it. Back then I drove from Stowe Vermont back to NYC with my Healey's rotor socket glued together and from Philadelphia to Scranton to NYC and back to Philadelphia on 1 carburetor (great mileage). Today we seem to be more sensitive to unresolved issues and back then took them as part of the norm and part of our Red Badge of Courage. Many more incidents but why brag.

    Happy Motoring,
    Ray(64BJ8P1)
    Last edited by RAC68; 02-12-2020 at 07:53 PM.

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    Re: Clutch Master Cylinder Leak

    Quote Originally Posted by Rob Glasgow View Post
    Ray, I considered rebuilding the MC from inside the car and I think it's possible but in the end, I decided to replace with a new unit so I have never tried it. It would take some major twisting and contortions I would think.


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    Re: Clutch Master Cylinder Leak

    There may be more luck than skill involved in whether the new MC or rebuild kit sold today will leak. I experienced a leak in a new cylinder recently, followed by success (fingers still crossed) with a replacement kit (replaced with considerable grumbling from the supplier.) Probably can't blame this design or deficiencies in replacement parts on Lucas either.

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