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  1. #1
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    Default Assembly of the brakes master cylinders.

    Good morning everyone,


    I have a problem with the assembly of the master cylinders.
    When I torque the elbow (SP96004-001) in the master cylinder (SP96005-001), I can only put 2 tread in it. If I force, the torque is too strong. There are 7 treads outside (1/4"), which seems unacceptable to me.


    What should I do?
    Tapping the master cylinder? Bof...


    I feel that either the cylinder or the elbow is not good Ö


    Thanks for your help.

    Yves

    MASTCYL.jpg
    Attached Images Attached Images

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    Senior Member Andy's Avatar
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    Default Re: Assembly of the brakes master cylinders.

    Quote Originally Posted by PBY Catalina View Post


    What should I do?
    Tapping the master cylinder? Bof...
    I was surprised to see an NPT thread here but I found a Grove drawing that confirms 1/8 inch NPT.

    I have used pipe thread fittings for a variety of applications and there is a lot of variation in thread taper and size. I expect everything at your local hardware store is metric but I'd want to replace or modify the elbow before I attacked the master cylinder. If all else fails I'd run a die up the elbow before taking a tap to the master cylinder.

    Sorry I didn't see this message earlier as I flew this morning and could have checked my FX-3 installation. I'll look next time I'm at the hangar.

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    Senior Member Andy's Avatar
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    Default Re: Assembly of the brakes master cylinders.

    This reference - https://en.wikipedia.org/wiki/National_pipe_thread shows 1/8 NPT should mate 4.26 turns hand tight.

    This reference - https://www.gamurdock.com/img/docume...eadInstall.pdf says 3.3 turns hand tight

    Other references suggest hand tight + 2 turns.

    A sample of 3 NPT fittings from my air tools box all engaged 3-4 turns hand tight with no tape or sealant.
    Last edited by Andy; 06-05-2021 at 05:41 AM.

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    Default Re: Assembly of the brakes master cylinders.

    Hey, Andy!
    Thank you for your answer, I like your rigorous approche.


    We tried an elbow in AN and itís good!?
    It is therefore curious because the master cylinder is well planned for a 1/8 NPT elbow.
    It seems to us, however, that there is a non-correspondence of tread.


    Questions, Andy:
    - How did you first see that the elbows are NPT?
    - Do you advise me to correct the elbow tread?
    - If so, would you have a reference for a die?
    - What would be a maximum acceptable torque value to tie the brass elbow in the alu master cylinder ?


    Thanks again for your help.
    Last edited by PBY Catalina; 06-05-2021 at 02:53 AM.

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    Senior Member Andy's Avatar
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    Default Re: Assembly of the brakes master cylinders.

    Quote Originally Posted by PBY Catalina View Post

    Questions, Andy:
    - How did you first see that the elbows are NPT?
    - Do you advise me to correct the elbow tread?
    - If so, would you have a reference for a die?
    - What would be a maximum acceptable torque value to tie the brass elbow in the alu master cylinder ?


    Thanks again for your help.

    Hi Yves,

    I recognized the elbow as NPT because of the tapered threads and the general appearance. I have used similar fittings.

    I confirmed Grove uses NPT thread with a Google search for "grove brake master cylinder drawing". That returned drawings of several different master cylinders and they all seem to use NPT.

    I saw that one of your images showed a partial part number so I refined the search and found this drawing -

    https://www.groveaircraft.com/672-3dwg.html

    If yours is a different dash number you can probably edit the URL to match.

    I have some very old English adjustable pipe thread cutting dies and some more modern fixed dies but I don't have any die recommendations. I think you should first approach Kit Support and ask why they have provided incompatible fittings.

    I have never used a torque wrench on NPT fittings. All my applications were non-critical and I used the "that feels about right" method. Typically pipe thread fittings seal at quite low torque.

    BTW I found several AN fittings that use pipe thread (e.g. AN914) but I could not find an AN male/male elbow. Most of this series seem to convert pipe to flare. If the AN fitting that threaded ok is pipe thread that would seem to confirm the master cylinder thread is ok.

    Does the flexible brake line connect directly to this elbow. If so, what is the brake line fitting? I would expect flare not pipe.
    - edited to add - the elbow goes to the parking valve which seems to be 1/8 NPT)
    Last edited by Andy; 06-06-2021 at 10:27 AM.

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    Default Re: Assembly of the brakes master cylinders.

    Quote Originally Posted by Andy View Post
    This reference - https://en.wikipedia.org/wiki/National_pipe_thread shows 1/8 NPT should mate 4.26 turns hand tight.

    This reference - https://www.gamurdock.com/img/docume...eadInstall.pdf says 3.3 turns hand tight

    Other references suggest hand tight + 2 turns.

    A sample of 3 NPT fittings from my air tools box all engaged 3-4 turns hand tight with no tape or sealant.
    I have replaced the bronze elbow by an AN911-1D and AN914-1D with NPT thread;
    I have been able to hand tight 4 turns and now they fit perfectly without over-torquing.

    new elbow.jpeg

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    Senior Member Andy's Avatar
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    Default Re: Assembly of the brakes master cylinders.

    Yves,

    Here are a couple of pictures of the right brake installation on FX-3 serial 0100. Awkward location so not the best photos but hopefully adequate to count exposed threads.
    Attached Images Attached Images

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    Default Re: Assembly of the brakes master cylinders.

    Quote Originally Posted by Andy View Post
    Yves,

    Here are a couple of pictures of the right brake installation on FX-3 serial 0100. Awkward location so not the best photos but hopefully adequate to count exposed threads.
    Useful pictures Andy, thanks !

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    Default Re: Assembly of the brakes master cylinders.

    One modification you might consider is to upgrade the brake fluid reservoir to a larger one. The factory ones I did not like in regards to volume.

    I used these: GROVE BRAKE FLUID RESERVOIR 067-050 | Aircraft Spruce

    And if on planning to go 'off road' now is the time to go with braided brake lines.
    Dan Arnold
    KEUL

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    Default Re: Assembly of the brakes master cylinders.

    Quote Originally Posted by aeroaddict View Post
    One modification you might consider is to upgrade the brake fluid reservoir to a larger one. The factory ones I did not like in regards to volume.

    I used these: GROVE BRAKE FLUID RESERVOIR 067-050 | Aircraft Spruce

    And if on planning to go 'off road' now is the time to go with braided brake lines.

    The problem, if there is one, with the small reservoirs is that it's too tempting to add fluid when it drops a bit. The manual cautions to allow for the volume displaced by the top plug but I expect many owners spill some before learning to leave them alone.

    The thing I'd like to change is the parking brake valves. They are an accident just waiting to happen for anyone used to the "press pedals to release" parking brake design. It looks like Grove does have a press to release master cylinder but it's probably too big to fit.

    Still, I'd rather bleed the FX-3 brakes when I have to than the ones in my PA-28. It has FIVE master cylinders and they all interconnect!

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