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  1. #1
    Newbie Rattle's Avatar
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    Default Plugs for Brake Master Cylinder

    Hi all

    New to the forum, so a few words about me ....
    Have owned my VK Brock for around 25 years I guess. Was a member of the Brock Commodores forum (which seems to have since shut down) until kids came along.. all of a sudden I had no free time . Most of my lifeís pleasures were unintentionally put on hold including driving the girl. Reckon sheís only done about 150 kmís in the last 5 or so years.

    Anyway, I'm starting to get back into the groove and will be bringing her home from where she is stored as soon as I replace the brake master cylinder. I want to do a final isolated test of the cylinder before I go purchase another, by disconnecting the brake lines and inserting flared plugs into the ports.

    I donít have the convenience of having the car in my garage to inspect immediately, but assuming the master cylinder is equivalent to the original spec, anyone know what size and thread plug I would need?

    Cheers

  2. #2
    casual poster Lacksballs's Avatar
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    Just go & get 3 brake hose clamps & attach them to the rubber lines (2 fronts & 1 rear), a lot easier & no mess.

  3. #3
    Newbie Rattle's Avatar
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    Would that be a normal method of testing.. to clamp it so far away?
    I am not even close to being above average spinning spanners on a vehicle, but I’m not stupid and learn fast ��

  4. #4
    casual poster Lacksballs's Avatar
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    YES, it isolates the callipers & or rear wheel cylinders. (Note there are proper hose clamps NOT vicegrips many back yarders use).

  5. #5
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    HI
    After long storage brake fluid will have moisture in it . Normal change interval is 40,000km /2yrs . Flush and bleed brake fluid to all 4 wheels ,then reassess . If needing to, clamp front calipers 2 lines and single rear line after fluid change .

    Master cyl. are different disc/disc , disc/drum

    Master cylinders do fail . They bypass internally and pedal can goto floor under light pressure with engine running . Early commodores occasionally leak vacuum from booster also . U can hear it in most cases. These fail from age and brakefluid leaking out the back of master and going into booster .

  6. #6
    Newbie Rattle's Avatar
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    If the master cylinder is failing, would you expect to see any fluid still pump out of the ports if the lines were disconnected from the master cylinder and the peddle is depressed?

  7. #7
    Part of the furniture monaroman76's Avatar
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    Quote Originally Posted by Rattle View Post
    If the master cylinder is failing, would you expect to see any fluid still pump out of the ports if the lines were disconnected from the master cylinder and the peddle is depressed?
    Yes. There is no pressure acting against the piston seals so you'd expect that they would still move fluid. When there is pressure in the brake lines, worn seals will allow fluid to bypass and the pedal will slowly fall to the floor.

  8. #8
    Newbie Rattle's Avatar
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    Thanks for the info guys....

  9. #9
    casual poster 1time's Avatar
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    To plug the rear brakes on the commodore master cyl the fitting i used was an "AN3 to M12x1.0 Inverted Flare" in stainless, and capped the AN3 with a stainless cap. I used stainless as opposed to Aluminium so that i wasnt constantly worrying about it potentially bursting in use - they're a little dear though.

    I couldn't find an M12x1.0 inverted flare plug hence the AN adaptor and capping the AN fitting.

    I believe the front brake threads on the master cylinder are M10 x 1.0 but you'll need to research that, i only know the rear for sure as i recieved the fittings and they worked mint.

  10. #10
    casual poster 1time's Avatar
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    That was a VH brake master

  11. #11
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    HI
    When flushing /bleeding .
    If pumping by foot never go all the way to the floor in an older car [10yrs+] . There is likely to be sludge in the bottom of the master and the piston will get stuck. This area is also unworn and minimal clearance to the piston.

    Change around 500ml to a 1ltr of fluid
    Lube the brake slides with silicon fluid or anti seize . If the calipers are real old [greater than 10yrs ] squirt some silicon fluid between piston boot and piston .

  12. #12
    Newbie Rattle's Avatar
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    Swampy’s comment about moisture has me wondering if I’m barking up the wrong tree.
    I pretty much assumed the master cylinder was the cause of the peddle going straight to the floor I have given things a brief visual. No leaks to see, and the reservior is still full. I realize fluid absorbs moisture, however that would not be the sole issue would it?

    I know this is a stupid question given I really haven’t provided much info, but based on experiences, would most of you agree the master would be the culprit? I only ask because I now have to move the car today ... leaves me in a predicament. I don’t really have time to clamp and isolate the master for testing so was just going to jump in and replace the master. But, that might be an expensive incorrect decision. Thoughts?
    I know I’m asking a lot from nothing , but your thoughts appreciated.

  13. #13
    Part of the furniture monaroman76's Avatar
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    Have you bled the brakes?

  14. #14
    casual poster 1time's Avatar
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    +1 bleed brakes and re-assess

  15. #15
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    HI
    My old master use to go to the floor every 6mths or so at traffic light very slowly . OK while driving every day no big issue . After it became a garage queen master cylinder did not last long at all .


    ### Masters can internally bypass and IS NOT evident by a leak .


    ## If master drops to floor within a few seconds IE quickly change ASAP to prevent an accident . OBVIOUS....

    Crimping OLD brake hoses with pliers/ vice grips can occasionally cause them to collapse internally . Use the right tools !!!!!
    Last edited by swampy; 14-06-2019 at 07:25 PM.

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