Trophy Brake Master Cylinder Problems?

Discussion in 'Sprint & Trophy' started by TT600Des, Jun 10, 2015.

  1. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Trophy 900. 1993. Twin front non floating discs.

    Dear Madge,

    I've just rebuilt all three callipers inc' pistons. new brake hoses, rebuilt the rear master, and rebuilt the front one also.

    The front master has two very small holes in the base of the resevior (over the piston and cylinder). The one furthest (countersunk) hole away from the lever constantly blows air bubbles when the lever is operated. Thinking the original rebuilt Master was Dog Food - I bought a new one. The New one (from Sprint) does the same as the old one, and blows air bubbles from the same hole. If you pump the lever it's quite possible that it'll blow fluid 'clean' out of the resevior!

    Would we all agree that I've bought a duff-un? OR Is there something I'm not understanding here?

    Any / all advice very welcome indeed, I'm getting pis*ed off trying to bleed brakes!

    Yours sincerely.

    'Worried of Willen' aka 'Des'.
     
  2. thebiglad

    thebiglad Old fart, still riding !

    Sep 25, 2013
    5,066
    1,000
    Central France
    This couldn't be anything to do with allowing for the movement of air above the level of brake fluid in the master cylinder could it?
     
  3. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Hi Dave, I just don't know. I've never seen air bubbles (a lot of them) rising up through the fluid before and it being considered "OK". I would have thought that there should be no air the fluid at all within the master cylinder (or anywhere else come to that).

    I'm stumped - I don't know whether the New Master is faulty? Further - I'm stumped as to why I can't get a good solid lever either. The only 'none-standard' thing I've done is to replace the 'three brake hoses splitting into two' arrangement with two going from the master direct to each caliper.

    I'm just praying that someone will read this having had a similar problem and come up with an answer.

    Thank you for yours !
     
  4. thebiglad

    thebiglad Old fart, still riding !

    Sep 25, 2013
    5,066
    1,000
    Central France
    Right. Do the bubbles arrive when you squeeze the brake lever, or when you release it?

    Sounds like air is getting in somewhere it shouldn't, to me.
     
  5. crispey

    crispey crispey creme de la creme

    Nov 6, 2014
    7,229
    1,000
    Uk
    Yup sounds like air getting in. Small split in hose near connections maybe? Are the bleed needles , connectors screwed in tight?
     
  6. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Morning Crispey and thank you for your reply:
    Braided hoses all new, as are brass compression washers - Banjo bolts tight. Bleed nipples all tight - I'm at a loss frankly, and just pumping and pumping clear fluid through time after time.

    Any idea why there's air coming up though from the master piston and cylinder though the fluid?

    Des
     
  7. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Hello Dave, Air bubbles appear when I'm squeezing the lever, and from the countersunk hole (nearest the middle of the resevior). Leave the lid off and it'll squirt out!
     
  8. thebiglad

    thebiglad Old fart, still riding !

    Sep 25, 2013
    5,066
    1,000
    Central France
    This is just a guess, but it sounds to me like there might be an obstruction somewhere in the pipework not allowing the brake fluid to flow. To check for this you could undo the calliper bleed nipples to ensure the fluid is getting through?

    PS Sorry mate I've just re-read your post no.6 and the fluid is obviously getting through.

    Can't think of anything else, sorry.
     
  9. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Oh well, thank you very much anyway Dave. I very much appreciate your efforts.
     
  10. MetalliKarl

    MetalliKarl Active Member

    Mar 15, 2015
    62
    28
    UK, Germany and Touring
    Is there any fluid coming out of the Caliper bleed nipple? Is the diaphram in place when bleeding? , used to have this problem on other bike .. fill resovoir tie brake lever back and leave over night. If as you say everything is tight bleeding should be straight forward. Peace
     
    • Like Like x 1
  11. TT600Des

    TT600Des Member

    Nov 5, 2014
    9
    8
    Buckinghamshire
    Sorry not to reply sooner - been in France for a few days any thanks I'll try that, in fact the lever has a cable-tie on it as I message. Des
     
  12. capt

    capt Elite Member

    May 8, 2016
    3,051
    750
    western Australia
     
  13. Oldyam

    Oldyam Grumpy Old Git

    May 14, 2017
    610
    500
    ireland
    Hi @TT600Des

    Please don't be offended as I don't know if you've done brakes before, but this is how I work through a system.

    When I bleed out brakes for the first time after a rebuild I usually top up the master cylinder and open the bleed nipples one at a time and let the fluid run through until I'm getting fluid flow at the caliper, whilst making sure the reservoir is kept topped up.

    I also usually use a length of plastic hose over the bleed nipple so I can see fluid and bubbles coming out.

    Do this on both calipers.

    Then close the bleed nipple on each of the calipers and drop a coin or Stanley blade or similar into the master cylinder reservoir ( over the hole that's bubbling to stop brake fluid being ejected onto the paint work ).

    I usually soak a rag in water wring it out and lay it over the paintwork as an added precaution against spillage.

    Start bleeding one caliper till it runs clear whilst keeping the reservoir topped up, close up the bleed nipple and start all over again on the second caliper.

    Check brake operation by feeling the lever pressure, check fluid level, if a little soft tie lever back to the bars.

    A word of caution if your brake system is more than a few years old I would tie a block of wood to the grip behind the brake lever to limit travel as often old cylinders have a ridge of sludge and debris from the brakes built up on the internal bore of the master cylinder which can damage the seals.

    Sometimes to fully bleed out the brakes can take several bottles of brake fluid.
    ** Don't forget to remove the object you have dropped into the reservoir **

    Good Luck with the brake bleed.
     
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