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Brakes / Bleeding Diagnosing Hydraulic Brakes

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by phil01, Nov 2, 2012.

  1. Bleed brakes 101 (please ignore urges to pump up pressure
    or anything wildly aggressive).

    Beer bottle/ cordial bottle n clear hose that fits neat over bleeder.
    Pipe to very bottom of bottle.
    Master lid, now you have to be careful with on a bike because of spillage.
    Brake fluid is like acid to paint so protection peeps.

    Loosen bleeder
    depress lever
    close bleeder
    now carefully allow lever back.
    It’s important its slow n steady back - depending on how fast your
    particular master compensates.

    Repeat over etc.

    Now a note here on methods, may people including mechanics will not use this method because.
    A mechanics are about speed – it only about the fastest way – then refer to above if theres a problem.
    Non mechs just do whatever they / you do that worked last time or what you heard somewhere , its no problem and if it works it works , this guide is for people that are stuck because the common home method of pumping up brakes variants off etc will get you stuck – eventually. ( reason is different systems respond different – especially with say a
    Reconditioned sleeved master)

    If unsuccessful - reasons / options and diagnose.

    Ok so if maybe you have a very slow compensating master cylinder this
    will catch out people trying to bleed in a hurry.

    You can see this problem if you open bleeder after lever is returned a bit, and fluid in tube sucks back up.- you can see ifluid returning up back into caliper - bad

    If this is a problem rapid bleeding pump up etc. will actually make system
    worse as air will suck in from bleeder. – very common problem .

    options for above
    return lever even slower and wait longer between each return.
    Gravity bleed; leave bleeder open and have a few beers,
    be careful that master reservoir does not run out. - this works pretty good but takes
    several beers, if its heaps slow you can even take a risk on fluid level
    and leave overnight

    pressure bleed, messy without proper equip but pressure from
    master fluid i.e. a lid with say a tube / hole and gentle air pressure
    gentle will force fluid through system.

    Vacuum works same opposite end - from bleeder- that mean sucking fluid out bleeder

    you can actually diagnose a faulty instead of randomly repairing / bleeding etc.

    Adding here first a basic concept of a hydraulic system on ya bike
    - Reservoir of fluid connects to a master cylinder ,
    - The master is connected to calipers where the pistons are and this connection
    - Is by flexible and or steel pipes.
    Now whats important is this connection and components are sealed ….
    So by pulling lever the pistons will move in proportion to the lever .
    If not the fluid must be going somewhere as its it sealed right ?
    Or there is air in the system , brake fluid will not compress air wil compress, hence t\\
    The spongy feel symptom .
    So there fore if there is no air the fluid is either not getting pushed through at all
    (faulty master) or its going somewhere- remember – it must go somewhere this is
    Important to remember – the fluid must go somewhere if you have a excessive travel.

    To diagnose problem to identify master fault or hose etc.

    You need a brake hose clamp (not vice grips). Rounded type clamp so line will not be damaged
    Apply clamp to top part if hose.

    Lever should be rock hard if master is good with no air in master. ( and no leaks above clamp)

    Now a few options here depending on result.
    if rock hard put at bottom of hose to be sure hose is ok
    if hose us faulty to level your saying though it would be visibly
    swelling - lots from an internal rupture ( braided lines have no
    advantage buy a std one unless you want it to look pretty )

    that pretty much tells you now where the what problem is.

    You can further test as you improve / repair buy doing
    a drop test to see how far lever moves when you remove clamp
    other reasons and symptom for excessive travel

    Warped rotor , a warped rotor whilst traveling will push / return pistons back further than normal
    - First grab will have excessive travel and there will be vibration through lever
    - Hose leak or internal rupture causing a swell ( bit like a garden hose bubble)- not going
    To be as likely issue on bikes because flexible hoses have massive pressure ratings and bikes
    Are fairly low pressure compared to cars etc – its just your hand with no booster.
    A leak will cause excessive travel – remember the fluid must go somewhere…
    Look on the floor.
    Master cylinder bypass – hard to describe but here goes.
    The master ( simplistically is like a bike pump) if you blocked the end of a pump it will be rock hard and you cannot depress it , but if you depressed it will light pressure the handle will gradually depress as air passes past the seal .
    Same with a master light pressure ( a tickle) could cause fluid to pass past the main seal.
    Symptom usually is full pressure on a hard grab , holding lever at say lights a creeping travel
    On the lever
  2. Not a bad write up mate :).
    Just for peoples reference i bought a vacuum bleeder kit on ebay a short while ago thats perfect for my needs for 30 bucks.

    Cant say the link will last long so ill attach a photo too! Its only cheap but how often are you going to bleed brakes really?!

  3. that sucks
  4. I've got one them-absolutely useless,do not buy.
  5. think he bought it for his bike though blabbs
    • Like Like x 1
  6. Worked fine for me (on the brake topic, havent tried it elsewhere...)!