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bleeding brake problem-- again

Discussion in 'XJ Technical Chat' started by bensalf, Jul 4, 2015.

  1. bensalf

    bensalf Well-Known Member

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    so ---- i've been completely rebuilding my xj 600, it's near completion now, after 3 years and I have a problem bleeding the front brakes, i've rebuilt and cleaned the master cylinder with a new rebuild kit. installed a new stainless steel brake line to each side calliper from the master cylinder.
    new copper washers and banjo bolts all round, cleaned and renewed all seals in the callipers, fresh 4dot brake fluid , and I can't get any resistance on the brake lever.
    read through all the threads on here and tried most of the sugestions but still no joy.
    I have a non return valve bleed line on the bleed nipples , ptfe tape on the nipple threads.
    after I spilled brake fluid on my freshly painted front wheel, I removed the complete brake system from the bike (intact) and rigged it up on an old handle bar on a work bench.
    I've tried bleeding by pumping in fluid with a syringe from the bottom up.
    I've tried raising the callipers up above the master and bleeding them, all to no avail.
    I replaced the new seals and piston back with the old ones, still no pressure build up
    if I remove the outgoing banjo,s and put my thumb over the hole on the master, with a little oil it does push my thumb away
    I get some fluid and bubbles at the bleed nipples when pumping the lever , but the fluid just pushes out then goes back in again.
    I have this master cylinder.
    [​IMG]
    [​IMG]
    any help would be appreciated.
    thanks
    stu
     
  2. Ribo

    Ribo Prefectionist

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    I see you have a syringe - are you sucking it out from the nipple ( oh god - did I say that! ) ? I found that to be the best way to get all the bubble out but you gotta be careful to keep the res full - easier with 2 people.

    Silly question - you are tightening both nipples when you test for pressure right?
     
  3. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Are you remembering to close the bleeder before the lever reaches the end of its stroke?

    Squeeze the lever, open bleeder, close bleeder just before the lever reaches full travel, release lever, repeat. Do this with everything on the bike.

    For the initial fill you can attach a length of hose to each bleeder and put them into 1/2 filled glass bottles. Leave the bleeders open. tie the brake lever to the grip, fill the master cylinder, and leave it overnight. Gravity will pull the brale fluid down, and the air will be free to travel up the lines.

    The one last step that helps is to tie the brake lever to the grip, and use a vibratory sander (sans paper) to work the air bubbles out of the calipers and lines. Start at the bottom, and work your way to the master cylinder.
     
  4. bensalf

    bensalf Well-Known Member

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    yes, I used the syringe to pump fluid into the bleed nipples, and got a steady "fountain" up at the master hole on each calliper.
    yes again to the tightening nipple job , i've done this countless times on cars, also bled the rear brake system first time without any trouble.
    tried the overnight tying the lever to the bars thing, (but not with the bleed nipples loosened). hmmm, that might be the next try.
    interesting thing with the sander though, ??
    cheers
    stu
     
  5. Polock

    Polock Well-Known Member

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    i'am thinking the actual pump section of the MC still has air in it. think like a bubble! you always want to go up. there's 2 holes in the reservoir, the small on releases the pressure and any air in the pump cylinder. position the mc so that hole is up and just bump the lever a few times. see if you get small bubbles out of the small hole. if you squeeze the lever fully, you push any bubbles out and down the line, then since their bubbles they go to the highest place and get stuck or sucked back into the pump. try the bump rather than the squeeze
     
  6. tabaka45

    tabaka45 Well-Known Member

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    When I completely rebuilt my brake system, calipers, master cylinder, stainless lines, I used the syringe method to pump the fluid in from the bottom. I too got a good flow of fluid in the m/c. Before putting the cap on the m/c I squeezed the brake lever gently several times and found that there was some air trapped in the newly rebuilt m/c. So I continued to lightly tap the brake lever until there were no more air bubbles. Probably took 10-12 taps. I had my front wheel turned so that the m/c was positioned so that the air bubbles would float into the reservoir rather than back into the m/c or brake line. My complete process from completely dry system to good brakes took about 15-20 minutes.
     
  7. bensalf

    bensalf Well-Known Member

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    "success" . so I decided to have another go yesterday morning, doing exactly the same as the previous few days , and this time it worked??.
    weird aint it,,
    so yesterday I refilled the system from the bottom up, by pushing fluid in the bleed screws with the syringe till I got a steady fountain at the master hole (just as before)
    then started to pump the lever, and noticed the pads begin to move, so put a spanner between the pads and continued pumping, and gradually it began to stiffen up , till it was solid, then released and pads withdrew enough to release the spanners. tied the lever back to the bar and left overnight , then this morning ,tried again , and all was well.
    replaced complete system back on bike (whilst keeping master cylinder level) and ,brilliant, system working as it should.
    thanks for all your feedback
    it just shows you have to stick at these problems, with the determination to see them through, (with help from here)
    cheers
    stu
     

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