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master cylinder issue

Discussion in 'XJ Technical Chat' started by schnarr, Jan 8, 2009.

  1. schnarr

    schnarr Member

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    81 seca 750 sleeping for the winter months went to move it and it was hard to push brakes were dragging drove around a bit a played with them and they were fine again. calipers were rebuilt last spring so i was the only other thing i could think of is the master cylinder right??? and if i am rebuilding the master is there a tool i can buy to help me bleed because im not looking forward to spending 3 hours pumping the brake to get fluid through the system again.

    thanks in advance
     
  2. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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  3. hammerheadx

    hammerheadx Member

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    I just did this on my '82 XJ750J Maxim.
    I bought a rebuild kit from Chacal for about $34US. He's awesome to deal with. Quick and knowledgeable. My Haynes manual called for the wrong part number and had the wrong drawing for the master cylinder. Chacal knew that and set me the right part, the first time.
    Work slowly, thoughtfully and your new religion is CLEANLINESS.
    There's a very, very tiny "blow back" hole that is a return passage in the bottom of the resevoir bowl that must be clean. It's a litte teeny spec of a hole. I made sure that it was clear by watching the mist of cleaner spray up out of it when i hit the main output hole with my air compressor.

    As far as bleeding? Took 15 seconds, without a mightyvac. The key is using the right procedure.

    1. attach a clear plastic hose to the bleed valve on a caliper.
    2. Fill a small bottle (i used a clean katsup bottle) with brake fluid such that when you insert the other end of the bleeder hose in the bottle, it stays below the level of the fluid at all times.
    3. Fill the master cylinder resevoir.
    4. Open the bleeder valve at the caliper and give the brake lever a few pumps. Each pump should be done slowly, on a count of three down and up. You should see some of the fluid in the bottle get sucked up into the hose.
    5. Now squeeze the brake lever down slowly to the handle and WHILE HOLDING IT DOWN, close the bleeder valve. (this is key)
    6. Slowly release the brake lever.
    7. Then re-open the bleeder valve and squeeze the brake lever to the handle bar again, hold it there and close the valve again.
    8. Repeat until you're getting clean brake fluid out the bleeder valve, with zero air bubbles, even tiny ones.
    9. Keep fluid resevoir topped off or you'll have to start again.
    10. Repeat for other caliper, if dual brake equipped.

    If you have to pump steps 5-9 more than about 15-20 times, something else is wrong. Done right, it's very simple and quick.
    I even re-bled after a short ride, just to make sure all the air got out.

    Piece of cake.

    Good luck,
    Christopher.
     
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  4. schnarr

    schnarr Member

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    maybe that was my issue i bled it like i would a car, pump it, hold it, crack the bleeder, let it shoot out it's fluid, close it repeat it. Took so long to build pressure though. also keep in mind i had the whole system empty calipers off and master off the bike (wish i would of rebuilt the master then) and i have 4 bleed screws because i have those "anti-dive" forks up front, with dual calipers
     
  5. hammerheadx

    hammerheadx Member

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    Yes. the exact sequence is important.
    I also had the system totally emptied. Including having the brake lines off and blown out with an air compressor.
    If you want to do that, just carefully vice grip the removed banjo bolt back to one end of the line, then blow air into the bolt end (inlet). Works GREAT!!
    A lot of black crud came spraying out!
     
  6. Danilo

    Danilo Member

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    There are a couple of 'tricks' that works for me on Yama Masters.
    First is to pump the brake lever in v quick short strokes for a minute or 2. Often that works. Second one is to use one of those disposable plastic 2 ounce Vet Syringes (approz $1) Using a piece of fuel tubing (or whatever is handy) attach it to the bleeder nipple then Pull fluid thru. takes approx 5 mins and yer brakes are good to go. IF the above does not work THEN you have ..forgotten ...to clear the teeny barely visible hole in the bottom of the Master's recervoir.
     
  7. CaptNemo

    CaptNemo Member

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    This is the legendary "Why the bleep did they put it behind the headlight" Seca 750 master cylinder. The picture shows the bypass hole just above the main hole. My welding tip cleaning set didn't go small enough so I used a .009" guitar string, cut off 2" from the ball end for a handle, a set of these is actually handy to have.

    [​IMG]
     
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  8. wizard

    wizard Active Member

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    I'm not cutting the strings off my guitar, even if it would make the wife happy. :wink:
     

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