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bleeding xj750 seca brakes

Discussion in 'XJ Technical Chat' started by joejr2, Jul 26, 2017.

  1. joejr2

    joejr2 Active Member Premium Member

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    Well I just finished rebuilding the calipers and master cylinder on an 81 xj750 seca
    the master cylinder has a fill tube on the side of the brake fluid reservoir, but no window to see
    where the fluid level is at. Is there an easy way to add fluid to the reservoir while bleeding
    the brakes and how does one keep from overfilling it ? If there is an existing thread already
    covering this question I would appreciate someone posting a link. Oh! and by the way, the
    master cylinder rebuild kit that Chacal sold me fit perfectly.
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    When I did mine pulled 2 bolts from headlight bucket and move it forward and remove cover and fill with a long funel .
     
  3. k-moe

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

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    What I do to bleed the system.
    1. get a large syringe from a farm store and about a foot of vinyl tubing (you can also use a 2-stroke oil mixing syringe).

    2. Cut 6" of tubing and attach that to the end of the syringe. Remove the Syringe plunger. You now have a funnel to fill the master cylinder with.

    3. Break loose all four bleed fittings (be sure to put down cat litter or drip pans).

    4. Tie the brake lever to the grip.

    5. Fill the master cylinder and syringe.

    6. Wait overnight (or at least a few hours)

    7. You should now see brake fluid coming out. Close the bleeders, and untie the brake lever.

    8. Bleed the brakes as normal, starting with the anti-dive bleeders, then the brake caliper bleeders. Remove the funnel.

    9. You aren't done yet. There will still be some air in the system. The next step cures that, no matter what method you use to fill and bleed the system.

    10. Use a vibratory sander (no sanding pad) and slowly run it along the brake lines, calipers, and distribution block from bottom to top. This will move any remaining air bubbles up into the master cylinder. Tap (or vibrate) the master cylinder to get the air bubbles to come out of the return hole. This process can also be done with a box-end wrench or other similar tool, and tapping the calipers and lines (it just takes longer).

    11. Do one final bleed normally, just to be certain that the calipers are fully bled.

    12. Use a flashlight to check the fuid level in the master cylinder. It should be below the fill neck. Unfortunately there is no dip-stick or sight glass on this master cylinder, so unless you empty it and measure out the fluid you will need to just eyeball it. If the fluid level is too high the brakes can hydrolock and not release.
     
  4. Dadoseven

    Dadoseven Active Member

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    A long, narrow funnel; a larger syringe, better if tubing can be attached. I have also used a bendy straw like found in some water bottles and a small bottle with a flip-top spigot that I used to squirt into the straw.

    Just have to view in the small fill port for proper fluid level; a flashlight is helpful. You should see fluid in the neck of the fill port, but not up to the top when done (except while bleeding, then it can fill up to the top of the neck)
     
  5. joejr2

    joejr2 Active Member Premium Member

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    I got a large syringe and attached a 1/8" i.d. clear tube to it. I then slipped a 1" section of 1/4" i.d. tube around that and fit the doubled up tubes
    ( with an "O" ring ) tightly into the filler neck. This allowed me to use the syringe body ( zip tied to the handle bar) as a fill reservoir and not
    have fluid leaking out when the level reached the top of the fill neck . That way I would have plenty of fluid to flow through the lines to the
    calipers. I cracked the bleeders and and attached hoses run into a can on each side to prevent a mess when the fluid got down there.
    After about 4 hours the level in the syringe had not dropped at all . The fluid was not going down. Yes, I tied down the brake lever.
    And yes, I did a meticulous job rebuilding the calipers, polishing the pistons and cylinders before fitting the new seals and putting them
    back together. The master cylinder got the same treatment with a kit from Len. The lines were blown out and I used new crush washers.
    Could I be doing something wrong ? Even when vibrating the calipers, lines, junction and master cylinder with a palm sander the level
    didn't go down. I left a couple of inches of fluid in the syringe when I quit. I'll see if any makes it down by tomorrow morning.
     
  6. joejr2

    joejr2 Active Member Premium Member

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    when the front brake lever is pulled in should the spring in the master cylinder be strong enough to pull
    the lever back out again ? I polished the cylinder until it was real shiney could roughness hang up the spring cup
    and make the spring not return or is it that usually the spring is bad ?
     
  7. Stumplifter

    Stumplifter Well-Known Member

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    More detail...
    Have you rebuilt your front brake system recently?
    What did you the polish the cylinder wth and how much material was removed during 'polishing'?
     
  8. k-moe

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

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    Merged for clarity.
    I just got home from a work trip and am not rested enough to think this out. Hopefully someone with a fresher brain can help before tomorrow afternoon.
     
  9. joejr2

    joejr2 Active Member Premium Member

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    The calipers were frozen so I popped them with compressed air and the polished the cylinders with wet paper around my finger
    first 400 and then 1000 grit and then shined them up with polishing compound, same on the pistons. cleaned it all with rubbing
    alcohol and reassembled with brake fluid for lube. I shot compressed air through all the caliper holes, but didn't use brake cleaner spray.
    Was that a mistake ? Tried to blow out the brake lines but it was hard to get full pressure from the air nozzle around the banjo fitting. Still no
    brake cleaner, Mistake #2 ? I got a master cylinder kit from Chacal and disassembled the mc . The spring and piston seemed OK but were a little
    tarnished with age, so I shined them up with a fine grade scotch brite pad. I clipped a chunk of that pad into a small medical forceps and spun it
    around and pushed it back and forth in the cylinder until it shined, blew it out and swabbed the bore with more rubbing alcohol. after cleaning out
    that tiny little hole with a wire from a wire brush, I installed the spring, cup, piston seal, pushed it in with fluid as lube and "e" clipped it. ( also used the purple grease
    from Chacals kit ) was that mistake #3 ? I cleaned and blew out the banjo bolts and assembled the whole front brake system with new crush washers.
    I set up a farm syringe and 1/8" id tube to fill the mc and dribbled fluid in till it was at the top of the filler neck.
    Now the problems ; I can't get fluid to go down the lines to the calipers and when I pull in the brake lever the spring isn't pushing the piston back out,
    after a few minutes it comes out slowly. Any Ideas ? I can take the whole system apart again and use brake cleaner on everything and hone out the mc bore with
    1000 grit and a home made hone. I know there is some advanced physics lesson in this, but this is the 5th set of brakes I rebuilt and no problems
    like this on the other 4 ( all bar mounted mc's )
     
  10. Stumplifter

    Stumplifter Well-Known Member

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    No, I see no mistakes in what you did. Are your brake lines braided stainless steel?
    It almost sounds like fluid is not getting into the brake line...
     
  11. joejr2

    joejr2 Active Member Premium Member

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    it seems that "dad of seven" is having the same problem with his xj750 front brakes. I've been following it at Len's suggestion.
    lots if tips in that thread. I'll start at the top and follow Len's trouble shooting sequence. then I'll check the anti dive devices on both sides,
    the brake sides first. I've got an extra set of ADs so I can practice with those and also use them as assembly guides. Same problem where
    the piston return spring is slow or doesn't return in the MC and can't get fluid to go down from the MC reservoir. Will the fork oil leak out if I
    remove only the brake side of an AD device ?
     
  12. Dadoseven

    Dadoseven Active Member

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    I had more success with filling the lines from the bleeder valves using a syringe and tubing. Reverse bleeding. With bleeder valve open, push fluid in, then pull back on syringe pulling bubbles. The bubbles would rise to the top in the syringe barrel, then I could push more fluid in. Repeat until the syringe is full of air or no more large bubbles come out on the withdrawal.

    I think I must have had a small air leak in one of the AD units, but mysteriously, never saw any leaking fluid. Maybe there was never enough pressure built up to force it out but it still was able to suck air back in??

    If you only remove the brake side of the AD unit, it will NOT leak fork oil. There is only a mechanical connection from a piston in the brake side that pushes a plunger on the larger fork side. I've actually ran mine without the smaller, upper brake section by disconnecting the short AD brake line and using the single banjo bolt from the AD unit on the caliper. This is how I confirmed and isolated the problem to the AD unit. Once I did that, I immediately got pressure in the lines.

    Good luck! There are a number of brake bleeding problems on these 750 SECAS. You are not alone.
     
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  13. tabaka45

    tabaka45 Well-Known Member

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    Bled my XJ700N brakes after a complete rebuild in about 15-20 minutes with reverse bleed method, but a little different than Dadoseven's method. I filled the syringe with fluid, attached the tubing to the bleeder valve, opened the bleeder valve an slowly pumped the fluid into the caliper until I saw fluid in the master cylinder. (If one syringe full of fluid isn't enough, close the bleeder valve and refill the syringe. Reattach the tubing, but let any air in the tubing float up into the syringe so that the tubing is full of fluid. Open the bleeder valve and continue pumping the fluid in until fluid shows in the master cylinder.) Repeat for the other side but go very slow to allow the air to enter the master cylinder without blowing out the fluid already in it and making a mess. Once I finished I lightly tapped the brake lever a few times to get any air out of the master cylinder. I then had a very firm brake lever but did a standard bleed just as a precaution. 20 minutes and done.
     
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  14. Steve R

    Steve R Member

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    Did you flush all the brake lines out with brake cleaner? Almost sounds like you creating some type of vacuum. And once you do a flush them out with brake cleaner, make sure you flush them with brake fluid to remove the brake cleaner.
     
  15. rocka

    rocka New Member

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    AD unit?
     
  16. Chitwood

    Chitwood Active Member

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    Anti dive
     
  17. Robb

    Robb Member

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    I totally destroyed my front fender when rebuilding my front brakes. I'd covered it with plastic but the whole ordeal with the location of the master and having to guess on the fluid level and all the other things that suck about bleeding the brakes on these bikes; fluid ended up leaking under the plastic and bubbled the paint, along with the paint on the caliper itself and parts of the frame. I was planning on painting the bike anyway, so this just prompted me to quit procrastinating on that. I'd really like to change to braided stainless lines, but cringe just thinking about going through this again... and I've got the paint looking show room now so messing that up would be a blood pressure spiking event. Wouldn't you like to find the Yamaha engineer that designed this system, then strip him naked and tie him on an ant hill after pouring maple syrup all over him?
     
  18. k-moe

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

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    It's actually not a bad system to work with. Bleeding it is a bit more involved than most, but not bad once you figure out how (and practice a bit).
     
    Last edited: Oct 21, 2017
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  19. Polock

    Polock Well-Known Member

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    this sounds like you're using old lines, quit everything and get new ones.
    unless you're just practicing
     
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  20. joejr2

    joejr2 Active Member Premium Member

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    Yes You are correct. I followed previous advice and replaced the brakelines with stainless braided ones.
     

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