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Help Spongy brakes ZXR250A

Discussion in 'Kawasaki 250cc In-line 4's' started by kz1000a, Mar 15, 2019.

  1. kz1000a

    kz1000a Member Premium Member

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    I recently had my forks rebuilt & rechromed.
    While my bike was off the road, I overhauled the front & rear braking system.
    I have replaced all rotors and pads and also removed all caliper pistons and replaced the 2 rubber seals per piston with parts from Impex. Pistons and bore were in good condition.
    I admit to cheaping out and buying this triple set of organic pads for $37
    upload_2019-3-15_20-52-9.jpeg

    About the only thing I did not do was to replace the 2 copper? washers per banjo bolt with new.
    All banjo bolts and nipples are firmly tightened.

    Now that the bikes forks are back on and I have taken for a test run, I have found the front brakes to be very spongy. I have bled the front system 3 times now.
    I have noticed that the front brake lever will almost touch the rubber handle grip on the first squeeze.
    After pumping the lever a few times in succession, it then feels more normal and is about 2 -3 cm away from handle grip whist held in.
    But after releasing the handle grip and waiting 5 seconds and then squeezing it once only, it again almost touches the rubber handle grip.
    I have not touched the master cylinders, apart from refilling them whilst bleeding. Fluid level has never got so low that air has entered. No air bubbles are apparent in resovoir or the clear plastic bleed lines.
    The brake fluid DOT3 was new from an unopened container.
    Any ideas what may be the problem? I have a hunch that air is somehow entering the system, but I cannot see how.
     
  2. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Check that the inside pad (closest to the Pistons) is "clicked" into the right spot. I've found they sometimes fall out and that causes issues. The little metal holder pushes on that pad and helps hold it in place.

    KZ1000A.jpg
     
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  3. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

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    Try some fresh DOT4... bleed the master cyl by using lots of small, rapid pumps of the lever with the master at the highest point.

    With old bikes, the master cyl can also get crud buildup where the piston doesn't usually run during normal operation, but during bleeding most people squeeze the lever all the way in. This can damage the seal by running them over crud. If you can't get good consistent pressure, then I would suggest removing the master cylinder and inspecting the bore.
     
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  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    There's a tiny brake fluid return port in the brake master cylinder, if that's partly blocked then the fluid would be slow to move back into the reservoir when you left go of the brake.
    This may be hiding the air bubble's in the system
    You could try bleeding the brake's from the bottom up using a big syringe ful of fluid, but will need to remove some from the master first.
     
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  5. kz1000a

    kz1000a Member Premium Member

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    Very good point, I have sometimes noticed that the ‘notch’ was not always where it should be when reassembling the caliper assembly.
    I will try to have a look tomorrow, if the “minister of war” is occupied. :lolsign:
     
  6. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    When re using the copper washers I anneal them to soften them back up to get a better seal

    But I doubt thats your problem ... as mentioned , master cylinder crud ... only takes a spec .... been there done that :)
     
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  7. kz1000a

    kz1000a Member Premium Member

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    @Linkin
    Thx, I will try your method of small rapid pumps and see if it changes anything.
    @my67xr
    Cheers, is the tiny brake fluid return port visible in the fluid resovoir ?

    If the pads are correctly seated in their notches and the rapid pump bleed method or reverse flushing the brake lines does not correct this issue then I’ll go down the path of examining the master cylinder.
     
  8. sharky

    sharky Well-Known Member Premium Member

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    Some brakes I could never pump up fully, I solved that problem with a 20ml syringe & aquarium hose, put the hose over the bleed nipple & fully extend the syringe then crack the bleed nipple while under suction, repeat 2 or 3 times then bleed as normal, you will be surprised how much air is in there.
     
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  9. Andych

    Andych Well-Known Member Premium Member

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    The other method I have used is to ensure the Master Cylinder is mostly full.. then using a cable tie partially pull the brake lever... not too far, about half way. Use the cable tie to keep it there..then walk away for 24 hrs. I have done it that way many times now.. on bikes and cars and never had an issue.
    Sometimes when you are pumping the brake lever it is easy to actually go too far on them and it blocks the hole... I just found the gravity method above to be the most successful.
     
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  10. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    A is the main feed hole for the brake fluid which get's pumped to the caliper's, B is the return hole in the pic below
    You should be able to see a little raised spot in the brake fluid above hole B when you let go of the brake lever as it return's

    Generic brake master cylinder picture


    073117-Brake-Master-Cylinder-07.jpg
     
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  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    What @Linkin said, and unbolt the master cylinder so it can be tilted to allow bubbles a clear path. Also any junctions etc. It will self bleed very quickly.
     
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  12. TonyZXR

    TonyZXR Active Member Premium Member

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    I've always found when bleeding twin disc front you need to go back and forth a few times between the left and right caliper to get all the air out completely.
     
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  13. kz1000a

    kz1000a Member Premium Member

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    WOOHOO! Problem sorted!
    I removed LHS caliper to inspect if the notches on the inside pad matched up to the cutaway in the caliper holder.
    They did....
    But I had inadvertently allowed one of the tabs of the anti-rattle plate to be on the wrong side of the inside pad.

    upload_2019-3-16_14-2-37.jpeg

    I removed pad, realigned anti-rattle plate and reinserted pad. Reinstall caliper on disc.
    Squeeze brake lever, and hey presto, no more spongy brakes.

    Kudos to everyone for their contributions and huge thanks to Frankster. I reckon I owes you a beer or three!
    Awesome community!
     

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  14. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    No probs. I had a very experienced motorcycle person tell me the front brakes on a ZXR needed bleeding. I pulled the calipers off and clicked the pads in place, then reinstalled them fully operational. It's always easy when you know how!
     
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