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Help Suzuki GSX250F Across - Front Master Cylinder issue

Discussion in 'Suzuki 250cc In-line 4's' started by pokolbinguy, Jan 10, 2015.

  1. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Hi All,

    I am having a fantastic time (read as "pain in the butt) trying to get my front brake system working again after it locking up on me (for a second time).

    I have pulled the front caliper apart and given it a good clean up. The caliper seals were replaced about 12 months ago (only ridden twice in that time) after I had the brakes lock up on me the first time.

    This time around I suspected the master cylinder to be the culprit so pulled it apart to find some gunk in there like the brake fluid had gone "off", pulled it apart and replaced the piston & cup set.

    Pushed new fluid through the lines, all seemed good there.

    Now I can't seem to get the M/C to prime properly and force liquid down the lines. I can push liquid from the caliper all the way back up to the banjo at the M/C no issues and also into the M/C through the return port (while it does take a bit of a push on the syringe to get it to go back into the M/C.

    I have a vacuum bleeder kit and thought that would sort the issue but I can not for the life of me get the system to work properly and get pressure on the lever.

    It is sending me around the twist.

    Any tips?

    My next thought is to try and replace the M/C itself and probably the brake line.

    Anyone got a good condition / functioning GSX250F front master cylinder laying around?
     
  2. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    So I

    1 - pulled the master cylinder apart again, gave it another clean, put a pin through the return hole, cleaned up piston/cup set and put back together. MC is pushing liquid out as it should

    2- drained caliper of old (actually new but ditched it any) liquid

    3 - took brake hose off, no damage or cracks from what I can see.

    4 -connected brake line to caliper and pushed new liquid through (all at ground level (brake line off bike) and into a clean jar. Clean fluid came through, no gunk/cloudy liquid and stream was constant.

    5 - connected system back together on bike and can get M/C to push on pistons at caliper and liquid to flow out bleed nipple.

    6 - have pushed through or pulled through (with vacuum pump) easily 10 x MC reservoir full of liquid (didn't let run dry so no air entering at MC) but the pistons will not go hard on the rotor

    There is deffinatley pressure on the pads, if I hold the lever in and push the bike you can feel the pads rubbing the rotor. When you let go of the lever the pistons at the caliper retract which I assume is the problem.

    7 - after realising the pistons are moving back upon release of the lever I took the banjo off the MC to make sure it was bled properly. pull lever in, liquid comes out, finger over hole, let lever go to stop air being sucked in. All seems ok.

    8 - connected back up, can again push liquid from MC down the lines to caliper and out bleed nipple. Pistons at caliper still move out when lever pulled in, then when lever let out they move back and therefore won't go "hard".

    What am I missing????
     
  3. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Are you meaning that the pistons are retracting too far back into the caliper, so you have not enough fluid to make them move out far enough to touch the disc?
    If your having a bleeding problem, I have had success at getting the last bits of air out by pushing the pistons back fully into the caliper to push the fluid back to the M/C.
     
  4. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    The piston moves out till it pushes the pad against the rotor but not FIRM. If I watch the pistons while pulling the lever in they move out, let go and they move back, the same amount of distance.

    Might try pushing the pistons back with a clamp and see what happens
     
  5. Willrcr15

    Willrcr15 Well-Known Member Premium Member

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    Is there a second hole in the MC that is blocked that you have overlooked ?
     
  6. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Both ports in the MC are clear
     
  7. Willrcr15

    Willrcr15 Well-Known Member Premium Member

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    Can you cut some shimms that match the pads out of some 2 - 3mm steel.
    I had a problem with the CB250 on Friday, the pistons were out too far due to worn pads so we shimmed them out behind both pads. There a new set ordered. The pistons were kicking over & not retracting. I know thats not you problem but may be theyre just travelling too far for the stroke of the MC, they shouldn't get sucked back that far anyway. Is the new MC kit correct?
     
  8. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Pads are new

    MC kit is correct part and matches the one that came out
     
  9. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Given I seem to be going around in circles I think its time to resort to seeing a professional.

    Any tips on an "old school" bike mechanic in the Cessnock area NSW?
     
  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    If it was me with those problems , lock up and now no pressure , I would either pull everything to pieces again and rebuild the lot to make sure its correct or replace the MC or caliper or both

    When stripped down I would be checking thoroughly for damage or splits or wateva in the hose
    Also that the banjos are sealing correctly ...... the copper washers should be annealed before reuse.

    http://2fiftycc.com/index.php?threads/brake-bleeding-made-easy.1140/
     
  11. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    I have had a similar problem with an across master cylinder, but the good news is that I sorted it in the end. What I did was undo the brake line at the master cylinder then reattach it, then bleed again, its like there a bubble that wasn't moving when I was bleeding it. Eventually it came good.

    From what I have learnt lately, try removing the caliper from the fork leg and wedge something between the pistons so they are fully retracted before bleeding them, this reduces the area behind the pistons and will allow more fluid to pass out of the bleed nipple rather than getting lost in the void behind the piston. The less volume of fluid that is moved around with each pump of the lever, will make it easier to bleed.. well that's the theory anyway.
    tool.jpg
    make sure your double check there are 2 washers where the banjo bolt goes through the line, there should be a washer on wither side of the brake line.

    banjo.png
     
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  12. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Tried that.....a number of times

    Yep tried that. I ended up putting a spanner across the brake pad with a g-clamp on it to hold the pistons back and give a shorter distance for the pistons to travel before they go "hard". No luck.

    Yep all there. No leaks either.


    Round and Round I go. I feel like an idiot.
     
  13. Willrcr15

    Willrcr15 Well-Known Member Premium Member

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    Stupid question but is the rubber cup in the MC the right way around?, the pistons in the caliper shouldn't be getting sucked back like that.
     
  14. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Pretty sure they are but its worth a shot.

    Which way should they face? both in the same direction or one each way? I haven't got it apart at the moment so can't look at it but will take it apart again tonight.
     
  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    In part # 9 in the MC , that white plastic plate has a breather hole in the centre of it ....check its clear.

    Across1.jpg Across2.jpg
     
  16. Fox McScrooge

    Fox McScrooge Well-Known Member Premium Member Contributing Member

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    Hi mate. I know it's a frustrating thing and it's difficult for anyone to diagnose remotely. Assuming everything is assembled correctly, I find when I'm bleeding brakes, the best way to go is reverse bleed. Once that's done (ie no more bubbles coming out of the reservoir), I like to pump the lever (even if it feels like you are not getting any lever some pressure will build in the system) and quickly crack and reseal the various joins starting at the banjo bolt down, pumping the lever before you crack each join. More often than not, no matter how long I reverse bled the brakes, when I do that a bit of air escapes under pressure at each connection. Get's a bit messy though with the brake fluid. Have to wash it off straight away as it will dissolve paint really quickly. Once that's done, I think someone else mentioned it already, but when you have good lever pressure, use a cable tie or something to hold the lever on, take off the reservoir cap and leave it sitting on top of the reservoir then leave the bike like that overnight. Any final air in there should migrate out overnight.
     
  17. Willrcr15

    Willrcr15 Well-Known Member Premium Member

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    The cup should go with the open end facing the direction of positive movement, the cup should flare under pressure creating a stronger seal when the lever is pulled on. If there's a secondary one on the shaft it also should face the same way.
    Something simple is going on & I like Fox Mc Scrooge's idea make sure the reservoir can breathe, makes sense in your case.
     
  18. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Nice one, I didn't think of this. Will check it out.

    I'll check them out. I have a feeling they may be facing "towards each other". so that they are

    |****(*****)*****}}}}}#

    With

    | being the end of the bore at the handle end

    *** being the piston

    ( ) the cups and the way they are facing

    }}} the spring

    # and the "out" end.
     
  19. pokolbinguy

    pokolbinguy A bike that can't carry wine...a waste

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    Tried that

    Tried that aswell.
     
  20. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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    Hmm. Trying to think about it logically in a "root cause" kind of way...

    What has changed this time around that wasn't last time? This time around you changed the piston & cup set. Are you sure the pressure seal is installed correctly in the master cylinder without any cracking/grime etc..? Sure it wasn't stretched? It seems you are having problems with it holding pressure despite being able to get a bit of initial pressure behind it (at least enough to move fluid),

    I could be way off, but just a thought.
     

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