Thumb Brake

Discussion in 'Technical Help' started by M55russ, Jan 17, 2018.

  1. Has anyone got any tips on bleeding a thumb brake.
    The MC does not have a bleed nipple so I am trying to bleed it from the rear caliper but no look getting any pressure.
    I have checked the brake line and there are no leaks and full of fluid.
    Any tips would be appreciated
     
    #1 M55russ, Jan 17, 2018
  2. #2 Robarano, Jan 17, 2018
    • Like Like x 1
  3. I thought that you have to bleed high up on this and not low down?
     
    #3 XH558, Jan 17, 2018
  4. I should of mentioned that there is a brake light pressure switch in the MC hence no bleed nipple. Also the brake is direct to the rear caliper and I have done away with the foot brake as due to a right leg/foot injury I am unable to use the foot brake.
     
    #4 M55russ, Jan 17, 2018
  5. sorry to hear about the injury,,Is there not a web site with fitting instructions?
     
    #5 XH558, Jan 17, 2018
  6. It was a fleabay purchase and there is nothing on Youtube either, its just baffling me and I am beginning to suspect the seals in the MC are shot
     
    #6 M55russ, Jan 17, 2018
  7. If the seals are gone you would get continuous air bubbles!?,,
     
    #7 XH558, Jan 17, 2018
  8. Can I ask what bike it's going on and to help, have you got a link to the thumb brake and any pics on how it's fitted?
     
    #8 noobie, Jan 17, 2018
  9. Its going on a hybrid project bike. The thumb brake is fork mounted to a S4r sssa.

    20180117_152933.jpg
     
    #9 M55russ, Jan 17, 2018
  10. Could try removing the lid on the reservoir and pushing the piston or pads in to the caliper?
     
    #10 Blakey749s, Jan 17, 2018
    • Like Like x 1
  11. you could just pump up the brake then slacken the pressure switch then re tighten.
     
    #11 finm, Jan 17, 2018
    • Like Like x 1
  12. Tried that one already. Thinking of removing the pressure switch and fitting a bleed nipple just to see if I can get the system to work.
     
    #12 M55russ, Jan 17, 2018
  13. Keep trying. I had to change the rear master on a bike a while back. It to me ages and lots of swearing to get the new master to start pumping fluid. I was about to chuck it away when eventually it started to draw fluid from the reservoir and into the circuit. I have no idea what I did that eventually made it start to work!
     
    #13 razz, Jan 17, 2018
  14. Make sure the M/C is able to return to fully extended. If by any chance the lever is holding it off it’s stop. That will prevent the M/C drawing the fluid from the reservoir.
    I tend to Force pressure bleed through the reservoir.
    And as said before crack the banjo bolt once your able to get some pressure build up.
    HTH
     
    #14 Northan Monkey, Jan 20, 2018
  15. Reverse bleed from caliper to m/cylinder? syringe with tube over bleed nipple and push fluid back through system to m/cylinder and up into resovoir?
     
    #15 Hughdg, Jan 20, 2018
  16. No you’d have to make a bung or cap to force fluid in from the reservoir.
     
    #16 Northan Monkey, Jan 20, 2018
  17. So a quick update, I swapped the pressure switch to the caliper and put a bleed nipple in the MC and after an hour of bleeding the system it finally firmed up. I also removed the caliper and pushed the pads back in a few times which seemed to help the cause. Now all I have to do is wire the pressure switch back to the headstock area and see if I have succeeded.
    Thanks for all the help and suggestions guys:upyeah:
     
    #17 M55russ, Jan 21, 2018
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