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front brake master cyl priming/bleeding issues (bit long)

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by davesta, Dec 13, 2007.

  1. Hey all, i've just bought a set of hel braided lines for my trx (with r1 calipers and r6 master cylinder). I've fitted them up and i am having a problem with priming the master cylinder. Basically i have gotten to the stage where the lines and calipers are filled with fluid, but the MC just doesnt wanna prime. I can pump the lever and basically have no feedback at all. When i pull the banjo off at the MC there is hardly any fluid inside the MC, its like the port that is connected to the reservoir is blocked (its not, i dissembled the MC and cleaned with brake cleaner). I can prime the mc by squeezing the brake lever (with hoses unplugged) then putting my thumb over the outlet as i release the lever. This fills the mc up fine but as soon as i connect the hoses again i'm back to square one. At one point i had half of what my lever should be (and bleeding the fluid at the calipers revealed no bubbles) but it still felt like there was a huge air bubble somewhere and it was taking a lot of pumps after each bleed just to get any feel back into the system at all. Sorry this is so long, do any of you guys/gals have any ideas/hints to help me??

    (oh the mc is not new to the bike, i have had it a while and it primed fine when i originally put it on with the original hoses about 6 months ago)
    cheers all

  2. I've had this problem on a couple of bikes. Persistence and experimentation with pumping rates has eventually yielded results most of the time.

    In desperate circumstances (and if you try this, you will swallow brake fluid and die, so don't do it :shock: ), I've connected a bit of tube to the bleed nipple furthest from the m/cylinder and sucked on it while pumping the lever to get the system to prime.

    Brake fluid tastes really really nasty. And is.
  3. Prime the MC and lines first by:

    Connect your line to the MC banjo and then pop the free end of the line into the MC reservoir.

    Fill the res and pump the lever. This basically fills the line and the fluid coming out feedbacks into the res as a closed circuit. Try slow squeezes and quick 'jiggles' until no more bubbles are seen out of the line or the MC res port.

    Note: Careful you don't overdo the lever pump and spray fluid everywhere.

    With your MC and line now primed and air free connect your line to your caliper and bleed as normal. This method for me is a lot faster than connecting everything up and trying to prime by bleeding at the caliper.

    Once your primed and bleeding, if you can't get pressure then some things that have worked for me are:

    1. Crack the banjo's slightly with lever pressure. This should expel any air lurking near the banjo's.
    2. Tap the caliper, line, banjos with a rubber mallet to dislodge any trapped air.
    3. Strap the lever to the bar and leave overnight.

    If thats not working then consider changing your bleed method - try reverse bleeding - get a 'horse' syringe and a small length of tubing. Prime it with clean fluid and push the fluid from the caliper nipple up to the MC. Again, change stroke type, firm even then quick jiggling etc. Again watch out for it shooting out the other end! Fnar Fnar.

    If you have a compressor you could also consider getting a vacuum bleed kit but tbh you should be covered by normal (lever assisted) bleeding and reverse bleeding.

    If nothing is working you have to consider you don't have a closed circuit so check leaks at the banjo's, piston seals and MC.

    As for sucking on the tube :shock: You would be a braver man than I... try using an empty syringe and pull the fluid through ... it's a little safer :grin:
  4. Nice write up sloth. U pretty much covered everything/

    Getting a feel, with a totally dry system is a right bi^CH!!. I use the syringe method, but i suck the fluid out of the system. It helps to prime the MC.

    Once u get some decent pressure, i tape the brake lever to the handle bar so the system is pressurized overnight, it forces the bubbles up. Then bleed again, works a treat.
  5. The best way to bleed hydraulic systems is by using a power bleed system. This involves the use of a pump which pressurises the master cyclinder reservoir and forcing fluid into the system and out of the bleed nipples at a controlled rate.

    If such a kit is available for bikes, that'd be the way to go if you or your mates do this work regularly. If you can make up a plate with a rubber gasket or seal that can be clamped over the reservoir and that has a hose fitting connected to some sort of pump then you're in business.
  6. Thanks a lot for all your help guys, its done and i have a really firm lever now. Just gotta do one or two things then take it out for a test ride and check to see how much better the brakes are after the braided lines and caliper rebuild. I'll post back and let you know. The system that worked best for me was reverse bleeding the system. I had about half feel thru the lever and then just kept putting fluid in from the bleed nipple ends until the reservoir was about half full. Then i zip tied the lever fully on and left it overnight. The next day the lever feel was pretty much there and a quick bleed and flush bought it to 100%. I would love a power bleed system but this isnt something i would do very often and the cost is pretty high. Next time i do this (won't be a while) i'll definitely have to try Sloth's suggestion of putting the brake line ends in the MC reservior. Thanks again guys :cool: