Results 1 to 10 of 10
  1. #1
    mtbr member
    Reputation: Major Clanger's Avatar
    Join Date
    Feb 2012
    Posts
    185

    Self-Bleeding Tip

    The old hands out there will be familiar with this, but here's a good thing to do periodically to your hydraulic brakes.....

    Hold them on overnight once per fortnight using a rubber band between the lever and handlebar grip. It doesn't have to be super tight; just enough to keep the master cylinder piston open. This means that any tiny bubbles of air in the system will find their way upwards and then out into the resevoir.

    It'll only work with brakes that are already bled-up and will give you a much better feel at the lever. I used to do it all the time with my motorbikes and it works!
    Using yesterday's technology, to create tomorrow's problems, today.

  2. #2
    LightJunction.com
    Reputation: lightjunction's Avatar
    Join Date
    May 2011
    Posts
    774
    I'm a fan of this method too. Seems silly at first, but it's really good preventative maintenance. Every now and then I'll also unbolt the calipers, rotate them around and tap them with the rubberized end of a screwdriver to make sure there aren't any air pockets trapped in the calipers.
    We sell quality bike headlights and flashlights.
    www.LightJunction.com

  3. #3
    Fat boy Mod Moderator
    Reputation: donalson's Avatar
    Join Date
    Apr 2004
    Posts
    2,359
    it's called gravity bleeding in the car world... great on pre ABS systems
    - Surly Disc trucker
    - '82 trek 560 roadie

  4. #4
    Clyde on a mission!
    Reputation:
    Join Date
    Dec 2011
    Posts
    664
    Quote Originally Posted by donalson View Post
    it's called gravity bleeding in the car world... great on pre ABS systems
    I really can't see that ever working on a car.

    On a bike the brake lines usually go uphill all the way from the calipers to the master cylinders meaning that an air bubble will eventually make it all the way to the master cylinder.

    On a car the brake calipers are usually not the lowest point, the rear brake lines start at the brake calipers, then go downwards to the rear axle if the car has one of those, then upwards and downwards once again through a piece of hose to allow the suspension to move, under the car and finally upwards again to the master cylinder. From the front brakes there are a piece of hose allowing the suspension to work too, typically mounted in an upwards arc, then some brake lines running to the master cylinder, sometimes running low before going upwards again. Air bubbles are usually generated at the brakes, but they will never make it to the master cylinder from there unless they develop the skill to run downhill somehow.

  5. #5
    Fat boy Mod Moderator
    Reputation: donalson's Avatar
    Join Date
    Apr 2004
    Posts
    2,359
    it's more of on a car that you go around and open all the bleed screws and the fluid slowly seeps down...
    - Surly Disc trucker
    - '82 trek 560 roadie

  6. #6
    re member
    Reputation: net wurker's Avatar
    Join Date
    Sep 2007
    Posts
    6,847
    Yes, gravity bleeding works great on cars, at least, as was mentioned, on pre-ABS brake systems. One step not mentioned is you have to remove the master cylinder cap, and monitor the brake fluid level. Don't let it get below the bottom of the reservoir and down on into the master cylinder, or you will introduce air into the cylinder.

    Once you crack open a bleeder screw, the fluid starts moving down and out the bleed screw, carrying with it air pockets. If you are patient and watch the fluid flowing out of the bleed screw, you will see a steady stream of brake fluid, then you will see patches where it gets all bubbly and gurgley. This is what you see as air bubbles/pockets are evacuating from the system.

    An example of when you might use this technique while working on cars is after you have replaced a rubber brake hose, like where one connects the steel brake tubing that runs along the frame and joins to a caliper.
    Quote Originally Posted by My Avatar
    WOOF!
    My videos on Vimeo

  7. #7
    mtbr member
    Reputation: OneEyeMan's Avatar
    Join Date
    Aug 2005
    Posts
    608
    Awesome trick.
    I had my brakes (XO) bled about 2 months ago.
    Recently, the front brake lever has been coming almost back almost to the bar.
    Breaking performance was still strong, but the feel wasn't there.
    I think this was due to 2 things:
    - I take the front wheel off everytime I load the bike in my car.
    I do this by putting the bike upside down. So the bike is upside down 2 times for every ride.
    - I lay the bike down on its side in my car

    I have a feeling that both of these things allow air bubbles to reach the calipers.
    I tried this tip over night and the lever feel is now just as it was right after the bleed.

    Does my logic make sense?
    Will this fix be permanent as long as I don't invert the bike or store it on its side?
    Thanks guys,
    Lenny

  8. #8
    mtbr member
    Reputation: Major Clanger's Avatar
    Join Date
    Feb 2012
    Posts
    185
    Hello Lenny,

    It shouldn't matter whether your bike is leant on its side or inverted as long as the hydraulic system is sealed. That way no air can get in regardless of the bike's attitude. All you need to do is put the band on the lever periodically and it will do the hard work for you.

    All fluid (apart from DOT5) is hydroscopic though and this means that over a long period of time tiny amounts of air can find their way in if the lid's been off the master cylinder (water is almost always oxiginated). That's why it's good to bleed through every year.

    I'm referring to motorbikes here but the same applies to MTB brakes I assume.
    Using yesterday's technology, to create tomorrow's problems, today.

  9. #9
    007
    007 is offline
    b a n n e d
    Reputation: 007's Avatar
    Join Date
    Jun 2005
    Posts
    5,283
    eeeenteresting. I shall try this . . . .
    Alcohol may lead nowhere, but it sure is the scenic route!

  10. #10
    mtbr member
    Reputation:
    Join Date
    Sep 2007
    Posts
    531
    I thought the reason this worked was in part because it pushed the pistons in the caliper away from the o rings giving them the chance to expand thereby giving less throw on the lever. I used to do this when I had k24s but it was only a temporary fix. I never left the master cyllinder cap open though, so that might be the difference. I would occasionally take the brakes off the bike and just hang them overnight, and if I couldn't see fluid in the reservoir I'd bleed it again.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •