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dmc2028372

Bleeding brakes

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Syringe, and I found an extra pair of hands is the easy way to do it - make sure nobodies looking down at the resevoir without eye protection though, as you can get a surprising brake fluid jet wash going on by accident!

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don't let the tube slip off the bleeder. the pads are toast after they are contaminated with brake fluid. the reverse method works great

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Remove the brake pedal and use a phillips screwdriver (carefully) to pump the piston. This serves two purposes. One is to get a full flow of fluid moving. You did put new pads in? And all you need is a 4 ft clear hose straight up from the caliper. This will cause it to gravity feed and works the best. But it has to go up at least 3 feet.

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I've always just put a clear tube on the bleed nipple so that it goes up a few inches before bending over into a bottle to catch the waste fluid.

Open the nipple and press the lever down then close the nipple and allow lever to return.  After a couple of cycles like that, the hose is filled with fluid and you can just leave the nipple open and pump away while keeping the reservoir topped up, as no air can enter the system.

The plunger needs to be traveling through a good range of stroke and returning fully when the lever is released.  Make adjustments to the stop or lever play if necessary (close the bleed nipple if you are pausing the pumping at all)

You can quickly pump plenty of fresh fluid through the system and push any air bubbles through at a good rate.  Once the fluid is clean and clear of bubbles you can close the bleed nipple.

I have used this method on front and rear brakes of all my bikes and has always worked well.

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Yep. that is how the books tell you to do it. But if you never get the level above the master cylinder resevoir you will never get the one bubble out that is causing the grief

 The other real life method is to take the whole system off the bike and hang it it so the air can only travel up. But that is more work than you really need to do.

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7 hours ago, lineaway said:

Yep. that is how the books tell you to do it. But if you never get the level above the master cylinder resevoir you will never get the one bubble out that is causing the grief

 The other real life method is to take the whole system off the bike and hang it it so the air can only travel up. But that is more work than you really need to do.

Why is that?  If you are pushing fluid through faster than bubbles can float back up through the line, surely any bubbles would get pushed out.

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17 hours ago, bluey said:

Why is that?  If you are pushing fluid through faster than bubbles can float back up through the line, surely any bubbles would get pushed out.

 You can push fluid through repeatedly and you can still have a pocket of air trapped especially in the caliper. Spending money does not change it. Sometimes you have just got to change the angle of the line. Sure it is easy to bleed a system that really did not need bleeding in the first place. I have done several hundred bikes this way.

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Once you have bled the hydraulic brake system, use a bungy or cut inner tube elastic band to hold the brake lever in the on position overnight this will cause any tiny (microscopic) air bubbles to rise to the fluid reservoir. Release the bungy etc and operate lever it should now feel more positive. For the rear brake rest a weight on the pedal or tension with some bungy etc and the same effect will be achieved👍

Brake fluid is hygroscopic which means it absorbs moisture readily from the atmosphere. Keep any spare fluid in an airtight container and avoid shaking the container as this induces air bubbles into the fluid. If possible transfer spare fluid to a smaller container this stops air contaminating the fluid, bit like wine keeping. Fully synthetic brake fluid shouldn’t absorb moisture or attack painted surfaces but take care not to spill any just in case!

Edited by section swept
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On 12/15/2017 at 11:56 AM, section swept said:

Once you have bled the hydraulic brake system, use a bungy or cut inner tube elastic band to hold the brake lever in the on position overnight this will cause any tiny (microscopic) air bubbles to rise to the fluid reservoir. Release the bungy etc and operate lever it should now feel more positive. For the rear brake rest a weight on the pedal or tension with some bungy etc and the same effect will be achieved👍

Interesting.  I do wonder why the bubbles could not rise with the lever at rest though?  When the lever is out, the bubbles could travel all the way up to the reservoir could they not?

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