Author Topic: Brake bleeding a new brake line  (Read 4145 times)

Offline George R. Young

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Brake bleeding a new brake line
« on: October 28, 2011, 01:21:21 pm »
For periodic air removal from a full system, it's fine to simply open the caliper bleed bolt, squeeze the lever, close the caliper bleed bolt, and repeat a few times until you see no more bubbles and the fluid looks pretty clear. This chases bubbles trapped in the body of the caliper.

In everyday operation, bubbles of air which originate in the brake lines rise to the top and get expelled thru the 2 little holes in the master cylinder (inlet port, compensating port) the next time you apply and release the brakes.

Things are slightly different when there's a large amount of air in the system, for example if you've just installed a shiny new stainless brake line. Effectively, there's a single large bubble filling the entire brake line, and there's no fluid in the line to float the bubble to the top. A different technique is called for.

This worked for me on 2 different stainless line installs. First make sure with a toothpick or something that both holes in the bottom of the master cylinder are clear. Orient the bars so the master cylinder is at the highest point. Then with the caliper bleed bolt closed, squeeze the lever gently and then release sharply, and you should see air bubbles rise out of those little holes. Repeat until either the brake line firms up and no more bubbles appear, or your wrist gets sore. Tapping the line now and then helps the bubbles rise.

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Offline lt1

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Re: Brake bleeding a new brake line
« Reply #1 on: February 13, 2012, 01:43:12 pm »
Good info.  I w/b very cautious with/about using a toothpick.  Breaking off the tip will just about guarantee a plugged hole.  My general procedure includes a rough bleed at the calipers, then follow your procedure above.  Then strap the lever to the grip, leaving about 3/8" clearance, overnight (or a bit longer).  That usually will force the remaining air bubbles out.
Eyes, Brain, Hands.  Repeat.