Homemade Power Bleeder

I have brand new Hayes Prime hydraulic disc brakes on my two race mountain bikes.  Great brakes.  Reasonably light.  Easily adjustable.  Like all hydraulic brake sets, they come pre-bled from the factory.  The bummer is they come with 75′ long hydraulic lines, just in case you are installing them on a tandem or other gigantic bike.  Well, I ride a small frame bike so I have two options: 

Option one is to leave the system pre-bled and roll up the extra 3 feet of brake line and tape it to frame or handlebars.  Definitely falls under the “you might be a redneck if…” category.  Option two is to shorten the lines to properly fit the bike.  But that means breaking the factory seal and allowing the possibility of air going into the system.  More often than not, it can be done without getting air in the system, but when you do you get to bleed the brakes.

Now I’ve been in the automotive business for decades and have worked extensively on hydraulic systems.  Hydraulic brakes are pretty simple compared to electronically controlled automatic overdrive transaxles.  I’ve bled hundreds of automotive and motorcycle brake systems, generally without incident, but for some reason, bicycle hydraulic brakes have been a major pain, generally requiring several attempts before finally getting the systems bled. 

I’ve bled the front brakes on my single speed Raleigh race bike in what has amounted to a futile attempt to purge the system of air.  I’ve watched technical videos, read manuals, and tried several different methods only to be five miles into a ride, bombing down a hill and have my front brake lever go all the way to the handlebar grip.

Power bleeder 480

$15 at Walmart and I built an awesome power bleeder for my mountain bikes.

After six unsuccessful attempts and six frustrating sessions I decided there had to be a better way.  I’d always used power bleeders on automotive systems and had never had a problem bleeding even the most complicated systems, so I decided to power bleed my bicycle hydraulic brakes.  Only one problem:  Nobody has made a power bleeder for a bicycle application… until now.  After searching high and low for a power bleeder for a bicycle, I decided to build my own. 

For those unfamiliar with a power bleeder, it is a tool that supplies steady, uninterrupted hydraulic pressure to one end of a brake system.  You then open the other end and allow the hydraulic fluid to push the air bubbles out until there are no more bubbles, and then, while the system is still pressurized, you seal the system again.  There is no interruption like when manually bleeding the brakes.

Here is my invention.  It cost me about $15 of supplies I found at Walmart.  One sealing canister made of shatter-proof plastic — $7; one aquarium air pump — $5; and one 20′ roll of aquarium air hose. I drilled two holes through the lid of the canister and ran one end of the hose into the canister to where it just cleared the bottom.  This line is the hydraulic line.  The other line I ran just through the lid of the canister so it would be well above the fluid line.  This line is the air supply line.  I then cut the single 20′ line in the center so each line was 10′ long.  I sealed the lines to the canister with silicon sealer and allowed it to dry. 

Now it was time to test it.  I put a quart of Dot 4 brake fluid in the canister and sealed the top.  Next I hooked the hydraulic line to my bleeder fitting and screwed it into the port on the brake caliper.  I then connected a line from the master cylinder bleed port and ran it to my catch bottle so there would be no mess as the bleeder pushed out the air and fluid.

I plugged in the power bleeder and watched as the pressure built above the fluid and began to steadily push fluid down the line into the caliper fitting. Soon bubbles were coming out of the system while I manipulated the lines and grips to make sure there were no trapped pockets of air.  In about two minutes there were finally no more bubbles and I sealed first the caliper and then the master cylinder fittings.  I put the bleeder aside and used a fresh shop towel and rubbing alcohol to clean up the few drops of brake fluid that had spilled.  Now it was time to check the brakes.  Oh. My. God.  They were perfect.  No squishiness whatsoever.  They feel better than the rear brakes.  Love my new bleeder.  I’ll let you know how it does on the trail, but I can tell you it already feels better than it has ever felt.