Brake Bleeding – All By Yourself

By – Lawrence Mazza <lawrence.mazza@stratos.net>

I like working on cars. And although modifications are what I enjoy most, there is some amount of gratification I feel by doing routine maintenance and repairs. I was recently doing a brake job on my car and got to a point where I needed a helper to bleed the fluid in the brake lines. I had completed a rebuild of all the calipers, so I needed to bleed the entire system. Bleeding the brakes usually requires two people -- one to push the pedal and the other to crack the bleeder screw and yell "Push!" and "Release!" And so began the search for a willing helper.

On occasion, I have asked my wife to do the pushing (I asked her to get under the car and work the bleeder screw, but you can guess what she said about that). My daughter is always willing to help, but she's just too small to reach the pedal and push with enough force. I've also asked my neighbor to help when I just couldn't do something myself, but today the family was out shopping and Gene wasn't available. So there I was, all alone needing help. Time for a beer.  While I was waiting for someone to come home, I was thinking about how to bleed the system by myself. I decided that a check valve would be a good thing to use, so I finished the brew and went looking for parts.

Bleeder Screws

Photo 1 shows two bleeder screws. On the left is a cross section of a standard bleeder screw. During normal operation, the screw is tightened into the caliper and the angled face of the screw makes a seal in the bottom of the hole. When you bleed the brake lines, you unscrew the bleeder about a half turn or so which pulls the sealing face from the seat. As you push the brake pedal, the master cylinder forces brake fluid past the bottom of the bleeder screw, through the cross drilled hole and up through the hollow screw and into a discharge tube.

If you were to release the brake pedal with the bleeder open, you would risk sucking air into the system, so that's why you need someone there to close the screw before you release the pedal.

The Check Valve

An old tire valve makes a nice check valve. I happened to have one in the junk drawer, but you can buy one at any parts store. Or, if you take a trip to the local tire dealer, they'll probably give you as many as you'd like since they pull them from every wheel that gets a new tire. Even if it's after hours, go to the dealer anyway -- there's probably a few of them laying around in the parking lot.

Once you secure a tire valve, you need to remove the rubber part to get to the metal core in order to put on a discharge tube. Saying "remove the rubber part" is very easy, but actually removing it is quite difficult. I started by slicing the rubber length-wise in a few places, then, using a wire cutter, I cut and pulled the majority of the material from the metal core. To remove the final bits of rubber, I used a wire wheel and it cleaned and polished the core very nicely.

Modifying the Bleeder Screw

Simply attaching a check valve to the bleeder screw won't work. Since the threads on the screw don't make a seal, releasing the pedal while the screw is open may allow air to be drawn into the system. So you need to modify a spare bleeder screw by plugging the side hole and drilling the top hole straight through. I chose to solder the side hole because it's quick, and I was afraid that epoxy might not hold.

When soldering the side hole, you may want to drill it out a bit so you can get clean metal for the solder to wet. Fill the hole with solder and don't worry if you get some inside the bleeder. However, don't get any solder on the angled face of the screw since this is the surface that makes the hydraulic seal. Then, using a drill just smaller than the top hole in the screw, drill from the top all the way through the bottom of the screw, so you now have what resembles a threaded tube (see Photo 1).

Resist the tendency to drill a larger diameter hole through the screw. As mentioned earlier, the angled bottom of the screw is what makes the seal as it presses against the seat in the caliper. If you drill it out, you may remove too much material and won't be able to affect a seal.

Once you have a check valve and modified bleeder screw, you need to connect them together. Cut a small tube to connect between the top of the bleeder screw and the threaded end of the tire valve. I used a piece of gas line hose 1/4" I.D. X 1/2" O.D. X 1-3/8" long. Make sure you use tie wraps or hose clamps on this tube since it will take several hundred pounds of pressure to open the Schraeder valve in the tire stem (Photo 2).

Bleeding the Brakes

Remove the original bleeder screw from the caliper and install the bleeder/valve assembly. Connect a 2' long piece of 1/4" X 3/8" hose to the core of the tire valve, and put the other end into a container to collect the old fluid. Now, slowly pump the master cylinder several times until you feel the fluid flowing out of the bleeder screw smoothly. Listen for trapped air as it exits the system, and don't push too hard because you could rupture the hose or break the tie wraps. Push and release slowly so that the master cylinder can replace the fluid without bubbles, and be careful not to pump the master cylinder dry. Be sure to thoroughly bleed the system - brake fluid is cheap. "If in doubt, push it out." After you are comfortable that both the line and caliper are bled properly, remove the bleeder/valve assembly and reinstall the original bleeder screw.

If you're bleeding only one caliper, you are finished. However, if you are doing the entire system, make sure you follow the car manufacturer's instructions and procedures about which wheel to bleed first. In general, you want to bleed the furthest caliper first, the right rear, then work your way closer to the master cylinder. So, the left rear would be second, the right front third, and the left front would be last. Also, remember to top off the master cylinder with fluid when you're finished.