What they didn’t teach you in brake bleeding school

There are always unforeseen problems when working on cars. Bleeding the brakes is no exception.

There are lots of different ways to bleed the brakes. I use a hand vacuum bleeder. It can be purchased for less than $30 and makes brake bleeding a one man job. Another very cheap tool is Speed Bleeder one-way valves.

Have a glass jar nearby to collect old brake fluid. When using a vacuum pump, put the vacuum tip into the jar before removing the collector from the vacuum pump to avoid spillage.

Always keep the master cylinder topped off. Occasionally take a break by closing the bleeder valve and go check on the master cylinder.

Bleeder valve is Frozen

Yes, you are doing the right thing. You are trying to loosen the piece that has a nipple on one end and that threads into the brake cylinder on the other end. It will be above the brake line fitting. Just make sure you are trying to turn the valve the right way. Lefty loosey, but it’s reversed if you’re coming from the other side. Use the box end of a wrench to loosen the valve. If the valve has not been opened in a long time, don’t risk breaking it — spray PB Blaster or Kroil or similar catalyst penetrating oil onto the screw and let it soak in for a day or two. If you break the valve off, your job just got a lot more painful. The valve only needs to break loose and move at most 1/4 turn for you to do the job. When you reinstall a valve, put some axle grease on the exposed threads to help protect it from future corrosion.

Air Rises

This should be obvious, but sometimes the obvious escapes us. The vacuum pump and collector must be held in the air ABOVE the bleed fitting in order to accomplish the bleeding. Also, if there are any high spots in the system, the end of the car being bled must be elevated (elevating might be a good idea in general — it certainly doesn’t hurt).

When using a vacuum pump, pump it to about 20 mm Hg and pump some more whenever it goes below 15 mm Hg.
First, you want to get old brake fluid out and discard it. Old fluid will be dark with moisture and contamination, new fluid will be clear and beige-colored. Secondly, you want to purge the air from the system. You should see lots of bubbles at first, eventually trailing off and running clear.

Nothing happens

You might have to tap the brake pedal to push a clog out of the bleeder nipple, especially if it was missing the rubber cap.

The bubbles won’t stop

You’ve been bleeding for a while. The bubbles seem pretty consistent, not trailing off, or there is a distinct foam to the pumped fluid. You might even hear a hissing noise. The problem here is not anything you’re doing. It is air passing the threads on the bleeder and being pulled in with the brake fluid. This would not be a problem except it makes it impossible to tell when you have actually bled the system. To fix this, you must take the bleeder valve out all the way (I used a 5/16 socket to make this easier) and wrap teflon pipe thread tape around the threads several times. Reinstall the bleeder valve and try again. Like magic… hopefully. If it still seems to be leaking air, you may simply have too much corrosion on the bleeder valve for it to correctly seal. Go and buy a new bleeder valve, wrap it with teflon tape, and you should have no more bubbles.

Hopefully this is all the information you need to get the air out of your brakes. When you’re done, top off the master cylinder, reinstall the cap, and remember to pump your brakes to build up pressure while the car is still parked. (If you did not also install a new master cylinder, don’t allow the pedal to hit the floor though, or your master cylinder is likely to be damaged.)

4 Responses to “What they didn’t teach you in brake bleeding school”

  1. Manuel Guillen says:

    I did exactly what you said with the teflon and after 3 days of trying to find where the air was coming from. Changed the master cylinder changed all the break lines . Really appreciate your willing to share.

  2. Phil Lee says:

    Thank you for sharing. I got endless bubbles when bleeding brakes last month. Will follow your tips.

  3. B says:

    It’s pretty maddening. I think I’m experiencing the air around the thread scenario. So I tried teflon tape. Brake fluid eats it. So then I bought speed bleeders with thread sealant on them. Still not working. I have 2 new calipers from different places, I’m starting to think the threads on both are crap as odd as it sounds. I’ve never experienced anything like this.

  4. David says:

    Thanks for this post, although I’m not sure Teflon tape applies to all vehicles, since not all come with tapered threads?

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