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I installed new rear calipers on both sides, new pads on all four wheels, and bled brakes with engine off, then with engine on, two times each. The pedal is hard when the engine is off and extremely soft when running. It can be pushed to the floor with little effort.

I'm aware that there is probably air in the system somewhere, but I've bled through a significant amount of fluid with no bubbles coming out. Would air trapped in the ABS affect the pedal feel? Are there other possibilities that I should check, or is the best course just to keep bleeding?

The vehicle is a 2002 Buick Lesabre.

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  • you might have a brake fluid leak somewhere, are you sure you tightened all the brake line nuts?
    – amphibient
    May 6, 2015 at 19:08
  • Pretty certain. Leakage is something I was considering, I'll have to check for that. Thanks!
    – Neil
    May 6, 2015 at 19:34

3 Answers 3

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It possible that could be air still in the system. In general if it's air you should be able to pump the pedal and have it come up and be firm and hold that level. Air compresses while the brake fluid does not. If you allowed the fluid level in the master cylinder to drop to the point it could draw air in you may have air trapped in the ABS unit. Bleeding through the ABS can be a time consuming and tedious process without a scan tool that will cycle the ABS unit. (or some aggressive braking to activate it if you can safely)

If you pump the pedal and it goes firm but slowly drops while you hold it you may have an additional leak somewhere or you could have a bad master cylinder. During normal use brake fluid can become contaminated and the master cylinder wears internally but only for the length of your brake pedal travel. If you used the pump the brakes method to bleed them your pedal travel is greater than normal (perhaps ever in the history of the car). This will push the internal seals over new territory which may have some internal rust, a wear ridge, etc... causing the seals to tear. Once this happens the break pedal will never hold firm again. Pumping the pedal may help but under pressure it will have a slow drop.

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Got it resolved (at least mostly). There was air in the system, and roughly 1.5 hours of continuous bleeding pushed it out. Thanks for the answers!

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  • Where possible I much prefer to use a pressure bleeding tool to bleed brakes than relying on pumping the pedal as it seems to be a far more effective (and time saving) way to force all of the air out of the brake lines.
    – Steve Matthews
    Dec 29, 2016 at 12:29
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I'd look for leaking as the bleed off valve(s) might not have been tightened fully, or air remaining in the system.

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