Brake pedal goes lower when I am not accelerating

2005 HONDA ACCORD
218,000 MILES • 3.0L • 6 CYL • 2WD • AUTOMATIC
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ETHER727
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When I am not accelerating, the brake pedal drops lower before engaging the brakes, otherwise braking is normal. Brake pedal does not sink to the floor when pressing hard on the pedal. Tests: Pumped brakes and held kept brake my foot on the pedal for over 30 seconds after turning the engine off, pedal did not change. I pumped up brakes and held my foot on the pedal then started it up and the pedal dropped down a little.

I bled the brakes, passenger rear, driver rear, passenger front, driver front, no bubbles in line.

I did a smoke test but I'm not sure if I did it properly, I don't have bi-directional scanner.

Sincerely, Paul
Jun 11, 2022 at 10:39 AM
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KASEKENNY
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There are a number of things that can cause this but based on what you have done the brake booster is what makes the most sense.

However, here is a guide that will help with this:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

I am attaching the testing for this as well from the manual and the process to replace it as I suspect this is the issue.

Please run through this info and let me know if you have questions.

Thanks
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Jun 12, 2022 at 10:24 AM
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ETHER727
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The test passed in addition, when I" turn off the engine and press the brake pedal 3-times it rises up a little each time. If I disconnect the Power Booster Vacuum line and plug both the engine and Power Booster port will the car perform as if I had regular brakes? I don't understand how the brake pedal can drop so low when not accelerating. Thanks!
Jun 16, 2022 at 6:45 AM
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KASEKENNY
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The only connection that the brakes and engine have is the brake booster as it uses engine vacuum.

So, I suspect you have an internal leak in the booster. I understand it may have passed the functional test but that is the only thing that makes sense based on what you are telling me.

When you are not accelerating that is when the engine vacuum is at the highest. So, if the pedal is dropping more than it should before it applies the brakes makes me think we still have an issue in the booster.

However, let's take a step back and find out how this started. Did you just buy this vehicle, and you feel it is too low? Or did you do a repair and then this started?

Just let me know the history of this and we can go from there.

Thanks
Jun 16, 2022 at 9:57 AM
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ETHER727
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I got the car in 2020, and since then have put 13,000 miles on it. I replaced the rear brakes and calipers last year. Thanks for the info! Paul
Jun 16, 2022 at 1:56 PM
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KASEKENNY
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Okay. So, when did this issue start? When you put the calipers on? If that is the case, we could have a caliper issue.

Use vice grips and crimp off the rubber brake line one at a time and then retest the pedal. When it feels normal again, you eliminated the problem.
Jun 16, 2022 at 5:15 PM