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Brake pedal sometimes goes all the way to the floor

own a 2006 Toyota Solera with 170,000 miles. Took it in to the shop because brake pedal went almost to the floor. They replaced the brake master cylinder, fluid and bled the lines. Got the car back and same thing happened. Long story short, mechanic replaced all 4 calipers (one was leaking at the seal) and all seemed fined until it happened again, but intermittently now. He tells me the lines are fine. Any thoughts on what else could be causing this?

Thanks

Either the power brake booster or the ABS modulator. I lean more heavily to the ABS module.

Assuming, of course, that all the prevous work was done properly.

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thanks for the suggestion. Ill have those items checked out.

The other possibility is that you have a bad master cylinder. I know you just replaced it, but it’s not unheard of for them to be bad out of the box. Just to be safe, your mechanic should diagnose with an open mind, and not assume that anything “can’t be it” because he already replaced it.

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It’s not the power brake booster.

** Power brakes are a universal feature on current vehicles, and nearly all of them rely on engine vacuum to produce their power assist. The vacuum brake booster between the brake pedal and the master cylinder is the last possible source of a low brake pedal that we’ll discuss here.

On a brake system that does not have a power assist, the brake pedal is directly connected to the master cylinder. When a manual brake system is working properly, the brake pedal always feels high and hard when it’s applied. This changes in a subtle way when there’s a brake booster between the brake pedal and the master cylinder. The pedal should still feel solid while braking, but it’s normal for there to be a small amount of pedal travel before the brakes begin to apply. This is to be expected—it’s just the brake booster doing its thing.

A quick check of the brake booster must be conducted with the engine off. Pump the brake pedal slowly several times. This will gradually deplete the vacuum assist stored in the brake booster. Once all of the vacuum has been depleted, the brake pedal should feel as high and hard as it’s going to get. However, the vehicle would be a good deal harder for the driver to slow and stop in this condition. If the pedal doesn’t feel high and hard, you’ve eliminated the brake booster as a potential source of the problem and will need to look elsewhere.

If the brake booster has failed, it would cause a symptom that’s just the opposite of what we’ve been discussing here. Rather than complaining of a brake pedal that’s too low, the vehicle owner would be complaining of a brake pedal that’s high and hard, and a vehicle that requires a good deal more pressure on the brake pedal to bring to a stop because there’s no power assist.— Karl Seyfert**

Tester

True. Happened to me with my 1983 Corolla. After much rigamarole I took it back and they gave me another one. Problem solved.

Master cylinders need to be bench bled. Not every “mechanic” is that thorough. Just sayin’.

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The master cylinder is where brake fluid gets compressed. Pressure on the brake fluid cases the brakes to be applied to the wheels. … There’s one more thing that could be causing the brake pedal to go all the way to the floor: you, the driver. The more the brakes are used, the hotter the brake fluid gets.

@donnaeastman
Brake fluid doesn’t compress.

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Donna , find another ’ Hobby ’ and stop posting nonsense from other web sites.

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Oh come on now. This happens when you drive street cars on a race track. The likelihood that OP is boiling his brake fluid on the street, AND is not getting arrested for how he’s driving is pretty remote.