Brake pedal goes to the floor when the engine is on

My brother has a 2000 Blazer. When the car is on, the brake pedal has no brakes and they get down to the floor. But when the car is off, the pedal feels solid. I'm not sure if I should change all calipers or check for air.
Experienced mechanics share their insights in answering this question :
The first thing you’d want to do of course is pull off all the wheels and look for the leaks. But if you have no leaks, yours is the classic sign of a bad brake booster. When brake boosters go bad, you step on them with the engine off and will notice the pedal is nice and hard. When you start the engine, they go right to the floor. If this is what you are seeing, it’s probably a brake booster. But check for leaks first because brake boosters are pretty expensive and are no fun putting on. If you want to have to have this looked at first, a technician from YourMechanic can come to your home of office to inspect your brakes and replace your brake booster if necessary.

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ANSWER: Maybe you have a bad booster. The brake booster increases the mechanical force from the pedal to the master cylinder. If that extra boost of mechanical force is reduced by a blockage or leak, the pedal won`t engage as engineered and the brakes won`t function properly.
If the brake pedal sinks to the floor when the engine is running then there may be a problem with the brake booster.
A bad break booster will cause spongy and a bit loose pedal and even if the car is off then also it will be the same due to the crack or leakage in the booster part will not let the to make the pressure inside it while pressing the peddle and assist while you breaking.
The most common causes of your brakes not releasing is a seized caliper or brake pad. This typically occurs due to rusting or ageing.
As such, the air in your brake lines results in you pushing the brake pedal down to the ground. You`ll need your mechanic to bleed air out of the brake line. Bleeding the brakes will help restore the brake fluid pressure in your braking system.
The most likely cause of a sinking pedal with no external leakage is a faulty brake master cylinder that`s leaking internally. Were the brakes hot, we might consider boiling fluid due to moisture contamination or friction material gassing.
A vacuum leak from the brake booster can cause unregulated air in your induction system and create a lean fuel mix in the engine. You`ll also notice a drop in engine RPM and possible engine stall.
Brake pedal difficult to push – The most common sign of a brake booster leak is your brake pedal feeling “harder” than normal. It will require more force to work and increase your stopping distance. If you notice this, you should get your car inspected as soon as possible. This is because it can affect your safety.
Brake pedal difficult to push – The most common sign of a brake booster leak is your brake pedal feeling “harder” than normal. It will require more force to work and increase your stopping distance. If you notice this, you should get your car inspected as soon as possible. This is because it can affect your safety.
Driving around with a failing or bad brake booster is quite dangerous, as it can lead to complete brake failure down the road.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Supportive bar attached to brake pedal interrupts proper braking process
ANSWER : It’s possible to have someone alter the brake pedal or adapt a brake pedal from a different vehicle. You may call around to some customization shops to see if anyone is interested in taking on the project. But first, I would try reaching out to the selling dealer with your concern – especially since it is a new model. Good luck.

Why is my brake pedal going all the way down to the floor?
ANSWER : If you are having to refill the brake fluid from it getting low and the brakes go to the floor means you have a leak in the brake system somewhere. You may have a broken brake line, leaking wheel cylinder or caliper. You should not drive the vehicle until the brake system is inspected and repaired from the leak.

Low brake pedal and anti-lock brakes are not kicking in.
ANSWER : The brake pedal is working to stop the vehicle, but there may be air in the controller unit causing the ABS brakes to not function. I recommend bleeding the brake system from the farthest location from the master cylinder to the master cylinder including the ABS unit. If the brakes are still spongy after a full bleed, then the controller will need to be replaced. If you need further assistance with your brake pedal being spongy, then seek out a professional, such as one from Your Mechanic, to help you.

Brake pedal goes 3/4 way to floor
ANSWER : Hello there. This is a more unusual problem, especially given the amount of parts you have replaced. In most cases, the pedal travel is due to either the master cylinder or the brake booster, sometimes both.

Given that these have been replaced, there may be other causes. The most likely fault that comes to mind would be that there may be air in the brake fluid system or one of the brake calipers could be stuck requiring extra travel to engage.

This can occur over time and brake fluid attracts moisture or from replacing the brake components. Some vehicles may be difficult to remove all of the air from when bleeding and require the vehicle to be bleed different ways. If the brake system was vacuum bled then it may need a mechanical bleeding to resolve the issue. If you would like to have this done, a certified mechanic can diagnose your brake pedal issue and determine what should be done next.

Car stops slower & brake pedal goes to floor
ANSWER : Sounds like you may have some internal leakage in the brake master cylinder. The brake master cylinder, if it is leaking internally, will maintain fluid level and allow the pedal to drop. It is possible that the leak is small enough to support the pedal when it it is pushed when the engine is off, but may continue to drop further when the power assist is active from the booster.

The master cylinder may need to be replaced and the brake system bled. Due to this repair having high safety concerns, we have to recommend that you enlist the help of a mechanic, such as one from YourMechanic, who is qualified to safely and accurately diagnose the brake hydraulic issue and carry out the needed repairs to the braking system.

Brake sensor is to sensitive causing brakes to flicker while driving. 2005 Mercury Montego
ANSWER : Hi there – your brake light switch needs a minor adjustment. It is adjusted too "tight" or close to the brake pedal lever, or possibly has failed. Adjusting/replacing it will eliminate this flickering problem. I recommend a brake light isn’t working inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.

When I put my foot on the brake my back left brake light goes off, when I take it off the brake the brake light comes on
ANSWER : I would suggest trying to disconnect and reconnect the wiring to the rear lights. I have seen these older Toyota vehicles rear lighting short out on the lights themselves due to the way the light circuit was made on the lamp housing. Look at the housing circuit on the light to see if one is touching another, and that could tell you why it is malfunctioning. There could also be a problem with the brake light switch. If you are not comfortable dealing with wires, I recommend getting in touch with a certified mechanic who can look at your brake light issue for you to see what’s going on.

Hard brake pedal and rear brakes locking up.
ANSWER : Hi. I will help you with this issue you are having with your 2001 Durango. Unless you bled the master cylinder, it is possible there is still air in the system. If you car is equipped with ABS, air could have also gotten trapped in the ABS modulator. If ABS equipped, a bi-directional scan tool would be essential to manually activate the ABS system to clear air from that segment of the lines while you are bleeding the system. It is also possible that in all of this work somehow the proportioning valve has been affected causing the desired pressure differential, front versus back, to get out of spec. Using a 2,500 PSI gauge, you can check the pressures at each wheel and that will definitely give you a clue as to which brake circuit is the issue (or both), whether the proportioning valve is working properly and whether the line pressures at each wheel are within spec. Should you need a second opinion, by all means feel free to contact YourMechanic for assistance and we will diagnose and repair the issue for you.