Could the brake servo booster that the master cylinder attaches to cause the brake pedal’s excessive travel?
I have a Toyota avensis 2008 model. My issue is the brake pedal is traveling to the floor when brakes are applied. I have inspected the brake lines, calipers and have changed the master cylinder. But the problem has not gone. The only other option am remaining with is the brake servo booster that the master cylinder is attached to. When I step on the brake pedal a sound like of some pressure being released comes. Could this servo booster be the issue?
My car has 150000 miles.
My car has an automatic transmission.
Experienced mechanics share their insights in answering this question :
Hi there. Typically, when a brake booster fails, the result is a hard to push brake pedal. The pressure release you hear is engine vacuum and may be normal considering, the brake pedal travels to the floor. With no apparent leak(s) in the hydraulic braking system, the master cylinder internally bypassing is the most common failure. Having replaced the master cylinder, this leads me to believe, there may be air trapped and a flush may resolve this concern. Assuming, the vehicle is equipped with ABS (anti-lock brake system). The ABS hydraulic modulator assembly may be internally bypassing. I recommend having your vehicle’s brake pedal issue diagnosed and repaired by a certified technician, such as one from YourMechanic.
How to Identify and Fix Common car Problems ?
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A brake booster, also known as a `brake servo` or `vacuum booster`, does exactly as the name suggests, it helps to `boost` the performance of the brakes. A brake booster makes it easier for the driver to brake by increasing the force exerted without the need for additional force applied on the foot pedal.
EXCESSIVE BRAKE PEDAL TRAVEL Possible causes include worn brake linings front or rear (or both), misadjusted drum brakes, or air in the brake lines. This can be dangerous because the brake pedal may run out of travel before the brakes are fully applied.
The brake booster is under vacuum and when it is released to push on the master cylinder it should vent out the pressure. I recommend replacing the brake booster and master cylinder to stop the problem.
Driving around with a failing or bad brake booster is quite dangerous, as it can lead to complete brake failure down the road.
The most common fault with brake servos will be a split breather pipe resulting in a sucking or whooshing noise. This can give you the effect of a very hard brake pedal.
Stiff brake pedal action is a strong indicator of brake booster failure because the booster will have lost its ability to amplify the force of your foot to the brake, requiring you to use more pressure.
Inconsistent Brakes – When a master cylinder begins to fail, sometimes the brakes will feel fine one second and lose braking power the next. If the fluid is leaking past the seals inside the cylinder, the pedal may feel firm for a moment but won`t hold steady; it`ll feel spongy and keep sinking towards the floor.
A malfunctioning Anti-lock Braking System (ABS) can also cause a hard brake pedal. The ABS system is responsible for preventing the wheels from locking up during emergency braking. If the ABS system malfunctions, it may cause a loss of hydraulic pressure, resulting in a hard brake pedal.
Common signs of a faulty vacuum brake booster check valve include the brake pedal being difficult to engage, feeling spongy, or not working at all.
Sometimes, brake booster issues are a problem that can be easily fixed with a repair. It could also be a problem with the valve or the booster vacuum hose. The hose or valve would most likely need to be replaced.
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.
There are no serviceable components in a brake servo as it is a sealed unit and as such is replaced as a whole. Tampering with the unit can have a detrimental outcome of its ability to work correctly.
Servo Motor Shuts Off After Reaching High or Full Speed
If your servo motor starts fine but turns off after reaching a high speed, it indicates a serious malfunction. This problem may be a little harder to repair. A few factors may cause your motor to shut off, such as: Defective overload protection system.
In older cars, brake booster failure may cause the engine to run lean with insufficient fuel in the cylinder. Without the full cooling action of the proper measure of gas, friction increases and the temperature of engine parts rise, leading to pre-ignition (the fuel ignites before the spark plug fires).
Your engine RPM might drop, and it may feel like your engine stalls each time you press the brake pedal. This particular problem could lead to more than just bad brakes — it can also cause costly engine problems.
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.
With the car turned off, pump the brake pedal four or five times until you get a hard brake pedal. Continue to hold the brake pedal down with moderate pressure and start the vehicle. The brake pedal should drop. If this brake pedal remains hard, there is a problem with the brake booster, such as a ripped diaphragm.
Yes master cylinders can fail without leakage, the clutch master cylinder has a piston inside and there are separate channels for hi-pressure line and return(low pressure) line and their location in the cylinder differs for manufacturers.
Resetting Your ABS Dashboard Warning Light
Step One: Disconnect the positive cable from your car battery. Then, hold down the brake pedal to drain the vehicle`s electrical system. This will result in a reset of the car`s central computer. Plug the cable back in to restore power.
Removing a wheel speed sensor will disable ABS—and sometimes, stability control. If your car has a yaw sensor, you can unplug that for results. You can also try simply unplugging the ABS module, though that could adversely affect your car`s braking performance.
Air in the brake line(s) is the most common cause of a soft/spongy brake pedal. If air gets into the brake lines, it can prevent brake fluid from flowing properly, causing the brake pedal to feel spongy or soft. If the brakes are soft or spongy, this is a good time to change or flush the brake fluid.
Generally, the hydraulic brake booster will last as long as your car does. There are some factors that can lead to the booster being damaged and having to be replaced.
Use a screwdriver to press and hold the plunger in the rear of the master cylinder. The plunger should be very firm, if not immovable, past a few millimeters. If the plunger keeps moving in, this indicates a fault of at least one of the internal seals.
Relevant Questions and Answers :
the most relevant questions and answers related to your specific issue
Could the brake servo booster that the master cylinder attaches to cause the brake pedal’s excessive travel?
ANSWER : Hi there. Typically, when a brake booster fails, the result is a hard to push brake pedal. The pressure release you hear is engine vacuum and may be normal considering, the brake pedal travels to the floor. With no apparent leak(s) in the hydraulic braking system, the master cylinder internally bypassing is the most common failure. Having replaced the master cylinder, this leads me to believe, there may be air trapped and a flush may resolve this concern. Assuming, the vehicle is equipped with ABS (anti-lock brake system). The ABS hydraulic modulator assembly may be internally bypassing. I recommend having your vehicle’s brake pedal issue diagnosed and repaired by a certified technician, such as one from YourMechanic.
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.
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.
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.
Changed brake master cylinder, bled 10 times, and the pedal is soft The rear brakes are not locked but close. Truck now running rough.
ANSWER : You will have to bleed the brakes from the farthest location all the way to the master cylinder. There is still air in the lines causing the issue. Check the vibrations on the vehicle to see if the engine mounts are damaged or if the brakes are not releasing causing the engine to run harder than normal to overcome the braking force. If you need further assistance with your vehicle’s brake system, then seek out a professional, such as one from Your Mechanic, to help you.
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.
Soft brake pedal after replacing rear brakes and master cylinder 2003 Audi A4
ANSWER : Hello. If you have no pressure to the rear calipers at all and if the master cylinder is new then you may have forces some debris into the ABS unit when you compressed the pistons in the rear calipers. In some cases the system can be pressure bled to fix it but it may need a new ABS unit.
I just replaced my brake master cylinder and the brakes still feel soft. What do I need to do after I replace the master cylinder
ANSWER : From what you’ve described you will have to bleed your brakes. Also, I believe you may have a leak in one of the lines. You may want to use a wrench and tighten the lines a little more. If you’re unable to fix this yourself, consider YourMechanic, as one of our mobile technicians can come to your home to bleed your brakes, diagnose the Check Engine Light, and help you make the appropriate repairs to your car.
