Replaced master cylinder and brakes still going to the floor and not working. Bed both master cylinders and each wheel.
Replaced master cylinder and brakes still going to the floor and not working. Bed both master cylinders and each wheel.
My car has an automatic transmission.
Experienced mechanics share their insights in answering this question :
Hi, thanks for writing in. At first it sounds like you may still have air in the system. The other option is that you may have a leak somewhere. Try to bleed the master cylinder and the lines again. The new master cylinder must be bench bled off of the vehicle exactly as the instructions say. The other problem could be a leak on the system. You should check for drips, puddles forming, or other signs of leaking brake fluid. Worst case scenario, the replacement master cylinder may have come to you faulty in the first place. This is rare but can happen, especially when it comes to remanufactured master cylinders. New ones typically don’t have issues. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.
How to Identify and Fix Common car Problems ?
Our sources include academic articles, blog posts, and personal essays from experienced mechanics :
Sometimes when new brake pads are installed, sediment can inadvertently be pushed back into the hydraulic system. This sediment can damage the master cylinder. A worn or malfunctioning master cylinder. If the master cylinder isn`t performing as designed, it may need to be replaced.
The most common master-cylinder failures occur from piston-bore wear and piston-seal failure. The classic symptom of a failing master cylinder is a brake pedal that “dives” or sinks slowly to the floor while pedal pressure is being applied. Another sign to look out for is any leaks around the master cylinder.
This can be due to a number of problems: a leak in a brake line, a loss of pressure within the master cylinder itself due to a failed seal, or air being introduced into the braking system. Your first reaction to encountering spongy brakes should be to rapidly pump the brake pedal with your foot.
When brakes are not as responsive as what they should be, or if the brake pedal “sinks” down to the floor, this is a possible indication of a braking system leak. It could be a brake fluid leak, or a brake hose air leak.
One of the most common reasons for your brakes touching the floor would be an issue with your brake fluid. Your fluid being low or air reaching the brake line will prevent the fluid from flowing properly, resulting in a spongy pedal. A bad brake booster is another common cause for a malfunctioning pedal.
The ABS modulator is the hydraulic assembly in vehicles that use the anti-lock braking system (ABS) to optimize the brake pressure. A damaged modulator may lead to malfunctioning of the brake valve resulting in spongy brakes.
This pressure travels from the master cylinder, through the brake line, and acts on the brake caliper and brake rotor. However, if air bubbles are in the brake line, hydraulic pressure is reduced, making your entire braking system less effective and your vehicle more difficult to control.
Low Brake Fluid: If your brake fluid is low (and it`s not due to brake pad wear), then the system will be unable to create enough pressure for normal operation and you may have to pump the pedal.
Brake Booster Check
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.
These could be some reasons you have no brake pressure after bleeding your brakes: Air in the brake lines. Brake fluid leak somewhere in the system (check your fluid level to make sure it`s remained at the right amount) Faulty seal in the master cylinder.
A bad master cylinder can cause your brakes to fail, which can be extremely dangerous. If you`re experiencing any brake problems, make sure to take your car to a mechanic right away to have it checked out or change the master cylinder yourself.
Brake Fluid Low but No Visible Leak? While a leak is many times the cause of low brake fluid, there are a few other possible culprits: Leakage into the brake booster. Sometimes brake fluid can leak internally into the brake booster.
When your ABS system malfunctions are can also cause a spongy brake pedal. Your ABS system is designed to allow the driver to maintain more control of the car in a high-speed stop.
Usually, your brake pedal will sink if the ABS or master cylinder cannot maintain the proper hydraulic pressure. This inability to maintain hydraulic pressure will not only make your brake pedal sink to the floor, but it will also make it much more difficult to stop your automobile.
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.
Bleeding brakes by gravity
Then you can let gravity do the bleeding for you. This method works for nearly all modern cars, as long as the master cylinder is up high on the firewall, above the level of the wheels. All you have to do is fill up the master cylinder reservoir with fresh fluid.
If you need to replace or install a brake master cylinder, you`re going to have to “bench bleed” it before bolting the assembly to your firewall. That`s because, due to the angle at which the master cylinder sits when installed, bubbles can become trapped in an un-bled master cylinder`s fluid passages.
Typical brake line pressures during a stop range from less than 800psi under “normal” conditions, to as much as 2000psi in a maximum effort.
Master Cylinder Pressure
Most hydraulic brake systems operate at a safe maximum of 1,000 to 1,200 psi, with regular braking pressures below this figure. The hydraulic pressure in the system is a function of input pressure from the pedal and the piston area of the master cylinder.
As a general rule, your pedal ratio should not exceed 6:1 for manual brakes with a 1” bore master cylinder and 4:1 for power brakes with a 1-1/8” bore master.
The reservoir should not be filled past this line. As you drive your car and apply your brakes, your brake system heats up, including your brake fluid. As brake fluid heats up, it expands. The path of least resistance leads the brake fluid to expand back into the master cylinder reservoir.
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.
If the pedal doesn`t move at all, insufficient vacuum is being generated and there is definitely a fault in the servo system. Check the entire vacuum system including all connected components such as the exhaust gas recirculation (EGR) valve, engine vacuum pump and fuel pressure regulator.
Relevant Questions and Answers :
the most relevant questions and answers related to your specific issue
Replaced master cylinder and brakes still going to the floor and not working. Bed both master cylinders and each wheel.
ANSWER : Hi, thanks for writing in. At first it sounds like you may still have air in the system. The other option is that you may have a leak somewhere. Try to bleed the master cylinder and the lines again. The new master cylinder must be bench bled off of the vehicle exactly as the instructions say. The other problem could be a leak on the system. You should check for drips, puddles forming, or other signs of leaking brake fluid. Worst case scenario, the replacement master cylinder may have come to you faulty in the first place. This is rare but can happen, especially when it comes to remanufactured master cylinders. New ones typically don’t have issues. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.
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.
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.
abs light on brake line broke have been replace I bleed brake line but brake pad still go to the floor now wheels lock up
ANSWER : Hello. If the brake pedal is going to the floor then that means that it is not building pressure. If the brake system has been fully bled and there is no air in it then most of the time it is a bad master cylinder or it can be caused by a bad ABS module. If the brake fluid was low and if air got into the system then the only way to properly bleed it is with a scan tool that would allow you to open and close the valves in the ABS unit. Air gets trapped in these easily if the brake fluid gets low. This can also explain why the brakes are locking up. I would usually use my scan tool to bleed the system out first before going any further. I would also scan the brake control module to see what it is reading as a fault. If there is no air in the system and if there is no prominent code then I would replace the master cylinder first. If you want to check out why your brakes are locking up, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair this.
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.
EPC light on 2004 Jetta. Code said brake switch faulty, but brakes lights worked. Replaced brake switch, now no brake lights.
ANSWER : Hi there. The first thing that pops in my mind beyond of what you have listed is perhaps the electrical harness attached to the brake switch. Perhaps the harness itself is damaged or you have an exposed wire, loose ground wire somewhere. You might want to have a professional mobile mechanic come to your location and complete a brake lights not working inspection to help you diagnose this issue.
Brakes keep going out replaced master cylinder but not helping?
ANSWER : There are two possible vehicle recalls pertaining to the issue are having. The ABS is the cause of most of the problems similar to what you are experiencing. I recommend contacting a dealer with your vehicle VIN number to see if you have active recalls.
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.
