Why does the brake only work when the car is running?
It’s likely an MC. The seals in the pistons are probably passing fluid. The power assist only helps apply the brakes. It’s simply a diaphragm pulled by engine vacuum in line with the rod that pushes into the MC when you apply the brakes. If it fails, the assist disappears but the brakes still work.
Why is the soft brake pedal hard when the engine is off?
You need to take it somewhere and get it fixed. Of course the pedal is hard with the engine off, there is no power assist to help push the pedal down. Probably the seals on the calipers and/or master cylinder have been damaged by the contaminated fluid. I agree with Tardis. Trying to fix this yourself is way too dangerous.
What happens when you push the brake pedal?
Pushing the pedal slowly pushes brake fluid down the lines while letting air float back up. Releasing the pedal quickly washes any air bubbles into the reservoir along with the brake fluid that is rushing back. There are always different piston diameters available for any given master cylinder design.
How does a power assist affect the brakes?
It’s simply a diaphragm pulled by engine vacuum in line with the rod that pushes into the MC when you apply the brakes. If it fails, the assist disappears but the brakes still work. A failed power assist manifests itself as a hard pedal, but does not affect the function of the brakes.
Why does the brake pedal go to the floor when engine is running?
The air prevents brake fluid from efficient flow inside the brake lines, damaging the brake lines and giving the feeling of spongy soft feel, instead of the firm feel of the brake pedal when depressing. Although having your brake pedal goes to the floor when the engine running is bad and dangerous, it is very noticeable and easy to diagnose.
What does it mean when your brake pedal is spongy?
If you’re dealing with a spongy brake pedal, that usually means air is trapped in the brake system. Of course, air trapped in the system isn’t the only possibility. All of the following problems are common causes of a spongy brake pedal: A soft brake pedal usually indicates a loss of hydraulic pressure.
Why does my car lose brake pressure when I start it?
You can lose brake pressure after starting your car if you have a leakage in any of the brake components. If the brake pedal goes to the floor but no leaks, the problem might be related to the brake booster that has a vacuum leakage.
What to do when your brake master cylinder is replaced?
If the vehicle has ABS, here’s the bleeding procedure when the brake master cylinder is replaced. When using pressure equipment, use a special tool to depress the metering plunger on the combination valve. Gravity and vacuum bleeding are not recommended for this system.