robo_porsche

When I changed the brake fluid I accidentally happened to get some air in the system. I have been bleeding the brakes but feel a little paranoid if all the air really come out. I have never had air in the brake system before so I really do not know what it would feel like in the pedal if you have air in the system. The pedal is supposed to feel spongy, but how much? I don't remember exactly what the brake pedal felt like before...

Are there some simple way to determine if there is air in the system (except bleeding)?

Otherwise I have to bleed again just in case, but it would have been interesting if I could test it first.

Another thing. The front brakes take the brake fluid from the rear part of the container and the rear brakes take from the front. Does that mean that any air in the rear brakes only affects the rear brakes? Or does the brake fluid mix between the front and the rear system?

Robert

fpb111

If there is enough air in the pressurized part of the system to cause problems you will know by how the brake pedal feels and how far it travels.

Air in the container won't mix with the fluid unless you take the container off and shake it up. Any air that gets back to the container will dissipate into the atmosphere.

The only way you can get air from the container into the system is to run one of the chambers dry and then add more fluid, that traps the air in the pressurized side of the system.

Air that has migrated into the front or rear brake lines will not mix with each other they are two separate systems.. Further air that is trapped in the right front caliper or lines will not mix/migrate to the left side.

Sneaky Pete

Like ^^ he said. The brake line fluid does not circulate through the entire system. Each corner has it's own dedicated line.

Hurdigurdiman

Simply bleed them all again until you see clean fluid coming out. Brake fluid is cheap. Keep your eyes on the top up reservoir. Always keep that topped off as you are bleeding the system. If you have a helpers foot involved, ask them to pump twice and to hold the foot down until you loosen and tighten the nipple again. Rear right, rear left, front right, front left.

Macster

Just a warning. It is not a good idea to fully depress the brake pedal when manually bleeding the brakes. Doing this puts the master cylinder piston in a region of the cylinder into which it never gets to at other times. If this region's walls are rough, rusty, this can damage the piston seals perhaps the piston itself and this can cause problems.

sjg1138

Now you tell me Macster. Never heard that before.

Sneaky Pete

I knew a girl like that......and yeh it caused problems alright

Ahsai

For brake pedal feel, just press on the brakes like 10 times when car is off. The pedal should feel progressively harder and less free play (as you're using up the remaining stored vacuum for the brake booster). At the end, it should feel pretty hard and I don't think you would describe that as spongy.

alpine003

I'm a bit slow but how else are you suppose to do it if doing it the old manual way? Cars have been done like this for years.