Brake bleeding

[B5fourspeed]

Most forums or articles say that if you have a low soft brake pedal that air is still in the system.I would like to know what was the most times someone on this forum had to bleed their brakes to get a good pedal.I know there are other reasons for a low pedal but I am curious about the amount of bleeding that was performed by someone.Thanks

[pschlosser]

Most forums or articles say that if you have a low soft brake pedal that air is still in the system.I would like to know what was the most times someone on this forum had to bleed their brakes to get a good pedal.I know there are other reasons for a low pedal but I am curious about the amount of bleeding that was performed by someone.Thanks

The amount of bleeding?  As in how many times one must bleed?  Or the amount of brake fluid being bled?

Because oil and water do not mix, brake fluid is designed to absorb water, so water doesn't stay in contact with the metal parts of the braking system and cause rust or even rust-through failures.  The fluid must be changed, periodically, to refresh its ability to absorb water.

Once the system is bled, and working, the pedal doesn't normally just "go soft."  When nothing has changed, a soft pedal, particularly, one where pressing and holding the pedal slowly goes to the floor, is likely a leaky, worn, and/or bad Master Cylinder, or a leaky Brake Caliper/Cylinder.  Otherwise, if nothing leaks and all the air is bled, the pedal should depress to some point and then stop, and hold there.

On the other hand, after a repair, or change to the braking system, it is possible that air may be introduced into the hydraulic system.  In those cases, the air is removed by pushing it through the system and out the bleeder screws at the brake cylinders/calipers.

The braking system kind of starts at the M/C, and gets split into four circuits, each one going to a wheel.  When air is introduced at the M/C, all four circuits must be bled to remove the air.

A change at the very ends of the system, where air may enter the brake calipers/cylinders, bleeding is faster, and more simple, as the air can be quickly bled out the ends of system.  But a change at the M/C will take more fluid and longer to bleed the air out.  But no more fluid (or time) than the periodic changing of the fluid to refresh its ability to absorb water.

So, once the system is properly bled (many can do this with a one-time effort) of air, and if the M/C and cylinders do not wear out, you're done.  You need not bleed the system again for years and years, if you choose.

If you find yourself having to bleed the system, again and again, to eliminate a soft pedal, something else is going wrong.  Either the bleeding technique is not removing the air, or there is a loose connection or fitting continually introducing new air into the system, a leaky/failing M/C, or a leaky/failing brake cylinder/caliper.  I cannot think of any other causes.  

If you cannot figure it out, then simply take the care in to a brake repair mechanic, and have them figure it out.  Brakes are messy, but not normally that complicated.  Many can do these repairs themselves.  But if during the car's 50-year history, if someone altered the factory brake setup, changing this component or that, if they made a poor choice in hardware, there could be a more complex problem to resolve.

Just because a part is new, doesn't mean it isn't faulty or the wrong part for the car.

[Cuda Cody]

I have a vacuum for bleeding the brakes and I will use it to get most of it done, but I find myself going back to putting someone in the seat and being under the car myself.  I'm not sure if it works better or not, but I like to be on the end of the bleeder watching for air bubbles and making sure I get a good feeling pedal.  By starting with the vacuum pump I'm able to get the system putting full before doing the last by hand.  If you're doing it all by hand (and foot) then it's going to take a bit.

[b5cuda]

Speed bleeders are helpful too, especially if you're working alone.

[RUNCHARGER]

It really doesn't take that long. I too like to use a helper as you have to be at the bleed screw end to make sure the fluid is solid as it comes out. Start at the furthest one away, bleed until the fluid is solid, then go to the next furthest one and so on.
With a fresh, dry system, I think maybe 5-10 cycles on the first point and the other 3 points probably 5.
Lots of people seem to have lots of trouble with brakes. Personally I think a lot of people don't do a proper bench bleed of the master cylinder to start with or run the master cylinder out of fluid while bleeding.