Educate me, brake failures

[seattlejester]

So I am going to put it out there, I am not all to familiar with brake failures/overall how the system behaves during a failure.

 

Story:

I was bleeding the rear brakes with a friend and we found it kept going to the floor. After a couple tries of bleeding we wanted to see if their was air in the fronts. So when he pushed the brake pedal, it went straight to the stop, but the fronts had locked. The rears still spun with little to no resistance.

 

We eventually bled the rears to lock as well, but this made me wonder about a few things.

 

Now I understand that the master cylinder is basically a large plunger and pushes fluid forcing it through the line. And I understand in an open system, or a poorly bled one, the fluid will be displaced in the line with more flexibility, but what happens to the closed line, is it just residual pressure that gives it a little bit of brake pressure?

 

In the stock system you had the splitting block where if you loose pressure to the rear, the light comes on and a check valve isolates the front allowing pressure to the front (I think that is correct). 

So what happens when you delete the block? Does the fluid just pump out of the leaking line, while only supplying the bare minimum to the other lines? Or do you slowly loose the braking force as the fluid finds an easier route to escape?

 

I have always been taught that if a brake failure happens, put it in low gear, pump the brakes, and aim for something soft. Would that be preferable or once you realize that you are loosing fluid, would it be better to put the pedal to the floor to at least get the drag on the working calipers?

 

Just trying to understand the actual mechanics behind the system.

 

[Miles]

What modifications have been made to your brake system?

 

Did you remove the brake switch under the master cylinder?

 

Sounds like you have air in the system.

 

Did you let the MC run dry? If so you will have to bleed the air out. 

[seattlejester]

Yes, no brake switch for my application, we did manage to bleed it, it just took a bit longer then expected. Just for the record I am not very worried about my lines. They were all replaced and everything is brand new. 

 

This is just for the theoretical case where someone without a modern abs splitting module or maybe someone who bypassed the brake check valve, what would actually happen, let's say if the brake line burst from old aged or was cut while driving.

[Miles]

Yes, no brake switch for my application, we did manage to bleed it, it just took a bit longer then expected. Just for the record I am not very worried about my lines. They were all replaced and everything is brand new. Are the brake lines to the front tied together with a three-way connector block and separate from the rear brake line?

 

This is just for the theoretical case where someone without a modern abs splitting module or maybe someone who bypassed the brake check valve, what would actually happen, let's say if the brake line burst from old aged or was cut while driving.The pedal would sink. It would behave exactly like when you open a bleed valve on a wheel when bleeding the brakes.

[seattlejester]

Yes, front and rear are separate of each other.

 

I suppose you are right, we just had the fronts lock up while the rear line was open, I guess if he stayed on the pedal  over time it would just bleed all the pressure out of the rear and the fronts would let up?