Brake pedal operation

[Achias]

After working on Ilsa's brakes and bleeding them three times, I find the following situation that concerns me:

With the engine on, the brakes work normally near the beginning of the brake pedal travel; but if I keep pushing the pedal, the pedal continues all the way to the floor with the hiss of moving air.

A fellow R owner (thanks, Ron) tried his and it does the same thing.

Is this normal (and safe)?

[lou7777777]

I take it you didn't have this problem BEFORE you bled the brakes. Is it with the engine on
the pedal keeps going down or is it when you have the engine off that the pedal goes down? What happens at a stop light and you have the brakes on....does it slowly go to the floor??? That can't be right.

I know when I put different covers on the brake pedal and I'm sure pushed on them for some time with the engine off the pedal went down. In fact down enough to give me a couple indicators on the DIC.....which cleared shortly after re starting and moving a block or two.

[Achias]

I can't remember if this happened before or not. So far, I've heard from one R owner who says that his does the same.

Everything is normal except it sure feels weird to have the pedal go to the floor.

Engine off, pedal goes down a little on first pump - is rock solid and hardly moves on the second pump (normal operation).

Engine on, brakes engage solidly shortly after pedal operation - after vehicle is stopped, more pressure on pedal will push the pedal to the floor; but pedal does not fade is more pressure is not applied.

I'm hoping that one of our gurus will explain what goes on here.

By the way, the garage dudes found evidence of fluid leakage below the master cylinder, so they took it off and found signs that it was indeed leaking a little through the seal between the cylinder and the firewall. I saw the area on the cylinder mount where this was happening. So they replaced it with a new Delco one. The pedal works just like it did before, so I'm going to assume that it is normal.

Feel free to try it on your own R and let us know if this is true.

Also, I'd advise owners of older R's to keep an eye on the fluid level in the master cylinder reservoir to make sure that your seal is not starting to deteriorate. Ilsa's fluid was dark, which is why I changed it. She only has 45K miles, but she is going to be eight years old on Friday.

[lou7777777]

So your master cylinder was replaced?!? I am surprised that replacing of the MC didn't fix the problem. What I believe happens is at a certain pressure (not too moch and not too little) the fluid seeps past the seal and therefore the pedal goes down. This is usually a result of the MC inner wall getting a film on it from old fluid and allowing fluid to get past the plunger. One would think that a new MC would not have that problem. I certainly don't want to badmouth your repair company, but are you confident they put a new unit on the truck?

[Achias]

I think so, because I have the old one.

I'm still waiting to hear if anyone else has tried this.

Originally Posted by lou7777777

So your master cylinder was replaced?!? I am surprised that replacing of the MC didn't fix the problem. What I believe happens is at a certain pressure (not too moch and not too little) the fluid seeps past the seal and therefore the pedal goes down. This is usually a result of the MC inner wall getting a film on it from old fluid and allowing fluid to get past the plunger. One would think that a new MC would not have that problem. I certainly don't want to badmouth your repair company, but are you confident they put a new unit on the truck?