Soft Brake Pedal!!

[evil_twin]

Hey, show me your set up with this vacuum reserve canister :)

[e30polak]

Just did SS lines in my swap car and made a world of difference in pressure and consistency. With the 320 booster I also use a vacuum reserve canister, which helps with pedal effort. You may want to look into that.

[einstein57]

that means the master is going bad

Booooo :(. So should i do the 735i mc?

[twothrees]

I just replaced my mc this weekend for these exact same reasons. Works great now. I can't believe how disgusting the resevoir was;filled with black, nasty crap. I don't think anyone had ever changed the brake fluid. One of my bleeder valves had rusted shut too.

[92 mtechnic cabrio]

Mine does this. What does that mean?

that means the master is going bad

[einstein57]

"The pedal doesn't drop to the floor so I don't think it'd be a bad MC."

-->The pedal does not need to go to the floor for the master to be bad.While you are sitting at a traffic light pump the pedal a few times and see if the pedal gets firmer as pump.

Mine does this. What does that mean?

[Massive Lee]

Bigger master cylinder should have more feel to it and less travel... so there is a problem... it sounds like the booster is working fine, but a problem with air in the system

"More feel" and "feeling more to your taste" are two different things. Having more feel from a brake system is usually caused by stiffer calipers with no play and properly bled lines.

Because the MC shoots more fluids, and requires less travel at the expense of more force, is not necessarely equal to more feel. The flex in the caliper is still there.

[cracker5947]

if you want more pressure, get smaller diameter m/c. Nitro is right, bigger surface area means less pressure. look up pascal's law : )

[e30evolution]

More travel, but less pressure, meaning you have to press harder to brake.

he said the pedal felt soft

[AndrewBird]

Bigger master cylinder should have more feel to it and less travel... so there is a problem... it sounds like the booster is working fine, but a problem with air in the system

More travel, but less pressure, meaning you have to press harder to brake.

[e30evolution]

Bigger master cylinder should have more feel to it and less travel... so there is a problem... it sounds like the booster is working fine, but a problem with air in the system

[bostonbmw]

"The pedal doesn't drop to the floor so I don't think it'd be a bad MC."
-->The pedal does not need to go to the floor for the master to be bad.While you are sitting at a traffic light pump the pedal a few times and see if the pedal gets firmer as pump.

I dont think you can just write off that its NOT air in your master cylinder without properly bleeding it on the bench.There is no way you are going to be able to bleed the master properly on the car and be sure of it.

[soflawussbag]

when you get the mc situation fixed some stainless steel brake lines wont hurt (if you dont have them already)

[AndrewBird]

It's not a problem with bleeding, it's the size of the master cylinder. By going to a larger cylinder, you might have changed how much fluid it moves, but you decreased the pressure by increasing the surface area (bigger piston). The bigger master cylinder will move the brake pads faster (more fluid) but at less pressure. It's all about Pascal's law.

[bostonbmw]

Bench Bleed Your Master !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!