Soft Brake Pedal!!

[mazur]

Ever since I have done my swap I have had a soft brake pedal. Since then, the brakes have been bled 3 times and it still feels really soft.

If I slam on the brakes it's delayed and just feels like shit. In my E36 it would take little effort for the brakes to grab and as you pushed the pedal down, you almost immediately felt like your hitting a brick...that's the stiffness I'm looking for. My friend's civic has the same good feeling...


I'm using, I believe a master cylinder from a M5 (using IX booster).
I never bench bled the master cylinder, but don't see how it would still have air after all the bleeding I have done. The pedal doesn't drop to the floor so I don't think it'd be a bad MC.


Any suggestions?

[Brian D]

Hi Richard, what were your reasons for running the bigger master? Did you change the master at the same time as the engine swap?

[Massive Lee]

Bleeding the brakes is not easy, especially when the MC was changed. I highly recommend using a pressure bleeder ($50) while you pump the brakes relentlessly. Be prepared to waste at least one litre of fluid. Use some cheap one initially. Then, when you are satisfied with the feel, swap to better fluid.

[static]

strange i also have problem with soft brakes after the conversion even with all SS lines (i am using ix booster and new m5 master)

[mops]

do they sell brake master ( and clutch for that matter) cylinder rebuild kits ?

[DEV0 E30]

Do you have a check valve from your intake manifold to your booster? I didn't realize I put mine on backwards last time I had my engine out. Brake pedal would sit correctly but would barely slow the car.

[scabzzzz]

You probably need to run another vacuum line to the intake below using a t connector. This is pretty common on M50 swapped cars.

[vivalegreg]

does it go to the floor when the car is off?

[bostonbmw]

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

[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.

[soflawussbag]

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

[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.

[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

[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]

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

he said the pedal felt soft