[tsm007]

Hello, I have a 2008 328xi. Recently I've been having brake issues. The brake pedal goes all the way down when I brake. I replace all the rotors and brake pads. I also put in fresh brake fluid. From reading around I'm thinking it might be the brake master cylinder.
Did anyone face the same or similar problem?
If so, what did you do?
And what are the exact parts that I need?

[feuer]

This started happening after you replace the rotors, pads and put fresh fluid? If yes, you either damaged parts in the process and did not do it correctly. I will advise you to take the car to competent mechanic to sort out the issue for you as you do not want to take chances with brakes.

[tsm007]

Originally Posted by feuer

This started happening after you replace the rotors, pads and put fresh fluid? If yes, you either damaged parts in the process and did not do it correctly. I will advise you to take the car to competent mechanic to sort out the issue for you as you do not want to take chances with brakes.

That's what I thought at first but everything was double and triple checked. And it's all OEM and Brembo components. I'm think I should just go to a dealership or shop and get it diagnosed.

[SpartaEvolution]

It's possible that there's a fault with the master cylinder, but not likely. Did this start happening before or after you changed the pads/rotors? What is your bleeding procedure? Does the pedal ever feel stiff, or has it gone straight to the floor ever since the pad/rotor change?

[tsm007]

Originally Posted by SpartaEvolution

It's possible that there's a fault with the master cylinder, but not likely. Did this start happening before or after you changed the pads/rotors? What is your bleeding procedure? Does the pedal ever feel stiff, or has it gone straight to the floor ever since the pad/rotor change?

This problem happened before I installed the new pads and rotors. The brake pedal isn't stiff, it has little/ no pressure. When I brake it feels as if the whole car is thrown off alignment. The car doesn't stop in a straight line.

[SpartaEvolution]

Was there a lot of air when you bled the brakes? Was the fluid reservoir still full when you changed the pads/rotors? A mushy pedal almost always means you have air in the lines or boiled fluid, but if it's still mushy after the bleed that would indicate a leak.

The leak could be from a busted seal in the master cylinder or one of your calipers, a pinhole in one of your brake hoses, or a pinched hard line. If your master cylinder ran dry from a leak, that could have caused additional damage.

I would inspect every part of the brake system, starting with the back of the pedal/master cylinder, trace every hard line leaving the master cylinder, every hard line -> hose connection, every hose -> caliper connection, and every caliper piston. If you have a helper, have them pump the pedal as you inspect. If you still can't find anything, then it's definitely time to take it to a shop.

Good Luck!

EDIT: Forgot about the car pulling part to the side when you brake - that makes me think the leak is somewhere after the master cylinder, because pulling to the side would mean one caliper is providing more pressure than another. Having said that, I would probably avoid driving the car until you have a firm pedal again.

[tsm007]

Originally Posted by SpartaEvolution

Was there a lot of air when you bled the brakes? Was the fluid reservoir still full when you changed the pads/rotors? A mushy pedal almost always means you have air in the lines or boiled fluid, but if it's still mushy after the bleed that would indicate a leak.

The leak could be from a busted seal in the master cylinder or one of your calipers, a pinhole in one of your brake hoses, or a pinched hard line. If your master cylinder ran dry from a leak, that could have caused additional damage.

I would inspect every part of the brake system, starting with the back of the pedal/master cylinder, trace every hard line leaving the master cylinder, every hard line -> hose connection, every hose -> caliper connection, and every caliper piston. If you have a helper, have them pump the pedal as you inspect. If you still can't find anything, then it's definitely time to take it to a shop.

Good Luck!

EDIT: Forgot about the car pulling part to the side when you brake - that makes me think the leak is somewhere after the master cylinder, because pulling to the side would mean one caliper is providing more pressure than another. Having said that, I would probably avoid driving the car until you have a firm pedal again.

I put in fresh break fluid. What I'll do now is check all the components. Checking the pedal, master cylinder, hoses, caliper connections, and caliper pistons. Thank you for the advice. I'll post after I can figure out what's going on.

[Aus335iguy]

Originally Posted by tsm007

I put in fresh break fluid. What I'll do now is check all the components. Checking the pedal, master cylinder, hoses, caliper connections, and caliper pistons. Thank you for the advice. I'll post after I can figure out what's going on.

Bleed the brakes on the opposite side to the direction the car is pulling in.

[juld0zer]

How did you replace the fluid? Tell us the steps you followed.

Do this test:
Start engine, idle for 10 seconds and then press the brake pedal quickly several times until the pedal stops, so as to pump it up until the pedal is higher/normal height and firm.

Maintain foot constant foot pressure on the brake pedal and observe what happens.

[feuer]

Originally Posted by tsm007

That's what I thought at first but everything was double and triple checked. And it's all OEM and Brembo components. I'm think I should just go to a dealership or shop and get it diagnosed.

I have coupe of brake master cylinders from 335i that are in perfect working condition. Make me an offer.