Brakes have failed😟 FIXED!!

[X5only]

The brake pedal sinks to the floor and have to push very hard for the car to stop. I can hear whooshing sound from the brake pedal area. No codes thrown but no communication with DSC module. Brake fluid is filled to max. All the rotors and pads are within spec. This started happening all of a sudden but been noticing the brake pedal slowly sinking to the floor when the car is started. Where do I start?

[X5chemist]

The brake booster is toast. Time to replace it. Check the vacuum hose first. It could have a hole somewhere on it. Is idle steady or does it swing?

[EODguy]

Vacuum pump on my 4.8is did the same thing but it made a gurgling sound instead.

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[X5only]

Managed to have DIS to talk to DSC system - no errors and I could do tests like running the pump, measuring brake pedal pressure, checking brake fluid level, etc. I visually inspected the vacuum line from the vacuum pump and all look fine to me. The engine idles steady. Wouldn't an error be thrown if there were problems with the brake booster?

[cn90]

Brake pedal to the floor = master cylinder issues. Get a rebuild kit or get a new MC.

Bad booster = hard brake pedal.

The symptoms are different.

[X5only]

Makes sense as booster helps in driver brake pedal effort, thank you. Any info on good source of rebuilt MC? It's amazing no error thrown when such a critical failure occurs. As much as I love this vehicle, but this issue shows the tech age of the E53.

[Clavurion]

How much was the brake pressure with diagnostics when pressing the brake pedal? Should go above 80 bar with max pedal force.

[X5only]

Originally Posted by Clavurion

How much was the brake pressure with diagnostics when pressing the brake pedal? Should go above 80 bar with max pedal force.

Thank you Clavurion Is this pressure value with engine running or off? Brake pedal is solid stiff with engine off. As soon as I turn the engine on, the pedal falls right to the floor.

[X5only]

Originally Posted by Clavurion

How much was the brake pressure with diagnostics when pressing the brake pedal? Should go above 80 bar with max pedal force.

Pressure at max force:
Engine off - 31 bar
Engine running- 29 bar

[X5only]

From ECSTunning:

$274.49
OEM (TRW) BMW Power Brake Booster - 34336760461

Has your brake pedal become stiff and hard to depress, or goes right to the floor with no pressure or feel, most likely the brake booster unit has failed.
Power Brake Booster Failure Symptoms
Hard pedal with no braking power
Longer stopping distance
Engine stalls with brakes applied
Brake pedal position higher than normal

$200
OEM (TRW) BMW Brake Master Cylinder - 34316757743
Brake Master Cylinder Failure Symptoms
Spongy Pedal Feel
Loss of brake operation
Poor brake performance
Internal fluid leaks
External fluid leaks

I found a great DIY for installing both MC and booster, but I hate brake bleeding, especially when dealing with air in the braking system. Might just take this work to a shop if cost is reasonable. Or maybe do all the parts install myself and have the vehicle towed to a shop just for brake bleeding.

https://xoutpost.com/bmw-sav-forums/...inder-diy.html