press the brakes the master cylinder has a humming sound

2000 NISSAN ALTIMA

115,000 MILES • 4 CYL • FWD • AUTOMATIC

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First my pedal is iffy. some times i have a good pedal and most of the time i have very little pedal. Then when bleeding brakes the left front and right rear have nothing. but the left rear and right front have a full stream. not sure what would cause that. i checked for leaks and dont have one. The resavare is still full. Also when you press the brakes the master cylinder has a humming sound in it and it expands.

Feb 6, 2009 at 5:59 PM

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SQM

CAR REPAIR CONTRIBUTOR
6,383 POSTS

Hello,

Not having fluid out while bleeding could be due to clog in the bake hose or faulty brake proportioning valve.

On this vehicle the proportioning valve can be built into the master cylinder or it could be a standalone unit.
The valve could fail and can stop flow to the brake.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.

Images (Click to enlarge)

Oct 15, 2021 at 9:07 PM