Brake pedal, it goes right to the floor

Tiny
BOMPOO
  • MEMBER
  • 2006 GMC SIERRA
  • 5.7L
  • 4WD
  • AUTOMATIC
  • 286,000 MILES
When I push down on the brake pedal, it goes right to the floor. No leaks as master is still full and no wet spots on any wheel. One day it worked 100% and the next day nothing.
Sunday, March 29th, 2020 AT 11:10 AM

2 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

This sounds like the master cylinder has failed and needs to be replaced. I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back.

Roy
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Sunday, March 29th, 2020 AT 11:19 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
The most common cause of this being so sudden is the master cylinder. There normally is no warning other then maybe when stilling at a stop light or foot on the brake the pedal slowly drops. However, this is not a guarantee.

The best way to test this is to remove the outlet lines from the master cylinder and cap off the lines and then push the brake pedal (clearly make sure the vehicle is left in park because you will not have brakes). If it still goes to the floor then it is the master cylinder because the rest of the system has been removed.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Let me know if you have questions. Thanks
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Sunday, March 29th, 2020 AT 3:09 PM

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