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Pedal is still sinking to the floor

Tiny
KELVIN MORRIS
  • MEMBER
  • 2001 GMC YUKON
  • 5.3L
  • V8
  • TURBO
  • 308,051 MILES
I replaced the brake calipers and master cylinder and the pedal is still sinking to the floor. What is the problem?
Tuesday, September 13th, 2016 AT 2:48 PM

7 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
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.
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
DDUNCAN70
  • MEMBER
  • 3 POSTS
Did you ever get this figured out.I have the same problem no leaks new master cylinder new calipers. Had a mechanic pull it in to his garage to check for leaks and bleed the system still no pedal. They worked fine until a brake line blew out and I replaced some line two calipers and master cylinder. Everything was bled and checked for leaks
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Hello,

You need to have a scanner connected the ABS system so you can open the ABS valves which will get the air out.

This video will show you how to connect the the ABS system.

https://youtu.be/rTtAnsOlZU4

This guide can help as well

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

Please let us know what you find.

Cheers, Ken

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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
DDUNCAN70
  • MEMBER
  • 3 POSTS
I bought a scanner and did an abs auto bleed. Still no luck you can feel the abs push against you when the pedal goes to the floor. You can hear humming when you hold the brakes to the floor.I have someone looking at it soon.I agree maybe it’s in the abs
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Sure sounds like it but to be sure lets use four vise grips and gently close off the rubber flex hoses. Once complete check the brake pedal it should be hard if there is a wheel issue and soft if it is the master or ABS.

Please report back

Cheers, Ken
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
DDUNCAN70
  • MEMBER
  • 3 POSTS
I took my Yukon to a second mechanic. Found out the calipers were on opposite sides. The bleeder valves have to be on top.I had replaced the rear calipers and those were fine but the front ones were mixed up. Not sure how they bled them before but if the bleeders are not on the top they are on wrong they won’t bleed correctly. Thanks for the replies. Brakes are great now
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Yep the calipers need to be on the correct side that's for sure quick pictures of the brakes and I could have lead us to the conclusion. Glad you got it fixed.

Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken
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Thursday, March 11th, 2021 AT 1:21 PM

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