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Brakes not working propperly?

Tiny
HAYES5
  • MEMBER
  • 2000 GMC JIMMY
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 390,000 MILES
Pedal went almost to the floor but stopped the truck. Hissing sound in the cab so we changed the booster. Pedal is now hard to push with little braking power and still a slight hiss. Checked out the check valve seems to be okay.
Wednesday, April 19th, 2023 AT 7:26 AM

7 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
It sounds like the brake master cylinder went out here is how to replace the unit which must be bled before it is installed. Also, check the front and rear brake pads/shoes. Here is a guide and a video to help and the instructions on how to replace the master on your truck in the diagrams below:

https://youtu.be/WDxvEQrMkBg

and

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

This guide may help as well:

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

Check out the images (below). Please let us know what happens.

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Thursday, April 20th, 2023 AT 8:48 AM
Tiny
HAYES5
  • MEMBER
  • 4 POSTS
I bled the master cylinder and then bled the brakes. The pedal felt better but the brakes did not work.
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Friday, April 28th, 2023 AT 8:12 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Can you explain the brake not working, do you have good pedal? Does the brake have pedal but not stop the car? Can you please shoot a quick video with your phone so I can see what's going on? That way I can tell for sure what's going on. You can upload it here with your response.
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Saturday, April 29th, 2023 AT 11:29 AM
Tiny
HAYES5
  • MEMBER
  • 4 POSTS
Yes, the brake has pedal but does not stop the car.
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Sunday, April 30th, 2023 AT 3:01 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Okay, start the car and then shut it off, then remove the vacuum check valve from the booster and you should hear vacuum escaping, if not the booster is defective and needs to be replaced.
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Monday, May 1st, 2023 AT 10:14 AM
Tiny
HAYES5
  • MEMBER
  • 4 POSTS
After I bled the brakes, the braking system is now fully functional. Thank you Ken L for your knowledge and helpful hints.
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Tuesday, May 9th, 2023 AT 8:51 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Thanks for letting us know, we are here to help, please use 2CarPros anytime.
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Wednesday, May 10th, 2023 AT 10:54 AM

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