Brakes not working propperly?

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

KEN L

MASTER CERTIFIED MECHANIC
48,363 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

HAYES5

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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

KEN L

MASTER CERTIFIED MECHANIC
48,363 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

HAYES5

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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

KEN L

MASTER CERTIFIED MECHANIC
48,363 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.