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Brake goes to the floor. Doubt it's a fluid leak. Want to figure it out rather than change parts blindly


Phil Elwood

Question

Hi community I have a break problem. Hoping to find help here. 

I wanted to get home tonight and when I pressed my break pedal to put the truck (04 Silverado 1500 LS 5.3) in D the pedal went to the floor hitting the break switch which turned on the warning. I tried pumping the pedal which made it a little bit stiffer but when I kept my foot on the pedal it would sink to the floor almost effortlessly. I bled breaks on older trucks before and it didn't feel like a fluid leak to me. Got out in the cold to check the fluid reservoir it was at the max level so all the way full. Tried some more but virtually no breaks. Walked around the truck with a flashlight (just in case) but all the wheels were dry no sign of fluid leak at the cylinders. Then I shut the truck off and pressed the break pedal. With the hood shut and all doors closed I could hear air being pushed out somewhere under the hood, again the pedal went to the floor. I was alone so I couldn't ask anyone to check where the air escaped unfortunately. I did it again a few times and it felt like I was pumping a tire with a foot pump, sounded like it too. 

Very weird, it seems like it can't be a big problem so I'd like to know if anyone has a hunch or encountered anything like this. I'd prefer to find the issue and fix it rather than change parts blindly. It was really cold and I wanted to get home so I called a buddy to pick me up and didn't check things like blowing and sucking on the check valve. I hope I'll have time for that tomorrow but I would be happy if someone has suggestions to what I can check or which parts I should buy and replace first

Appreciate any help! 

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28 minutes ago, BlaineBug said:

I believe an internally leaking master cylinder would be suspect if there is no leaking anywhere else in regards to the lines, wheel cylinders, or calipers.  That could be it, it's hard to diagnose without seeing it though.

Agree

:)

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Well it's pretty clear in the daylight. Drove up to the truck and saw a big puddle underneath it which was weird because it's way below freezing. Master was empty and when I layed under it this is how the lines looked. Got stainless steel oe replacement line kit by doorman from advanced auto that I'll be throwing in hopefully soon. 

Again thanks to yall for your help, I feel pretty stupid putting "doubt it's a fluid leak" in the title now... Oh well you live and you learn. 

20200117_101348.jpg

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A bad master cylinder generally shows up under light braking, for example after your truck has stopped at a red light.  If you lift your foot to the point it is applying just enough force to prevent rolling, you will feel the pedal drop away from your foot.  Pushing hard on the pedal will usually give you a good pedal due to the design of the cup shaped seals. Sometimes you may find a small leak out the rear of the master, that will run down the front face of the booster, but, more times than not, there will not be an obvious leak.  The internal leak generally just ends up back in the reservoir via the compensating port. 

 

Something I noticed over the years is that women drivers noticed a bad master first when spouses shared the car. The husband would bring the car in because the wife complained about the pedal dropping.  Husband brought the car in to show her the brakes were fine. 

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3 hours ago, Phil Elwood said:

Well it's pretty clear in the daylight. Drove up to the truck and saw a big puddle underneath it which was weird because it's way below freezing. Master was empty and when I layed under it this is how the lines looked. Got stainless steel oe replacement line kit by doorman from advanced auto that I'll be throwing in hopefully soon. 

Again thanks to yall for your help, I feel pretty stupid putting "doubt it's a fluid leak" in the title now... Oh well you live and you learn. 

...

I had a feeling you'd find something leaking under there. Glad you found it.

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