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Phil Elwood

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

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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With no fluid loss, a mushy pedal out of the blue can only be the master cylinder. Air escaping sounds like a bad booster, so you'd better investigate what's going on under the hood there.  Never in my life have I ever seen a booster fail with the master at the exact same time.

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10 minutes ago, Jsdirt said:

With no fluid loss, a mushy pedal out of the blue can only be the master cylinder. Air escaping sounds like a bad booster, so you'd better investigate what's going on under the hood there.  Never in my life have I ever seen a booster fail with the master at the exact same time.

Thanks for the quick answer. Makes sense to me that the master might be the problem, after all it's directly connected to the pedal so it has to pump when the pedal move right 

I might add that now that the problem surfaced, looking back there were situations the last few days when I was breaking to get to a stop and had to push it in more than usual to come to a stop

 

Edited by Phil Elwood

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Does this truck have a hydraulic assist brake master cylinder, or vacuum assist?

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11 minutes ago, BlaineBug said:

Does this truck have a hydraulic assist brake master cylinder, or vacuum assist?

Not sure but I think it's vacuum see the big hose coming from the manifold in the pic. Don't let the shadow fool you the reservoir is full

 

20200116_185317.jpg

Edited by Phil Elwood

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If there was a vacuum leak, I would think that the brakes would be hard as heck to push.  But your problem is quite the opposite.  Definitely sounds like a leak, somewhere.  Your reservoir shouldn't empty itself as the brakes should have a zone between front and rear as far as I know, that's how it used to be in the past.  Can you attempt to re-bleed all 4 corners?

 

Basically, if you had a vacuum assist OR hydraulic assist system, a LACK of assist would result in an even harder pedal, not one that drops to the floor.

Edited by BlaineBug

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He heard a vacuum noise in addition to the sinking pedal. If you're hearing vacuum when applying the brakes, that's a torn booster diaphragm. You won't necessarily have a stiff pedal depending on how big the tear is.

 

If there was a leak, you'd see it at the leak source, and in the master. Front brake leaks will empty the rear chamber of the master, and vice-versa for the rears.

Edited by Jsdirt

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25 minutes ago, BlaineBug said:

If there was a vacuum leak, I would think that the brakes would be hard as heck to push.  But your problem is quite the opposite.  Definitely sounds like a leak, somewhere.  Your reservoir shouldn't empty itself as the brakes should have a zone between front and rear as far as I know, that's how it used to be in the past.  Can you attempt to re-bleed all 4 corners?

 

Basically, if you had a vacuum assist OR hydraulic assist system, a LACK of assist would result in an even harder pedal, not one that drops to the floor.

I get your point. Is it possible that the fluid is bypasssing inside the master cylinder and the sound I heard when I pushed the brake with the engine off was from the diaphragm pushing air through the vacuum hose? Is there a blow off or something like that in the system or is maybe the check valve at the end of the vacuum hose where the air comes out? 

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I don't know so I can't be much help.  All I know is that a pedal that drops to the floor means that there is air in the system.  Because air compresses, whereas fluid does not.

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1 minute ago, BlaineBug said:

I don't know so I can't be much help.  All I know is that a pedal that drops to the floor means that there is air in the system.  Because air compresses, whereas fluid does not.

Thanks yes you're right. I wonder how air is supposed to get in though since it got bad very fast and a hole would leak fluid. I want to check tomorrow if the master has an internal leak that lets fluid cycle straight back into the reservoir and therefore getting the pedal to the floor. 

 

 

To the question about bleeding the breaks, I heard that it's quite the task on these newer trucks, read that you need a computer to cycle the automatic bleeder. Can I still bleed the breaks at the wheel cylinders like with old cars and trucks or will I need the computer? 

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I don't know about that.  I have used both a hand-pump vacuum pump, and the much superior compressed-air powered vacuum pumps to bleed the breaks on Fords and Toyotas with ABS in the past and didn't have a problem.  I'm not sure if it is an absolute necessity to cycle the ABS pump or not.  All of this new technology makes it harder and harder to "do it yourself!"

 

The easiest and cheapest is to buy the Harbor Freight vacuum pump, start the air, and crack the bleeder and let the fluid come out at each corner, starting furthest away from the master cylinder and making your way closer.  So it's passenger rear, driver rear, passenger front, driver front generally.

Edited by BlaineBug

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If you have no leaks, you don't have air in the lines. A bad master cylinder will act exactly like air in the lines, or a leak, and go straight to the floor. 

 

Sometimes when this happens, it will go to the floor once or twice, then be fine the rest of the time. Other times, it's exactly like a blown line.

 

Bottom line is, you need to inspect under the vehicle, and around the front, and rear drums or discs for signs brake fluid leaking.

Edited by Jsdirt

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Take a look at Scotty Kilmer's  video  Although somewhat simplistic, he tells you how to check for a bad master cylinder vs and bad brake booster.

 

Good luck.

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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.

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