Very soft brake pedal, engages near floor: Woosh sound when pressing the pedal

[Cursh]

X posting this question from a longer post I made in the BlazUrban forum.

When I hit the brake pedal I hear a loud WOOSHing sound coming from under the dash.

Any idea what that is? The brakes work better than the sound led me to believe that they would, but they are only engaging at the floor.

Original equipment all around: disc front/ drum rear.
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[Just call me Sean]

The booster is bad.

[Dead Parrot]

Some 'woosh' sound is normal. That is the vacuum doing its thing when you press the pedal. One test for booster leaks is to start and run the motor for a minute or so, then stop and walk off for 10 minutes. Then without starting, press the brake pedal. If you still hear a woosh, booster probably good, otherwise, suspect a leak. A booster leak can also cause an idle issue due to the idle mix going lean.

The engaging at the floor could be a bad master cylinder or low fluid.

[Cursh]

Thanks y'all!

I do think it was the brake booster, but I love the test method and wish I'd tried that.

My eager ask* already took the old one off and bought a new one, so here is to hoping it isn't the master cylinder. I did pop the lid off the master cylinder and there is a ton of fluid in there, so it shouldn't be low fluid.

While removing the booster I cracked the booster side of the check valve. It looks like those things are unobtanium now, but I'm also looking into what it does and it seems like I can get a 3/8" filter and a 3/8" one way valve and I've go the same functionality in a slightly different form factor. Is that correct?

The original that I broke doesn't seem to "check" at all. It's just a filter. Is that what it's supposed to do and mine didn't? or did I just buy a couple check valves just to be prepared for a future situation where I need a check valve for something else because this aint it.

LMC parts diagram for clarity and dog for engagement.

[Cursh]

Originally Posted by Cursh

While removing the booster I cracked the booster side of the check valve. It looks like those things are unobtanium now, but I'm also looking into what it does and it seems like I can get a 3/8" filter and a 3/8" one way valve and I've go the same functionality in a slightly different form factor. Is that correct?

The original that I broke doesn't seem to "check" at all. It's just a filter. Is that what it's supposed to do and mine didn't? or did I just buy a couple check valves just to be prepared for a future situation where I need a check valve for something else because this aint it.

In case anyone else has this question and stumbles upon this dead post in the future, I got an answer elsewhere.

I called a buddy of mine who’s more mechanically inclined than me (he builds custom shocks for pre release test vehicles for a major strut manufacturer; that is to say its not coming from this dopey DIYer in AZ) they told me that the check valve can be any old one way valve that is rated for air. The flow is TOWARDS the engine to keep pressure in the booster if the engine is off or in idle.

Ive got two ****ty ones on the way just because sometimes ****ty ones don’t work out of the box.

Cheers
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[87chevy.com]

More than likely you have a bad master cylinder.

Brake booster does one thing, make pressing the brake pedal easy. If the pedal goes to the floor, master cylinder is probably leaking internally.

Brake booster testing is pretty simple, engine off, press the pedal till it no longer has assist. usually 3-4 presses. when its hard, one more press while starting the truck, the pedal should slowly sink to the floor as it now has assist. As far as it making noise, to some extent its normal.

I'd recommend replacing the master, bench bleed it and then make sure when you bleed it, use or make a proportioning centering tool. if you don't you can make the valve move to one side or the other and it will block the flow of brake fluid to front or rear depending on which way it went. resetting them is a pain in the butt.

if you have an extra old brake sensor for the proportioning valve, you can make one, easy, remove guts, tap to metric 6x1.0 or whatever standard size will thread into it. put the pin part back in, use the screw to push the pin to its end stop and thats it.

http://87chevy.com/images/tools/brake_bleeder_mod.jpg

or you can buy one and i recommend modifying it so the nipple doesn't break off...

http://87chevy.com/images/tools/brak...er_upgrade.jpg

clint

[87chevy.com]

Originally Posted by Cursh

In case anyone else has this question and stumbles upon this dead post in the future, I got an answer elsewhere.

I called a buddy of mine who’s more mechanically inclined than me (he builds custom shocks for pre release test vehicles for a major strut manufacturer; that is to say its not coming from this dopey DIYer in AZ) they told me that the check valve can be any old one way valve that is rated for air. The flow is TOWARDS the engine to keep pressure in the booster if the engine is off or in idle.

Ive got two ****ty ones on the way just because sometimes ****ty ones don’t work out of the box.

Cheers
Posted via Mobile Device

also the brake booster doesn't hold pressure, its vacuum that it needs and holds if the check valve is working properly.... he may not be as mechanically inclined after-all

[Just call me Sean]

The check valve is #4. I don't know what #5 is but could be a secondary.

[ron350]

Part #5 is a charcoal filter that prevents gas fumes from reaching the check valve and the vacuum booster.