Soft pedal after emergency stop

[Duallylife]

I have a 93 gmc k3500, on my way to work today someone blew a stop sign so I slammed the brakes on and locked up the tires, just as I came to a stop though I felt a pop in my pedal and it almost hit the floor, now my brakes are extremely soft and my pedal almost hits the floor and I have very little brakes. When I got to work Iquickly pumped them and saw no drips, and the fluid is still full, everything on my brakes on all 4 corners, lines pads rotors wheel cylinders etc are all brand new as of this summer, everything except rear drums they were 2 summers ago. Even the master was a rebuilt one. Any ideas? Oh the booster hasn't been changed but that's just for assist?

 

[Erik the Awful]

Oh the booster hasn't been changed but that's just for assist?

Correct. Pull those brakes apart and check for broken hardware and pad material.

Also, hydroboost or vacuum assist?

 

[mr_josh]

As was said, time for an investigation at the wheels.

But: when you come to a stop, does the pedal gradually drop off or is it just soft? I’m thinking a seal may have failed in the master cylinder.

 

[Supercharged111]

Is there a button on the front of the proportioning block to reset it? How rusty is your truck? May have blown a hard line.

 

[Schurkey]

Is there a button on the front of the proportioning block to reset it?

There's a "button" on the combination valve (it activates the metering/holdoff valve part of the combo valve) that's useful when using a pressure bleeder to bleed the front brakes.

There's no button to "reset" the combo valve or the proportioning valve.

How rusty is your truck? May have blown a hard line.

Yup. He says fluid is full, and no drips, though.

I'm going with failed master cylinder.

 

[thinger2]

Yep, sounds like master cylinder blowing fluid out of the rear seal into the booster.
Dont drive it.
If you get really really lucky.
That fluid is pooled up in the master/booster void and is not leaking into the booster.
I would replace the master and the booster.
Go cheap on air freshioners, steal flowers from the neighbors yard so your doesnt think you forgot her birthday.
Do all of that before you cheap ass on the brakes.
Fix that ****.
You can kill someone and if you do your life will be entirely and completely ******.