Suddenly today my pedal goes to the floor and the ABS, and Brake light come on. When checking the basics first, I found that the master cylilnder is full to the rim. I regularly check fluids, and know that it was between the ad and full mark recently. I had not seen this symptom in other posts.

Is the MC shot? Possibly the proportioning valve? How do I tell if it is one or the other.

Pedal goes to floor when truck is off or running.

2001 Dakota 4.7

Tonight I purchased a new MC and speed sensor, but wanted to see if I am on the right track.

Thanks.

 

Also check your brake lines. Same thing just happened to me and turned out I blew some of my rusty brake lines.

 

I have not found any signs of leaking. Did you master cylinder stay full even though your brake line blew?

 

Changed out the master cylinder tonight. Pedal still going to the floor.

 

do you have 3 channel abs. you might have a decay valve sticking open

 

My build sheet shows

BGJS Pwr Disc/Drum Rr Anti-Lock Brakes

 

Being that fluid appeared out of thin air, its possible that your system has been contaminated, water or moisture has invaded the system, or possibly the vacuum system in the brakes has failed and allowed all the fluid up from the system. just two possibilities. however a vacuum leak would throw up a check engine light. Perhaps a bleeder valve let air into the lines...try bleeding the brakes...