2005 Supercrew, 5.4L 4WD with approx. 99,000 miles.

Pulled out of the driveway last night and noticed the pedal felt a little soft. Drove down the road and bam; pedal to the floor with zero pressure. Used the e-brake to stop. Pulled into a parking lot and checked the fluid, the reservoir was full and had no leaks I could see. Pumped the brakes a few times and had pressure, then drove down the road again and the pedal went to the floor with zero pressure again.

What do you guys think?

I am leaning towards the master cylinder since there is no fluid leakage, all input is greatly appreciated.

 

There is a recall for brake hose.. Might check that.

 

The only recall I've seen is for the vacuum hose to the booster. This has NOTHING to do with a loss of brake pressure. If you have a vacuum leak your pedal gets hard, it won't go to the floor.

You say you lost "all brakes"... are you sure you didn't lose half the brakes... try pushing it all the way to the floor and see what happens.

Your brake system has 2 independent circuits. When one gets a leak it might seem like you have no brakes (since you have to fully compress the springs in the master cylinder bad circuit before building pressure) but you do have half your brakes.

Park somewhere dry and pump your brakes 10-20 times and then get out and look for a leak. A very small leak can still make the pedal travel that far so you might have to look close. It could be on one of the frame rails so maybe the fluid isn't running right on to the ground.

Once you are sure you don't have a leak, then you know its a bad master cylinder. Need to replace it and rebleed the entire system.

 

Sounds like a bad master cylinder......

 

Thank you for the reply.

I am pretty sure that I lost 100% braking pressure; but I don't know for sure. The pedal went to the floor and it didn't appear to have any impact on slowing or stopping the truck. I used the e-brake when it appeared as though I wasn't going to stop.

I understand what your saying about the 2 circuit system, which is why I was concerned. I don't see any leaks and the fluid level has remained the same. I am pretty sure I'm going to replace the master cylinder and see what happens.

Is it possible to bleed the system myself after the master cylinder is replaced? I was reading a post where a special machine was required to perform the bleed on a ABS equipped vehicle. Any words of advice?

 

if you don't see any leaks then the master cylinder is leaking internally... the fluid goes back into the reservoir.

You can bleed it yourself. Just be very thorough and don't start the truck till you are done. If you start the truck I think the ABS module may cycle (not sure about this) and get air inside the valves.

As long as you don't get air in the valves of the ABS module you don't have to have it bled by a shop.

So be sure the system is fully bled before taking it for a test drive.


Also - if your truck is older, this would be a good time to replace the flex lines at the wheels. You have to bleed the entire system anyway and thats the hardest part of putting new flex lines on.