For the past few weeks, when I come to a stop light and have to hold down the brake, the brakes will slowly lose power and I'll have to push the pedal down all the way to the floor to avoid rolling forward. I've been told that this is either the master cylinder or the brake valve, but there's no way to really tell which one, and both replacements are kind of pricey. I was wondering if anyone has experienced this problem or know of anyone who has and what it turned out to be so I can take an educated guess as to which one to replace. Any help or insight would be much appreciated!

 

Just out of curiosity - are you losing brake fluid also?

 

Actually, there is no sign of any brake fluid leakage. The resovoir is at the same level as the last time I filled it up which was about 4 months ago.

 

Apply the e-brake. Get two pipe plugs that will fit the openings on your master cylinder, and remove the lines, and install the plugs. Start the engine, and push on the brake pedal. If it moves, the master cylinder is bad. If it's rock solid, and doesn't fade, the problem is elsewhere. I seriously doubt it's your proportioning valve, but it could be a wheel cylinder or a rubber brake line between the frame and the front calipers.

My money is on the master needing new seals (needs to be rebuilt).

Take care,
~Chris

 

Thanks. When I get a free moment, I'll give it a try and let you know what happens.

 

Brakes are fixed. Turned out to be that damned old RABS valve. It's been giving me problems for almost 4 years now, glad I finally got the problem pinpointed and solved. Any ways, on to the next problem: my idle is still surging. When I'm at a stop light, my pedal no longer depresses to the floor, but my idle jump up to 1000 rpm, then go back down to 600, back up to 800, then down...etc...pretty annoying Any ideas?

 

When does it do it? Hot, cold, both? If you have an automatic, does it do it in both drive and park? Have you checked to see what codes are stored? A KOER test would probably isolate it.

 

TF, mine is currently doing the same thing, it has to be hot and it does it when not in gear, auto. Aggrivating, it actually died on me once when it did it, have yet to figure it out.

 

Well, my idle was fine this morning. I don't know what's going on with my truck. This problem comes and goes. It has surged in Park as well as Drive, in the heat as well as when it's cool. I am going to pay close attention over the next week or two and monitor exactly when the idle surges so I can try and figure out what's going on.