I've been trying to diagnose a hard brake pedal at low speed. I'v3e read thorough many forum threads to see what the common issues are, and I've ruled out the vacuum related possibilities (i think). The hard brake pedal has only happened in low speed parking lot situations, mostly backing into a parking space, but it has happened going forward as well. The truck has 90k miles on it and this is the first issue I've had with it. The brake pads/rotors are original, and the brake fluid is also original. I have plans to get the brake fluid flushed when i do the first brake job. Currently the fluid doesn't look to dark. Its kind of the color of watered down ice tea.
Here's is what I've done so far.
vacuum pump - I disconnected the vacuum line and put a gauge directly on the pump. It pulled 27Hg of vacuum.
Brake booster - With the engine off, i pumped the brake pedal 3 or 4 times until it was hard, and with my foot still holding it down, i started the engine, the pedal sank with a little resistance. I kind of shuddered down, not smooth. Since I wasn't satisfied with that test, i disconnected the vacuum line and used a mity-vac to pull a vacuum on the brake booster. I was able to hand pump 13 Hg of vacuum and it's holding steady.
I'm starting to think this issue is not vacuum related. Is it possible it's a sensor, or something within the ABS system?
