Given the combination of a mushy brake pedal and apparent blockage in one line, the first thing that comes to mind is the brake fluid is contaminated with a petroleum product like engine oil, transmission fluid, power steering fluid, or even axle grease. That will cause all rubber parts to swell and expand. The lip seals in the master cylinder will grow past the fluid return ports. That will block fluid flow when gravity-bleeding the brakes, and they won't retract far enough to take a new bite of fluid when pedal-bleeding with a helper. The clue to fluid contamination is the rubber bladder seal under the reservoir cap will be blown up and mushy. The only proper fix is to remove all parts that have rubber that contacts the brake fluid, flush and dry the steel lines, then replace all the parts with rubber in them.
Another, less common cause of blockage is pushing the brake pedal all the way to the floor when bleeding the system or when you're surprised by a sudden leak. The pedal should never be pushed more than half way down unless the master cylinder is less than about a year old. Crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Running the pedal more than half way down runs the lip seals over that crud and can rip them. That results in a low and mushy pedal or one that sinks slowly under steady foot pressure. In rare instances some of that corrosion can break loose and get pushed into one of the steel lines. If you suspect that, you can often clear it by disconnecting that line at the master cylinder, opening the bleeder screw on the caliper, then giving it a quick, short burst of compressed air into the bleeder screw.
There's going to more wrong than just blockage in one steel line because that would cause a higher brake pedal that's unusually firm. If that line was loosened, brake fluid would flow from the connection even though it doesn't flow at the wheel.
Sunday, March 23rd, 2014 AT 11:11 AM