Rats. When the brake fluid releases at the master cylinder, that means it's the master cylinder that is trapping the brake fluid. Normally that is due to the fluid being contaminated with a petroleum product. Rubber parts used in the brake hydraulic system are not compatible with petroleum-based products and will swell up and get soft and mushy. The lip seals grow past the fluid return ports and block them.
This also proves the rubber flex hose is not what's trapping the brake fluid.
In this case there's two clues that point away from fluid contamination. Most importantly, the rubber bladder seal under the reservoir cap is still its normal size and shape. Second, the master cylinder was recently replaced. A lot of import cars have adjustable push rods coming out of the power brake booster. Those have to be checked and / or matched to the new master cylinder. Anything that holds the brake pedal down a little will keep the brakes from releasing. That includes that push rod being adjusted too long, and the brake light switch being misadjusted and holding the pedal down a little. Next time the brakes lock up, loosen the two nuts that hold the master cylinder to the booster, then pull it forward 1/8". If the brakes release, that proves the seals in the master cylinder are okay and fluid contamination is not the cause. Check if the push rod has a threaded end that can be adjusted. Also feel if you can pull the brake pedal back further than where it sits when it's at rest. If you can, the return stop or brake light switch adjustment is okay too.
Thursday, October 10th, 2013 AT 4:41 AM