Here's my story! Two days ago I had to take my boat to town for service! About 35 kms. Not many stops between my home and the service area. When I did arrive my brake pedal went almost to the floor? I could smell brakes? I discovered the parking brake pedal had not fully released to the top position. Did some errands in town and drove back home. I removed the rear wheels and drums to inspect the brakes and discovered the rear shoes were almost to the rivets? The leading shoes were OK! I purchased new shoes and installed them with little difficulty but after re-installing the drums and adjusting the brakes, the pedal was soft/spongy? Reading here on the forum about making sure the adjustment was correct I re-did the adjustment very tight then backed them off before taking a test ride! The brakes were too tight and started to smoke? I couldn't understand why the new brakes made the brake pedal soft/spongy so did a little research here on the forum! Could it be the vacuum assist? That should make the pedal hard not soft? The truck is new to me only a year ago and the master cylinder has checked Dec/09? It looked full and clear so I thought it was OK? Not! Upon closer inspection I believe the park brake cables are not releasing and was holding the rear shoe onto the drum. But that heat caused the brake fluid to boil and that is the reason for the spongy feel to the brake pedal! Today I did a rear only brake fluid flush and now were back to normal! I usually only use the truck in the bush so don't think I need the park brake for my normal use? The only reason for this long dissertation is I couldn't believe the cooking of brake fluid only could cause such a dramatic change to pedal sensitivity? Sorry for being so long winded!
Yeah boiling brake fluid will cause a spongy pedal. Every few years you should drain/flush your whole system, especially if you tow a lot. Sounds like you got it figured out though. Parking brake cables tend to freeze up over time if not used, then if you do push it, it gets stuck applied. Make sure you got the adjusters on the right way, they are different threads for different sides
Yes I will bleed the fronts soon, but in the mean time I can't believe the improvement? As I said the truck is mainly used in the bush so a parking brake is not a high priority if ever used? My reason for posting was a result of trying to find out why my brake pedal was soft in spite of replacing the shoes with new? Lesson learned!