Spongy Brakes Question

[LSUMurse]

My brakes have become spongy, to the point that my dash brake light comes on. Most of the time, as I come to a stop at a stop light, they perform so-so and stop the truck. As I am sitting there, the brake pedal slowly depresses further and requires more pressure to keep the truck from moving. Sometimes it goes straight to needing the aforementioned amount of pressure with no stoppage in between.

I have converted the truck from manual to power brakes, but it didn't start doing this until after I put a new engine in her. I did not break the system, I unbolted the master cylinder from the booster and pulled the MC over to get it out of the way.

I went to bleed the brakes today and didn't get much force from the bleeder valves, mainly just a trickle. I never noticed any bubbles. The passenger side rear valve was gummed up so bad I had to remove it and basically drill it out.

I pulled all the drums and did a rudimentary inspection of the system. I didn't notice anything that looked wrong, though I am not incredibly familiar with drum brakes.

Should I open the lines at the tee in the rear and see if I am getting good flow? Maybe something dislodged and stopped up the lines? I'm not sure where to go from here.

[mario1128]

sounds likeyour gonna need a new master cylinder

[67 chevelle]

replace the 3 rubber lines , then take the maser off and see if fluid is seeping out the back into the booster , if so you will have to replace the master , probably a good idea to do that anyway

[SS Tim]

Do not continue to drive the truck like this!
If the light is on you are/were seeing a pressure differential between the two sides of the system. Spongy is due to air in the system. If you can't get a good flow at the bleeders its probably the master cylinder. Sounds like the system has not been serviced (or flushed) in a while if you had to drill out a bleeder. Did you carefully check all four wheel cylinders for leakage, including under the cups?
Might just want to pull up the factory manual and do a systems review in chaper 5 on the brakes and the distribution valve/warning lamp functions.

[LSUMurse]

I did not check under the cups, I will do that the next time I get a chance to work on it. I rarely drive the truck now, mostly just to test something I've tinkered with the engine about. I guess I'll get a new MC and flush the system and see if that helps.