Alright, when I bought the car i noticed that there was excessive play in the brake pedal. Then a few weeks later the brake light kept lighting up. I replaced the front pads and then rebuilt the cylinder carefully. Bore was not pitted or scratched and the washers that i removed were not dryrotted, cracked, or worn. When I reassembled everything and bleed the brakes (from back right, left, front right, left) there was still excessive play in the pedal. Then i drove the back end of the car up an incline, since the master cylinder is on an incline as well. i bleed the system right at the cylinder and i did get some air out of the secondary. Fluid still shoots up out of the primary with the cap of the master cylinder off, but i thought that that was due to the valve inside of the resivor. What is the function of the valve? Could it have went bad? The pedal still has as much play as it did, and the brake light still comes on. Could it be the proportioning valve? My car is an 86 iroc - z 305tpi, 4 wheel disks, and only 23,000 miles on it. Thank you for taking the time to read this.

 

i dont know much about the master cyclinder or brake booster however spongy brake feeling is sometimes caused by low fluid or failing brake hoses... or of corse air in the system still...

i think you have to bleed the brakes start from the side thats that furest away from the master cyclinder and work by getting closer to it..

thats all i really know, if this does not help sorry maybe someone else will respond...

 

Does your e-brake still work? Just curious I know from experience that the rear calipers will go bad. I had same problem. Hope it helps some.

 

When the master cylinder goes bad you can feel a two part pressure release on the pedal.

The instructions for install on a new master cylinder require an adjustment to the shaft between it and the booster. This could take up some slack you have even though it's the original but rebuilt.( I have never moved this adjustment myself).

A bench bleed (in a vice)of a new mast. cyl. is also indicated.(never did this myself,allways in car).

Fluid should shoot out with a rapid brake pump during bleeding (RB83L69).

Doubt it's the proportioning valve.