Soft Brakes (pedal to floor)

[mpierce9]

Hello - Been working on this a month and have exhausted all the options I have found in these forums. 1975 Chevy blazer disc front, drum rear.

My brake pedal travels to the floor before stopping. Slamming the brake pedal to the floor at about 30 MPH takes about 30-40 yards to come to a complete stop.

The pedal also returns slowly after being applied.


Done so far:
Overall System:

• I've been through two master cylinders (I've bench bleed both extensively)
• I want to clarify that I "pumped" each MC up to 150 times and saw zero air bubbles
• New brake booster
• Extended pedal link to booster to engage the booster immediately
• Resolved all leaks
• Bleed the entire system multiple times with the "One person pumps the pedal five times and holds it down, while the other person opens the bleeder" resulting in no visible air bubbles.
• Confirmed the Combination / Proportioning valve is working as expected (i.e. the light isn't on)

Front brakes:

• Replaced both calipers, discs & rotors
• Replaced both soft brake hoses, banjo bolts and washers

Rear brakes:

• Replaced both wheel cylinders
• Tightened both shoes to sit very close the drum

General notes

• Each bleeder has excellent fluid flow when bleeding
• With the engine powered off, the brake pedal returns quickly
• With the engine powered on, the brake pedal returns slower
• Feels like most of the braking is being done by the rear brakes
• This started with a bad wheel cylinder resulting in my proportioning valve becoming tripped
• On the MC I plugged the ports and attempted to press the brake pedal down this resulted in a completely firm & unmovable brake pedal (which I believe indicates the MC has been properly bleed and is working as expected.

Any help or direction would be greatly appreciated. Minus the hard lines, and Combination/Prop valve almost everything has been replaced.