Problem: Soft brake pedal.

With the engine off, I can push the pedal until it gets firm. The pedal has a bit of give, about 50% of the travel. (should this be rock solid, immovable?)

Holding the pedal down, starting the engine, the pedal sinks to the floor.

The check valve for the booster is working based off this.

I've bled the brakes a few times now. when bleeding, i use a hose on the brake nipple,and run that to a bottle half-filled with brake fluid. I did bench bleed the master before installing it.

89 Civic
Stock brake booster
1990 Prelude 15/16" master (new from rock auto)
4040 prop valve from integra
legend dual pot front calipers
RSX rear calipers
New pads and rotors all around

I've been having this issue ever since the RSX rear upgrade + prop valve.

The calipers are all mounted upside down so that they fit and are utilized properly. I un-do the bottom caliper bolt, flip the front calipers UP, use a block of wood so the piston has something to push against, and zip tie the caliper in place.

The rear ones, I flip the caliper DOWN and use a block of wood so the piston has something to press against.

I have a couple ideas, but I'm honestly kind of fed up and wanted to bounce these off some other people.

1) the rear calipers should be flipped UP when bleeding, so that the bleeder is higher up

2) the master NEEDS to be bench bled again

3) faulty brake booster

 

did you adjust/check the MC piston to booster gap?

 

I have not.

Hey Tyson, should the pedal be hard as a rock when the car is off? I also read that maybe my rear calipers aren't adjusted "snug" enough by spinning the piston.

 

you really need to when you mess with MC and Booster swaps.

the rear caliper is self adjusting. pull on the hand brake, it will adjust itself.

 

I bench bled the MC again to see if it was done properly. There were no bubbles.

It was a combination of issues:

1) was missing a crush washer for one of the brake lines on the rear caliper. I found a constant leak where I continuously saw bubbles when bleeding.

2) bleeder valves were fairly corroded and had buildup on them. Joys of old used parts... Cleaned it up with a file to allow a proper seal when the bleeder is tightened down.

3) manually adjusted the e-brake and calipers. with the cable disconnected, I turned the piston until I could just barely slip the caliper over the pads and rotor. I then adjusted the e-brake cable until I had a small amount of drag on the rear calipers. Just a very small amount.

Brakes work great now. I didn't mess with the MC piston to booster gap, nor was I able to find any official documentation on adjusting this... I didn't think it was necessary as this is a replacement spec master cylinder, and I didn't change the booster.

 

thanks for the update.