As context I have a 1994 dx hatch, with the rear disks from an integra.

I had replaced my pads and rotors about a month ago and completely flushed and bled my system with fresh dot 4 and the pedal was nice and hard. A few days ago the car would start randomly let the pedal go all the way to the floor to get the same pressure about 1/20 times. Most times you went for the pedal though it felt completely normal and would hold pressure.

Forum guidance led me to believe it was a failing seal in my master cylinder, so I took the opportunity of replacing it to upgrade to the 15/16ths one out of a 1991 ex sedan that bolts right in. Today we bench bled the new MC, swapped it in, and again bled the system with fresh dot 4.

Now the pedal is even harder, bites high, and the car stops hard... accept for the 1/20 times the pedal still goes all the way to the floor

I've checked under the car multiple times and there are no leaks, and the fluid stays at the same level. I've basically serviced the entire system and still have this intermittent issue, what is there left to check? Have I done something wrong? So lost here

 

Do you have ABS? Did you change or refresh the proportioning valve?

 

It does not have abs, so the module is out. And I haven't because I didn't think a proportioning valve would cause that symptom. Do you think that's a likely culprit?

 

I am not an expert, I am just bringing all information to light for those that are.

I am not versed on the behavior of a faulty proportioning valve.

I do know that you informed everyone all the other parts of the brake system but did not mention if you had or did anything with an ABS unit or if you did anything with the proportioning valve.

The other thing that should be asked.... Have you checked all the soft lines to see if there is any bulging?

 

No ballooning to mention here, we have already checked for that. Right now the leads in working is a bent slide bolt for the front caliper, and a slightly wiggly wheel bearing that might be opening the caliper when it moves. I'll be replacing them tomorrow and see how it progresses from there