the brakes originally felt great but the pads were on the way out so i upgraded to brembo x drilled rotors and KVR pads. after replacing i did not bleed the brakes, and i went to break them in. the pedal was very weak and the brakes would barely slow the car after the firs few stops. my friend said that when i compressed the caliper pistons sometimes air enters, so i bled them the next day at his shop. the pedal firmed up quite a bit, but it still feels weak and is very uncomfortable in tight stops. the old brakes felt good. my friend said it is probably small deposits on the MASTER CYLINDER SEAL, causing poor pressure. i can only guess the MC and booster are as old as the car.
has anyone else had a similar problem?

 

dirty cap can make a world of difference.. happened to me about a month ago. I Just decided to "clean it" but the rag wasn't too clean. It got Dirty and drove it. Spongy and overall it sucked. Cleaned with a clean rag and it went back the way it was.
Now my mc is fucked so im buying a new one today

 

the brake mc cap is not pressurized, it makes zero impact in brake performance, until the reservoirs goes dry.