Hi there! so far I've always found useful information on this forum, and also for this problem I have - I need some confirmation from more experienced people than me and my mechanic.
I have Civic 1.8 from 2010, made in UK. To date, I have not had any problems with this car. Regular maintenance, I changed the filter and oil, shock absorber mounts, brake pads. The car is 14 years old and has traveled about 170,000 kilometers.

• In March 2024, I notice on a downhill that my brake is kind of spongy, more precisely:when braking for a longer period, the pedal asks me to press it all the way. It's spongy, but not always.
  I should mention that the reaction and speed of braking was always precise and good, except for long braking.
• After visiting several mechanics, I decide to change the brake pads, bleed the system, new brake oil. The situation is slightly better, but I still have the same problem.
• In June, however, I changed the master brake cylinder. After that - The brakes work perfectly, without any problems, no more spongy feeling.
• After 5 months the problem returns.I drive the car to the official service, where they re-maintain the brakes (brake bleeding) and new brake oil.They suggest replacing the discs and replacing the brake pads again, if the problem reoccurs.

This is my logic:

When the mechanic installed a new brake cylinder, the situation improved drastically, but soon it went wrong again: either the mechanic installed a faulty cylinder, or a poor quality cylinder, or the problem is somewhere else.
I researched other symptoms to rule out the ABS module, air hose and brake booster. After the complete diagnosis was done at the authorized H repairer, I eliminated the ABS module, and the brake booster (servo) I think would show another problem: extremely hard brakes.

I decided to change the discs and brake pads, and get a new brake cylinder.Any experience is welcome.

Thank you for the information.

 

I had to change my CMC out 3 times in 3 months, bc I kept replacing it with autozone parts. which were actually broken in the inside plate which leaked brake fluid back into the system. but bc of it, I had minor oil pressure. but not full. I finally took it to my mechanic with an upgraded CMC (removes the Dampner diaphram, which was the part that kept breaking.) haven't had the issue since.

 

Tnx @shai x boi racer for you reply. So you're saying that getting a decent spare part (maybe ATE) instead of no-name spare parts mechanics usually use can solve this problem?
Or, there's another hack to do with Dampner diapharm? I'm not sure where's that diapharm located. Can you explain more, please.
Thank you!

 

@Civic_cro Sorry I didn't reply in a while. forgot to check on this... I don't do social media if I don't have to. but I decided to check up on this.

I re-read your post. I was just saying, it could be just a bad replacement part. but maybe, instead of your mechanic try a different one. I know I am saying basic stuff. but... technically speaking, you paid for something ... if it's less than the warranty period of driving...(Depends on the mechanic) then bring it back and say it's back... sometimes it's a guess and check thing.

sorry, maybe I thought when you said you upgrade your master cylinder... I thought you meant clutch... hence my reference. Keep trying, you'll figure it out.. maybe remove and look over the brake master cylinder again, break it down and see what is wrong with it. you did say you replaced the brake master cylinder and everything worked great. also... verify your brake pressure. if it does start strong, but slowly decrease over time... then maybe you have the same issue on a different part. Maybe I was sharing my experience to maybe give you a clue on what it could be... by breaking down the master cylinder.

also. it could also be the brake pads/rotors themselves. some really cheap ones, are good for a minute... and then they just naturally overheat with over use or long braking glazing the pads and rotors making it more like trying to stop using glass on glass contact. since you say the short braking is good but long braking is bad... maybe the brakes just don't work as well when heated up. COULD BE! Maybe Not... worth a check tho.