brake pedal goes all the way down when braking

YOU HAVE 1 OF 2 PROBLEMS,OK 1 SOLVED BAD WHEEL CYLINDER, DID YOU BLEED ALL THE AIR OUT OF LINE,SOMETIMES WHEN YOU REPLACE ONE IT IS GOOD TO REPLACE THE OTHER SIDE AS WELL,YOU MAY HAVE TO BLEAD ALL 4 WHEELS OR YOUR MASTER CYLENDER IS BAD LOOK WHERE IT BOLTS TO BOSTER SEE IF WET AROUND M.C.IF SO REPLACEMASTER CYLEMDER DONT FORGET TO BENCH BLEED BEFOR INSTALLING.

Agreed, I would bleed the rear wheels (both sides now that you have driven it a bit) starting with the passenger side rear wheel. Then determine if MC is bad after making sure rear wheels are fully bled.

Thank you for your advice, but I did bleed all wheels. MC looks dry around the its base. I even checked the vacuum hose that goes to the power booster for air leaks or faulty valve, but it all looks fine. now my next step is to replace MC or power booster, I just don't know which one may be out. thanks for your help,

The booster won't make your pedal go to the floor. If you bled all the brakes, and there is no leaks, then its most likely the master cylinder. You can take them apart and clean it, but if the seals are to bad then you should just replace then bleed the brakes again.

'now the car brakes but the pedal gradually goes all the way down' This generally means the master cylinder is bad or that you have a slow leak... Air in the system generally won't act this way... well since the air is too compressible... It's not a gradual feeling... If it were air you'd push the peddle all the way down and it would barely brake if at all... the gradualness of the drop means you are loosing pressure and to maintain the pressure that you have, you have to force more fluid into the system... Usually this is traced back to a bad master cylinder but it's possible that you have a slight high pressure leak elsewhere. Double the work you've done... Put the car on stands have someone pressure up the brakes and see if it's leaking slowly from anywhere you just worked on... Since it happened after the repairs, then this is a good place to start... If it's not that then it's likely the master cylinder...

Did you replace all pads, or shoes if fitted,if so,when you returned the brake caliper piston,if you did it very quickly,pushing the piston in that is,then you stand a very good chance of reversing the rubber seals in the master cylinder,this will also give you a very bad brake.to correct it ,in most cases,removal,strip and rebuild,possible new seals,check the bore has not gone ovel or damaged in any way.

97 civic just replaced both rear wheel cylinders and shoes, adjusted parking brake. Replaced booster and MC (and bench bled) blended all the air out of the lines no bubbles no leaks. And brake pedal still goes to floor any suggestions?

We replace the master cylinder and the power brake booster, a leaky brake in and front brakes. Bled It several times on my 1989 Honda Civic CRX and the brakes still go to the floor! Any advice or help

Same thing happened to my 95 Civic EG DX sedan. I converted the front knuckles to the 94-01 Integra, so now I have 10.3 inch rotors and a bigger caliper. I also swapped the MC (master cylinder) to the 91 Civic since it’s bigger (15/16 bore size) original is 13/16. My pedal still touches the floor when I turn the car on. Of course I bench bled the MC. Bled the lines in sequence. I even got steel braid lines for all sides and new wheel cylinders for the rear. A lot more suspension upgrades as well. I’m no noob but idk what the heck is going on now. All I can think of is that my brake booster has a leak and is sucking too much air. That’s why my brakes go soft when the engine is running. Other than that my brake are stiff when the car is off and when I pump no leaks since I did replace the lines. Please let me know what it could be or what I should look for. I’ve invest a s*** Tom of time and money into the car. Hate to sell it to someone who wouldn’t appreciate it