so i have a 94 cx hatchback and when im going to stop i start to break and the brake pedal sinks slowly and slowly until its all tha way to the floor..and i release it and it gets hard and again sinks slowly...i think its the brake booster and this mechanic in town said it was some valve in my rear drums..but idk.. any help would be appreciated.. thanks.

 

It could be the master cylinder. But have you tried simply bleeding the brakes?

 

Could be air in the lines or a leak somewhere. I would bleed the brakes first.

 

i have the same problem too
ive already bleeded the breaks, and everything seemed ok. when the car is not started, there is a decent ammount of pressure on my break pedal, but as soon as the car is turned over and idling the break pedal sinks.

 

yeah dude same here..i pump the brakes when its off and when i start it it sinks little by little...but i haven't bled the brakes yet..