1995 Accord. Occasionally, about a third of the time when I go to brake, the pedal sinks. Not all the way to the floor, but it steadily sinks. If I try to pump it up, it will just sink again. No leaking whatsoever. At first, I thought it was air in the lines. Bled them, and problem returned same day. Like I said, most of the time the brakes work just fine. Master cylinder or booster?

 

Sounds like master cylinder to me.

 

I would say the brake master is bypassing internally.
The most common description of the problem is "the brake pedal creeps down at stop lights"

FWIW; if the booster is losing vacum the brake pedal becomes stiff and harder to push.

 

Yep, that's a good description.

 

KGP: Just had that exact same problem with my 94 Accord and replaced the master cylinder with a rebuilt unit from NAPA. Now it's fine. Dave.

 

Thanks Dave. Question: Did you bench bleed the master cyl when installing? I have a Haynes manual and it reccomends it...

 

My description is the pedal sinks slowly & smoothly with NO leakage out.

I replaced MC on 95 Integra without bench-bleeding. I had to bleed A TON of fluid before finally getting all the stupid little air pockets out of the MC. So it IS possible, but...

 

bleed on the bench first, it's easy. You can just run two tubes back in to the reservoir and hand pump. You can get all the air out later, but bench bleeding saves time

 

as has been said, it is the master Cylinder. I bought my replacement for my 95 from hondaautomotiveparts.com. Bench bleed it unless you want to waste a bunch of brake fluid when you have to bleed all the air out of the lines after it is installed.

 

Yes, I bench bled it. I had to bleed a bit more air out once it was installed, but it only took a few cycles. Dave