ok, 2002 Accord SE 4cyl, 5spd. Car has 194k with an 80k engine.

Just within the last few days all of a sudden when I apply brakes the initial pedal push sinks deep, on second pump solid strong non sinking pedal. I've owned the car for 3 years, motor was replaced 2 years ago. Brakes on this car have always been excellent, best stopping vehicle I have ever owned. So this really puzzles me. Fluid is at normal level for pad wear. Rotors and calipers function normally.

Reading the forum and the web leads me to a couple possible possible causes.

1) ABS module? Haven't a clue how to isolate this as cause.
2) Master Cylinder
3) brake Booster

I'm sure there are potential other causes but these stood out. I thought about maybe brake hoses, but couldn't rationalize in my mind how it was only a problem on initial push. OH, yes it is every application. Not like it goes away, every time I apply brakes I have to double pump. It went from the best braking car I owned to the one that sits cause it's a little hairy to drive! Thought anyone?

Thank you!

 

Hard to call....I would still inspect the brake lines. If you hold the pedal with the engine running with somewhat hard pressure does it seem to "sink" to the floor?

 

Does not seem to, seems solid, just much closer to the floor. One pump and it's back up to what I'm used to with this car. It's very odd, I even have taken it and hard braked it to engage ABS, that seems to work. Like I said it's only on initial step, brake lines all look good I've had it up on my lift looking for leak some place and not finding anything. It doesn't seem to act like air, but it's been years since I've had one with spongy brakes, I don't quite remember that feel. I'm going to get a buddy to run the pedal and bleed then just to isolate that out. Nothing special there I don't believe, rr, lr, rf, lf is normal order. Not sure if Honda with ABS is any different. Thanks for the Reply!!

 

Is this a 4 wheel disc brake car? Or does it have drums in the rear? Just asking as it could also be either a brake adjustment, or the pads might be getting thin (not quite enough to get the "squealers" to hit. That would be my 2nd check, with the first looking for fluid dripping on the clean concrete.

 

To me, the most likely thing is air in the lines - not a very "odd" situation. Bleed your brake system.

Air in the lines is the classic way to get a soft initial pedal. If you pump the pedal you compress the air bubbles & the pedal becomes hard. When you release the pedal, it takes probably less than a minute for the air bubbles to expand again.

The other "classic" failure is when the pedal is initially hard, but then sinks slowly & smoothly down when you hold with moderate or light pressure. When this happened to me, it wouldn't sink much under hard pressure - sinks more noticeably with lighter pressure. That would most likely have been a bad master cylinder.

 

OK, this morning with the car off pressing the brake pedal to obtain a firm pedal, held it, no sinking. Started the car and it sank a little bit. I believe that is normal. I have it on the lift now with all 4 wheels off, and everything appears normal no leaks and pads just under 50%. Now when I replaced then a year or so ago I bled them and it's got super great brakes. So if 50% pad wear would deplete the master cylinder enough to suck air? it was low when I checked it, nothing that I would consider uncommon for pad wear. I intend on bleeding them again before I do anything else, just have to find a body not working on a Monday.

Oh, no evidence of leakage in car or at the master/booster mating area.

 

If bleeding fixes the problem, you are still left with the question of how air got in there. It's unusual for this to develop within a year.

 

I was thinking the same thing! If I'm correct isn't there a check valve or something in the master cylinder to hold pressure so that you don't have the sinking pedal on initial press? because with one pump it's good. I say good, good for that brake application, next time it's the same pump then good again.

 

The MC piston seals form that "check-valve". But when you release the pedal, it opens a vent to equalize the system. This equalizing is how it auto-adjusts for the pads wearing down.

It takes a bit of time for the air bubbles to expand, pushing fluid back through that vent. So that makes it soft again for the next time you need the brakes.

Possibly look for corrosion in the brake lines as they run along the underside of the car on the drivers side (or for that matter anywhere). Seems to me that would let brake fluid leak out, which you aren't seeing. But who knows...

Some people have seen the rubber hoses weaken (they dilate when you press the brakes), but I don't think the pedal would pump up hard if that's the case.

 

Jim, I have it on the lift and the brake lines look great! Traced front to rear, clean and dry. Semi southern car here in Kentucky! Called and ordered a master cylinder, Honda is HAPPY to get me one! But as I've learned over the years, Hondas have great reliability, so replace Honda parts with Honda parts!! Thanks for the feedback!!