i am having a problem with my brakes after the car is driven for a short time. after stoping at a stop light, the brake pedal strats falling to the floor. if i just hold the pedal in the same spot, it will sart to roll. i have change the fluid and the pads are in great shape. what would cause this?

 

If you don't have any external leaks, it is likely the master cylinder.

 

ya, inspect the master/slave cylinder areas.

 

that is the master cylinder with out a doubt because if it was a leak you would have a soft pedal at all times, i just went through this and talk to many people about it, also you may not want to drive it much more because before you know it the pedal will just go straight to the floor because its the seals that are going (i believe that is what it was) but here i got a great video for you to watch. i watched it and it helped me out a lot:

http://www.youtube.com/watch?v=trotrlIG2sk

 

thanks guys!! i better get this fixed STAT, its my wifes car. should i buy a used master or rebuild it? i cant watch the vid at work.

 

In the process of changing the fluid it is possible to damage a good master cylinder. The seal normally travels a short distance during typical operation, when bleeding the brakes by pushing the pedal to the floor, you can damage the main seal by pushing it through a sludge buildup area where the seal does not normally travel...in effect you scratch up the sealing surface and allow a "bleed by" of fluid during light pedal pressure. The brakes will act normally when the pedal is pressed hard, but the pedal will fall to the floor with light pressure, as when setting at a traffic light. Sorry to say, you need to rebuild the master cylinder or replace it to make this repair once the damage is done. Next time, place one foot UNDER the brake pedal when bleeding the brakes to prevent pedal travel forcing the main seal into the sludge ring. Cheers

 

good to know, thanks! the only reason i flushed out the old dot 3 was because i though that was the problem. its still there after new dot 3. i found new break masters at autozone for 60ish dollars. should i just buy one or rebuild?

 

Thanks so much for posting this, even though this thread has moved on. Using the search button I found it & was able to realize how easy it will be in changing the MC out on a 95 Integra.

 

master cylinder X1k

 

In my 1995 Accord I have this problem, the only issue I have is that when I bleed the MC on the car, and at each bleeder, the pedal is nice and firm. When I turn the ignition on, the pedal sinks down. They catch, but really, really low.

Still air in the lines somewhere?

 

One thing I believe is the case is that when you bleed the brakes you should open and close so fast that the pedal does NOT hit the floor.

If you've ever done clutch cylinder bleeds you know that when you open bleeder valves you see a small amount of fluid coming out even before the pedal is pressed. I think brakes work the same way 'though it's harder to tell. They say that as long as the pedal doesn't come up when bleeding brakes that you're ok, but I think that fluid still comes out letting air get in.

Crack and close real fast, imo. Might take a lil longer but You know that as long as the pedal doesn't hit the floor there is no air in there.

Also, when you turn the car on, the booster turns on making it easier to press the brakes.

 

Yea good post!!!

 

Did you ever bleed your brake lines while your ignition was turned on and you had someone pump your brake from inside your car when you were bleeding???

 

Yes, I had done that. No luck. I think I have a defective reman MC