My car has been sitting for a few months or so and i just started driving it again yesterday. I didnt touch the brakes, motor, nothing while it was sitting. And just like yesterday it was pretty hot and i can only imagine what the bay was like. I had the ac on and all. And at first it didnt do the problem tell it got super hot outside.

Heres the problem

when i press the brake pedal down, at first it has preasure then it loses it slowly at lights and i have to pump to get some preasure back. It doesnt drop to the floor super fast but it still drops.

Last night i took the car out, not hot outside at all... and it didnt happen once. Just like today when i first started it up and drove it around for a while, it didnt happen. but when i noticed a change in heat outside it happened.

i searched and most peoples problem is the MC. But i havent seen a problem like mine where it happends only when its hot. Could it be the same thing? Could it be that its starting to go out and these are the signs?

 

I had the same problem a couple weeks ago, it was the m/c, only when hot, pedal would crrep to the floor, but was ok when cold.
Seems the master expands with the heat just enough to allow fluid to bypas the rubber seals.
New m/c fixed it.
Don't forget to bench bleed the m/c if you replace with new.

 

this happened in my DD civic hatch auto. while waiting at a stop light, the pedal would start going slowly towards the floor and the car would start to creep foward. i changed the MC and the problem disappeared.

 

awsome thanks for the help guys

 

is it possible to have similar problems if your booster is going out.....i have very little pedal pressure and have to push pedal to floor before it feels like im slowing down

 

How to check your booster.
Start the engine, run it at idle for 20 seconds, turn it off. wait 2 minutes, press pedal a few times, it should be gradually get harder to push after 2 or 3 pushes.

Then start the engine while hodling the brakes pedal down, it should rise up a little when running.

Repeat.

if it doesn't work like this, you have a booster problem or air leak on it.

This will in no way test yor hydaulics though.

 

If you changed the master cyl. you may need to ajust the push rod a little longer. (its a bolt (12mm) on the end of the pedal arm, make sure the rest postition is flat against the switch) screw it a little longer to compensate, but not too far or your brakes will rub.
I have seen clone masters that have the push rod hole a little deeper than oem and then the brakes work fine but the pedal is much lower to the floor than it should be.

This is assuming all other hydaulic parts are working well and you have no air in the lines.