i have a 93 coupe ex, and when im sitting at a redlight or stopped anywhere the brake pedal goes soft sometimes, and if i pump it up it will build some pressure than drop again, why does this happen? i'm thinking its the master cylinder but i'm not sure, the front brake pads are fine and i havnt pulled the rear drums yet to see how they are, but i know the lines arent leaking because the resivoir is full. let me know what you guys think about it and help me out, please.

 

I would think it was the master cylinder also. I would try bleeding the brakes first before anything though, just to see if it helps.

 

Make sure you check your rear wheel cylinders. I figure you know what they are, but if not, they are the horizontally mounted cylinders that push the brake shoes out against your drums when you hit your brakes. If these are leaking, a spongy pedal will result from a loss of fluid. Also be sure to check the master cylinder and bleed the whole system thoroughly.

 

the resivior is full so i dont think that is it, i dont know what happens when the booster goes up but i dont htink that is it. i think it might be the master cylinderi think the pressure is leaking by the plunger inside.

 

master cylinder is bypassing on the inside. replace the master cylinder, bleed the brakes and you are good to go.

 

that is waht i figured, that the o rings on the piston inside are worn and the fluid pressure is passing by it. i guess ill have to go get one.

 

did you happen to flush your brakes out before this started happening?

also, be sure to do a visual on the rears before deciding it's the MC. you might have a very slight leak that might not be big enough to drop the level for you to see.

 

sign of the leak, most likely secondary o ring on the master cylinder

 

i also have this problem and i just got done bleeding the brakes and it got soft again. i syphooned all the old fluid out first then filled it with new fluid and bled it till all the old fluid was gone. does anyone have a picture of where to check for leaks? how hard is it to replace a master cylinder? and how much would it cost?

 

I had the same problem and mine was a bad master cylinder. I had no mechanical knowledge at all and replacing it was even easy to me. Go to Auto Zone or whatever and pick up a master cylinder. I think mine was $75. Also, make sure you have two or three people there when you are bleeding your brakes.

 

yeah i replaced the master cylinder, bleed the brakes, and adjusted the rear brakes and they work like a charm now.