I have some issues, and I hope some of you who are mechanically inclined can help me out.
1. I recently changed the brake pads in my mom's car. Prior to changing the pads, the brake pedal was really soft.
2. I bleed all the lines, and the first time I did it, I didn't pay attention to the master cylinder and let it dry out.
3. I rebleed the whole thing again and when the car is off, the pedal get hard after a few pump.
4. The problem is, when I turn the car on, the pedal went soft again.

Do i need to change the master cylinder? The car has 155k miles, and I don't think my mom ever service the brakes at all. Should I try bleeding the master cylinder first before buying a new one?

 

needs to be bled more most likely.

 

Did you bleed the brakes in correct sequence for the model year?

 

with the car in neutral and the car on will the brakes activate with the pedal pushed down. do you hear a hissing sound under the hood around the brake master cylinder with the car on? could be a bad brake booster(the round black thing the brake master cylinder is installed on), the vacuum line going to the brake booster, or a bad seal between the brake master cylinder and the brake booster

if the master cylinder holds pressure with the car off then you bled correctly

 

The Master cylinder is located on the front driver side. So i started from the Passenger rear, driver rear, passenger front and driver front.

 

The brake will activate, but it goes all the way down before it stops. I don't think I hear any hissing sound with the car on. Im not sure.

I tght a bad brake booster usually makes the brake pedal hard to push not soft?!

 

When or what kind of signs will I need to know that the brake has been bled enough?

 

It does hold pressure. How do I know that I need to bleed the master cylinder itself since I let it dry out the first time I bled it?

 

the engine running does not mess with the hydraulic fluid in the brake lines. just with the vacuum going to the booster. perhaps the valve in your booster line has gone bad.

mine does the same thing and my lines have been correctly bled. i have yet to troubleshoot it yet though due to financial problems. could be the seal on the master cylinder as well though im not leaking fluid under the dash. no booster does make it hard to stop but thats just because you have to press it to the floor. ever had to cut an engine off because it was overheating and then had to brake? you get the same effect due to a lack of vacuum going to the booster

consider the booster more of an amplifier of how far you depress the brake pedal

 

So do I have to replace the whole brake booster or I can just replaced the booster line? How abt the master cylinder? How do you know that it's probably because the master cylinder is going bad?

 

Taken from about.com


Brake Pedal Too Firm.
If you step on the brake pedal and all of a sudden it feels like you're doing leg presses at the gym with a new personal trainer, your brake pedal may be too firm. This symptom points to a few potential problems, all of which need to be fixed as soon as possible.
Vacuum Problems: Your brakes are easier to press because of a brake booster that gives your foot the strength of 10 men. This booster uses vacuum to help you activate the brakes. If there is a vacuum leak somewhere in the system, it won't have enough negative pressure to do its job. Check the vacuum system for leaks. If you find none, your brake booster is probably bad and will need to be replaced. This can be tested by a shop if you want to be sure.
Brake Line Obstruction: It's possible for something to block brake fluid from reaching a portion of the system. This could be something in the line like a chunk of rust, or it could be a pinched brake line. Visually inspect the brake lines and replace damaged brake lines as needed.

 

Brake Pedal Goes To Floor. If you step on the brake pedal and it has little to no pressure and goes all the way to the floor, especially if you're getting no braking:
Low Brake Fluid Level: Check your brake fluid. If it's low, top it off to the mark on the side of the reservoir.
Air in the Brake Fluid: Even though your brakes operate in a closed system, contaminants can still work there way into the works. Air can enter the system through the smallest hole. There's not really any way to check for this, but bleeding your brakes will remove the air and replace it with new fluid.
Master Cylinder Bad: A bad master cylinder will cause your brakes to have no pressure. Master cylinders cannot be repaired and will need to be replaced.

 

the line probably does not need replacing. you can check under the hood for hissing. if the line is damaged before the valve(engine side) you would be getting a bouncing idle so thats not your problem. it sounds like your brake booster is not holding pressure to me. if you know that the master is going bad replace it. you dont wanna be driving down the road and then it happens. however if you can drive the car and it stops fine but with just more effort like stated then its probably just the booster leaking.

was really hoping one of the seniors here would chime in. donde esta muffinman

the masters are not that expensive. stay away from autozone. they keep giving me bad clutch master cylinders. replace the master and if that dont work return it saying it was the wrong one and replace the booster


***another possibility is that your getting air in the line at the bleeder through the threads. but your car is new compared to most on here so this may not be the problem

 

try removing the bolts that hold the master to the booster and pull it away to see if you have any brake fluid leaking into the booster. if so the master is leaking and needs replacing

another check for the master is with the car off. apply light pressure to the pedal. if it begins to creep down on its own then the master is leaking and needs replacing.

try the second one first though

 

This sequence is correct for my 97 Accord, but for my 04 Odyssey, the sequence is different ... driver front, passenger front, passenger rear, driver rear. It might be worth confirming the correct bleed sequence for your model year. Not sure that it really makes a big difference.

 

ThNks for all the help guys.
Ill check the hissing noise as well as the pedal thing. Which is more expensive to replace? The booster or the master cylinder? It seems easier to change the master cylinder though...or should i take it to just brakes and let them diagnose it? Lol

 

Just trying to make sure, if i didnt bleed correctly, the pedal wont be hard when i press it when the car is off correct?

 

Don't know the answer to that.