Air entering my front brakes, and mushy pedal, please help!

[5LugFoxFanatic]

I am having a problem with air getting into my brakes. I did an SN95 5 lug disc brake conversion, and here is what is happening. Without any warning, my pedal with go to the floor. When I first bleed the brakes, I get a nice firm pedal that allows me to stop on a dime. As time goes on, I lose pressure. I have not bled the brakes in about 9 months, so it is not a fast problem. When I do bleed them, I get air coming out of my passenger front line only. The rears and driver fronts are air free. I had to use a special adapter to fit the 99 Mustang dual piston caliper to fit onto my hard line but no fluid is leaking that I can see. I am just trying to figure out how air is entering my system. Anyone know of ways air can enter the system and cause my brakes to become spongy and them go to the floor? When the pedal goes to the floor, I have to pump it up to build pressure, but as soon as I drive more than 5 feet, I get mushy brakes again. I do have an adjustable proportioning valve if that helps. This sucks, I do not want to lose brakes when I need to make a panic stop in traffic.

 

[Shakerhood]

Sounds more like your M/C is going bad. My first car did that for a little while before it pretty much had no pedal at all and it was the M/C.

 

[jrichker]

Sounds more like your M/C is going bad. My first car did that for a little while before it pretty much had no pedal at all and it was the M/C.

Another vote for the M/C since it works good sometimes but not others.

 

[5LugFoxFanatic]

I guess it is possible that I could be leaking fluid at some point. If there were an air leak, would it not be noticeable as soon as I bled the brakes? It should not take that long for air to enter the system right? It has basically been like this since I did the conversion in December of 2003. The funny thing is, that it is only the passenger side caliper that is getting air in the lines. Could the caliper itself be bad and letting air in gradually?

 

[BlackGT89]

I agree that it is probably master cylinder related. It almost sounds like the fluid level in the master cylinder is dropping enough to allow air to possibly enter there, then traveling through the line and showing up when you bleed the brakes. Since air will compress then you get the mushy feeling. If that is the case then you may have a leak in the line somewhere causing the level to drop on a regular basis. If the fluid in one reservoir well seems to stay lower than the other most of the time that could be a tip as to where your leak is, if you have one. But most master cylinder problems I've had experience with begin as a steady fall of the pedal while sitting at a red light with slight pressure on the pedal (more noticeable with an automatic). Of course the reason being that the internal seals in the master cylinder go bad and allow brake fluid to escape past the piston. The brake pedal would quickly come back up if the pedal was pumped. Of couse the brakes have a dual system so if one half fails the other should act as a backup.

 

[5LugFoxFanatic]

yes the fluid does drop. The MC is practically brand new, so I guess it could be, but would it not mess up all of the brakes? Not just the passenger side?

 

[BlackGT89]

yes the fluid does drop. The MC is practically brand new, so I guess it could be, but would it not mess up all of the brakes? Not just the passenger side?

Well, if your fluid got low enough in the front reservoir to allow air to enter, then it would only effect your front brakes (dual system). Then maybe the air would tend to settle in either the left or the right side. Make sure your master cylinder reservoir isn't leaking, it's only a plastic tank sitting on some rubber grommets.

 

[Fishhawk]

Have you checked the area around and under the M/C? Any paint being eaten away? If so you have a leak. Also, have you tried just bleeding the M/C?

 

[5LugFoxFanatic]

Well, Bled the brakes on Sunday, and already the pedal is no longer that stiff. It is just a matter of time before they go out. I am going to take this advice. I am replacing the MC, and my friend suggested that I replace the front line with braided lines and get rid of the stock rubber lines. Hopefully this works.