I am going to make this simple:

Situation:
-It was 8 degrees last night
-I drove my car yesterday afternoon and when I did so it worked fine for about 30 mins, then out of no where my pedal went all the way to the floor.
-After this happened my car could still stop but took alot more brake pedal travel to do so
-Did not appear to initially loose fluid but I topped it off and applied the brakes heavily 20 times are so and it dropped about a 1/2 inch.
-Braking is getting progressivly worse

What I think:
-I think it may be a cracked line from such a cold night, brake fluid shouldn't freeze but I would not be suprised if it absorbed some water or even externally some water wedged its way into a crack.
-I also think it could possibly be a bad Master Cylinder because the fluid was dark and not clear as it should be.

What I want to know:
-Does anyone have any suggestions of where to check first? Or any similar experiences.

 

If you have a cracked line, the most common place I've seen the brake line fail is where it makes it's run to the rear of the car on the drivers side above the gas tank. There are some white clips that keep the brake and fuel lines from rubbing each other, it appears as though water likes to get trapped in these clips causing the lines to corrode. I've seen these lines fail on 4 separate Rx7s.

 

the only thing that makes me think it may not be the rear is that when I slammed the brakes to the floor the back brefily locked up but the front didn't do much. Only time I have had the back lock before the front. I was only able to lock them once and after that no wheel would lock up

I will deffinitly check though

 

ive had that exact line fail on an fc before.

 

If you have a failed line, it should be easy enough to find- there will be fluid leaking.

However, if you cannot find a leak but the fluid level still drops, it's almost certainly the master cylinder and the fluid is filling the booster.

 

I didn't even think about the boost filling with fluid, visually I can see corrosion under the master on the brake booster perhaps from brake fluid leaking at the connection. May explain the black looking fluid. Will check that also once it stops raining.

 

Sounds like a bad master to me. If you press lightly does it go to the floor, but offer resistance if you stomp on it?

 

I would say That pretty much describes it. If I pump it will have more resistance also. I just find it strange that it happened out of no where. Car has always stopped strong than one day nothing.

 

I changed the master and it stops alot better but still takes alot of pedal effort, I am sure I got alot of air in the system when changing the master and plan to bleed it later this week.

 

did u check the booster for fluid, that would not be good if you still have fluid in the booster may cause some problems down the road also it may or may not allow the vacum to buid enough which could cause the extra effort to the pedal, you can take a coat hanger and pop out the vac line and stick it carefully down there and pull it out then check to see if there is any fluid on the metal, also just make sure that your check valve is functioning properly just remove the line and stick a straw in it (so you can put your lips on it) try and suck and blow, air should only travel from the booster towards the engine, any check valve in the Help section of the parts store will work, as long as it has the correct size for the vac line

 

alright the problem is now fixed. After driving around and braking still feeling crappy I decided to bleed the brakes and found a hairline crack in the passanger front hard brake line. I guess it wasn't the master but I am still glad I changed it now my brakes work great.