Wrong, classic textbook example of a bad master cylinder. Sorry bud, first hand experience talking here.

Most likely a master cylinder. BUT, check for leaks at the wheel cylinders, calipers, and the brake lines first. The diameter of the brake lines and the wheel cylinders (to a certain extent) are small enough that a small leak would not reduce the fluid level a noticable amount (over a short period of time) but still let the pedal drop slowly. These items can be checked visually. The last thing you want to do is change the MC then still have the same problem only to discover that if you had only taken the wheel off and looked you would have saved yourself a lot of trouble (and $$).

not necessarily...even though the brake lines blew on the back there was minimul loss of fluids and I still had brake pressure to the front brakes...so it is very likely that it is a burst rear brake line...although I do realize it could be a piston seal leak in the MC...I'm not a first time brake newb I've done it hundreds of time on varied vehicles...

Hey i didnt say you were wrong. Saying that i dont have expierance is kinda annoying, dont act like im a newb, just because im a newb to rx7's and rotaries doesnt mean im a newb to cars them selves. Now im going to stop before i start to sound like a newb myself.

:0 sorry man, meant no offence. Just last spring I had the following symptoms on my 7.

1. Sitting at stop lights with light pressure on the brake pedal, pedal would slowly drop to the floor.
2. I could lift the pedal and regain pressure again, but the process would continue and the pedal would drop again.
3. Stomping hard on the brake pedal yielded good results, and the pedal had little or no tendency to drop (enough pressure to deform the bad seal and make it work).
4. Zero loss of brake fluid.

Replaced the master cylinder and all was fine. I have also experienced these exact symptoms with my '71 Le Mans and a '90 Mazda MPV. Each time it was proven to be the master cylinder.

The key item in his original post is "I am losing no brake fluid". Otherwise the prognosis would be totally different. I didn't mean to imply that you are a newb Chedda, just that your diagnosis was (according to my experience) incorrect. And since I have been there and done that, I am pretty confident that the MC is bad. We are all here to learn from each other, and I have been corrected by other forum members as well (to my benefit). Anyway, like I said I meant no offense Chedda.... :)

Haha no im not offended, i was sure i was going to get flammed for saying what i did anyways so it doesnt matter. I think tourettes guy describes it best when he says "AHH BOB SAGET".

I misread it the first time and got confused when I saw "from the sending unit?" and followed by "maybe?" . I saw that as a broken sentence and couldn't tell if you were trying to ask a question or make a statement and accidentally placed the question mark in. Plus, when you stuck in "I ALSO" it made me wonder if you meant that you had a brake fluid leak at a sensor in the master cylinder. I say this because I've driven vehicles where when brake fluid is low, the sensor turns the "Brake" light on to let you know it's dangerously low. A misunderstanding on both our parts.


But, anyways, yes, it's quite possibly the master cylinder. I've also gone through personal experience with the same problem you've had: pedal to the floor, car not really stopping, and the proper fluid level in the resevoir. I changed the master cylinder and fixed the problem. And, do check out the rest of your brake system as well, like everyone else has given for helpful insight. It doesn't hurt and you might come across a small problem before it turns out to be a bigger problem.

Its cool 85 FB, I was sleepy and had to work in a few hours so I just threw the post up and got some ZZZZZZ.

I looked at the brake system all day went over every thing. Found no damaged anything anywhere. Tomorrow (maybe) ill get a new MC and tell you guys if that fixed it. Thx for the help everyone.

You should be all set then. Good luck, eh!