Brakes go to the floor
 

They stop the car but while im seting at a spot light the ssssllllooowwwlllyyy go to the floor. what should i check.

there is no fluid coming from the master and the fluid is full.

Replace your Master Cylinder with a new one. MC rebuilds are not a good idea.

ok. I also have an oil leak coming from the sending unit? maybe?

Oil leak? You mean MOTOR OIL or brake fluid? And please try to make your statements and questions understandable. Otherwise we won't be able to help you that much, y'know?

yeah its your master cylinder. Get that replaced.

Yeah, as long as you are not losing brake fluid then there is no doubt about it. Replace the MC and you should be set. Check www.rockauto.com for parts...

Before you go replacing your master cylinder (like I did) check that there is no brake fluid coming from your brake calliper. Give the rubber boot a squeeze to be sure.

Well seeing how I posted and got a response then made my own reply saying Ok. then following it with another "question" (kinda i guess) "I ALSO (<-key word) have an oil leak".


But ill retype my ?


I noticed I have a Motor Oil leak, looks like it coming from the oil sending unit (if thats what that is) right beside the drain plug.


ok i will go squeeze the rubber to see if thats the prob now. =)

be gentle

The sending unit with 3 bolts, the larger one, is the low oil sensor, the other is, iirc, for the sub-zero start assist. If it is the 3 bolt unit leaking, re-torques the bolts, gently. If it is the other one, it may need the threads cleaned and wrapped with teflon tape,

just because the pedal went right to the floor doesn't mean that the master cyclinder is busted...had the brakes go like that in my 3/4 tonne and my 1/4 tonne but more times then not its just that the rear lines have burst somewhere...replace the rear brake lines...

If he's not losing fluid, it is a piston seal leak inside the MC. If he were losing fluid, it could be anywhere (but usually the slave). He also has brake pressure, so it's not a burst line. This is a classic piston seal problem.

Another thing to consider is that on the drum brake equipped models, the wheel cylinders can go bad, which is what happened to my '79. More than likely it's your master cylinder though.

Sure...and you'd be losing fluid. The MC the the only place in the system capable of an internal leak.

Oh, I didn't know that. I didn't notice any leaks in my case but then again I didn't look too terribly hard because I switched over to rear discs not long after.

Good to know.

this happend to me, but it could be something very simple called the vaccum hose is leaking on the mc itself. Im saying this because if you take it off and try to use your brakes, they are there, but they are right at the floor, if there is a small leak i could see them slowly going to the floor. If there is no fluid leak in the rear cylinders or piston boots and there is no vaccum leak on the hose then the gasket in the MC is gone.

Chedda, are you sure about that? The brake hydraulic system is a sealed unit. The booster only multiplies the pressure that you apply via the pedal. I believe that if you remove the vacuum line to the booster you will have a very hard pedal, not one that goes to the floor.

Someone please correct me if I'm wrong about this.

Just so there is no misunderstanding, you can have a small leak only under high pressure (hard stops) that may not give you a noticable drop in fluid level over the short term (usually feels "mushy"), but what he is describing is the pedal sinking to the floor -- no matter how slowly it happens, a LOT of fluid is being displaced that must go somewhere. The MC is the only component with seals that can leak internally (around the piston, back to the unpressurized MC reservoir). Every other seal is external. If you have a pressure drop, the fluid is getting around a seal. If the pedal is sinking to the floor, it's a BIG leak. If the fluid is not going down hand over fist, then it's an internal leak in the master cylinder and the fluid is just recycling to the reservoir. Hope that is more clear.

Im damn sure that when you have the vaccum line on there, it will make your pedal harder. Without the hose, it makes it limp like a 80 year old :balls: . Thats what it does on my car anyways, i know that if the valve is installed backwards it will also do the same thing where its soft as hell.

Ya i was thinking that, i was just sharing my experiances.

er - have you checked the brake fluid level? It's also possible that the level is a bit low due to a very slight leak anywhere in the system and has, over time, allowed air into the system to the point where the 'mushy' feel becomes noticeable..

Nevermind...time for bed. :)

Wel to tell you the truth, as of right now i have a small problem. The pedal is "wedding" cock stiff but it takes a tonne of pressure to get anything out of it. How does this fill your hypothesis?

the Fluid is full and has been full since i got the car. just drops verry slowly to the floor, then i can lift my foot off the pedal and press the brakes again and the pressure is back for a sec then slowly goes down every time.

See that sounds like a vaccum leak to me...kinda

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!