My brakes failed on me today (Why?)

quicksliver · Post by **quicksliver** » August 24th, 2005, 9:58 pm

Ok, so i got disc brakes on the front and drum brakes on the back.

Today i backed into a very steep drive way. Threw my car in park (no emergency brake), and left. 2 hours later i come back, get in the car and start her up. At the very first stop sign i go to hit the brakes and the brake pedal litterally just DROPPED with no resistance at all and then just before it hit the floor there was finally some resistance and i pressed harder to stop. It was like a SLIDING stop....not the typical pulling feel stop. If you know what i mean :\.

So i stopped the car, and took the keys out. Pumped the brakes 2-3 times and the brake pedeal felt like a brick.

So i start the car, and before i move i try the brake pedal 2-3 more times. This time it goes about half way down and then i get the pedal feel im used to. So im like AWESOME....lets rolll.

I throw the car in Drive, and start driving. Then the first stop sign i come to, i go to hit the brakes and it happens AGAIN. The pedal drops with no reistance, and then just before it bottems out i feel some resistance in the pedal and i have to press harder and harder to stop. It almost feels like a SLIDING stop.

- Brake pads all around are less than 4 months old
- Im' NOT loosing any brake fluid at all.
- I DON'T have ABS
Any ideas?

Grants · Post by **Grants** » August 24th, 2005, 10:56 pm

First thing is to check your fluid and then bleed the brakes. Sounds like air in the system.

quicksliver · Post by **quicksliver** » August 24th, 2005, 11:10 pm

How did air get into the system? I was driving for months with no problems...and then all of a sudden, i got virtually no brakes :\.

mitmaks · Post by **mitmaks** » August 24th, 2005, 11:11 pm

sure sounds like air in system

schuttie2002 · Post by **schuttie2002** » August 25th, 2005, 1:03 am

Just basically when there is air in the system, the air/fluid in the lines becomes compressable which means when you hit the brakes and push on the pedal the air/fluid can compress so your pushing on the pedal, but nothing will happen. When there is no air in the lines, your pedal will be firm all the time, and will work, because liquid is not compressable.

The air in the system may have gotten there by two ways. One when you recessed the cylinder in the calipers, it pushed fluid out and your resevoir overflowed and air got in your system. ( in a sence thats about how it works)
The other way it gets in the system is because brake fluid wants to absorb water. I believe that property is hydroscopic maybe. Anyhow, the fluid wants to absorb water. If that happens and the water in the fluid gets hot, it will boil. that means air(hydrogen and oxygen) get in your system, which brings us back to the system being compressable.

Now All that said, I do not believe air in the system may be the problem because like you said you had all this brake work done 4 months ago so why would it happen now. Id start by bleeding the system, but to me it sounds more like you have a bad master cylinder. When that goes bad, your pedal will feel spongey like you say, but will them pump back up and get better temporarily. You will want to fix that asap if thats your problem though because eventually it will go completely bad and your brakes wont work at all and you could seriously hurt yourself or someone else.

Good luck

schuttie2002 · Post by **schuttie2002** » August 25th, 2005, 1:10 am

Ok after writing all that I realized Im wrong on some things. First off the term is hygroscopic. And that means the brake fluid wants to absorb water.

Secondly, when you recess the cylinder in the caliper all that does is move the fluid back up the lines it wont actually put air in the system. Its just a common practice to bleed the lines after your do that, because it will push dirt and crap in the lines back up toward the master cyclinder. Sorry bout that, I think I was just on a roll.

PATDIESEL · Post by **PATDIESEL** » August 25th, 2005, 1:12 am

The brake booster could have lost its vacuum also. Check the hose that goes from the intake manifold to the booster. If it is torn replace it. The hose also uses a one way check valve in it that stops air from being pressed back into the intake manifold when you press the brakes. The check valve may have worn out also, so maybe just replace it anyway. Mazda is the only place to get it. I don't think it costs much.
Look for rust on the under side of the brake booster, it may have an air leak if it rusted through. Most I have seen are rusting on the bootom side which is not a good sign.

neutral · Post by **neutral** » August 25th, 2005, 6:17 am

Sounds like the brake master cylinder needs replacing.

jschrauwen · Post by **jschrauwen** » August 25th, 2005, 10:57 am

OK, I'll bite on the not so obvious. I'm going to assume that since the brakes were done faily recently it's not a malfunction in that area. I like the possible vaccum issue but I'm still going with the not so obvious. The brake master cylinder, hmmmmm, I'm still going to go with the not so obvious. It is quite apparent that there is air in the system that needs to be purged and the Q is how did it get there all of a sudden. Since you did the brake job not to long ago, I'm going to assume that the reservoir was left at the appropriate level, or maybe just a little lower than the full mark (just a guess). Now he just finished parking @ss first on a very very steep hill. Now the fluid in the reservoir is going to remain level but may have been at a lower than full level so that this "tipping" of the angle of the reservoir due to this extreme parking has now let that air pocket that resides in the top part of the sealed reservoir into the master cylinder. Like I said a pretty wild guess, but it's all based on a previous lower than normal brake fluid level and an extreme attitude of the vehicle allowed the air in the reservoir to enter the master cylinder. All because he parked @ss backwards. Ya I know, it's out there alright. Of course I have no way of proving this as it's all theoretical and subjective.

neutral · Post by **neutral** » August 25th, 2005, 12:33 pm

Good points John. After reading your post and the others again, may not be a bad master cyl. because a worn out MC shouldn't have allowed for the brake pedal to firm up like a brick, as was indicated by quicksliver. If the MC is worn out - it's worn out all the time not just some of the time. I like your theory on how air got introduced too. Not so "out there" after all... but maybe sound logic (ok then, sound speculation at least)

Grants · Post by **Grants** » August 25th, 2005, 5:24 pm

I agree too jschrauwen.

I noticed that bit about the steep hill and considered the same. Wondered why quicksliver mentioned it at all if it wasn't relevant... Bit like a detective story.

It still sounds like air - if it was the booster you'd have a hard pedal - not to the floor.

I'd also like to add that relying on "park" on a steep hill isn't advisable.

Rick Johnson · Post by **Rick Johnson** » August 25th, 2005, 9:04 pm

Damn I missed out on this one early, But I will add my opinion <which is shared by others>

It was definitely cause by the steep hill you were parked on.

Your booster is fine, and Master cylinder is probably ok too, it does just sound like air was somehow introduced because of the steep hill, perhaps when you hit the brakes before you pulled out and it gulped a little.

And food for thought: What would happen if on a turbocharged K-series you flipped the vac hose, which has a one way check valve.... heh

Gro Harlem · Post by **Gro Harlem** » August 25th, 2005, 11:08 pm

i concur.

and might i add.

STOP BEING LAZY AND FIX IT!

shiiiett y0. if u gotat pump the brakes to get pressure that = AIR. BLEED DAT SHIZTNITZAL

PATDIESEL · Post by **PATDIESEL** » August 26th, 2005, 10:14 am

If you flipped the one-way-valve hose you don't have power brakes. I know I've done it...
As for the air in the system b/c of the incline. I highly doubt that. He would have to be super low to get the angle so that the fluid was missing from the front side (the rear side is more likely, but that would cause air in the clutch not the brakes). Also if anywhere near full the fluid would not be totally level since it would back-up against the lid and still only leave a small gap in the rear side. Just FYI, I just checked this by parking on a steep hill in the neighborhood with full brake fluid. There is almost no difference in the level in the rear since it backs-up against the lid.

Rick Johnson · Post by **Rick Johnson** » August 26th, 2005, 8:00 pm

Pat I wasn't saying that a full resevoir parked on an incline will pull in air. I was saying that could be possible that while moving on a steep incline <hitting the brakes while moving forward down a steep slope> With a less then full resevoir it could possibly gulp some air.

Where else could this air have come from? it wasn't there before. Any ideas?

And the point about flipping it, yes you would lose power brakes, thats obvious no vac - no brake boost. The point was it might be possible to build a postive pressure in the booster, which would make it almost impossible to apply the brakes.