My Brakes Went Mushy Today

[warwick.hoy]

Car = 1995 Honda Accord Station Wagon.

As far as I know it's a stock brake system. I know that some Wagon owners have modified their cars to have a rotor over hub in order to cut down on labor for brake jobs. I've owned the car for almost a year and the brakes were done shortly before I bought the car.

Today as I was running errands; maybe 10 miles there and back in 95 degree weather. The the brakes went a bit mushy on me about the last 3/4s of my running around.

I was able to stop but I seemed to loose pressure in the system and had to push the pedal almost to the floor to come to a complete stop. This was around 4 o clock my time. I let the car rest and a few minutes ago checked the master cylinder and a smaller cylinder (slave?) and both were full of fluid. I took the car around a few blocks and applied the brakes a bunch of times; coming to a full stop each time and all seemed normal.

Brakes aren't something I want to have go out on me while driving and I really don't put a whole lot of miles on the car so this is the first time I've noticed it. I'm wondering if it was just a weird fluke, or if you car guys might be able to shed some light on what might be going on. Maybe I need a brake job but there was no grinding, squealing or vibrations. I tried to put pressure back into the system and stiffen the pedal back up there seemed to be a little bit of labor put on the engine while pumping the brakes. I was running the AC FWIW.

[username n/a]

Wait until Saturday and call Car Talk.

[seanm]

Sounds like air in the system... you may have developed a leak somewhere.

[xray]

Get the system bled. Doesn't cost that much and will clean the air out. Make sure they use new brake fluid.

[MakiSupaStar]

Bubble in the brakeline.

[tjmdetroit]

Can you still back up and then hit you brakes to adjust them? self adjusters?

[MadMan118]

Sounds like leak in the system somewhere that let air in.

[Jools4001]

Brake fluid is highly hygroscopic and will readily absorb moisture from the air - this happens even in a system that is, supposedly, completely sealed. Water vapour somehow finds it's way into braking systems through seals and joints and is absorbed by the brake fluid, especially if vehicles aren't used much. Living in areas with high humidity means more moisture will get in.

Hydraulic braking systems work on the principle that you can't compress a fluid, so all the pressure you apply to the brake pedal gets transferred to the brake slave cylinders on each wheel and clamps the brake pads onto the discs (or drums). However, brakes work on the principle of applying friction to the discs, thus turning the kinetic energy of the rolling car into heat. Brakes get hot, very hot! Quite a bit of this heat gets transferred into the braking components and into the brake fluid, that's why brake fluid is specially formulated not to boil even at extreme braking temperatures. But....if it has water absorbed into it, the water will still boil and turn back into vapour - a gas. You CAN compress a gas, so now, a good proportion of the pressure you apply at the brake will go into compressing the 'steam' and far less pressure will be transferred to your brakes.

So if the brakes are spongy all the time, it has air in the system, if the brakes only get spongy when they're hot there's water vapour absorbed into the brake fluid. Either way, the brakes need bleeding though with fresh fluid. If it's air in the system you may be lucky and see little streams of bubbles in the fluid being bled off, you can stop bleeding the brakes when you see the bubbles have stopped. If it's water vapour absorbed into the brake fluid, you'll see the fluid has become emulsified and milky (should be completely clear amber liquid).

Bleeding brakes is dead simple in theory, but can be hit and miss in practise - I've done it hundreds of times on my motorcycles and it can still prove frustrating. I've now got a device called a Mittyvac that helps, but it may just be better taking it to a shop

[guroove]

Originally Posted by MakiSupaStar

Bubble in the brakeline.

^ This. It's common in very hot weather. Have the brake lines bled.

[Schlyder]

No brakes is bad, M'kay. Fix them before they ruin your day.

[Absentia]

Sounds like air so bleed the breaks, your master cylinder can go bad and still hold fluid, my 1986 Buick Century (god damn i miss that car) has a busted master when I bought it the entire life of the car I had to break with 2 feet.

While you're bleeding the brakes change your pads and make sure your rotor don;t need to be turned, check under the car for wetness and all that.

[jp58]

The brakes in my honda from 89 completely failed on me. If it wasn't a 5 speed, I probably wouldn'tve been able to stop it.

Not fun at all man.

[69limeRev]

The master cylinder is certainly a possibility. I had a very similar problem on my 95 civic two years ago. The symptoms began with slightly spongy brakes, and as the seals continued to degrade it got to the point where stopping became rather adventurous.

...John

And re-reading the OP leads me away from a simple bleeding of the system being a fix. Air in the system would be a more consistent and duplicatable problem. This one acted normal after sitting a while, right? That def leads towards Jules4001's post of water in the system. If you start seeing it with the system cold (right after you start driving it), it would point more to the master cylinder.

[king_biscuit]

It could also be the soft lines are bulging when the brakes are depressed. btw, brake fluid is highly caustic and will strip the paint off of your car down to the metal. Be careful! My advice is to take it to a mechanic -- not budget brakes or super lube, etc. -- and get a proper repair.

[funkydjembe]

yep, sounds like air

[T-Bird]

Hi.

Brakes just don't fix 'emselves, either find the cause and fix it, or take it in.

Originally Posted by Jools4001

Brake fluid is highly hygroscopic and will readily absorb moisture from the air - this happens even in a system that is, supposedly, completely sealed. Water vapour somehow finds it's way into braking systems through seals and joints and is absorbed by the brake fluid, especially if vehicles aren't used much. Living in areas with high humidity means more moisture will get in.

Hydraulic braking systems work on the principle that you can't compress a fluid, so all the pressure you apply to the brake pedal gets transferred to the brake slave cylinders on each wheel and clamps the brake pads onto the discs (or drums). However, brakes work on the principle of applying friction to the discs, thus turning the kinetic energy of the rolling car into heat. Brakes get hot, very hot! Quite a bit of this heat gets transferred into the braking components and into the brake fluid, that's why brake fluid is specially formulated not to boil even at extreme braking temperatures. But....if it has water absorbed into it, the water will still boil and turn back into vapour - a gas. You CAN compress a gas, so now, a good proportion of the pressure you apply at the brake will go into compressing the 'steam' and far less pressure will be transferred to your brakes.

So if the brakes are spongy all the time, it has air in the system, if the brakes only get spongy when they're hot there's water vapour absorbed into the brake fluid. Either way, the brakes need bleeding though with fresh fluid. If it's air in the system you may be lucky and see little streams of bubbles in the fluid being bled off, you can stop bleeding the brakes when you see the bubbles have stopped. If it's water vapour absorbed into the brake fluid, you'll see the fluid has become emulsified and milky (should be completely clear amber liquid).

Bleeding brakes is dead simple in theory, but can be hit and miss in practise - I've done it hundreds of times on my motorcycles and it can still prove frustrating. I've now got a device called a Mittyvac that helps, but it may just be better taking it to a shop

^This.

IME water -> steam in the system is the most likely reason. No bleeding will be but a temporary solution. Get the fluids changed and if You value Your life, get the master cylinder checked/rebuilt as well.

Regards
Sam

[Hookus]

Maybe someone was trying to kill you....

Any enemies?

[jonathan_matos5]

take it in. tow it if you have the means.

sounds like a leak. could be the master cylinder. get brakes checked ASAP!

[Yerf Dog]

Change out the brake fluid. And until then, become very familiar with your emergency brake.

[varunkapahi]

that happens to me sometimes as well, but then am not too sure if its was really what i thought it was because it doesnt happen again