Brakes? Am I going to crash today?

Break pads need to be replaced about once a year on an older car, at least that is what my FIL tells me (he's worked in the auto industry all his life).

How old is your car?

Sounds like either brake fluid or brake pads. Neither should be taken lightly. If no warning light has come on it's probably pads. Experiment in a safe place to see if pumping the brake pedal brings any improvement. It's still not safe to drive but may work better. If you drive to a service station drive slow and if people honk, ignore them. The faster you drive, the harder it is to stop. Do not drive far without having this checked. Remember the limit for extra lives is zero. And as they say those are the brakes.

Here's some info on braking systems. See if it helps.

RAKE SYSTEM OPERATION

Braking System Automotive 101 home
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Brake System Overview

Brake System Operation

Brake System Operation

Below is an explanation of this system's operation

Master Cylinder

The master cylinder displaces hydraulic pressure to the rest of the brake system. It holds THE most important fluid in your car, the brake fluid. It actually controls two seperate subsystems which are jointly activated by the brake pedal. This is done so that in case a major leak occurs in one system, the other will still function. The two systems may be supplied by seperate fluid reservoirs, or they may be supplied by a common reservoir. Some brake subsystems are divided front/rear and some are diagonally separated. When you press the brake pedal, a push rod connected to the pedal moves the "primary piston" forward inside the master cylinder. The primary piston activates one of the two subsystems. The hydraulic pressure created, and the force of the primary piston spring, moves the secondary piston forward. When the forward movement of the pistons causes their primary cups to cover the bypass holes, hydraulic pressure builds up and is transmitted to the wheel cylinders. When the brake pedal retracts, the pistons allow fluid from the reservoir(s) to refill the chamber if needed.

Electronic sensors within the master cylinder are used to monitor the level of the fluid in the reservoirs, and to alert the driver if a pressure imbalance develops between the two systems. If the brake light comes on, the fluid level in the reservoir(s) should be checked. If the level is low, more fluid should be added, and the leak should be found and repaired as soon as possible. BE SURE TO USE THE RIGHT BRAKE FLUID FOR YOUR VEHICLE. Use of improper brake fluid can "contaminate the system". If this occurs, ALL of the seals in the brake system will need replacement, and that is usually a VERY expensive operation.

Brake Warning System

The brake warning system has been required standard equipment since 1970, and is connected to the master cylinder. It monitors differences in pressure in the brake lines of the two hydraulic sub-systems, and alerts the driver with a light if an imbalance occurs. When you turn the key to the Ignition position, the brake warning light on the dash comes on during a "self-test". You should not drive a car if the warning light does not come on during the startup self test.

The brake system is divided into two sub-systems to increase safety. A pressure differential switch, connected to the warning light, is positioned between the two. If a major leak occurs, and therefore pressure in one of the lines is sharply reduced, pressure from the other side forces a piston to move, activating the pressure differential switch and turns on the dashboard warning light.

There are two types of pressure differential switches; mechanical or hydraulic. Mechanical switches are activated by excessive brake travel. Hydraulic switches are activated by a difference in pressure between the front and rear system. When pressure in one of the lines is sharply reduced, pressure from the other side forces a piston to move. A plunger pin then drops into a groove in the piston, activating a switch that turns on a dashboard warning light.

The brake warning light is also connected to the brake fluid level sensors in the master cylinder reservoir(s). If the brake warning light comes on, the fluid level should be checked. If the level is low, more fluid should be added, and the leak should be found and repaired as soon as possible. BE SURE TO USE THE RIGHT FLUID. NEVER IGNORE THE BRAKE WARNING LAMP, AND ALWAYS NOTE WETHER IT WORKS DURING THE STARTING SELF-TEST.

Power Brakes

Power brakes (also called "power assisted" brakes) are designed to use the power of the engine and/or battery to enhance braking power. The four most common types of power brakes are: vacuum suspended; air suspended; hydraulic booster, and electro-hydraulic booster. Most cars use vacuum suspended units (vacuum boosters), which employ a vacuum-powered booster device to provide added thrust to the foot pressure applied.

In a vacuum booster type system, pressure on the brake pedal pushes forward a pushrod connected to the pistons within the master cylinder. At the same time, the pushrod opens the vacuum-control valve so that it closes the vacuum port and seals off the forward half of the booster unit. The engine vacuum line then creates a low-pressure vacuum chamber. Atmospheric pressure in the control chamber then pushes against the diaphragm. The pressure on the diaphragm forces it forward, supplying pressure on the master cylinder pistons.

Hydraulic booster systems usually tap into the power steering pump's pressure, and use this power to augment pressure to the master cylinder. Electro-hydraulic booster systems use an electric motor to pressurize a hydraulic system which augments pressure to the master cylinder. This allows the vehicle to have power assisted brakes even if the engine quits.

You may wish to compare the difference between power and non-assisted braking in a safe area; while driving slowly, turn the ignition key off (don't turn it into the locked position, because the steering wheel will lock, which is highly unsafe.) As the car coasts along, press the brakes hard. The force of your foot is now the only thing stopping the car. The safe driver is always ready to apply the total force needed to stop their vehicle, even if the engine quits (thereby removing the power assist).

Filler Cap (Brake Fluid Reservoir Cover)

The cap on the brake fluid reservoir has a hole for air, or is vented, to allow the fluid to expand and contract without creating a vacuum or causing pressure. A rubber diaphragm goes up and down with the fluid level's pressure, and keeps out any dust or moisture. If the cap's seal becomes distorted, it usually indicates a brake fluid contamination problem.

Vacuum From The Engine

Engine intake manifold vacuum is used for augmenting the foot's braking power in vacuum assisted power brakes. This vacuum is created by the pistons as they draw downward, sucking air into the cylinders. When you push the brake pedal down, the vacuum control valve lets the engine draw a vacuum in the front section of the booster unit. The atmospheric pressure on the other side of the diaphragm provides significant additional braking force.

Brake Fluid

Brake fluid is a special liquid for use in hydraulic brake systems, which must meet highly exact performance specifications. It is designed to be impervious to wide temperature changes and to not suffer any significant changes in important physical characteristics such as compressibility over the operating temperature range. The fluid is designed to not boil, even when exposed to the extreme temperatures of the brakes.

Different types of brake fluid are used in different systems, and should NEVER be mixed. Most cars use "DOT 3" or "DOT 4" brake fluid. Some newer cars use silicone brake fluids. These should NEVER be mixed together, because the seals in each car are designed to work with only their specific fluid types. For example, the mixing of "Silicone" brake fluid and conventional glycol based DOT 3 or DOT 4 fluids should be avoided, as the two fluid types are not miscible (they will not mix together). DOT 3 brake fluids and DOT 4 brake fluids can be mixed.

One of the WORST things that can happen to your car is if the brake fluid becomes contaminated, because the seals are designed to work with only pure brake fluid. "System contamination" means that all of the piston seals and hoses are deteriorating, and therefore must be replaced, a MAJOR expense. So, be VERY careful what you put in the master cylinder reservoir!

It should be noted that brake fluid is highly corrosive to paint, and care should be used not to get it on your car's finish.

The brake fluid in your car should be changed every (See Owners Manual) to prevent corrosion of the braking system components.

My car is fourteen years old. I'm low mileage. (My honey laughs when I say that.) It's been a LONG time since I've had the brake fluid or the brake pads checked . . . will do that today! Yikes.

WOW!!!
great info BOB!
( humph )
and all i was going to add to this thread was brake fluid.
hehe.
In my experience, with older cars, ( 1972 catalina , wich i no longer own ) overnight brake problems were ALWAYS solved with a check of the brake fluid. Somtimes, I could just add it myself and no problem. Most of the time ( being 60%of the time i would say... ) I had to have brake lines replaced...

Once, on my old car, I needed to have 3/4 of my gas line replaced. And 4 of the 6 cylinders were clogged. It's a wonder i made it to the shop!

My money is on brake fluid.


BTW: This is just another illustration of how you take your life in your hands when you buy cigarettes.

Fine post for someone with a cigar in his mouth. Hrumph! Hrumph!

We all flirt with death one way or another . . .

Ahhh .... but I don't inhale. I see a difference. :wink:

A cigar is not just a cheap nicotine delivery device ... it's an experience!

And did I mention I don't inhale?

If the brake pedal went closer to the floor before engaging the brakes, its definitely a bad master cylinder. No offense to anyone else who posted, but brake fluid's condition can sligthly adversely affect braking performance, but it won't compress no matter how crummy it is.

At first glance you could assume that the fluid became low and allowed introduction of air into the system, but that wouldn't be the case since the return trip was fine.

Since the return trip was fine, its definitely the master cylinder. The seals wear inside and allow fluid to sneak by. Since there are two sections of pressurization in the master cylinder each one pressurizing two brakes, what you experienced was this: As you pressed the brake pedal, one of the piston's seals failed to seal to the cylinder and that piston offered little or no pressure to its two brakes on that stroke. The remaining cylinder was operating fine, but you have to almost floor the pedal to get enough braking to stop the car. On the return trip, it just so happened that the failing piston was able to achieve seal those strokes. Did you ever have one of the old bicycle tire pumps that was on its way out? Every third or fourth stroke the seal would fail and you'd almost fall on your face. That is exactly what happens with the master cylinder when it starts to fail.

The only way to fix it is to rebuild or replace it. Depending on the car they're dirt cheap; as little as $18 or as much as $100 to buy. If you do it yourself, you'll need brake fluid. If you have someone else do it, it should be a two hour job. Expect under $200 if you just take it to a shop.

There are a couple other remote possibilities that I'll mention that should be explored. Its possible that a brake pad fell out. What would happen in this case is the fluid being pumped would push the piston out of the caliper with each pump. The first several pumps of the pedal would push the piston closer to the rotor (disc). This unresisted pumping would simulate a bad master cylinder. Then when it met the rotor it would repressurize. This results in a nasty noise since you are exerting braking force with a steel piston agains a cast iron rotor. Not pretty. Since you didn't mention this noise I'm guessing it is not the case.

Another idea is (if you have drum brakes in the rear) that one of the wheel cylinders blew a seal. Since there would be no containment of the pressure, it would just squirt fluid and also feel similar to what you described. However, again, since you said the return trip was fine this could not be the case.

One last idea is that you have boiling fluid. Brake fluid is hydrophillic, meaning it absorbs water whenever it encounters it. Each time you open the reservoir to add or check fluid, it sucks some water from the atmosphere. This water can boil off when your brakes get hot. Since gasses are compressible, it will cause a spongy pedal. Since you had no problems on the return trip when the brakes would have been hotter, this is counterintuitive.

When you have the master cylinder replaced, many shops will just hook it up with new fluid in the reservoir leaving old fluid in the lines. Since this is the most important fluid in the system it should be flushed. Bleeding the brake lines involves opening the bleeder valves at each wheel and using the brake pedal to flush new fluid through. That insures you have new, dry fluid the whole way. Its something you'll have to make sure they do. Sometimes you'll have to request it and it might add another half hour of labor to the bill.

If they allow you in the shop, watch the fluid that comes out when they bleed the system. Its yucky and brown. New fluid is almost colorless and very clear.

OMG. I think all that technical stuff just flew over my head and out of my range of comprehension! Now I KNOW how people feel when they read my legal posts . . . . LOL

Okay. Deep breath. Most likely: Bad master cylinder. Possible: Brake Pad fell out, etc. Important: Make sure mechanic bleeds the brake lines to ensure new fluid throughout system. What to do: Take to shop and pay the repair bill. Sounds like a plan.

BETTER plan: Buy new car.

Hmmmm.

You got the exact synopsis ! Follow the exact layout you proposed, and if they don't give you what you want, file an appeal within 90 days....

The best course of action is to take it to a trusted garage and have them drive it until the problem repeats itself for the mechanic. In the absence of a "trusted" garage, select a national chain like Midas, Meineke, Gemini, Firestone, etc. Surprisingly, the tire and muffler chains seem to all do brake work as well. The fact that they are national doesn't mean you won't get screwed, but you'll have two things working in your favor; big chain, flat-rate pricing, and national culpability. They'll have competitive prices, and if you aren't satisfied and decide to squeal, they have a national reputation to worry about... not to mention a national budget that doesn't mind sucking up costs to keep you silent. With a local shop, if you voice displeasure to the owner and he doesn't want to help you, you're forced to file charges or suck it up. With a large company, chances are you can easily get satisfaction by just going up the chain of command a few steps.

What am I saying? You're a lawyer. You already know that angle

Curtis, that was an exceptional analysis of the problem.

Thanks :blush: