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Hagerty Employee

7 brake system basics you should know

When it comes to an automobile’s critical systems, the one that makes you stop might just be the most important. Anyone that has experienced the sheer terror of brake failure will likely agree with that assessment, as the joy of driving dissolves when your safety relies on you steering your beloved vehicle into the softest thing in sight. The first step to working on brakes is understanding how they work. Here are seven brake system terms to get you started on the basics ...


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Pit Crew

Brake fluid moisture absorption - Especially in cars that get less use and more storage.


I'm presently dealing with a stuck piston on a disc brake system. This has resulted in times of the brake pedal sinking close to the floor when the brake fluid gets too hot (800 degrees) due to the stuck pad at the rotor. Brake fluid boils, causing low pedal. More technical information but might be helpful for those working on hydraulic brakes.


Brake systems  were OK but hardly anyone acknowledges the fine particles that go into the air and cause cancer. Brakes should be designed to work in wet conditions and the fluid around them would collect the fine particles and pump them to a filter which could be changed and thrown out. I know some of you will say it wouldn't work, but the clutch pack in your automatic  transmission can cause the rear wheels  to burn out when power is applied. Thake a good look at the dirt at the front wheels of any disc brake car. There is the proof of fine particles that escaped getting into your lungs.


Your first sentence in the "Disc Brakes" section is total BS.  MANY (I'd wager most) cars and trucks still use drum brakes in the rear as they do provide a few advantages -- most significant for the manufacturer is likely cost, but performance gains inherent in disc brakes are less necessary for rear applications. The increased size, weight, drag, complexity, and cost of disc systems precludes their use in all but high performance cars and some trucks where ultimate performance is required.


Now drums on all 4 corners (like my first car, a '66 Valiant) thankfully haven't been commonly installed in decades -- especially with modern distractions many people seem unable to ignore while behind the wheel, but rear drums are still very common and likely will remain so indefinitely.


Not sure where you get your information, but it’s not true at all.

The discussion of hydraulic brakes should include mention of Pascal's Law, the principle on which they operate: The pressure applied to any part of the enclosed liquid will be transmitted equally in all directions through the liquid.'s_law

Pit Crew

No mention of power vs. manual brakes, or the booster (usually vacuum, though hydraulic and electric are also used) that reduces pedal effort.  Speaking of the pedal, adequate "pedal ratio" is necessary to reduce the pedal effort to a reasonable level.  A minimum of 6:1 for manual brakes or 4:1 for power brakes.  


It is ironic that the picture of disc brakes is a modified Ford Model T. Model Ts were built from 1908 to 1927.


The Model T's original brakes are considered by some in the hobby as inadequate for today's roads and speeds. Unmodified Model Ts have small mechanical drum parking brakes on the rear axle. They are actuated by the hand brake lever connected by rods and levers to the rear axle brakes. They were really only intended as parking brakes but can be used in an emergency. The main brake to slow and stop the car is a floor pedal attached to a band in the transmission that grabbed and slowed the drive train and thus the rear wheels. The main pedal band brake has its own issues.


This picture of hydraulic disc brakes on the rear axle of a Model T is the adaptation of modern Ford parts to provide safer, higher performance brakes on Model Ts that are frequently driven without concern over originality and authenticity. They are hydraulically actuated by the original brake pedal and the mechanical parking/emergency brake part of the caliper is connected to the original hand brake lever.


Cars with breaks should be repaired before going out to test the brakes.  


New Driver

This does not cover the air brake systems on large trucks.

New Driver

Unless you were severely limited on word count, a mention of brake rotors and more info regarding brake pads and brake fluid would have been appropriate, and probably more helpful than the info on proportioning valves and hard vs. soft brake lines.  As an overview of brake systems the article falls well short of the acumen of most of your readers.  The antique wheels with modern adaptations are not particularly helpful either.

New Driver

This article was to just discuss in short the very basics of brakes.  Reading the other comments on here, what do you expect...a whole book the size of a shop manual on operation and technology of brake systems? 


Especially for mechanical brakes, the best shoes are not good at all.  We did a complete brake system tune-up on my Model A (many years ago) and my Dad insisted on the best brake shoes.  Poor results!  The shoes were made to last but when we changed the shoes to the cheap shoes, the softer brake lining stopped the car with ease.  


Y'all need to Stop....

Pit Crew

I believe that the intent of this article is the provide "basic" information about common automotive brake systems. It doe that clearly. It could be described as the first chapter of "Brakes 101". The following chapters would illustrate or discuss the technical issues associated with each braking system such as types of braking material, adjustment and maintenance of these systems. So it is what it is nothing more. It is a good article you would be surprised how many automotive enthusiasts do not have knowledge of basic systems in their vehicles like brakes.

Intermediate Driver

People should also know the "slang" term for hydraulic brakes is "juice brakes".

Pit Crew

Just one comment in regards to soft lines.  Since most here have collector cars, soft lines can look fine on the outside and not have any leaks.  However, it's not uncommon for the inside of the line  to swell and restrict fluid flow causing brake drag.  If they haven't been changed in 10 or 20 or 30 years, it's a good idea.  Also, flushing brakes every couple of years is a good idea to avoid moisture related problems.


It might be nice to give a break down of how to adjust and test mechanical bakes for the person new to this type of brake system


After the entire system has been confirmed to be correct and each individual wheel adjustments have been set to the "just before drag" adjustment then mechanically position the brake pedal down 2 1/2 inches and adjust the front brake rods to the lock-up position. Repeat for the rear brakes with the pedal set to the 2 inch down position. This will give the rear brakes priority for a Model A Ford. Use a similar procedure for other mechanical brake systems.
Advanced Driver

The most important difference between drum brakes and disk brakes is that as metal heats up it expands; with drum brakes this results in the drum expanding and increasing the distance between the drum and the brake shoe, decreasing the braking effect, but with disk brakes the more the rotor expands the smaller the gap between the rotor and the brake pads, improving the braking enough to offset the decrease in efficiency caused by the brake pads heating up.

Advanced Driver

Along with the many already-suggested topic additions: Single-Versus-Dual Compartment Fluid Reservoirs, for the sake of safety. 

I can't always remember what day of the week it is, but I also recall that The Master Cylinder was also the Moon-dwelling villain from Felix the Cat. Pity me. 


Most of the brake fluids used today are hydroscopic (they absorb water) because they are alcohol based. This can lead to corrosion of the master cylinder, brake cylinders and brake lines. One way to prevent this is to periodically purge the brake system of the old brake fluid and replaced it with new brake fluid.


Another option would be to replace the alcohol-based brake fluid with a silicone-based brake fluid since they are not hydroscopic. The minor downside to using silicone brake fluid is it compresses slightly under heavy braking pressure, so the driver is likely to feel a softer brake pedal when under extremely hard braking.


Intermediate Driver

I like brakes.

New Driver

The picture of the drum brake is the duo-servo drum brake.  They are designed to help assist braking by having the primary shoe drive the rear or secondary brake shoe into the drum at the bottom of the drum by way of the brake adjuster.  The secondary shoe has longer braking material bonded/riveted to the brake shoe since it performs about 75% of the braking on that wheel.

There is so much more than 7 system basics.  I was told in high school auto class that the brakes have to generate the same amount of heat energy to stop the vehicle as the engine generated to get the vehicle up to speed.  Doubt its factual, but it was one of things I hung onto for some reason.


A bit elementary don't you think. Hopefully any car enthusiast would be wasting his time reading this.

New Driver

Let's see an article explaining the more complex Roll Royce brakes. It would make great reading for sure. 


I recently had my drum brakes done on my 1968 Mustang and they keep sqeaking.  I'm being told by the shop its because of the materials they use now vs in 1968. 

Any suggestions?

Community Manager

I would ask them which brand and material they used when re-doing the brakes, then go to a parts store and see if there's a better alternative. Odds are there is another brake vendor they could use that will be quieter. 

Pit Crew

HEY ! That car has no brakes.

WELL; That won't stop me !


Might be better to do a story on why many cars have pulsating brake pedals and how it’s not a warped rotor. 

Or better yet how to bed brakes in properly. 

These two things cause people more grief and most have no idea what causes it or how to do it. 

The basics here are a bit too basic for an enthusiast site. 

Might add about drilled rotors are only for unsprung weight or cosmetic reasons and that solid rotors are better to deal with heat. 

Most people have the basics but most are not informed on the most common issues or myths. 


Thanks for explaining the terminology.  Maybe you would--but maybe you wouldn't believe all of the terminology used "out here" due to mis-understanding of the purposes these parts play.  I add that although brakes are about the most important part of a vehicle, I constantly run into vintage car owners who are looking for "deals" on brake parts.  Believe you me--I don't want to spend money just to spend it, but each of the parts which you describe is part of an integral life-saving system.  I tell people to buy the best parts available.  The life you save may be your own!  jay