from Goss’ Garage by Pat Goss

Much more important than making a car move is being able to make it quit moving. Think about it, brake failure is about as serious as it gets. Fortunately, there have been brake system improvements over the years to help prevent total brake failure. Unfortunately, those improvements sometimes confuse technicians.

Brakes work when you depress the brake pedal, which forces hydraulic fluid through metal lines and flexible hoses to either push brake shoes against the insides of brake drums or to squeeze brake pads against brake rotors. This action creates friction and it’s friction that actually stops your car.

To prevent total brake failure modern brake systems are divided into two independent subsystems. So if there’s a loss of brake fluid it only affects two wheels which leaves two wheels with working brakes to stop the car. Years ago brakes had only one system and any fluid leak meant the driver had absolutely no brakes, period! Although a split system will bring the car to a stop it won’t be nearly as effective as when all four brakes are working. But any amount of braking is better than the total lack of brakes on an old fashioned non-split brake system.

When split brake systems were first introduced the split was from front to rear. If something failed in the front you still had rear brakes and vice versa. The problem with this design was that it often created brake lockup due to all braking being placed on either the front or rear brakes. In those early split systems, if you developed a leak and lost half your brakes during a panic stop you often wound up sliding sideways due to unbalanced brakes and still having an accident.

To overcome this tendency brake systems are now split by linking each rear wheel to the opposite front wheel, this is called a diagonal split. Loss of brake fluid in part of the system still leaves only two wheel braking but because the remaining wheels are on opposite ends and opposite sides of the vehicle it will usually stop straight without skidding.

Although this is a significant improvement over front to rear split systems it often creates confusion for technicians when unusual brake problems occur. For example, the car pulls to the left during braking so the technician concentrates on the left wheel. The assumption is the brakes on the left wheel are over reacting. Over reacting? Possible, but very rare! A more typical cause is that the brake on the opposite side is under reacting. If one front brake is working normally but the opposite is not working the car will pull to the side where the brake is working normally because it has the greater stopping power. To complicate matters, in a diagonally split system a rear brake malfunction can affect brake operation on the opposite front wheel.

The moral is, things aren’t always what they seem. If your car pulls to one side during braking, brakes on one wheel get too hot, pads wear significantly more on one wheel or any single wheel anomaly occurs; don’t guess and don’t swap parts in a effort to fix the problem. Find the true cause by checking brakes on all four wheels but concentrate on the wheels on the opposite side of the car and opposite end of the car. Brakes don’t normally over react unless there is a problem with the affected wheel’s diagonal partner. Normally one-wheel brake problems are caused by something that prevents the opposite wheel from doing its job properly. A bit of understanding about how stuff works can save a bunch of money.