Auto Terminology

A Big O Tires Tech Explains A Few Common Car Terms ...

Master Cylinder
The master cylinder is a holding tank for brake fluid. As the brake pedal is pushed down, the cylinder forces fluid to each of the wheels. A worn master cylinder can become leaky causing dangerously unreliable brakes. You should periodically check you brake fluid levels and the master cylinder for leakage.

Brake Pedal
The only visible part of a vehicle’s braking system, the brake pedal, is connected directly to the master cylinder. The pedal can be an indicator of brake problems if it travels too far, feels "hard" or "soft" or pulses. This can mean low or leaking fluids, damaged brake rotors or unevenly worn shoes or pads.

Combination Valve
The combination valve is comprised of a metering valve, proportioning valve, and brake warning light. It helps regulate the amount of pressure on each set of wheels to insure the front and rear brakes are applied appropriately for different braking situations. Problems with the combination valve can cause a vehicle’s wheels to lock up.

Drum Brake Assembly
A drum brake assembly is the most common method of stopping a vehicle’s rear wheels. The master cylinder’s fluid pressure forces the wheel cylinder to push brake shoes against the brake drums attached to the rear wheels. The resulting friction caused by the stationery shoes against the revolving drum is what makes the rear wheels slow to a stop. When brake shoes or drums become worn, stopping becomes unreliable and requires excessive pressure on the brake pedal.

Wheel Cylinder
The wheel cylinder is a very important part of the drum brake assembly. It is made up of fluid activated pistons that push brake shoes against the wheel drums to slow the vehicle. Leaking wheel cylinders are the cause of many brake problems, such as unreliable stopping, brake shoe damage and even partial brake system failure.

Disc Brake Assembly
Most cars use disc brakes for their front brakes because of their ability to withstand more heat than drum brakes. Disc brakes work when fluid from the master cylinder compresses brake pads against rotors attached to the front wheels. The friction caused by the stationery pads meeting the revolving rotors results in the rotors and the attached wheels slowing to a stop. Disc brake rotors and pads are subjected to abuse and should be checked for wear on a regular basis. Faulty disc brakes can vibrate during braking and can fail completely.

Toe (Alignment)
The tilted direction of the wheels toward or away from one another when viewed from above. Toe is generally considered the most critical tire wear angle. Tires that "toe-in" point toward each other. Tires that "toe-out" point away from each other.

Camber (Alignment)
The tilt of the wheels toward or away from one another when viewed from the front. Wheels that tilt in toward the vehicle have "negative" camber and those that tilt away from the vehicle have "positive" camber.

Caster (Alignment)
The angle of the steering axis in relation to an imaginary vertical line through the center of the wheel when viewed from the side. "Positive" caster is the when the vertical line is tilted back toward the rear, while "negative" caster is when it is tilted forward. A proper caster angle stabilizes the car for better traction.

Thrust Angle (Alignment)
The relationship of all four wheels to each other, as well as their overall relationship to an imaginary center line running from bumper to bumper. "Thrust line" refers to the direction in which the rear wheels are pointed. Thrust angle is correctable on cars with adjustable rear suspensions. If a vehicle has a non-adjustable suspension, then aligning the front wheels to the rear wheels compensates for thrust angle.