Braking Systems 101

Brake Fluids

Brake fluid has undergone quite a few changes over the last few decades with the introduction of new formulas, materials, and standards. Brake Fluid can be broken down into two types: Glycol Hygroscopic or Silicone Hydrophobic

GOLDEN RULE: Change your brake fluid OFTEN. At least every 2 years for a street vehicle – sooner for a track vehicle.

Glycol Hygroscopic Fluid
The majority of brake fluid currently on the market is hygroscopic (hygroscopic: Tending to absorb moistures from the air) and absorbs any moisture. Introduction of water increases the chance of the fluid boiling when experiencing extreme heat. Not only does water cause a degradation of braking performance, but it can also freeze and cause rust in steel brake lines.

The metric for evaluating brake fluid performance is the brake fluid’s boiling point, which is graded by the US DOT. The higher the DOT rating, the higher the brake fluid’s boiling point which is graded from 1 to 5. All Glycol based fluids can be mixed and combined, but performance is only as great as the weakest link.

Below are the DOT ratings. An unopened bottle of brake fluid is considered to be “DRY"

DOT 3:  The most commonly used brake fluid.

DOT 4: Considered by some as the absolute minimum brake fluid for optimal street braking performance and is typically considered the minimum requirement for track use.

DOT 5.1: A low viscosity glycol-based brake fluid. The lower viscosity was introduced so that the fluid could travel within the channels of ABS and DSC systems – which a “normal” viscosity brake fluid would have trouble traversing and result in reduced performance when the ABS and DSC system are enabled. However, in most street situations, viscosity is not a concern and any glycol based fluid can be used. It is not advised to use a low viscosity brake fluid for track use as the increase in temperature will result in the fluid thinning. It should also be noted that in colder climates, a low viscosity brake fluid may flow better. If a mushy or slow reacting pedal during an ABS stop is experienced during street operation, it’s likely that the wrong fluid is being used and switching to a low viscosity fluid will improve performance.

Silicone Hydrophobic (DOT 5)

Silicone based brake fluid which has a silicone content greater than 70% repels water and will not mix with water. Due to this, silicone brake fluid will have a higher boiling point due to the absence of water contamination. However any water present will pool and then boil at 212F and turn into vapor. This vapor can cause a spongy, or mushy, brake pedal due to the easily compressible vapor. This results in a brake system which has to undergo scheduled brake maintenance more often than glycol based fluids. Silicone based fluids can be used in brake systems which use Glycol, however the entire brake system must be flushed several times in order to remove the glycol fluid. Silicone based brake fluid (DOT 5) makes for an exceptional brake fluid for high performance situations.

Brake Pads

Organic

The standard brake pad on roughly 67% of new vehicles sold, are made from a combination of materials and fibers ranging from rubber, carbon compounds, glass or fiberglass, and Kevlar bound together by resin.

Pros:

• Low cost
• Generate moderate amount of friction without much heat generation
• Less aggressive on brake rotors
• Quiet

Cons:

• Tend to wear down quicker thus requiring replacement more often
• Do not perform well in extreme weather
• Overheat during High performance driving
• Higher Compressibility level – Driver has to press on the brake with more force to engage them.

Ceramic

Developed in the mid-1980s, ceramic brake pads are made from materials similar to what can be found in pottery which makes for a denser and more durable pad; along with embedded copper fibers to increase friction and heat conductivity

Pros:

• More reliable, broader range of temperatures and driving conditions when compared to organic
• Produce less brake dust
• Very Quiet

Cons:

• Cost, typically the most of expensive due to manufacturing process
• Not the best choice for extreme driving conditions
• Poor heat absorption

Semi-Metallic

Composed of materials such copper, Iron, Steel, and other composite alloys to create a pad which is 30%-70% metal. These materials are then combined with graphite and other fillers.

Pros:

• Great conductor of heat and tend to withstand more heat while allowing other braking components to cool more quickly
• Resistant to compressing, so less pressure is required to the brake pedal to engage
• Suitable option for high performance driving or extreme weather conditions

Cons:

• Loud
• More wear on brake rotors
• More brake dust than ceramic and organic

Which to choose?

Firstly, always follow the vehicle’s manufacturer recommendation for brake pads. If high-performance driving is common in the vehicle, semi-metallic brake pads should be considered. If the vehicle is used as a daily commuter without ever exceeding the speed limit, then ceramic brakes may be the pad of choice. If the vehicle rarely leaves the jack stands, is a show car, or is just rarely driven then organic pads may be the better option.

Brake Rotors

Full Face

Void of slots and drilled holes, a full face or flat face rotor will offer the largest surface area of any offered brake rotor. A full face rotor can be vented, which means there are vanes between the two rotor faces in order to help with heat control.

Slotted

Slotted rotors are constructed with slots, or grooves, into the face of the rotor. This design allows for heat, gas, and brake dust to escape via vents which will result in a reduction of brake temperature and brake fade. Although the slotted design allows for an reduction in brake temperature, it allows means less surface area for the brake pads to clamp onto. Slotted rotors are great for high performance driving scenario.

Cross Drilled

Cross drilled rotors have holes drilled across the face of the rotor. Much like the design of a slotted rotor, the cross drilled pattern aids in the reduction of brake temperature and brake fade. The downside to drilled rotors is that the drilled holes have the possibility to form cracks after heat cycles.

Cross Drilled and Slotted

Cross drilled and slotted rotors have holes and slots across the face of the rotor. This type of rotor will provide the least amount of surface area for the brake pads to clamp onto.