Chevrolet Trax: Brake fluid

The purpose of brake fluid is to:

1. Utilize hydraulic pressure to apply force on brake components that use a friction material to slow the vehicle
2. Protect the brake system from corrosion

Motor vehicle brake fluids are hygroscopic and absorb moisture when exposed to the atmosphere and in service.

Water contamination from any source, including mechanical or accidental additions of free water, will appreciably lower the original boiling point of the brake fluid and increase its viscosity at low ambient temperatures. Water contamination may cause corrosion of brake cylinder bores and pistons, and may seriously affect the braking efficiency and safety of the brake actuating system. While moisture is definitely an issue with brake fluids, no consistent and accurate measurement identifying the percentage of moisture that is detrimental to brake fluid performance has been found in the literature. In addition, no specification exists for an in-use brake fluid boiling point that can be identified by a testing procedure and therefore no recommendation for replacement based on moisture content can be made with confidence.

It has been demonstrated that corrosion inhibitors in brake fluid deplete over time and can be severely depleted by 36 months. The depletion of corrosion inhibitors results in corrosion. Copper is not found in new brake fluid and is used as a brazing alloy in the brake lines, which represent a high surface area for brake fluid contact.

Copper is the first metal to corrode in a brake system, and is a principle contaminate in brake fluid. Copper levels increase slowly and stably over time. The slow and steady increase in copper levels provides a means to predict the age of brake fluid under normal conditions. The age of the brake fluid can help determine when brake fluid should be serviced according to OEM recommendations when applicable. Copper can also directly affect ABS components as it can plate to the valve and valve seats.

Iron levels begin to sharply increase when the copper levels reach 150-250 ppm indicating corrosion of iron components. This also allows copper levels to be used to predict when iron levels will increase or the start of component corrosion and the depletion of corrosion inhibitors. Once iron corrosion begins copper acts as a catalyst to speed corrosion. At this point (iron corrosion) it is evident that the brake fluid no longer performs the intended purpose of protecting the system from corrosion.

A copper content of 200 ppm or greater indicates a depletion of corrosion inhibitors in the brake fluid and Brake Fluid Replacement is Required.

BATTERY

The automotive battery is an electrochemical device that produces voltage and delivers current. In an automotive battery the electrochemical action can be reversed, recharging the battery, providing many years of service. Batteries emit hydrogen gas while charging and the battery case cannot be completely sealed. Batteries (maintenance free) have small vents on the side forcing the gases to go through baffles to escape. This process allows the liquid to condense and flow back to the bottom of the battery.

The purpose of the battery is to supply current to the starter motor, provide current to the ignition system while cranking, to supply additional current when the demand is higher than the alternator can supply and to act as an electrical reservoir. Batteries are rated in cold cranking amps. This represents the current the battery can produce for 30 seconds at 0 degrees before the battery voltage drops below 7.2 volts.

Fig. 8: Typical Battery Components

BATTERY CABLES

Battery cables are large diameter, multi-stranded wire which conveys the high current (250+ amps) necessary to operate the starter motor. Some battery cables will have a smaller wire, soldered to the terminal, which is used to either operate a smaller device or to provide an additional ground. When the smaller cable burns it indicates a high resistance in the heavy cable.

Even maintenance free batteries need periodic inspection and cleaning to insure they stay in good working order. Inspect the battery to see that it is clean and that it is held securely in its carrier. Some corrosion naturally collects around the battery. Electrolyte condensation contains corrosive sulfuric acid, which eats away the metal of battery terminals, cable ends and battery hold-down parts.

POWER STEERING

Power steering is a system for reducing the steering effort on cars by using an external power source to assist in turning the wheels. Most vehicles have power steering and the trend to front wheel drive, greater vehicle mass and wider tires means that modern vehicles would be extremely difficult to maneuver at low speeds (e.g. when parking) without assistance.

POWER STEERING FLUID

Power Steering Fluid is the hydraulic component in power steering systems and is charged with pressure transfer and component protection. It fails when it stops performing one of its tasks. When a fluid becomes oxidized, its resistance to flow is greater and it decreases its ability to protect components and transfer pressure.

The more common failure mode of PSF is internal and external contamination, and excess particles in fluid promote component wear and can lead to component failures, including seals, shafts and gears.

Most power steering systems work by using a belt driven pump to provide hydraulic pressure to the system.

This hydraulic pressure is generated by a rotary-vane pump which is driven by the vehicle's engine. As the speed of the engine increases, the pressure in the hydraulic fluid also increases, hence a relief valve is incorporated into the system to allow excess pressure to be bled away. Some of the hydraulic systems also include an electronic pressure valve which can reduce the hydraulic pressure of the power steering lines as the vehicle's speed increases (Variable assist power steering).

Electric Power Steering uses sensors to detect the motion and torque of the steering column and a computer module applies electric motor to provide power assist. This allows variable assist power steering to be applied depending on driving conditions. In the event of component failure, a mechanical linkage such as a rack and pinion serves as a back-up in a manner similar to that of hydraulic systems. Electric power steering is usually limited to smaller vehicles rather than trucks and SUVs. Electric systems have a significant advantage in fuel efficiency because there is no hydraulic pump constantly running, whether assistance is required or not.

Fig. 9: Typical Front Suspension & Steering Components

WIPER BLADES

Worn wiper blades are dangerous. Ozone, airborne contaminants, oil, sunlight and dirt all act to weaken and reduce your wiper blades' ability to keep your view unobstructed. And exposure to sunlight and ozone cause the wiper blades to age, even if they're not used much. Weather also plays a critical role in your windshield wiper blades' deterioration. Freezing temperatures make the rubber in your wiper blades hard and brittle, which increases their tendency to crack or tear. Hot weather warps the rubber and prevents the blade from wiping your windshield cleanly.

Heavy use is hard on the wipers because dust, abrasives, road grime and bug juice wear away the cutting edge the blade needs to wipe cleanly. Even road dirt acts like an abrasive to wear away the flat surface necessary for a good squeegee effect. Rubber also deteriorates over time. As blades age, they lose their flexibility and are less able to wipe cleanly. They may develop a permanent set or curvature, which prevents full contact with your windshield.

A wiper blades ability to clean the glass depends on:

The slope and area of the windshield: Windshields are sloped for improved aerodynamics and a "cab-forward" windshield with a lot of surface area directs more wind against the wipers, and can force the blades away from the windshield at high speeds unless the wiper system is designed to resist lift.

The amount of spring tension on the wiper arm: This is important to keep the wiper blade in tight contact with the windshield and provide a squeegee effect.

The number of pressure points or claws holding the blade: The more claws a blade has, the broader the area over which the pressure of the wiper arm is spread. More claws also provide increased flexibility so the blade can more easily follow the curvature of a large, sloping windshield for full side-to-side contact.

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