Several times a year, vehicles are brought to us with major brake issues. Common symptoms include the brake pedal going to the floor or the wheels locking up. Often these are low mileage vehicles that had no previous problems. Someone has added the wrong fluid to the brake system, and the result is very expensive.
The rubber used in the braking system is designed for high pressure sealing. It is also designed to be used only with brake fluid. Inadvertently adding, the smallest amount of petroleum-based fluid to the brakes will result in severe damage. Oil-based fluid causes the rubber in the braking system to swell and deteriorate, very rapidly.
As the seals start to swell, they may block the passages that allow the brake system to function. For instance, the return ports in the brake master-cylinder may be closed off. This blocks the return of fluid when the brake pedal is released. As the fluid expands from heat, the brakes apply and lock the wheels. In time the contaminants will break the rubber down, and the system will fail. The most common symptom is the brake pedal going to the floor. Often the brake system may fail completely.
The most common mistake is adding power steering fluid to the brakes
Both fluids are clear to amber in color and the containers often resemble each other. People sometimes make this mistake on their own vehicles and other times well meaning quick lubes may make it for them.
When a petroleum-based fluid enters the brake system, damage begins immediately. The reservoir cap and master cylinder seals are first to be damaged. Once applied, the master cylinder will quickly pump the contaminant into the rest of the system. Most often, the only effective repair is disassembly, cleaning and replacement of every rubber component. Any contaminant left in the system will cause the process to repeat.
Proper repair can be quite expensive, especially on a modern vehicle with Anti-lock braking. Because of the costs, it may be tempting to replace only the master cylinder and perhaps the brake calipers. This results in repeat contamination as the petroleum soaked into other parts again enters the system with use. Failure to remove every contaminated component will cause future failure.
Brake systems are sealed, and a drop in fluid level means there is a reason
As the brake pads wear, fluid is taken into the system. A low fluid level often shows worn brakes. Another cause for fluid to drop is a leak in the brake system. The reason for the low fluid should always be checked. Virtually, all systems have warning lights to warn of brake fluid level that has fallen.
Should the brake system need fluid, purchasing a new, unopened bottle, of the proper type is best. Opened bottles of brake fluid absorb moisture and may also damage the system. Most domestic and Asian vehicles use DOT 3 fluids. European vehicles often use DOT 4, which has a higher initial boiling point. Both DOT 3 and 4 are alcohol-based and can be substituted in an emergency if certain cautions are followed. Check the brake fluid cap or owner’s manual for the proper type.
DOT 4 brake fluid contains more alcohol than DOT 3 and thus has a higher initial boil point. This also makes it more susceptible to moisture, and it must be replaced more often than DOT 3.
It is wise to always be cautious when topping off fluid levels or when having the engine oil replaced. Should power-steering fluid be put into the brake system, the vehicle should be towed. Reverse-purging of the system immediately may limit further damage.