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Brake Mistakes to Avoid
by
Mike Florence and Rob Blumer
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- Make sure you use the correct brake fluid
- The wrong fluid can cause major damage
- Upside down calipers cause brake failure
If you work on an engine and fail, the car won’t go. But if you work on your brakes and they fail, the car won’t stop.
Adding the Wrong Fluid to the Master Cylinder
Just because the brake system is a hydraulic system doesn’t mean that just any hydraulic fluid will work. In fact, most brake systems do not use hydraulic fluid at all.
Hydraulic fluid is a petroleum-based fluid of a type most often used in the power-steering system. Brake fluid is alcohol-based. When the rubber parts of the brake system come in contact with petroleum, they swell and deteriorate.
The mistake happens one of two ways. The home mechanic keeps fluids that are used in various systems of the car on a garage shelf. By mistake, a bottle of power-steering fluid is opened and poured into the master cylinder, and the home mechanic recognizes the mistake quickly. Or knowing that the brake system is hydraulic, the car owner’s brain, operating on just one cylinder, makes a connection: Hydraulic brake system . . . hydraulic fluid.
Both types of problems show up in the repair shop. Usually the first type of problem is less damaging. Within three days, the driver will notice the symptoms of system damage. The likely remedy will be a major brake system overhaul: Everything in the brake system that is made of rubber, including the master cylinder, calipers, wheel cylinders, and hoses, must be replaced.
On the other hand, if this is a problem you notice in an hour or so after pouring the contents of the wrong can into the brake system—if you haven’t driven the car, haven’t used the brake system—you will probably be able to take the master cylinder off, drain it, and bleed the system. However, if after draining and bleeding the system you still have a loss of brake-pedal pressure, the master cylinder must be replaced.
Putting Calipers on Upside Down
For all domestic cars, a mechanic takes the calipers off to get the brake pads out. On the front brakes usually there are two bolts that attach the caliper to the steering knuckle. The caliper can be turned upside down and remounted, and the brakes will work if there is no air in the line. And that is the problem. There will be air. Which means that the brake (usually that set of brakes—the front brakes or the rear brakes) will have little stopping power. And the pedal will press almost all the way to the floor.
If you have just done your own brake job and this is the immediate result, check the position of the brake calipers.
The problem with mounting the caliper upside down has to do with the location of the bleed screw, that part of the caliper directly connected to the brake line. If the bleed screw is positioned low when the caliper is mounted, the caliper is upside-down. A person doing a brake job at home may turn the bleed screw to make sure all the air is out of the line, get brake fluid flowing out immediately, and declare the brake line air-free.
But air rises and fluid sinks. The bleed screw must be at the top of the brake caliper to properly bleed the brake lines of air.
...from The Everything Car Care Book. For more books, visit Adams Media Bookstore.
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