10. Figure 71–2 Brake fluid absorbs moisture from the air at the rate of about 2% per year. As the brake fluid absorbs water, its boiling temperature decreases. Continued CAUTION: DOT 3 brake fluid is a very strong solvent and can remove paint! Care is required when working with DOT 3 brake fluid to avoid contact with the vehicle’s painted surfaces. It also takes the color out of leather shoes.
11. NOTE: Because brake fluid absorbs moisture over time, many vehicle manufacturers recommend changing the brake fluid as part of the standard services to be performed routinely. The typical recommended brake fluid change interval is every two years or every 30,000 miles (48,000 km), whichever comes first. This is particularly important for vehicles equipped with an antilock braking system (ABS) because of the problem of expensive brake component wear or corrosion caused by contaminated brake fluid.
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21. Figure 71–3 A brake fluid tester can test brake fluid for boiling point.
22. CAUTION: Mineral hydraulic oil should never be used in a braking system that requires DOT 3 or DOT 4 polyglycol-based brake fluid. If any mineral oil, such as engine oil, transmission oil, or automatic transmission fluid (ATF), gets into a braking system that requires glycol brake fluid, every rubber part in the entire braking system must be replaced. Mineral oil causes the rubber compounds that are used in glycol brake fluid systems to swell, as shown here. Figure 71–4 Both rubber sealing cups were exactly the same size. The cup on the left was exposed to mineral oil. Notice how the seal greatly expanded.
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24. Figure 71–5 New brake fluid is clear or amber in color as shown here. NOTE: Some experts recommend replacing the brake fluid if it looks like coffee, either black coffee or coffee with cream. Figure 71–6 This brake fluid is black in color and should be replaced. Continued
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29. CAUTION: Alcohol or flushing fluids should not be used because they cannot be totally removed and will contaminate the system. Disassembled parts, however, can and should be cleaned with denatured alcohol or spray brake cleaner where the parts can be visually inspected to be free of cleaning solutions.
35. Figure 71–8 The master cylinder piston seals are usually constructed from EPDM rubber, and the diaphragm of the vacuum power brake booster is usually made from SBR. Figure 71–9 Cross-sectional view of a typical drum brake wheel cylinder. Most wheel cylinder boots and cups are either SBR or EPDM rubber. Continued
36. Figure 71–10 Exploded view of a typical disc brake caliper. Both the caliper seal and dust boot are constructed of EPDM rubber. Continued
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44. Figure 71–15 Making an ISO flare requires this special tool. (a) Position the brake line into the two-part tool at the correct height using the gauge end of the tool. (b) Assemble the two blocks of the tool together and clamp in a vise. Turn the tool around and thread it into the tool block. The end of the threaded part of the tool forms the “bubble” or ISO flare. Continued (b) (a)
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46. CAUTION: The exhaust system near brake lines should be carefully inspected for leaks when diagnosing a “lack of brakes” complaint. Exhaust gasses can hit the brake line going to the rear brakes, causing the brake fluid to boil. Since brake fluid vapors are no longer liquid, they can be compressed, resulting in a total loss of brakes. After the vehicle is stopped and allowed to cool, the brakes often return to normal. Fast response time is critical for the proper operation of the antilock braking system (ABS). As brake fluid ages, its viscosity (resistance to flow) increases, resulting in longer response time. Continued
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51. Bend It Right the First Time - Part 2 Figure 71–19 Using a V-belt pulley in a vise to bend brake line. Always use a tubing bender to avoid kinking the brake line. A kink not only restricts the flow of brake fluid, but also weakens the line. To bend brake line without a tubing bender tool, use an old V-belt pulley. Clamp the pulley in a vise, lay the tubing in the groove, and smoothly bend the tubing. Different diameter pulleys will create various radius bends.
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56. Figure 71–23 All brake hose is carefully inspected and a 3-mm-diameter gauging tool is inserted through the hose to make sure the hose is not restricted. Note the small diameter of the tool compared to the diameter of the hose. Seeing how small the inside diameter of the hose actually is makes it easier to visualize how easy it would be to have a restricted or blocked flexible hose. Continued
57. Figure 71–24 Typical flexible brake hose faults. Many faults cannot be seen, yet can cause the brakes to remain applied after the brake pedal is released. Continued
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