The document provides information about various components in hydraulic brake systems, including:
1) A residual check valve keeps slight pressure in the system to prevent air leaks, while proportioning valves limit rear brake pressure to improve balance during hard stops.
2) A pressure-differential switch lights the brake warning light if pressure is lost in one circuit, while a brake fluid sensor does the same for low fluid level.
3) Common valves like metering valves and electronic proportioning systems work to properly time and balance brake pressure between the front and rear.
7. Figure 70–2 The momentary drop in pressure created when the brakes are released can draw air into the hydraulic system. Continued
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13. Figure 70–7 A movable contact brake fluid level switch. Figure 70–8 A magnetic brake fluid level switch. NOTE: Brake systems use either a pressure-differential switch or a low brake fluid switch to light the dash red “brake” lamp, but not both.
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16. NOTE: Many Japanese vehicles energize the relay that turns off the red “ brake” warning lamp from the output terminal of the alternator. If a quick inspection of the brake system seems to indicate that everything is okay, check for correct charging voltage before continuing a more detailed brake system inspection.
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18. Figure 70–9 Many proportioning valves are mounted directly to the master cylinder in the outlet to the rear brakes. Continued
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23. Figure 70–13 The proportioning valve piston can travel within the range shown without reducing pressure to the rear brakes. Continued
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25. Figure 70–14 At the split point, the proportioning valve piston closes the fluid passage through the valve. Continued
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28. Figure 70–15 A height-sensing proportioning valve provides the vehicle with variable brake balance. The valve allows higher pressure to be applied to the rear brakes when the vehicle is heavily loaded and less pressure when the vehicle is lightly loaded. Continued
29. Figure 70–16 A stepped cam is used to alter the split point of this height-sensing proportioning valve. CAUTION: Some vehicle manufacturers warn that service techs should never install replacement air lift shock absorbers or springs that result in a vehicle height difference than specified by the manufacturer.
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32. Figure 70–17 A proportioning valve pressure test can be performed using two pressure gauges—one to register the pressure from the master cylinder and the other gauge to read the pressure being applied to the rear brakes. This test has to be repeated in order to read the pressure to each rear wheel. Continued
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37. Figure 70–18 A metering valve when the brakes are not applied. Notice the brake fluid can flow through the metering valve to compensate for brake fluid expansion and contraction that occurs with changes in temperature. Continued
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39. Figure 70–19 A metering valve under light brake pedal application. Continued
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41. Figure 70–20 A metering valve during a normal brake application. Continued
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