brakefluid_brakefluid是什么意思_brakefluid颜色(16)

When the vehicle is loaded with more weight in the rear, the frame sits closer to the rear axle and the valve is held open for greater rear brake action。 Removing weight from the vehicle causes it to raise thereby lowering the pressure available to the rear brakes。 These valves are not repairable, however, there may be an adjustment on the linkage rod。 When disc brakes first began to be installed on vehicles, engineers noticed that under hard braking on wet road suces, the disc brakes would have a tendency to lock up before the rear drum brakes began to work。

With the front brakes locked, it is impossible to control the direction of the vehicle。 The cause of the problem was the rear brakes couldn’t apply until rear the rear hydraulic circuit pressure was high enough to overcome the tension of the drum brake shoe return springs。 The front disc brake calipers have no return springs so they will apply instantly。 To overcome this, engineers developed the metering valve。 Installed in the front brake hydraulic circuit, the metering valve “holds off” or delays disc brake application until a preset amount of drum brake pressure is available to the rear brakes。

This can be consider a timing control valve。 Metering valves, like proportioning valves are not serviceable。 If defective, they must be replaced。 There is one important thing to remember when servicing the combination braking system: A metering valve will prevent pressure bleeding on the front disc brakes! It must be held open manually when bleeding brakes using this method。Figure 2-11: Holding open a pull type metering valve。 Some metering valves have push type stems。 Drum brake wheel cylinders have a tendency to draw in air when the brake pedal is released。

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