Learning event 3: Describe Inspection Procedures For Hydraulic Brake Systems

Wheeled Vehicle Braking Systems
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INTRODUCTION

The hydraulic braking system of the modern highspeed automobile must

be kept in a high state of repair. Not too many years ago, a small

defect in the braking system did not bother too much; in fact, it

might not even have been noticed. Today, however, improved road

conditions and higher vehicle speeds, plus more sensitive steering

and suspension systems, cause a poor braking action to be noticed

immediately. The brake system parts must be able to stand up under

high pressures and temperatures and still be able to work properly if

the vehicle is to be operated safely. To properly repair a brake

system so it is always in top condition, the mechanic must be well

trained and have a desire to do the best job possible.

BEFORE ROAD-TEST INSPECTION

The condition of the hydraulic service brakes of a vehicle can be

determined by inspecting the following items: fluid level in the

master cylinder, brake pedal free travel, total brake pedal travel,

feel of brake pedal (hard or spongy), leaks in the hydraulic system,

noise during operations, performance, and the amount of wear of brake

parts. Wear can normally be determined by checking one wheel of each

axle.

To inspect the fluid level in the master cylinder, first clean away

all dirt that may fall into the master cylinder reservoir. Remove

the filler cap and ensure the fluid level is at the level recommended

in the maintenance manual pertaining to the vehicle being serviced.

The level of fluid is determined by measuring the distance from the

top of the filler hole to the level of fluid in the reservoir.

If the fluid level is low, refer to the vehicle's lubrication order

for the recommended type of brake fluid and add fluid as needed.

Since the end of 1982, all military vehicles use silicone brake

fluid. Silicone fluid does not absorb water, provides good corrosion

protection, and has good lubrication qualities. The fluid is also

compatible with the rubber components of the brake system.

Check the master cylinder supply tank reservoir vent to make sure

that it is not plugged. On some vehicles, a small hole drilled in

the filler cap vents the supply tank. On other vehicles, the supply

tank is vented through a line and fitting connected to the top of the

master cylinder supply tank. A plugged vent can be easily cleared