13 Steps in Brake System Inspection and Training Part II
8. Vacuum Pedal Drop: after exhausting the reserve vacuum in step 7, hold the pedal down firmly and start the engine. The pedal should drop slightly as vacuum is applied to the booster.
9. Master Cylinder Inspection: Check the outside of the cylinder for signs of leakage. Wipe dirt away from the cylinder and remove the cover. The fluid level should well be within one-fourth inch of the top of the reservoir, and the fluid should be clear with no sign of contamination.
Watch the fluid in the reservoir as an assistant depresses the pedal one-fourth to one-half inch. A spurt or agitation indicates that the compensating port is closing correctly. This occurs only in the front reservoir in dual-chamber cylinders. Be sure the vent holes in the cylinder cover or cap are open and that the diaphragm, if used, is not torn or deteriorated.
10. Power booster connections: check the vacuum line at the booster and at th engine for signs of leakage. With the engine running, listen for hissing sounds, indicating a vacuum leak. On vehicles with Hydro-Boost hydraulic boosters, check the lines at the booster and the power steering pump for leakage.
11. Hoses, Lines and Fittings: inspect all hoses, lines and fittings for damage, chassis interference, or leakage. Do not overlook the rear hose, or hoses. Metal lines and fitting must be free from leakage. Be vigilant in your inspection so you don’t miss anything.
Raise the vehicle on a hoist and turn the steering from lock to lock. Brake hoses must not hit the chassis or wheels in any wheel position. Rub rings may contact the chassis as long as the body of the hose is not worn.
Inspect the brake lines for use of copper tubing in place of steel lines. Copper tubing is inferior in material and thus, is unacceptable for brake system use.
12. Parking Brake: inspect the parking brake linkage and cables for damage and fraying. Cables should move freely in conduits. Apply the parking brake and attempt to move the vehicle. On pre-1967 cars, the parking brake should hold the vehicle securely at two-thirds lever or pedal travel. Many 1976 cars as well as later models have a ratchet-type parking brake linkage that provides a greater mechanical advantage but which must be pumped up during application.
13. Drum Brake Components: remove the brake drums and inspect the drums, shoes, linings, wheel cylinders and all hardware. Brake drums wear in normal use. Some of the common wear patterns are:
Scoring—grooves worn in the drum surface by contact with the lining. If the lining is worn down to the rivets, or shoe surface, deep scoring will result
Bellmouthed—tapered wear which will also be seen as uneven lining wear.
Concave or convex—concave wear is occurs when there is greater wear in the center of the drum than at either edge. Convex wear is when there is greater wear at the edges than in the center.
Heat checks—hairline cracks in the braking surface caused by overheating from severe use.
Out of Round—an out of round condition may exist with any of the other wear patterns. This condition is verified by measuring the drum diameter in several places with a micrometer.
A slight amount of any of these wear conditions can be corrected by turning the drum on a lathe to restore a uniform surface finish and diameter.
As an aside, remember to check the lining for cracks or breaks that impair attachment, loose mounting, contamination with grease and oil or brake fluid. One must also be on the lookout for wire backing visible through lining material, bent shoes or broken welds and badly deformed slots or holes for springs, anchors, or pushrods.