Brake Lines, Hoses and Valves Flashcards

After a brake pedal release, the left rear wheel continues to drag. Loosening the left rear bleeder lets a spurt of fluid escape, and the drag disappears. Which is the most likely cause?

Answer: A collapsed inner liner in the flexible rear brake hose

A deteriorated hose liner can act as a one-way valve, trapping pressure at the wheel after the pedal is released. Opening the bleeder relieves the trapped pressure and frees the brake.

Which is the main purpose of the metering valve in a front disc/rear drum brake system?

Answer: To delay front brake application until the rear shoes have overcome their return springs

The metering valve briefly holds off pressure to the front disc brakes so the rear drum shoes can begin to move. This gives more balanced application at low pedal pressure.

A technician is replacing a section of steel brake line on a vehicle that uses SAE 45-degree flare fittings. Which type of flare should be formed on the tube end?

Answer: A double flare

SAE 45-degree brake fittings require a double flare. The doubled-over wall is stronger and resists splitting under high pressure.

Which is the main purpose of a proportioning valve in a brake system?

Answer: To reduce the rate of pressure increase to the rear brakes during heavy braking

During hard braking, weight shifts forward and the rear wheels unload. The proportioning valve limits the rise in rear pressure so the rear wheels do not lock prematurely.

What causes the red brake warning lamp to light through a pressure differential switch?

Answer: A drop in hydraulic pressure in one circuit shifts the valve piston into contact with the switch

If one circuit loses pressure, the higher pressure in the other circuit pushes the differential piston toward the low-pressure side. The piston closes the switch and lights the warning lamp.

A technician installs a gauge in the front line and another in the rear line to test a combination valve's proportioning function. What should the gauges show when pedal pressure is well above the valve's split point?

Answer: Rear pressure rising more slowly than front pressure

Above the split point, a working proportioning valve reduces the rate of rear pressure rise, so rear pressure falls progressively below front pressure.

Why is copper tubing not acceptable for replacing a steel brake line?

Answer: It work-hardens and cracks from vibration, and it cannot safely withstand brake system pressures

Copper work-hardens with vibration and flexing, which leads to cracking and leaks. It also lacks the strength needed for brake pressures.

After installing a new front brake hose, what check should be made before returning the vehicle to service?

Answer: Turn the steering wheel fully left and right and check for hose binding, stretching, or contact

Steering and suspension movement must not stretch, kink or rub the hose. Turning lock to lock confirms there is enough slack and clearance.

A technician needs to loosen a corroded brake line fitting at a wheel cylinder. Which tool is the best choice to reduce the risk of rounding the fitting?

Answer: Flare-nut (line) wrench

A flare-nut wrench grips most of the fitting's flats, which spreads force and helps prevent rounding the soft fitting nut.

A pickup with a height-sensing proportioning valve has its rear wheels lock up early under hard braking when the truck is lightly loaded. Which is the most likely cause?

Answer: A seized valve linkage or a misadjusted valve that holds it in the loaded position

A height-sensing valve should reduce rear pressure when the vehicle is lightly loaded. If the linkage is stuck or misadjusted as if loaded, rear pressure stays too high and the rear wheels lock early.

A technician finds a brake hose that appears swollen along part of its length when the brake pedal is firmly applied. What action is correct?

Answer: Replace the hose

A bulge means the reinforcing layers have failed and the hose could burst. The hose must be replaced.