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On a car with disc/drum brakes, the front brakes grab quickly when light
pedal pressure is applied. This problem could be caused by a bad:
A. Proportioning valve
B. Pressure safety switch
C. Metering valve
D. Residual check valve - ANSWER ✔✔The correct answer is C.
The metering valve delays the flow of brake fluid to the front calipers
,until the pressure in the system rises to a point where the wheel cylinder
can overcome the tension of the brake shoe returning spring. The
purpose is to have both front and rear brakes apply simultaneously. This
prevents the front brakes from locking up during light brake applications.
The driver of a vehicle with power disc/drum brakes says that the brake
pedal moved slowly to the floor while maintaining pedal pressure at a
stoplight. What could cause this problem?
A. Leaking primary piston cup in master cylinder
B. Leaking power brake booster
C. Leaking residual check valve in master cylinder
D. Internal leak in the combination valve - ANSWER ✔✔The correct
answer is A. if the primary piston cup in the master cylinder is leaking,
pressure will not build up ahead of the primary piston to increase
pressure to the rear brakes. The piston will then move forward until the
spring is compressed enough to move the secondary piston.
Consequently, this internal leak will cause the brake pedal to slowly drop
to the floor.
What is the purpose of the master cylinder residual check valve(s) on
vehicles equipped with drum brakes?
A. Allowed the driver to pump up the brakes
,B. Prevents air from entering the hydraulic system
C. Prevents wheel lockup by reducing the hydraulic pressure
D. Reduces pedal pulsation by controlling hydraulic pressure -
ANSWER ✔✔The correct answer is B. Residual check valve(s) are
used on drum brakes to keep residual low pressure (slight static
pressure) in the brake system at all times even when the brake pedal is
released. This pressure (5-20 psi) keeps the lips of the wheel cylinder
piston cups tight against the cylinder walls to prevent air from entering
the system when at rest (brakes released).
A technician has just overhauled the front brakes on a vehicle with front
disc and rear drum brakes. However, when he attaches a pressure
bleeder (pressurized to about 25 psi) to the master cylinder, he cannot
get any fluid to come out of the disc brake caliper bleeder screws. Which
of the following is MOST LIKELY the cause?
A. Bad proportioning valve
B. Bad pressure differential valve
C. proportioning valve release button not activated
D. Metering valve release button not activated - ANSWER ✔✔The
correct answer is D. A metering valve requires a minimum pressure
(typically 75-125 psi) to open. At this point pressurized fluid flows to the
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, front calipers. Since the bleeder tank is only pressurized to 25 psi, fluid
pressure is too low to open the metering valve during this procedure,
Therefore, when you use a pressure bleeder on a system with a
metering valve, you must manually keep the valve open by either
pushing the button in the end of the valve, or pulling the stem outward
on the end of the valve.
On a vehicle with single piston floating caliper front disc brakes, the
brake pads on the left side of the vehicle are almost completely worn
while the right side is almost new. Tech A says that too much rotor runout
could be the cause. Tech B says that a binding caliper piston could be
the cause. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B - ANSWER ✔✔The correct answer is B. Excessive
rotor runout would cause a pulsating brake pedal, but not uneven side-
to-side pad wear. A frozen caliper piston on the other hand, will keep
both inner and outer brake pads equally applied against the rotor even
when the brake pedal is released. This constant friction will cause rapid
pad wear in the affected caliper as well as the front-end pull