Chrysler RAM TRUCK 2500 1994 Service Manual page 163

5 - 4 SERVICE BRAKE DIAGNOSIS
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fluid, the system seals and cups will have to be re­
placed and the hydraulic system flushed.
(4) Check parking brake operation. Verify free
movement and full release of cables and pedal. Also
note i f vehicle was being operated with parking
brake partially applied.
(5) Check brake pedal operation. Verify that pedal
does not bind and has adequate free play. I f pedal
lacks free play, check pedal and power booster for be­
ing loose or for bind condition.^ Do not road test until
condition is corrected.
(6) I f components checked appear OK, road test ve­
hicle.
ROAD TESTING
(1) I f complaint involved low brake pedal, pump
pedal and note i f pedal returns to normal height.
(2) Check brake pedal response with transmission
in Neutral and engine running. Pedal should remain
firm under steady foot pressure.
(3) During road test, make normal and firm brake
stops i n 25-40 mph (40-64 Km/h) range. Note faulty
brake operation such as pull, grab, drag, noise, low
pedal, etc.
(4) Inspect suspect brake components and refer to
problem diagnosis information for causes of various
brake conditions.
COMPONENT INSPECTION
Fluid leak points and dragging brake units can
usually be located without removing any components.
The area around a leak point will be wet with fluid.
The components at a dragging brake unit (wheel,
tire, rotor) will be quite warm or hot to the touch.
Other brake problem conditions will require compo­
nent removal for proper inspection. Raise the vehicle
and remove the necessary wheels for better visual ac­
cess.
BRAKE WARNING LIGHTS
The red brake warning light is i n circuit with the
parking brake switch and pressure differential warn­
ing switch i n the combination valve.
The red light illuminates for approximately 2-4 sec­
onds at every engine start up. This is a self test fea­
ture designed to check bulb operation.
The red warning light illuminates when the park­
ing brake is not released. The light will also illumi­
nate i f a fluid pressure drop occurs i n either the front
or rear brake hydraulic circuit.
The amber antilock light is connected to the an­
tilock electronic control module and front or rear an­
tilock valve. The light only illuminates when a fault
occurs within the antilock system. Refer to the appro­
priate antilock system service section within this ser­
vice manual group.
DIAGNOSING SERVICE BRAKE PROBLEMS
PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is the result of a system leak. The leak
point could be at a brakeline, fitting, hose, or caliper.
Internal leakage i n the master cylinder caused by
worn or damaged piston cups, may also be the prob­
lem cause.
I f leakage is severe, fluid will be evident at or
around the leaking component. However, internal
leakage i n the master cylinder may not be physically
evident. Refer to the cylinder test procedure i n this
section.
LOW PEDAL
I f a low pedal is experienced, pump the pedal sev­
eral times. I f the pedal comes back up, worn lining
and worn rotors or drums are the likely causes.
A decrease i n fluid level i n the master cylinder res­
ervoirs may only be the result of normal lining wear.
Fluid level can be expected to decrease i n proportion
to wear. I t is a result of the outward movement of
caliper and wheel cylinder pistons to compensate for
normal wear. Top off the reservoir fluid level and
check brake operation to verify proper brake action.
SPONGY PEDAL
A spongy pedal is most often caused by air i n the
system. Thin brake drums or substandard brake
lines and hoses can also cause a spongy pedal. The
proper course of action is to bleed the system and re­
place thin drums and suspect quality brake lines and
hoses.
HARD PEDAL OR HIGH PEDAL EFFORT
A hard pedal or high pedal effort may be due to lin­
ing that is water soaked, contaminated, glazed, or
badly worn. The power booster or check valve could
also be faulty.
On diesel engine models, high pedal effort may be
the result of a low vacuum condition. I f the booster
and check valve are OK, the problem may be related
to a vacuum pump hose, hose connection, hose fit­
ting, pump diaphragm, or drive gear. Vacuum pump
output can be checked with a standard vacuum
gauge. Vacuum output should range from 8.5 to 25
inches vacuum. I f vacuum pump output is within
limits, check the power booster and check valve as
described i n this section.
B R A K E DRAG
Brake drag occurs when the lining is i n constant
contact with the rotor or drum. Drag can occur at one
wheel, all wheels, fronts only, or rears only. I t is a
product of incomplete brakeshoe release. Drag can be
minor or severe enough to overheat the linings, ro­
tors and drums.