Dodge ram truck 3500 1996 Service Manual page 192

5 - 8 BRAKES B R
DESCRIPTION AND OPERATION ( C o n t i n u e d )
BRAKE HOSES AND LINES
Flexible rubber hose is used at both front brakes
and at the rear axle junction block. Double walled
steel tubing is used to connect the master cylinder to
the major hydraulic braking components and then to
the flexible rubber hoses.
D I A G N O S I S A N D T E S T I N G
BASE BRAKE SYSTEM
Base brake components consist of the brakeshoes,
calipers, wheel cylinders, brake drums, rotors, brake-
lines, master cylinder, booster, and parking brake
components.
Brake diagnosis involves determining i f the prob­
lem is related to a mechanical, hydraulic, or vacuum
operated component.
The first diagnosis step is the preliminary check.
PRELIMINARY
BRAKE CHECK
(1) Check condition of tires and wheels. Damaged
wheels and worn,, damaged, or underinflated tires
can cause pull, shudder, vibration, and a condition
similar to grab.
(2) I f complaint was based on noise when braking,
check suspension components. Jounce front and rear
of vehicle and listen for noise that might be caused •
by loose, worn or damaged suspension or steering
components.
(3) Inspect brake fluid level and condition. Note
that the front disc brake reservoir fluid level will
decrease in proportion to normal lining wear. Also
mote that brake fluid tends to darken over time.
This is n o r m a l and should not be mistaken for
contamination.
(a) I f fluid level is abnormally low, look for evi­
dence of leaks. at calipers, wheel cylinders, brake-
lines, and master cylinder.
(b) I f fluid appears contaminated, drain out a
sample. System will have to be flushed i f fluid is
separated into layers,, or contains a substance
• other than brake fluid. The system seals and cups
will also have to be replaced after flushing. Use
clean brake fluid to flush the system.
(4) Check parking brake operation. Verify free
movement and full release of cables and pedal. Also
note If 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
being loose or for bind condition. Do not road test
until condition is corrected.
(6) I f components checked appear OK, road test
the vehicle.
ROAD TESTING
(1) I f complaint involved low brake pedal, pump
pedal and note i f i t comes back up to normal height.
(2) Check brake pedal response with transmission
in Neutral and engine running. Pedal should remain
firm under constant foot pressure.
(3) During road test, make normal and firm brake
stops in 25-40 mph range. Note faulty brake opera­
tion such as low pedal, hard pedal, fade, pedal pulsa­
tion, pull, grab, drag, noise, etc.
PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brakeline, fitting, hose, or
caliper/wheel cylinder. Internal leakage i n the master
cylinder caused by worn or damaged piston cups,
may also be the problem cause.
If leakage is severe, fluid will be evident at or
around the leaking component. However, internal
leakage in the master cylinder may not be physically
evident.
LOW-PEDAL
I f a low pedal is experienced, pump the pedal sev­
eral times. I f the pedal comes back up, worn lining,
rotors, or drums are the most likely causes.
SP010Y PEDAL
A spongy pedal is most often caused by air in the
system. However, 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, or
replace 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
lining that is water soaked, contaminated, glazed, or
badly worn. The power booster or check valve could
also be faulty.
PEDAL PtJLSAIIOl
Pedal pulsation is caused by components that are
loose, or beyond tolerance limits.
The primary cause of pulsation are disc brake
rotors with excessive lateral runout or thickness vari­
ation, or out of round brake drums. Other causes are
loose wheel bearings or calipers and worn, damaged
tires.
NOTE: Some pedal pulsation may be felt during
RWAL/ABS activation.