Dodge RAM TRUCK 1500 1995 Service Manual page 176

5 - 4 SERVICE BRAKE DIAGNOSIS
B R
PRELIMINARY BRAKE CHECK
(1) Check condition of tires and wheels. Damaged
wheels and worn, damaged, or underinflated tires
can cause pull, shudder, tramp, and a condition sim­
ilar to grab.
(2) If 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 reservoir fluid level will decrease as normal
brake lining wear occurs. Also note that b r a k e
fluid tends to darken over time. This is normal
and should not be mistaken for contamination,
if the fluid is clear and free of contaminants, it
is still OK.
(a) If fluid level is abnormally low, look for evi­
dence of leaks at calipers, wheel cylinders, brake-
lines and master cylinder.
(b) If fluid appears contaminated, drain out a
sample. If fluid is separated into layers, or obvi­
ously contains oil, or a substance other than brake
fluid, system seals and cups will have to be re­
placed and hydraulic system flushed.
(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 height and feel. Verify that
pedal does not bind and has adequate free play. Note
if pedal is low, or spongy. Do not road test if pedal is
extremely low; inspect, identify, and correct faulty
component.
(a) If pedal lacks free play, check pedal and
power booster for being loose, or for bind condition.
(b) If pedal is'extremely low and red light is on,
do not road test as serious leak has developed in
hydraulic system. Locate leak source and repair as
needed.
(6) If components checked appear OK, road test ve­
hicle.
ROAD TESTING
(1) If complaint involved low brake pedal, pump
pedal and note if pedal returns to normal height. Do
not road test if pedal remains low, or falls off. This
indicates system leak or severely worn brake parts.
(2) Check pedal response with transmission in
Neutral and engine running. Pedal should remain
firm under steady foot pressure. Do not road test if
pedal falls away as master cylinder fault has oc­
curred.
(3) If hard pedal or excessive pedal effort is expe­
rienced, return to shop. Problem is caused by faulty
brake booster, booster check valve, binding pedal, or
master cylinder.
(3) During road test, make normal and firm brake
stops in
25-40
mph (40-64 Km/h) range. Note faulty
operation such as pull, grab, drag, noise, low pedal,
hard pedal, noise, etc. If constant scraping noise is
noted, brakeshoe wear tabs are probably contacting
rotor surface.
(4) Return to shop, disassemble and inspect as
needed. 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.
PEDAL FALLS AWAY
A brake pedal that falls off under steady foot pres­
sure is the result of a system leak. The leak point
could be at a brakeline, fitting, hose, or caliper. In­
ternal leakage in 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. Refer to the cylinder test procedure in this
section.
LOW BRAKE PEDAL
If low pedal is experienced, pump the pedal several
times. If the pedal comes back up, worn lining and
worn rotors or drums are the likely causes.
If the pedal is extremely low and the red light
comes on, there is a major leak in the hydraulic sys­
tem.
Note that a decrease in fluid level in the master
cylinder reservoir may only be the result of normal
lining wear. Fluid level will decrease in proportion to
wear. It is a result of the outward movement of cali­
per and wheel cylinder pistons to compensate for nor­
mal wear. Top off the reservoir fluid level and check
brake operation to verify proper brake action.
BRAKE PEDAL HAS SPONGY FEEL
A spongy pedal is caused by air in 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 or replace thin drums
and suspect quality brake parts.