Chrysler RAM TRUCK 2500 1994 Service Manual page 162

• SERVICE BRAKE DIAGNOSIS 5 - 3
S E R W i C E B R A K E DIAGNOSIS
INDEX
page
Brake Warning Lights 3
Brake Warning Lights 4
Component Inspection . . 4
Diagnosing Service Brake Problems . . . 4
General Information 3
Low Vacuum Switch—Diesel Models 3
Master Cylinder/Power Booster Test 6
GENERAL INFORMATION
The diagnosis information i n this section covers
service brake components only.
Antilock system diagnosis is provided in the
appropriate antilock brake section. Refer to the
Rear Wheel Antilock Brake System (RWAL) and
All-Wheel Antilock Brake System (ABS) sections
as necessary.
Service brake components consist of the brake-
shoes, calipers, wheel cylinders, brake drums and ro­
tors, brakelines, master cylinder and booster and
parking brake components.
SERVICE BRAKE DIAGNOSIS PROCEDURES
Brake diagnosis involves determining i f the prob­
lem is related to a mechanical, hydraulic or vacuum
operated component. A preliminary check, road test­
ing and component inspection can all be used to de­
termine a problem cause.
Road testing will either verify proper brake opera­
tion or confirm the existence of a problem. Compo­
nent inspection will, i n most cases, identify the
actual part causing a problem.
The first diagnosis step is the preliminary check.
This involves inspecting fluid level, parking brake ac­
tion, wheel and tire condition, checking for obvious
leaks or component damage and testing brake pedal
response.
A road test will confirm the existence of a problem.
Final diagnosis procedure involves road test analysis
and a visual inspection of brake components.
BRAKE WARNING LIGHTS
The red brake warning light is i n circuit with the
parking brake switch and pressure differential switch
in the combination valve.
The red light illuminates when the parking brakes
are applied or when a fluid pressure drop occurs i n
either the front or rear brake circuit. The light will
also illuminate for approximately 2-4 seconds at ev­
ery engine start up. This is a self test feature de­
signed to check bulb and circuit operation.
page
Power Booster Check Valve Test 6
Power Booster Vacuum Test 6
Preliminary Brake Check 3
Road Testing 4
Service Brake Diagnosis Procedures 3
Testing Diesel Engine Vacuum Pump Output 7
The amber antilock light is connected to the an­
tilock system. The light illuminates only when a fault
occurs within the antilock system.
LOW VACUUM SWITCH—DIESEL MODELS
On diesel models, the red brake warning light is
also used to alert the driver of a low brake booster
vacuum condition. The warning light is iri circuit
with a vacuum warning switch mounted on the
driver side fender panel. The vacuum side of the
switch is connected to the power brake booster. The
electrical side of the switch is connected to the brake
warning light.
The low vacuum switch monitors booster vacuum
level whenever the engine is running. I f booster vac­
uum falls below 8.5 inches vacuum for a minimum of
10 seconds, the switch completes the circuit to the
warning light causing i t to illuminate. The warning
light is designed to differentiate between a low vac­
uum condition and a hydraulic circuit fault.
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) 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
drop in proportion to normal lining wear. Also note
that brake fluid tends to darken over time. This
is normal and should not be mistaken for con­
t a m i n a t i o n . I f the fluid is still clear and free of
foreign material, it is acceptable.
(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. I f fluid is separated into layers, or obvi­
ously contains oil or a substance other than brake