Dodge RAM TRUCK 1500 1995 Service Manual page 175

B R
SERVICE BRAKE DIAGNOSIS 5 - 3
S E R V I C E
BRAKE DIAGNOSIS
INDEX
page
Brake Drag . . 5
Brake Fade 5
Brake Fluid Contamination
6
Brake Noise .
6
Brake Pedal Has Spongy Feel . . . . . . . . . . . . . . . . 4
Brake Pedal Pulsation 5
Brake Pull . . 5
Brake Warning Lights
3
Brakes Do Not Hold After Driving Through Deep
Water Puddles , 6
Component Inspection 4
Contaminated Brakelining
6
General Information 3
GENERAL INFORMATION
The diagnosis information in this section covers
service brake components only.
Antilock system diagnosis is provided in the appro­
priate 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, brake booster, and
parking brake components.
SERVICE BRAKE DIAGNOSIS PROCEDURES
Brake diagnosis involves determining if 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, in 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.
BRAKE WARNING LIGHTS
The red light is in circuit with the parking brake
switch and pressure differential switch in the combi­
nation valve. On diesel models, the red light is also
in circuit with the low vacuum switch.
The amber antilock light is connected to the an­
tilock system. The light illuminates only when a fault
occurs within the RWAL or ABS system.
page
Hard Pedal or High Pedal Effort 5
Low Brake Pedal 4
Low Vacuum Switch—Diesel Models . 3
Master Cylinder/Power Booster Test . 7
Pedal Falls Away 4
Power Booster Check Valve Test 7
Power Booster Vacuum Test 7
Preliminary Brake Check 4
Rear Brake Grab or Pull 5
Road Testing 4
Service Brake Diagnosis Procedures . . . . . . . . . . . . 3
Testing Diesel Engine Vacuum Pump Output . . . . . . 7
The red light illuminates when the parking brakes
are applied, or when a pressure drop occurs in the
front or rear brake hydraulic circuit.
The red light also illuminates for approximately
2-4 seconds at every engine start up. This is a self
test feature designed to check bulb and circuit oper­
ation.
A pressure drop in the front or rear brake hydrau­
lic circuit activates the pressure differential valve in­
side the combination valve. A pressure decrease
moves the valve toward the low pressure side. As the
valve moves, it pushes the pressure differential
switch contact plunger upward. This closes the
switch internal contacts and completes the circuit to
the red warning light. The light will remain on until
repairs are made and normal fluid pressure restored.
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 in 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 red
brake warning light.
The low vacuum switch monitors booster vacuum
level whenever the engine is running. If booster vac­
uum falls below 8.5 inches for a minimum of 10 sec­
onds, the switch completes the circuit to the warning
light causing it to illuminate. The warning light is
designed to differentiate between a low vacuum con­
dition and a hydraulic circuit fault.