Download BENDIX TCH-020-007 User's Manual

Technical Bulletin
Bulletin No.: PRO-20-07 Effective Date: 1/1/91 Cancels: N/A Page: 1 of 3
subject: Ford F Series Truck Hydraulic Parking System HR-1
Hydraulic Relay Noise
SUPPLY RESERVOIR CONTROL
DELIVERY
PORT
TW-11
DELIVERY
EXHAUST
PORT
FRONT BACK
HR-1 HYDRAULIC RELAY VALVE
While some noise is inherent in the operation of a hydraulic brake system (pump, check valves and pressure regulating
valves opening and closing) operators occasionally report hearing excessive noise emanating fromthe HR-1 hydraulic relay
valve. The HR-1 is used on Ford truck model series 600, 700, 800, 900, 7000 and 8000. Described variously as a “buzzing,
humming, popping or groaning” sound, the excessive noise is often attributed to a faulty HR-1. Because the HR-1 is mounted
on the firewall, adjacent to the Hydro-Max booster, sounds are amplified. Excessive HR-1 noise can be the result of air in
the parking brake system.
PARKING BRAKE
CONTROL VALVE (TW-44)
RESERVOIR
PARKING BRAKE PARKING BRAKE
CHAMBER CHAMBER
LT
((О)) SAGINAW BRAKE DRUM
PUMP «й ASSEMBLIES
DISC BRAKE
BRAKE .
HYDRO-MAX (PARKING) J
| BOOSTER с |
(SECONDARY) | | |
| (PRIMARY)
DISC С 1 1
BRAKE | |
PARKING |
(©) | hn | sea oo
! ı CHAMBER |
! ' {
| | |
1
CA nn J PARKING BRAKE
dh -—= CHAMBER
TYPICAL HR-1 SYSTEM
In order to eliminate the excessive HR-1 noise it is necessary to bleed the air from the spring brake actuators, using the
vehicle manufacturer's recommended procedure. Ifthe HR-1 noise is only temporarily eliminated and reappears ina short
period of time, then it is likely that an external leak exists somewhere in the Hydro-Max and/or parking brake system which
allows air to reenter the system. Check for fluid leakage and repair or replace as necessary.
POWER
FLUID
(100-150 PSI)
FROM HR-4
RELAY VALVE
CAGE
ROLLER
WEDGE TUBE
BRAKE
BACIONG
SPRING BRAKE MATE TAPPET
PARKING ACTUATOR WITH LUCAS GIRLING EXPANDER
Most fluid leaks can be found by visual inspection, however the spring brake actuators can LEAK INTERNALLY INTO THE
EXPANDER unit of the Lucas Girling A2LS drumbrake. Internal, hydraulic spring brake leakage can not be detected visually
unless the actuator is removed from the expander and checked for “wetness” inside the wedge tube.
CAUTION: Thoroughly read the vehicle manufacturer's maintenance manual before attempting removal of the hydrau-
lic spring brake actuators. A VERY HIGH SPRING LOAD IS USED AND INJURY CAN RESULT FROM IMPROPER
HANDLING.
Input Tappet/Piston
MANUAL ADJUSTOR
BACKING
ADJUSTER PLATE Seal Posili
WHEEL EXPANDER/ eal Position
CYLINDER PARKING
WHEEL
CYLINDER O-Ring
3/4" TAPERED
LINING
AND SHOE
ASSEMBLY
Roller Tappet/
LINING
INSPECTION die SHOE Piston
HOLE URN
SPRINGS
Abutment
Tappet
TYPICAL LUCAS GIRLING A2LS BRAKE ASSY. LUCAS GIRLING EXPANDER
Both actuators should be checked for internal leakage. if evidence of internal leakage is found in either of the actuators,
it may be necessary to repair or replace all components containing BRAKE FLUID SEALS, that may have been exposed
to hydraulic fluid from the leaking spring brake actuator. The affected components are the: A2LS expander unit, A2LS
wheel cylinder and possibly the master cylinder. Drain, flush and replace the brake fluid in the service brake system to
eliminate any hydraulic fluid contamination.