1991 1999 ford explorer chilton User Manual

							Click to enlarge
If a leak occurs between the tubing and the tube nut, replace the hose assembly. If a leak occurs between the
tube nut and the pump outlet replace the plastic washer.
Check the fitting to determine whether the leak is between the tube and tube nut or between the tube
nut and pump outlet.
1. 
If the leak is between the tube nut and pump outlet check to be sure the nut is tightened to 30-40 ft.
lbs. Do not overtighten this nut.
2. 
If the leak continues or if the leak is between the tube and tube nut, remove the line.
3. 
Unscrew the tube nut and inspect the plastic seal washer. Replace the plastic seal washer when the
line is removed.
4. 
To aid in the assembly of the new plastic seal washer, a tapered shaft may be required to stretch the
washer so that it may be slipped over the tube nut threads.
5. 
If the rubber O-ring is damaged it cannot be serviced and the hose assembly will have to be replaced.
6. 
Connect the tube nut and torque to 30-40 ft. lbs.
7. 
CAUTION
The quick connect fitting may disengage if not fully assembled, if the snapring is missing or if the tube nut or
hose end is not machined properly. If the fitting disengages replace the hose assembly. The fitting is fully
engaged when the hose will not pull out. To test for positive engagement the system should be properly filled,
the engine started and the steering wheel turned from stop to stop.
Chilton® Automotive Information Systems. © 2004 Thomson Delmar Learning. HOW TO USE THIS BOOK
QUICK-CONNECT PRESSURE LINE 967 
						

							
SPECIFICATION CHARTS
Torque SpecificationsClick to enlarge
SPECIFICATION CHARTS 969 
						

							
BRAKE OPERATING SYSTEM
Basic Operating Principles
Hydraulic systems are used to actuate the brakes of all modern automobiles. The system transports the power
required to force the frictional surfaces of the braking system together from the pedal to the individual brake
units at each wheel. A hydraulic system is used for two reasons.
First, fluid under pressure can be carried to all parts of an automobile by small pipes and flexible hoses
without taking up a significant amount of room or posing routing problems.
Second, a great mechanical advantage can be given to the brake pedal end of the system, and the foot pressure
required to actuate the brakes can be reduced by making the surface area of the master cylinder pistons
smaller than that of any of the pistons in the wheel cylinders or calipers.
The master cylinder consists of a fluid reservoir along with a double cylinder and piston assembly. Double
type master cylinders are designed to separate the front and rear braking systems hydraulically in case of a
leak. The master cylinder coverts mechanical motion from the pedal into hydraulic pressure within the lines.
This pressure is translated back into mechanical motion at the wheels by either the wheel cylinder (drum
brakes) or the caliper (disc brakes).
Steel lines carry the brake fluid to a point on the vehicles frame near each of the vehicles wheels. The fluid is
then carried to the calipers and wheel cylinders by flexible tubes in order to allow for suspension and steering
movements.
In drum brake systems, each wheel cylinder contains two pistons, one at either end, which push outward in
opposite directions and force the brake shoe into contact with the drum.
In disc brake systems, the cylinders are part of the calipers. At least one cylinder in each caliper is used to
force the brake pads against the disc.
All pistons employ some type of seal, usually made of rubber, to minimize fluid leakage. A rubber dust boot
seals the outer end of the cylinder against dust and dirt. The boot fits around the outer end of the piston on
disc brake calipers, and around the brake actuating rod on wheel cylinders.
The hydraulic system operates as follows: When at rest, the entire system, from the piston(s) in the master
cylinder to those in the wheel cylinders or calipers, is full of brake fluid. Upon application of the brake pedal,
fluid trapped in front of the master cylinder piston(s) is forced through the lines to the wheel cylinders. Here,
it forces the pistons outward, in the case of drum brakes, and inward toward the disc, in the case of disc
brakes. The motion of the pistons is opposed by return springs mounted outside the cylinders in drum brakes,
and by spring seals, in disc brakes.
Upon release of the brake pedal, a spring located inside the master cylinder immediately returns the master
cylinder pistons to the normal position. The pistons contain check valves and the master cylinder has
compensating ports drilled in it. These are uncovered as the pistons reach their normal position. The piston
check valves allow fluid to flow toward the wheel cylinders or calipers as the pistons withdraw. Then, as the
return springs force the brake pads or shoes into the released position, the excess fluid reservoir through the
compensating ports. It is during the time the pedal is in the released position that any fluid that has leaked out
of the system will be replaced through the compensating ports.
Dual circuit master cylinders employ two pistons, located one behind the other, in the same cylinder. The
primary piston is actuated directly by mechanical linkage from the brake pedal through the power booster.
BRAKE OPERATING SYSTEM 971 
						

							
The secondary piston is actuated by fluid trapped between the two pistons. If a leak develops in front of the
secondary piston, it moves forward until it bottoms against the front of the master cylinder, and the fluid
trapped between the pistons will operate the rear brakes. If the rear brakes develop a leak, the primary piston
will move forward until direct contact with the secondary piston takes place, and it will force the secondary
piston to actuate the front brakes. In either case, the brake pedal moves farther when the brakes are applied,
and less braking power is available.
All dual circuit systems use a switch to warn the driver when only half of the brake system is operational. This
switch is usually located in a valve body which is mounted on the firewall or the frame below the master
cylinder. A hydraulic piston receives pressure from both circuits, each circuits pressure being applied to one
end of the piston. When the pressures are in balance, the piston remains stationary. When one circuit has a
leak, however, the greater pressure in that circuit during application of the brakes will push the piston to one
side, closing the switch and activating the brake warning light.
In disc brake systems, this valve body also contains a metering valve and, in some cases, a proportioning
valve. The metering valve keeps pressure from traveling to the disc brakes on the front wheels until the brake
shoes on the rear wheels have contacted the drums, ensuring that the front brakes will never be used alone.
The proportioning valve controls the pressure to the rear brakes to lessen the chance of rear wheel lock-up
during very hard braking.
Warning lights may be tested by depressing the brake pedal and holding it while opening one of the wheel
cylinder bleeder screws. If this does not cause the light to go on, substitute a new lamp, make continuity
checks, and, finally, replace the switch as necessary.
The hydraulic system may be checked for leaks by applying pressure to the pedal gradually and steadily. If the
pedal sinks very slowly to the floor, the system has a leak. This is not to be confused with a springy or spongy
feel due to the compression of air within the lines. If the system leaks, there will be a gradual change in the
position of the pedal with a constant pressure.
Check for leaks along all lines and at wheel cylinders. If no external leaks are apparent, the problem is inside
the master cylinder.
DISC BRAKES
Instead of the traditional expanding brakes that press outward against a circular drum, disc brake systems
utilize a disc (rotor) with brake pads positioned on either side of it. An easily-seen analogy is the hand brake
arrangement on a bicycle. The pads squeeze onto the rim of the bike wheel, slowing its motion. Automobile
disc brakes use the identical principle but apply the braking effort to a separate disc instead of the wheel.
The disc (rotor) is a casting, usually equipped with cooling fins between the two braking surfaces. This
enables air to circulate between the braking surfaces making them less sensitive to heat buildup and more
resistant to fade. Dirt and water do not drastically affect braking action since contaminants are thrown off by
the centrifugal action of the rotor or scraped off the by the pads. Also, the equal clamping action of the two
brake pads tends to ensure uniform, straight line stops. Disc brakes are inherently self-adjusting. There are
three general types of disc brake:
A fixed caliper.
1. 
A floating caliper.
2. 
A sliding caliper.
3. 
The fixed caliper design uses two pistons mounted on either side of the rotor (in each side of the caliper). The
caliper is mounted rigidly and does not move. HOW TO USE THIS BOOK
972 Basic Operating Principles 
						

							
The sliding and floating designs are quite similar. In fact, these two types are often lumped together. In both
designs, the pad on the inside of the rotor is moved into contact with the rotor by hydraulic force. The caliper,
which is not held in a fixed position, moves slightly, bringing the outside pad into contact with the rotor.
There are various methods of attaching floating calipers. Some pivot at the bottom or top, and some slide on
mounting bolts. In any event, the end result is the same.
DRUM BRAKES
Drum brakes employ two brake shoes mounted on a stationary backing plate. These shoes are positioned
inside a circular drum which rotates with the wheel assembly. The shoes are held in place by springs. This
allows them to slide toward the drums (when they are applied) while keeping the linings and drums in
alignment. The shoes are actuated by a wheel cylinder which is mounted at the top of the backing plate. When
the brakes are applied, hydraulic pressure forces the wheel cylinders actuating links outward. Since these
links bear directly against the top of the brake shoes, the tops of the shoes are then forced against the inner
side of the drum. This action forces the bottoms of the two shoes to contact the brake drum by rotating the
entire assembly slightly (known as servo action). When pressure within the wheel cylinder is relaxed, return
springs pull the shoes back away from the drum.
Most modern drum brakes are designed to self-adjust themselves during application when the vehicle is
moving in reverse. This motion causes both shoes to rotate very slightly with the drum, rocking an adjusting
lever, thereby causing rotation of the adjusting screw. Some drum brake systems are designed to self-adjust
during application whenever the brakes are applied. This on-board adjustment system reduces the need for
maintenance adjustments and keeps both the brake function and pedal feel satisfactory.
WARNING
Clean, high quality brake fluid is essential to the safe and proper operation of the brake system. You should
always buy the highest quality brake fluid that is available. If the brake fluid becomes contaminated, drain and
flush the system, then refill the master cylinder with new fluid. Never reuse any brake fluid. Any brake fluid
that is removed from the system should be discarded.
Brake Light Switch
REMOVAL & INSTALLATION HOW TO USE THIS BOOK
DISC BRAKES 973 
						

							Stoplight switch mounting
Click to enlarge
Lift the locking tab on the switch connector and disconnect the wiring.
1. 
Remove the hairpin retainer, slide the stoplamp switch, pushrod and nylon washer off of the pedal.
Remove the washer, then the switch by sliding it up or down.
2. 
On some vehicles equipped with speed control, the spacer washer is replaced by the dump valve
adapter washer.
To install: Position it so that the U-shaped side is nearest the pedal and directly over/under the pin.
3. 
Slide the switch up or down, trapping the master cylinder pushrod and bushing between the switch
side plates.
4. 
Push the switch and pushrod assembly firmly towards the brake pedal arm. Assemble the outside
white plastic washer to the pin and install the hairpin retainer.
5. 
Dont substitute any other type of retainer. Use only the Ford specified hairpin retainer. Assemble the connector on the switch.
6. 
Check stoplamp operation.
7. 
Make sure that the stoplamp switch wiring has sufficient travel during a full pedal stroke.
Master Cylinder
REMOVAL & INSTALLATION HOW TO USE THIS BOOK
974 REMOVAL & INSTALLATION 
						

							Cutaway view of the master cylinder assembly
Click to enlarge
WARNING
Vehicles with 4-wheel anti-lock brakes require an Anti-lock Brake Adapter (T90P-50-ALA) and Jumper
(T93T-50-ALA) in order to bleed the master cylinder and the Hydraulic Control Unit (HCU). Failure to do
so will trap air in the HCU unit, eventually causing a spongy pedal.
Before performing this procedure, ensure that you have the tools necessary to bleed the master cylinder
and the HCU unit. If the tools are not available, you can still perform the procedure. However, you will
need to tow the vehicle to a professional garage capable of bleeding the ABS system.
With the engine turned off, push the brake pedal down to expel vacuum from the brake booster
system.
1. 
Disconnect the brake fluid level sensor wire from the reservoir.
2. 
Disconnect the hydraulic lines (use correct tool, a Line Wrench) from the brake master cylinder.
3. 
Remove the brake booster-to-master cylinder retaining nuts and lock washers. Remove the master
cylinder from the brake booster.
4.  HOW TO USE THIS BOOK
REMOVAL & INSTALLATION 975 
						

							To remove the master cylinder, first disconnect the fluid level sensor wire
Next, loosen the fluid line fittings at the master cylinder with a flarenut wrench ... ... then disconnect the lines
HOW TO USE THIS BOOK
976 REMOVAL & INSTALLATION 
						

							If equipped, remove any bracket retaining nuts ...
... and pull the bracket from the mounting stud
Remove the master cylinder-to-power booster attaching bolts ... HOW TO USE THIS BOOK
REMOVAL & INSTALLATION 977 
						

							... then pull the master cylinder off of the mounting studs and remove it from the vehicle.
To install:
Before installing the master cylinder, check the distance from the outer end of the booster assembly
push rod to the front face of the brake booster assembly. Turn the push rod adjusting screw in or out
as required to obtain the length shown. Refer to illustration in this Section.
5. 
Position the master cylinder assembly over the booster push rod and onto the 1 studs on the booster
assembly. Install the attaching nuts and lockwashers and tighten to 13-15 ft. lbs.
6. 
Connect the hydraulic brake system lines to the master cylinder.
7. 
Bleed the hydraulic brake system (refer to procedure in this Section). Centralize the differential valve.
Then, fill the dual master cylinder reservoirs with DOT 3 brake fluid to within  1
/4  in. (6mm) of the
top. Install the gasket and reservoir cover. Roadtest the vehicle for proper operation.
8. 
When replacing the master cylinder it is best to BENCH BLEED the master cylinder before installing it to the
vehicle. Mount the master cylinder into a vise or suitable equivalent (do not damage the cylinder). Fill the
cylinder to the correct level with the specified fluid. Block off all the outer brake line holes but one, then,
using a long tool such as rod position it in the cylinder to actuate the brake master cylinder. Pump (push tool
in and out) the brake master cylinder 3 or 4 times till brake fluid is release out and no air is in the brake fluid.
Repeat this procedure until all brake fluid is released out of every hole and no air is expelled.
Power Booster
REMOVAL & INSTALLATION
Make sure that the booster rubber reaction disc is properly installed if the master cylinder push rod is
removed or accidentally pulled out. A dislodged disc may cause excessive pedal travel and extreme
operation sensitivity. The disc is black compared to the silver colored valve plunger that will be exposed
after the push rod and front seal is removed. The booster unit is serviced as an assembly and must be
replaced if the reaction disc cannot be properly installed and aligned, or if it cannot be located within
the unit itself. HOW TO USE THIS BOOK
978 Power Booster