1991 FORD SIERRA four wheel drive

Torque wrench settingsNmlbf ft
Caliper carrier bracket-to-hub carrier bolts . . . . . . . . . . . . . . . . . . . . . .51 to 6138 to 45
Front caliper guide bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 to 2515 to 18
Rear caliper guide bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 to 3523 to 26
Rear brake backplate nuts - P100 models . . . . . . . . . . . . . . . . . . . . . . .45 to 5433 to 40
Servo-to-bulkhead nuts (conventional braking system) . . . . . . . . . . . . .35 to 4526 to 33
Master cylinder-to-servo nuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 to 2515 to 18
Hydraulic unit-to-bulkhead nuts (ABS) . . . . . . . . . . . . . . . . . . . . . . . . . .41 to 5130 to 38
Hydraulic unit accumulator (ABS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 to 4625 to 34
Pump mounting bolt (ABS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 to 95 to 7
High pressure hose-to-pump union (ABS) . . . . . . . . . . . . . . . . . . . . . . .7 to 125 to 9
Wheel sensor mounting bolts (ABS) . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 to 116 to 8
General information
The braking system is of the dual circuit
hydraulic type. The front and rear circuits are
operated independently from a tandem
master cylinder, so that in the event of a
hydraulic failure in one circuit, full braking
force will still be available to two wheels
through the remaining circuit.
A deceleration sensitive valve on Saloon,
Hatchback and Estate models not fitted with
an Anti-lock Braking System (ABS), and a load
apportioning valve on P100 models, is
incorporated in the rear brake hydraulic
circuit. The valve regulates the pressure
applied to the rear brakes and reduces the
possibility of the rear wheels locking under
heavy braking.
All models are fitted with front disc brakes,
with solid or ventilated discs depending on
model. The calipers are of single piston sliding
type, which ensures that equal pressure is
applied to each disc pad.
Non-ABS models are fitted with rear disc
brakes or rear drum brakes, incorporating
leading and trailing shoes operated by
double-acting wheel cylinders. A self-adjuster
mechanism is fitted which consists of a
toothed quadrant which is kept in contact with
a toothed pin attached to the shoe strut by
means of a spring. The quadrant incorporates
an arm which locates in a slot in the leading
shoe. As the shoe linings wear the quadrant is
pulled from the pin when the footbrake is
operated, and automatically repositioned to
effectively lengthen the shoe strut.
ABS is available as an option for all models
except the P100. The system comprises an
electronic control unit, roadwheel sensors,
hydraulic actuator with electrically-driven
hydraulic pump, and the necessary valves and
switches. Disc brakes are fitted to all four
wheels. The front disc brakes are similar to
those fitted to non-ABS models, but the rear
brakes incorporate a self-adjusting
mechanism, and a mechanical handbrake
mechanism. The purpose of the system is to
prevent wheel(s) locking during heavy brake
applications. This is achieved by automatic
release of the brake on the locked wheel,followed by reapplication of the brake. This
procedure is carried out four times per second
by the control valves in the valve block. The
valves are controlled by the electronic control
unit which itself receives signals from the
wheel sensors, which monitor the locked or
unlocked state of the wheels. A pressure
regulating valve is incorporated in the rear
hydraulic circuit to maintain the desired
pressure ratio between the front and rear
circuits.
Precautions
Note: Hydraulic fluid is poisonous; wash off
immediately and thoroughly in the case of skin
contact and seek immediate medical advice if
any fluid is swallowed or gets into the eyes.
Certain types of hydraulic fluid are
inflammable and may ignite when allowed into
contact with hot components; when servicing
any hydraulic system it is safest to assume
that the fluid is inflammable and to take
precautions against the risk of fire as though it
is petrol that is being handled. Hydraulic fluid
is also an effective paint stripper and will
attack plastics; if any is spilt, it should be
washed off immediately using copious
quantities of fresh water. Finally, it is
hygroscopic (it absorbs moisture from the air)
old fluid may be contaminated and unfit for
further use. When topping-up or renewing the
fluid, always use the recommended type and
ensure that it comes from a freshly-opened
sealed container
Note: When working on the brake
components, take care not to disperse brake
dust into the air, or to inhale it, since it may
contain asbestos which is injurious to health.
General
1If any of the hydraulic components in the
braking system have been removed or
disconnected, or if the fluid level in the
reservoir has been allowed to fall appreciably,
it is inevitable that air will have been
introduced into the system. The removal of all
this air from the hydraulic system is essential
if the brakes are to function correctly, and the
process of removing it is known as bleeding.
2Where an operation has only affected one
circuit (front or rear) of the hydraulic system,
then it will only be necessary to bleed the
relevant circuit. If the master cylinder has
been disconnected and reconnected, or the
fluid level has been allowed to fall
appreciably, then the complete system must
be bled.
3One of three methods can be used to bleed
the system.
Bleeding
Two-man method
4Gather together a clean jar and a length of
rubber or plastic bleed tubing which will fit the
bleed screws tightly. The help of an assistant
will be required.
5Remove the dust cap where fitted, and
clean around the bleed screw on the relevant
caliper or wheel cylinder, then attach the
bleed tube to the screw (see illustration). If
the complete system is being bled, start at the
front left-hand caliper.
6Check that the fluid reservoir is topped up
and then destroy the vacuum in the brake
servo by giving several applications of the
brake pedal.
7Immerse the open end of the bleed tube in
the jar which should contain two or three
inches of hydraulic fluid. The jar should be
positioned about 300 mm (12.0 in) above the
bleedscrew to prevent any possibility of air
entering the system down the threads of the
bleed screw when it is slackened.
2Brake hydraulic system
(conventional braking system)
- bleeding1General information and
precautions
10•2Braking system
2.5 Removing the dust cap from a wheel
cylinder bleed screw
Caution: Refer to the
precautions in Section 1.

3Remove the wheel cylinder.
4Remove the driveshaft but do not refit the
securing bolts to the backplate.
5Remove the backplate.
6If required, prise out the handbrake stop
button.
7Refitting is a reversal of removal.
P 100 models
Note: When refitting the backplate, a new rear
hub nut and driveshaft O-ring must be used.
8Proceed as described in paragraphs 1 to 3
inclusive.
9Remove the driveshaft.
10Relieve the staking on the rear hub nut,
and using a 50 mm socket and a suitable
extension bar, unscrew the nut. Note that the
nut is extremely tight.
11Pull off the hub.
12Unscrew the six retaining nuts and
remove the backplate and the oil baffle (see
illustration).
13If required, prise out the handbrake stop
button.
14Refitting is a reversal of removal, bearing
in mind the following points.
15When refitting the backplate and the oil
baffle, coat the area of the oil baffle shown
(see illustration - Chapter 9) with sealant to
Ford spec SPM-4G-9112-F, then refit the
baffle and the backplate to the axle, tightening
the six securing nuts to the specified torque.
16Use a new rear hub nut, and tighten to the
specified torque. Stake the nut into the groove
in the axle tube after tightening.
17Refit the driveshaft, using a new O-ring.
Note: A suitable puller will be required to
remove the drive flange, and a new rear hub
nut must be used on reassembly.
Removal
1Loosen the rear hub nut with the vehicle
resting on its wheels. Note that the left-hand
nut has a left-hand thread, ie it is undone in a
clockwise direction. Before loosening the nut,
ensure that the handbrake is applied, and
chock the relevant rear wheel. A suitable
extension bar will be required, as the nut is
extremely tight.
2Loosen the relevant rear roadwheel nuts,
chock the front wheels, then jack up the rear
of the vehicle and support on axle stands (see
“Jacking and Vehicle Support”).Remove the
roadwheel and release the handbrake.
3Free the handbrake cable from its clip on
the suspension lower arm.
4Unscrew the two caliper carrier
bracket-to-hub carrier bolts, and remove the
caliper, supporting it on an axle stand to avoid
straining the flexible hose.
5Mark the position of the brake disc in
relation to the drive flange, remove the
retaining spire washer(s), and remove the
disc.
6Unscrew and remove the rear hub nut, and
using a suitable puller, pull off the drive flange.
7Unscrew the four bolts securing the hub
carrier and splash shield to the lower arm.
Remove the hub carrier and splash shield,
whilst supporting the driveshaft. Support the
driveshaft by placing axle stands underneath
it, or by securing with string to the underbody.
Avoid bending the driveshaft joints to
excessive angles, and do not allow the shaft
to hang down from one end.
Refitting
8Refitting is a reversal of removal, bearing in
mind the following points.
9When reassembling the drive flange and the
hub carrier, fit the drive flange to the hub
carrier in order to centralise the bearings, then
using a soft-faced mallet, drive the drive
flange/hub carrier assembly onto the end of
the stub axle.10Refit the hub carrier/splash
shield-to-lower arm securing bolts. Note that
there are two types of bolts used to secure
the rear hub carrier to the lower arm. The two
types of bolt must not be mixed on a vehicle
but can be changed in complete sets for the
alternative type. A complete set is eight bolts,
four each side. Note that the two types of bolt
have different torque wrench settings. When
renewing the wheel bearings a suitable puller
will be required to remove the drive flange,
and a new rear hub nut must be used on
reassembly.
11When refitting the brake disc, align the
previously made marks on disc and drive
flange.
12Fit a new rear hub nut of the correct type,
and tighten it with the vehicle resting on its
roadwheels. Apply the handbrake and chock
the relevant rear wheel when finally tightening
the hub nut.
Note: Before commencing overhaul obtain a
repair kit containing new pistons and seals.
Removal
1Depress the brake pedal several times to
dissipate the vacuum in the servo.
2Disconnect the wiring plug from the low
fluid level switch on the fluid reservoir cap
(see illustration).
3Place a suitable container beneath the
master cylinder, then unscrew the union nuts
and disconnect the two fluid pipes. Plug the
ends of the pipes to prevent dirt ingress.
13Master cylinder (conventional
braking system) - removal,
overhaul and refitting
12Rear disc splash shield -
removal and refitting
Braking system 10•13
10
13.2 Disconnect the wiring plug from the low fluid level switch
(arrowed)11.12 Brake backplate and oil baffle retaining nuts
Caution: Refer to the
precautions in Section 1.
Caution: Refer to the
precautions in Section 1.