2007 FORD FIESTA Workshop Manual

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206-07-2 Power Brake Actuation 206-07-2
SPECIFICATIONS
Torque Specifications
I Brake master cylinder retaining nuts I 25 I 18 I - I
Description
Brake booster retaining nuts
2006.0 Fiesta 1212006 ~28531 en
Nm
25
Ib-ft
18
lb-in
-
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206-0713 Power Brake Actuation 206-0713
DESCRIPTION AND OPERATION
Brake Booster
Emergency brake assistant (EBA) EBA operates purely mechanically, and is
completely integral with the brakeservo.
As ABS braking systems have become widespread,
it has emerged that because of incorrect use of the
Brake servo units with and without EBA are
brakes, many drivers are losing the safety benefit externally identical. For identification purposes,
which ABS
~rovides. brake servo units with EBA carry a white sticker I showing a large letter "A. Drivers are applying the brakes too timidly.
Because of this, the Anti-lock Braking System The tandem master cylinder
is the same for
(ABS) does not engage, and the maximum braking
vehicles with or without
effect is not achieved.
The EBA recognises from the driver's manner of
braking that an emergency situation is occurring,
and automatically applies full braking power.
This occurs in a matter of milliseconds, which is
faster than the driver could do it.
Furthermore, it was observed that after the first
heavy application of the brake pedal, the driver
releases the pressure on the pedal too early.
The EBA ensures that the ABS effect still continues
when the pedal pressure would normally lie below
the ABS range of control. The system is available
j as an option depending on market and vehicle
variant.
Function
In normal braking situations, the brake servo with
EBA operates in the same way as a conventional
brake servo unit. This means that the driver can
always modulate the brakes.
If an activation threshold defined by a characteristic
curve is exceeded during braking, the EBA
operates.
Determination of the activation threshold is based
on the pedal movement parameters, which are a
function of the pressure on the brake pedal and
the speed of movement of the pedal.
Depending on driving manner, EBA results in a The characteristic curve
is separately defined for
reduction in braking distance of 15% for each vehicle model.
experienced drivers, to over
40% for average The mechanical EBA uses the fact that in a brake
drivers. servo unit, the valve piston moves ahead of the
Because EBA decelerates the vehicle up to the control housing
when a braking operation starts.
wheel locking limit, emergency brake assist is only Because of this, there is a relative travel distance used in vehicles with ABS.
between the control housing and the valve piston
which can vary depending on the force applied to
Components the brake pedal and the pedal speed.
The relative travel distance is small when the pedal
moves slowly with low force applied to it. The
relative travel distance is larger when the pedal
moves faster with higher force applied to it.
Item Description
-
2006.0 Fiesta 1212006 GI 63289en
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206-07-4 Power Brake Actuation 206-07-4
DESCRIPTION AND OPERATION
Item Descri tio on
I 1 I Relative travel distance I
r2 bontro~ housing I
1 3 (Valve piston I
Normal braking
2006.0 Fiesta 1212006 GI 63289en
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206-07-5 Power Brake Actuation 206-07-5
DESCRIPTION AND OPERATION
Item Description
1 3 I Valve piston I
i '
1 4 1 Ball I
1 5 1 ~ock sleeve I
I
2
1 6 1 Ball cage I
Ball sleeve
Control housing
Active brake assistant
In a normal braking operation, pedal operation
causes the relative travel distance to remain so
small that the distance required for engagement is
not exceeded.
The lock sleeve is held in its rest position by the
force applied by the spring, the ball cage remains
free to move axially and the balls remain free to
move radially.
Item Description
I 1 I Relative travel distance I
1 2 1 Disc valve I -
1 3 1 Key I
If the activation threshold level is.exceeded
because of an emergency braking situation, i.e.
the relative travel distance of the valve piston is so
great that the balls are moved in over the slope of
the ball sleeve, then the lock sleeve can move
completely to its end position.
I
--
The balls are now locked, and the ball sleeve can
no longer be moved in the closing direction of the
disc valve.
The EBA is now active, the brake pressure is
increased up to the wheel locking limit, and the
brake pedal can be moved to its maximum
pressure point without effort.
The brake pressure remains at the ABS control
limit until the EBA is completely released again.
2006.0 Fiesta 1212006 GI 63289en
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206-0716 Power Brake Actuation 206-0716
DESCRIPTION AND OPERATION
Release of the brake assistant
Item Description
I I I ~ock sleeve I
1 3 IVacuum cylinder I
To release EBA, the brake pedal must be fully
released,
i.e. it must be returned to its rest position.
When this occurs, the control housing together with
the valve piston move back into the rest position.
The key is pressed against the stop on the vacuum
cylinder and by this the lock sleeve is slid back into
its rest position.
The balls can again be moved outward by the ball
sleeve, and the ball cage is again free to move
axially and the balls free to move radially.
Service
It is not possible to repair the EBA. A new brake
servo unit must be installed.
2006.0 Fiesta 12/2006 GI 63289en
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206-0717 Power Brake Actuation 206-07-7
DIAGNOSIS AND TESTING
Power Brake System
( , REFER to Section 206-00 [Brake System -
General Information].
2006.0 Fiesta 1212006 GI 751 9en
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206-07-8 Power Brake Actuation 206-07-8
REMOVAL AND INSTALLATION
Brake Booster - RHD(12 451 0)
Removal 2. Remove the brake booster actuating rod pin. (
1. Remove the brake master cylinder.
For additional information, refer to: Brake
Master Cylinder
- RHD (206-06 Hydraulic
Brake Actuation, Removal and Installation).
2. Disconnect the brake vacuum pipe from the
brake booster.
I. Unclip the brake vacuum pipe.
2. Disconnect the brake vacuum pipe.
3. Remove the instrument panel lower panel.
1. Remove the lower retaining screws.
2. Remove the upper retaining screws from the
stowage compartment.
3. Release the retaining clip. 5.
Remove
the brake booster.
Discard the gasket.
Installation
1. WARNINGS:
ADO not install an Emergency Brake Assist
(EBA) brake booster to a vehicle that is not
equipped with the Anti-lock Brake System
(ABS). Failure to follow this instruction may
result in personal injury.
ADO not use a damaged brake pedal.
Failure to follow this instruction may result
in personal injury.
4. Detach the brake booster actuating rod from CAUTIONS:
the brake pedal (accelerator pedal shown A Make sure that the brake booster gasket
removed for clarity).
is correctly positioned on the brake
I. Depress the clip. booster before installation. 41
A Do not drop or knock the brake pedal.
Failure to follow this instruction will cause
damage to the brake pedal decoupler
mechanism (if equipped).
2006.0 Fiesta 12/2006 G89214en
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