Opel Frontera UBS. Manual - part 2054

 

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Opel Frontera UBS. Manual - part 2054

 

 

5C – 28 POWER ASSISTED BRAKE SYSTEM

P & B (PROPORTIONING AND BYPASS) VALVE

Master cylinder
    (Primary)

Master cylinder
    (Secondary)

Rear brake

Front brake

INSTALLATION

To install, follow the removal steps in the reverse
order, noting the following points. After installing the
brake pipes, bleed brakes as described in this section.
1. Tighten the brake pipes to the specified torque.

Brake Pipe Torque

N·m(kg·m/lb·ft)

Master Cylinder Side

Others

12 (1.2/9)

16 (1.6/12)

The P & B valve contains two sections, each serving a
different function.
The proportioning section of the P & B valve
proportions outlet pressure to the rear brakes after a
predetermined rear input pressure has been reached.
This is done to prevent rear wheel lock-up on the
vehicles with light rear wheel loads.
The valve has a By-bass feature which assures full
system pressure to the rear brakes in the event of a
font brake mulfunction, also full front pressure is
retained in the event of rear brake mulfunction.
The P & B valve is not repairable and must be
replaced as a complete assembly.

POWER ASSISTED BRAKE SYSTEM  5C – 29

P & B VALVE REPLACEMENT

1

3

1

  

2

Removal Steps

1.

Hydraulic pipes

2.

Bolt

3.

P & B valve

Installation Steps

To install, follow the removal steps in the
reverse order.

REMOVAL

P & B valve is not repairable and must be
replaced as a complete assembly.

Care must be taken to prevent brake fluid from
contacting any painted surface.

1. Hydraulic Pipes

Plug the pipes to prevent the loss of fluid or the
entrance of dirt.

2. Bolt

3. P & B Valve

INSTALLATION

3. P & B Valve

2. Bolt

Bolt Torque

N·m(kg·cm/lb·in)

13 (130/113)

1. Hydraulic Pipes

Hydraulic Pipe Torque

N·m(kg·m/lb·ft)

16 (1.6/12)

After installing the brake pipes, bleed brakes as
described in Bleeding Brake Hydrauric System this
section.

5C – 30 POWER ASSISTED BRAKE SYSTEM

LOAD SENSING PROPORTIONING VALVE (LSPV)
(FOR EUROPE AND SOUTH AFRICA)

to rear wheel cylinder

from front master cylinder

from rear master cylinder

Structure and Operation

The following is an explanation of the structure and
operation of the linkage type load sensing device.
This device controls the fluid pressure to the rear
brakes in accordance with changes in rear axle load
(vertical displacements of the rear axle springs).

Structure

This device consists of a load sensing lever and a
valve.

The valve is mounted through a bracket to the
frame. One end of the load sensing lever is fixed
to the valve at the frame and the other end to the
rear axle housing through a spring.

F05RW003

POWER ASSISTED BRAKE SYSTEM  5C – 31

Operation

1) Outline

When the L.S.P.V. (Load Sensing Proportioning
Valve) detects a change in load weight, the load
sensing lever moves. Its reaction force is
transmitted to the bottom of the load sensing
valve to secure an optimum rear wheel cylinder
fluid pressure break point in proportion to the
actual load weight.
Besides, if the front brake system should fail, the
devices is designed to prevent the master cylinder
fluid pressure from decreasing and to apply it
directly to the rear wheel cylinder to obtain a
sufficient braking performance.

From rear
master cylinder

2) Operation

(1) When the fluid pressure is under the break point.

The fluid pressure of the rear master cylinder
passes through a clearance between the valve
seal and the piston and acts on the rear wheel
cylinder. At this moment, a downward force is
applied to the piston. However, the compression
spring force and reaction force of the load sensing
lever keep the piston in the upper position by
pushing upwards. (See the left figure.)

To rear
wheel cylinder

(2) When the fluid pressure is equal to the break

point.
As the rear wheel cylinder pressure increases, it
surpasses the compression spring force and
reaction force of the load sensing lever, causing
the pistion to move downwards, so that the
pistion butts against the valve seal to shut off the
fluid line between the master cylinder and rear
wheel cylinder. (See the left figure.)

(3) When the fluid pressure is over the break point.

When the fluid pressure increases further, the
piston moves upwards. The moment the piston
comes apart from the valve seal, fluid pressure is
applied to the rear wheel cylinder and the piston
moves downwards so that the fluid line is shut off
again. This process goes on repeatedly to control
the fluid pressure to the rear wheel cylinder.

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