Tandem Master Cylinder Notes

Tandem Master Cylinder

Introduction

  • Basic master cylinders pose a risk: a single fluid loss due to component failure can lead to complete brake system failure.
  • Modern vehicles are equipped with at least two separate hydraulic systems to mitigate this risk.
  • The tandem master cylinder was created to fulfill the requirement of having two separate hydraulic systems.

Structure and Function

  • Functions like two single-piston cylinders placed end-to-end.
  • Contains a primary and a secondary piston.
  • Each section of the cylinder includes:
    • Inlet and outlet ports
    • Compensating ports
  • Reservoirs:
    • Can have two separate reservoirs.
    • Can have a single reservoir divided into separate sections.

Operation

  • Brake application:
    1. The primary piston moves, closing its compensating port.
    2. Fluid pressure increases, acting on the secondary piston.
    3. The secondary piston moves, closing its compensating port and circuit pressure builds up.
    4. Both pistons move, displacing fluid into their respective circuits, activating the brakes.

Failure Scenarios

  • Secondary circuit failure:
    • The primary system continues to operate but requires increased travel.
  • Primary circuit failure:
    • No pressure is generated to move the secondary piston.
    • A rod attached to the primary piston pushes the secondary piston directly to maintain operation.

Warning Systems

  • Switches are used to detect:
    • Pressure loss in the front or rear circuits.
    • Low fluid level in the reservoir.

Addressing Low Pressure Issues

  • Single-piston master cylinders may experience low pressure when the piston returns rapidly while the fluid lags.
  • The tandem master cylinder resolves this using grooves in the primary cup's side.
  • These grooves allow fluid to flow from the inlet port into the low-pressure area.

System Configuration and Reservoir Size

  • Two operating systems activated by one unit.
  • Front and rear brakes are controlled separately using the cylinder.
  • Reservoir size indicates brake type:
    • Larger reservoir: typically indicates disc brakes.
    • Smaller reservoir: typically indicates drum brakes.
  • Most common configuration: disc brakes in the front, drum brakes in the rear.
  • Disc brakes usually have a larger reservoir because they require more fluid as the pads wear.
  • Drum brakes, on the other hand, do not have a change in reservoir level as the pads wear.

Identifying Dual Systems

  • All modern systems have dual systems, but you sometimes need to look inside to confirm how it's broken up.
  • It's usually easier to check the wheels to determine the brake setup.

Design Variations

  • There are different designs based on the manufacturer.
  • Manufacturers create distinct designs to differentiate their vehicles.
  • Some designs may include a sensor at the bottom to warn of low fluid level.

Material and Construction

  • Master cylinders are now fairly light.
  • They're often made of aluminum.
  • Compensating ports are included by design.

Seal Failure

  • If the brake pedal slowly sinks to the floor while holding pressure, it typically indicates the seals are damaged.
  • Seals:
    • Keep air and moisture out to keep the system closed.

Proper Fluid Levels

  • Fluid should be filled to the correct level during brake jobs, not above it.
  • Overfilling can lead to issues under real hot conditionsconditions.