Test and Service Equipment for Brake Systems

Frequently Asked Questions About Brake System Inspection and Maintenance

Brake systems consist of mechanical, hydraulic, pneumatic, and—increasingly—electronically monitored components. For reliable diagnosis and maintenance, it is therefore necessary to check the brake fluid, system pressure, system integrity, and bleeding, depending on the vehicle. Here, we answer frequently asked questions about the professional inspection and maintenance of brake systems in passenger cars, commercial vehicles, and machinery.

• What tests can be performed on a braking system?

  Depending on the vehicle and brake system, different inspection and maintenance tasks may be required.

  These include, for example:

  • Check the condition of the brake fluid
  • Change the brake fluid
  • Bleed the brake system
  • Measure hydraulic brake pressure
  • Check pneumatic brake pressure
  • Compare pressure differences between brake circuits
  • Check the brake system for leaks
  • Checking or adjusting the brake force regulator
  • Inspecting brake lines and connections

  Brake fluid testers, brake bleeding units, brake pressure testers for passenger cars, and brake pressure testers for commercial vehicles, agricultural vehicles, and off-highway vehicles are available for these tasks.

• Why does brake fluid need to be checked regularly?

  Many commercially available glycol-based brake fluids are hygroscopic and absorb moisture over time.
  
  As the water content increases, the boiling point of the brake fluid decreases. Under high thermal stress, this can lead to the formation of vapor bubbles more easily.
  
  In addition, moisture can promote corrosion within the hydraulic brake system.
  
  Therefore, the condition of the brake fluid should be checked regularly in accordance with the vehicle manufacturer’s specifications.

• Does brake fluid always need to be changed every two years?

  There is no one-size-fits-all answer.

  The recommended change interval depends on the vehicle manufacturer, vehicle model, and type of brake fluid used.

  Many manufacturers specify regular, time-based change intervals. However, the maintenance specifications for the vehicle in question are always the deciding factor.

  An additional brake fluid test can provide information about water content or boiling point.

• What happens if the brake fluid contains too much water?

  As the water content increases, the boiling point of the brake fluid decreases.
  
  Under heavy braking, this can cause vapor bubbles to form at lower temperatures.
  
  Since gas, unlike brake fluid, is compressible, this can impair hydraulic power transmission.
  
  Moisture can also promote corrosion within the brake system.

• What types of brake fluid are there?

  Various specifications are used in the automotive sector.

  These include, for example:

  • DOT 3
  • DOT 4
  • DOT 4 Plus
  • low-viscosity DOT 4 formulations
  • DOT 5.1

  Silicone-based DOT 5 differs fundamentally from the standard glycol-based DOT 3, DOT 4, and DOT 5.1 fluids.

  Only the brake fluid specified by the vehicle manufacturer may be used.

• How can you check the condition of the brake fluid?

  Depending on the testing device, it is possible, for example, to assess the water content or, by extension, the condition of the brake fluid.
  
  The Leitenberger EBT 03.3, for example, displays water content, boiling point, and a replacement recommendation, and supports various current DOT-3, DOT-4, and DOT-5.1 brake fluids.
  
  To ensure an accurate test, the correct brake fluid type must be selected on the device, or the specified test procedure must be followed.

• What is the difference between checking the brake fluid and changing the brake fluid?

  During the inspection, the current condition of the existing brake fluid is first assessed.

  When changing the brake fluid, the old fluid is removed or flushed from the system and replaced with new, suitable brake fluid.

  Brake bleeding units are available for professional fluid changes.

• Why does a brake system need to be bled?

  Air in the hydraulic brake system is undesirable because air is compressible.
  
  This can alter the pedal feel and impair hydraulic power transmission.
  
  Air can enter the system, for example, after the brake system has been opened, when hoses or components are replaced, or as a result of improper service work.

• How does a professional brake bleeder work?

  A brake bleeder tool feeds new brake fluid into the brake system at a specified operating pressure via the brake fluid reservoir.
  
  At the designated bleed points, the old brake fluid is drained from the system in a controlled manner along with any trapped air.
  
  Suitable tools thus enable a continuous and controlled brake fluid change.

• Why are different brake bleed adapters needed?

  Brake fluid reservoirs vary by vehicle manufacturer and model in terms of:

  • Thread
  • Reservoir opening
  • Cap
  • Diameter
  • Connection geometry

  The adapter must therefore fit the respective reservoir securely and be pressure-tight.

  Leitenberger offers various brake bleed adapters and adapter sets for this purpose.

• When is the brake pressure measured?

  Measuring brake pressure can be particularly useful in the event of operational problems or for further diagnosis.

  Possible reasons include, for example:

  • uneven braking performance
  • suspected hydraulic problem
  • testing the brake force regulator
  • comparison of two brake circuits
  • unreasonable braking behavior
  • testing pneumatic commercial vehicle brake systems

  The testing procedure differs significantly between hydraulic passenger car brake systems and pneumatic commercial vehicle brake systems.

• What is the difference between brake pressure testing for passenger cars and commercial vehicles?

  Hydraulic braking systems are predominantly used in passenger cars.

  Relatively high fluid pressures are generated here. Leitenberger passenger car testers therefore use, for example, high-pressure manometers rated up to 250 bar.

  In contrast, heavy-duty commercial vehicles, trailers, and various agricultural and off-highway applications use pneumatic brake systems.

  This requires special brake pressure testers for pneumatic brake systems with a correspondingly lower pressure range.

• Why are two brake circuits measured simultaneously in passenger cars?

  For safety reasons, modern hydraulic brake systems have separate brake circuits.
  
  Using a test device with two pressure gauges, both circuits can be measured simultaneously under the same conditions.
  
  This allows pressure differences to be compared directly with one another.
  
  This can be helpful when troubleshooting or testing brake force regulators.

• Can an electronic vehicle diagnostic system replace a brake pressure measurement?

  Not entirely.
  
  A diagnostic system can provide error codes, sensor signals, and electronic system information.
  
  Mechanical pressure measurement, on the other hand, shows the actual hydraulic or pneumatic pressure present in the brake system.
  
  In cases of complex fault patterns, electronic and mechanical diagnostics can therefore complement each other effectively.

• Can a brake system be checked for leaks?

  Yes.
  
  Depending on the brake system and test procedure, different leak tests can be performed.
  
  Leitenberger, for example, offers a digital leak tester for a drained brake system. With this device, a test gas can be introduced, and the pressure drop can then be monitored.
  
  The procedure must be performed using appropriate equipment and in accordance with the respective equipment and manufacturer specifications.

• What tools are needed for brake service?

  In addition to testing and bleeding tools, other specialized tools may be required depending on the repair.

  These include, for example:

  • Brake line cutting tools
  • Brake line clamps
  • Tools for preparing wheel hubs
  • Suitable adapters and connectors

  You can find these in the Tools for Brake Installation and Service section.

• What kind of brake testing equipment is suitable for a professional auto repair shop?

  The following items may be particularly useful for a multi-brand repair shop:

  • Brake fluid tester
  • Brake bleeder
  • A suitable assortment of brake adapters
  • Brake pressure tester for hydraulic brake systems
  • For commercial vehicles, a tester for air brakes
  • Appropriate installation and brake line tools

  The equipment required depends on the vehicle fleet and the brake services offered.