Brake Pressure Testers for Passenger Cars

Frequently Asked Questions About Brake Pressure Measurement in Passenger Cars

Unusual braking behavior cannot always be explained by visual inspection or electronic diagnostics alone. A mechanical brake pressure test shows the actual hydraulic pressure built up in the brake system and allows for a direct comparison of the brake circuits. Here, we answer common questions about professional brake pressure testing for passenger cars.

• What is the brake pressure in a passenger car?

  When the brake pedal is pressed, the pedal force is converted into hydraulic pressure by the master cylinder.
  
  This pressure is transmitted to the wheel brakes via the brake fluid.
  
  Brake pressure is therefore an important mechanical parameter for assessing the hydraulic function of the braking system.

• When should brake pressure be measured?

  A mechanical brake pressure measurement can be particularly useful during further troubleshooting.

  Possible reasons for diagnosis include:

  • Variations in braking performance
  • Abnormal pressure build-up
  • Suspected hydraulic problem
  • Testing a brake force regulator
  • Comparison of the two brake circuits
  • Unreasonable braking behavior
  • Verification of electronic diagnostic values against a mechanical measurement

  The measurement should always be performed in accordance with the specified test procedure and the vehicle manufacturer’s instructions.

• Why does a car have two brake circuits?

  For safety reasons, passenger car braking systems are divided into separate hydraulic brake circuits.
  
  If one part of the system fails, this is generally intended to ensure that braking force is still available through the other circuit.
  
  The exact configuration of the brake circuits depends on the specific vehicle design.

• Why are both brake circuits measured at the same time?

  Simultaneous measurement allows the pressure curves or pressures of both brake circuits to be compared under the same operating conditions.
  
  This makes it easier to detect deviations.
  
  Depending on the model, Leitenberger’s BDP and BDPD testers are equipped with two or more high-pressure gauges for this purpose.

• How is brake pressure measured mechanically?

  The test device is connected to the designated test points on the hydraulic brake system using appropriate high-pressure hoses and adapters.
  
  The brake system is then actuated according to the specified procedure.
  
  The pressure gauges display the actual hydraulic pressure built up.
  
  The measurement results must be compared with the specifications or target values for the vehicle in question.

• Where is a brake pressure tester connected?

  The exact measurement point depends on the vehicle and the test procedure.
  
  Leitenberger offers various BDA connection adapters with different threads for this purpose.
  
  This allows the test device to be connected to suitable hydraulic connection points on the brake system.
  
  The correct measurement point must be determined based on the vehicle or test specifications.

• What is the normal brake pressure for a passenger car?

  There is no universal brake pressure that applies to all passenger cars.

  The actual pressure generated depends, among other things, on:

  • Vehicle
  • Brake system
  • Pedal force
  • Brake booster
  • Operating conditions
  • Measurement point

  Therefore, the measured value must always be evaluated based on the manufacturer’s or testing specifications.

• Does a 250-bar pressure gauge mean that the brake system must operate at 250 bar?

  No.
  
  The pressure gauge's measurement range simply indicates the pressure range that the testing device can measure.
  
  It is not a target value for the vehicle.
  
  The actual expected brake pressure depends on the specific brake system and the prescribed test procedure.

• Was kann ein unterschiedlicher Druck in beiden Bremskreisen bedeuten?

  A noticeable pressure difference can have various causes.

  Depending on the braking system, possible causes include:

  • hydraulic malfunction
  • problem with the master cylinder
  • line or hose problem
  • brake force control
  • restricted flow
  • defective component in the affected brake circuit

  The pressure measurement initially reveals the deviation. The actual cause must then be systematically diagnosed.

• Can you test the master cylinder with a brake pressure tester?

  A pressure measurement can provide important information about hydraulic function and pressure build-up.
  
  However, further testing is required to determine whether an abnormal measurement is actually caused by the master cylinder.
  
  Brake pressure measurement is therefore a diagnostic tool and not an automatic component test that provides a clear “pass/fail” result.

• Can a faulty brake hose be detected by measuring the pressure?

  A mechanical pressure measurement can provide indications of unusual pressure conditions.
  
  A damaged or internally restricted brake hose can affect hydraulic performance.
  
  However, a definitive diagnosis also requires an inspection of the affected hose and, if necessary, further testing.

• What is a brake force regulator?

  A brake force regulator controls the hydraulic brake pressure or its distribution, depending on the specific vehicle system.
  
  For older vehicles or those with a corresponding design, a mechanical test or adjustment may be required.
  
  The Leitenberger BDP and BDPD testers are also designed for testing and adjusting such brake force regulators.

• Can the brake booster also be tested?

  With the appropriate equipment, the vacuum in the brake booster can also be tested.
  
  The analog BDP 06, for example, features a vacuum gauge in addition to the two high-pressure gauges.
  
  This allows hydraulic brake pressure measurement and vacuum testing of the brake booster to be combined using a single test kit.

• What is the difference between brake pressure and vacuum at the brake booster?

  Hydraulic brake pressure is generated within the brake hydraulic system itself and transmits the braking force to the wheel brakes.
  
  In certain systems, the vacuum at the brake booster is used to assist with pedal force.
  
  These are therefore two different measured variables and test ranges.

• What is the difference between an analog and a digital brake pressure tester?

  With analog testers, the measured value is read using a mechanical dial gauge.
  
  Digital testers display the pressure electronically.
  
  The digital Leitenberger BDPD models use precision digital high-pressure manometers and, depending on the model, come with factory calibration certificates.
  
  Which model is more suitable depends on the workshop’s requirements for readability, accuracy, and documentation.

• What is the difference between BDP 04, BDP 06, and BDP 08?

  The analog kits differ primarily in their measurement range.
  
  The BDP 04 features two high-pressure gauges for simultaneous measurement of both brake circuits.
  
  The BDP 06 adds a vacuum gauge to this configuration for testing the vacuum pressure in the brake booster.
  
  In addition to two 160-bar pressure gauges, the BDP 08 includes an additional high-pressure gauge with a measurement range up to 250 bar.
  
  The appropriate set depends on the desired scope of testing.

• What is the difference between BDP and BDPD?

  BDP refers to analog brake pressure testers.
  
  BDPD refers to the corresponding digital versions equipped with digital precision high-pressure gauges.
  
  The digital versions are also available in different configurations.

• What are the measurement ranges of the brake pressure testers?

  The exact configuration depends on the specific set.

  The analog versions include pressure gauges with ranges of:

  • 0 to 160 bar
  • or 0 to 250 bar

  , among others.

  The current digital BDPD models use high-pressure gauges with a range of up to 250 bar.

  The device’s measurement range must be suitable for the intended application.

• Which connection adapters are included with the brake pressure testers?

  The BDP and BDPD sets include standard adapters for various thread sizes.

  Depending on the set, these include connections such as:

  • M6
  • M7
  • M8
  • M10x1
  • M10x1.25
  • M12x1
  • M12x1.5

  Additional adapters are available for other applications

• Can an electronic diagnostic tool replace mechanical brake pressure measurement?

  Not entirely.

  For example, an electronic diagnostic system can:

  • display error codes
  • sensor signals
  • ABS/ESP data
  • ECU information.

  The mechanical brake pressure tester, on the other hand, measures the actual pressure present in the hydraulic circuit.

  In cases of complex fault patterns, both diagnostic methods complement each other.

• Can the brake system's airtightness also be checked using the brake pressure tester?

  Measuring brake pressure can provide indications of unusual pressure behavior, but it is not the same as a targeted leak or leak-tightness test.
  
  Special testing procedures and equipment designed for this purpose are available for the systematic leak-tightness testing of a bled brake system.

• Is it a good idea to check the brake pressure after a brake repair?

  Depending on the repair and the reason for the diagnosis, yes.
  
  For example, a mechanical pressure measurement can help check the hydraulic function and pressure distribution after certain repairs.
  
  In addition, all testing and bleeding procedures specified by the vehicle manufacturer must, of course, be performed.

• What is the difference between brake pressure testers for passenger cars and trucks?

  Passenger cars primarily use hydraulic braking systems with comparatively high fluid pressures.

  Heavy-duty commercial vehicles, trailers, and various agricultural and off-highway vehicles, on the other hand, frequently use pneumatic braking systems.

  These require different measurement ranges, connections, and test procedures.

  Separate brake pressure testers for commercial vehicles, agricultural vehicles, and off-highway vehicles are available for these applications.

• What other devices are useful for brake diagnostics?

  Depending on the fault symptoms and the type of service work, the following additional equipment may be used:

  • Brake fluid testers
  • Brake bleeding units
  • Brake bleeding adapters
  • Leak testing equipment
  • Electronic vehicle diagnostics
  • Tools for brake installation and service

  You can find additional solutions under Test and Service Equipment for Brake Systems.