Cardan shaft park brakes (also known as driveshaft or transmission type park brakes) are fitted to many small to medium trucks and a small number of passenger service vehicles. They're designed to hold the vehicle and its load but drivers must be aware of their limits, and take precautions to prevent vehicles rolling away.
Waka Kotahi NZ Transport Agency issued a safety alert following several incidents where a Cardan shaft park brake has failed. Four of these incidents in the last 10 years have resulted in fatalities.
This alert can be downloaded and supplied to vehicle owners and drivers.
It's important that owners and drivers understand how these park brakes are designed, how they function and how they should be used. Mechanics must be able to correctly diagnose, maintain and adjust these systems to the manufacturer’s specifications.
On this page, you can find out more information about these park brake types, how to maintain them and how to operate them safely.
Photo courtesy of TR Group
Parking your vehicle safely
Avoid parking on slopes – vehicles can roll away, especially if the load changes and/or the vehicle is parked on an unstable surface.
Leaving the vehicle in gear and/or turning the front wheels to the kerb may help, but may not be enough to stop a vehicle rolling away.
Use enough force when you apply the brake. The force required increases with slope and additional weight on the vehicle, unlike other park brake systems. Engaging the brake properly
Park on surfaces with good grip for the tyres. Avoid unstable surfaces like gravel, mud or snow – one wheel slipping can allow the other wheel to turn, which could let the vehicle roll away.
If you’re towing another vehicle or trailer, don’t use the brake to hold both vehicles on any surface. It will exceed the holding capacity of the park brake.
Engaging the brake properly
You must fully engage the park brake to the manufacturer’s recommended setting. It may need more force than you’re used to, especially if you don’t drive a vehicle with this type of brake regularly.
The amount of braking applied before loading may not be enough to hold it once loaded. These vehicles are designed to carry heavy loads, so the loaded weight may be more than double the unloaded weight.
Don’t engage the park brake while the vehicle is moving, it may damage the brake system. This damage is unlikely to be obvious.
Operating your vehicle safely
Vehicle owners must make sure:
the park brake is regularly maintained and adjusted in line with the manufacturer’s instructions
the park brake is regularly inspected for oil leaks from the engine or gearbox
a warning sticker is clearly visible to the driver.
Cardan shaft park brake units are relatively simple in construction, but must be operated and maintained correctly to avoid safety risks.
Cardan shaft park brakes use a foundation brake system, generally a single drum brake unit mounted to the gearbox housing. This acts directly on the driveshaft of the vehicle to provide the park brake function.
This type of park brake system brake usually consists of:
a lever on the floor or dashboard near the driver, providing the operating force
a linkage or cable system running from the lever to the brake unit
an actuator connected to the linkage or cable system, transferring the operating force to the brake
friction material attached to the brake shoes or disc pads, providing the holding power
a drum unit with a friction surface for the friction material to act on, bolted directly to the drive shaft.
The brake system may also include:
a mechanism to adjust the foundation brake and cable or linkages
an inspection port to check the brake’s condition.
How to maintain Cardan shaft brakes
Effective Cardan shaft park brake performance relies on following the maintenance schedule and adjustment techniques recommended by the manufacturer. Remember, this park brake is a separate unit and not connected to the service brake system.
The location of Cardan shaft brakes makes them prone to contamination, especially from a leaking gearbox output seal. The damage this causes won’t be visible. Other factors can contribute to poor park brake performance:
Worn, misaligned or damaged brake mechanisms will reduce clamping forces available to hold the vehicle.
Contaminated friction material (like dirt or grease) getting into the system will cause a loss of friction between the brake components.
Incorrectly adjusted components will lead to a low application force and poor friction between the brake shoe/pad and the brake drum/disc.
We recommend a heavy vehicle service provider or qualified technician maintains these brakes. However, this information may be useful for large operators with in-house service personnel.
Foundation brake
Check the friction material for contamination and wear and check all other components operate correctly.
Check the drum or disc rotor for wear, excessively deep grooves, contamination, signs of overheating or excessive corrosion that could affect performance. Consider resurfacing or replacement.
Check the mountings for security, misalignment or other damage.
Actuation system
Check linkages for excessive wear and or cables for stretch or seizure.
Check for aftermarket adjusters fitted to the cable, if they are fitted the cable could be stretched and should be replaced.
Check the lever and ratchet operation is smooth and locks correctly.
Check any other pivot pins, pulleys, levers, mountings and attachments for wear, excessive corrosion, misalignment and other damage.
Lubricate all components as required by the manufacturer.
Adjustment
Always start by releasing the linkage or cable at the actuator so that the foundation brake can be adjusted correctly.
Ensure the brake shoes or pads contact the friction surface square on and flat against the drum or disc, adjust so there is a small amount of running clearance, but that it is not binding.
Re-attach the linkage or cable and adjust to give approximately 6-10 clicks of the ratchet at the lever. Always check the manufacturer’s setting
Carry out a stall test with the vehicle loaded if possible. Alternatively, find a 1 in 5 gradient and ensure the brake is effective in holding the vehicle in both directions.
Repeat checks and adjustment at every scheduled service.
Owners must maintain park brakes and keep them in good condition. Don’t assume a current certificate of fitness (CoF) means the brake will be fully operational in all circumstances.
From 1 December 2022, most vehicles with Cardan shaft brakes must be tested with roller brake machines during a CoF inspection.
From 1 April 2023, a warning sticker must be displayed in the cab of any vehicle with Cardan shaft brakes. Testing stations will apply these stickers free of charge during CoF inspections.
If your park brake fails the test you may be asked to have the brake serviced and to supply a statement of compliance (4085D form) prior to submitting the vehicle for a re-test.
