What is a cardan shaft brake and why do they fail?

Some small, medium and heavy trucks (but mostly small trucks), as well as machinery such as telehandlers have a cardan shaft park brake. This is a type of park brake. They are usually activated by a handle which looks and feels the same as a handbrake in a car, and makes the same ratchet sound when the handle is pulled up.

Cardan shaft brakes are prone to failure. They work on the driveshaft rather than the wheels and are relatively weak. Their failure has lead to trucks running away downhill, sometimes causing incidents that have resulted in damage to property, injuries and even death.

On flat or very gently sloping ground, a cardan shaft brake is adequate to hold a vehicle when it is applied properly, however, the strength of the brake is easy to exceed when the vehicle is heavily loaded, the slope is steep and the brake isn’t applied strongly. The main ways the cardan brake’s stopping ability is overcome are:

• Using equipment mounted on the truck, such as a truck-loader crane or a tipper deck
• Parking on a steep slope when heavily loaded
• Not applying the brake hard enough – when fully loaded, the handle could require up to 60kg of pulling force to apply it strongly enough, which is too much for some drivers
• Filling or emptying a tank mounted to the truck, e.g. a water tank
• Altering the weight or load balance of the vehicle while parked on a slope, for example, loading heavy items onto the truck’s deck.
• Parking where one side of the truck has much less traction/grip than the other side (if this side slips, the other side wheels will roll because the cardan shaft brake permits the differential to operate).

Once friction is overcome and the truck begins to move, the cardan brake will not be able to arrest the truck’s movement, just slow it down.

Wear and tear reduces the effectiveness over time. The cables stretch, the braking mechanism can become misaligned, the friction material can become worn due to driving without fully disengaging the brake or engaging it before the truck has stopped moving. As it is on the driveshaft, any oil that leaks through seals can reduce the brake’s effectiveness.

Cardan brakes can be effective if the driver understands their limitations. Drivers must be trained in it and can learn more about this in the pre-trip inspection course. It’s important to use wheel chocks that are at least 25% of the diameter of the tyre when parking on a slope. The brake should be checked during regular servicing. When parking the truck while working, avoid pointing it towards people working, in case it does roll away.