5 minute read
The limitations and dangers of Cardan Shaft Parking Brakes
Cardan Shaft Parking Brakes are fitted to many light-to-medium weight (3.5 to 10 tonne) trucks, mainly of Japanese origin (Mitsubishi, Isuzu and the like) as well as other vehicles.
Advertisement
This type of parking brake acts by locking the driveshaft at the gearbox output shaft and may use either a single brake drum or a disc calliper, rotor and pad design. The brake drum is the most common and universally used on trucks. Disc brakes are generally installed on off-road equipment such as JCB Telehandlers and the like.
Cardan shaft park brake assembly fitted onto rear of gearbox.
Typically, a Cardan Shaft Parking Brake system uses a ratcheted handbrake lever and cable to apply the brake – similar to what you would find in your car. It can also be a ‘pull’ type lever next to the steering column.
Cardan Shaft Parking Brake Limitations
These brakes are not as efficient as other systems that act on the vehicles wheel brakes directly. They have a limited amount of holding capacity compared to other systems and are unlikely to hold
a vehicle stationary, especially when it is laden and parked on any significant
slope. This is in both the forward and reverse directions. Of particular concern, is that the drum type brakes may only have about 60% of the holding power when the vehicle is facing uphill compared to when facing downhill.
In two recent fatal accidents, the Cardan Shaft Parking Brakes were properly
maintained and adjusted and were correctly applied. The vehicles were parked on slopes well within their operating range.
As the braking is applied through the differential, any slippage of one wheel will allow the other wheel to roll and the vehicle to ‘run away’.
Similarly, if one wheel is jacked up, braking on the other wheel is lost and if on a slope the vehicle will move. The location of these brakes makes them susceptible to contamination, especially from a leaking gearbox output seal. Any such contamination will likely degrade the effectiveness of the brake, and this will not be evident to the driver. There are no practical means for a driver to effectively check the performance of a Cardan Shaft Parking Brake. The manufacturer’s specified ‘stall’ tests do not adequately represent the required parking brake holding requirement and a brake that The parking brakes held for a period of minutes before suddenly failing.
They are only a parking brake. They cannot be used to slow or stop a moving vehicle as to do so can severely damage the brake, gearbox or driveline.
Any damage to the brake will likely further degrade its effectiveness, and this
may not be evident to the Driver. passes such a test is still unlikely to hold on any significant slope, especially if the vehicle is laden.
The Bottom Line
There are many thousands of vehicles, fitted with Cardan Shaft Parking Brakes, that are currently in service. Notwithstanding that failures of such parking brakes have been responsible for a number of fatalities and serious injuries, knowledge of the inherent limitations and dangers of Cardan Shaft
Parking Brakes is considerably lacking among owners and users of affected vehicles.
These parking brake systems represent
a real and present danger to the vehicle users and other people that may be in the vicinity of a vehicle ‘roll-away’.
Mitigating the Danger
Check your vehicles to determine if they have Cardan Shaft Parking Brakes installed.
If they do, install a highly visible placard in the cab of the vehicle advising that such a parking brake is installed and include the information in this ‘alert’.
Advise all users of the limitations and dangers of such parking brake systems. In particular, advise them that the parking brake cannot be relied on if the vehicle is parked on a slope, especially if laden.
Parking on slopes should be avoided if at all possible.
Supply, and require the use of wheel chocks (both rear wheels) in all parking situations.
Wheel chocks should be approximately 25% of the vehicle’s tyre diameter and fit snuggly.
Note, however, that if the vehicle is on a slope, chocks should be placed by another person while the Driver holds the vehicle stationary on the Service Brake.
It is crucial that wheel chocks are used if a vehicle is jacked.
Be aware of any fluid leaks under the vehicle and have them checked ASAP to avoid contamination of the parking brake.
Ensure that the parking brake is properly maintained and adjusted.
Selwyn’s son, Graeme, was killed in a workplace accident early last year. The accident was directly attributable to the failure of a properly maintained and correctly set Cardan Shaft Parking Brake on a JCB Telehandler.
In the course of his investigation into the accident, Selwyn learned there are serious deficiencies with such park brake systems. Just nine months prior to Graeme’s accident one person was killed and another critically injured in very similar circumstances – that is, due to the failure of a properly maintained and correctly set Cardan Shaft Parking Brake on a waste disposal truck. Whilst the regulatory authorities have been aware of the issues relating to these types of parking brakes for a number of years, nothing has been done to address the problem and there is an almost total lack of knowledge among the Owners and Users of affected vehicles.
Selwyn has been actively working with the New Zealand Transport Agency (NZTA) to quantify the performance issues relating to the parking brakes including initial testing of several light/medium weight trucks. These tests confirmed the limitations of Cardan Shaft Parking Brakes. The challenge now is to ensure this knowledge has the widest possible dissemination and to have NZTA take definitive action to deal with the limitations and dangers of these types of park brake systems.
If you have had any experience with Cardan Shaft Parking Brakes relevant to Selwyn’s efforts, he would appreciate it if you could contact him accordingly. Similarly, if you are interested in any further information please do not hesitate to contact him.
Selwyn Rabbits,
+64 21 656 661
