Some 4WD vehicles are equipped with a part-time 4WD system which allows the driver to select between 2WD and 4WD depending on the conditions. In older 4WD vehicles, free wheeling hubs are used to engage and disengage the front half shaft (driveshaft) from the hub of the front wheels. When the device is locked, the drive shaft is engaged which allows the driver to select high or low 4×4 with power being applied to all four wheels. On the other hand, when the device is free then the drive shaft is disengaged allowing the vehicle to behave as a conventional 2WD with only the rear wheels being powered.
Why do vehicles have free wheeling hubs?
Free wheeling hubs were initially designed to minimise the amount of friction and moving parts in 4WD vehicles. Considering that 4WD vehicles drive on bitumen most of the time, powering all four wheels uses more fuel to spin the front axle, differential, and driveshaft which isn’t always needed. While the fuel savings are negligible when the hubs are disengaged, there are other advantages such as lower noise levels, less vibrations from the drive train, less wear in drive line components, and a generally smoother ride without the need for aftermarket suspension.
How do free wheeling hubs work?
Free wheeling hubs, also referred to as locking hubs, have a spring loaded collar that slides inwards when the actuator is set to ‘lock’. This action essentially locks the front wheels, differential, and driveshaft as one unit and when the transfer case has high or low 4×4 engaged, the car will operate as a 4WD and power all the wheels. On the contrary, when the actuator is set to ‘free’, the front wheels rotate independently of the front driveshaft and spin freely like a rear-wheel 2WD.
When the driver wants to select 4WD, they need to lock the front hubs and engage the transfer case to either high or low 4×4. It doesn’t matter whether the drive engages 4WD or locks the hubs first, 4WD will be selected when both these actions have taken place.
Automatic locking hubs
Rather than having to get out of the vehicle and manually engage the locking hubs, modern 4WD’s have automatic locking hubs which essentially uses the same process but the action can be performed from inside the vehicle. With automatic locking hubs, drivers can engage 4WD on the fly but to disengage the driver needs to reverse a metre or so once 4WD has been deselected in the transfer case. In general, automatic and free wheeling hubs can be converted from one to the other.
Can you lock your hubs without 4WD engaged?
Yes, free wheeling hubs can be set to the locked position without engaging 4WD and cause no damage to the vehicle. This allows drivers to engage 4WD whenever they anticipate they may need to switch without having to get out of their 4WD to set the actuator. For vehicles that drive primarily on bitumen with their hubs set to the free position, it’s recommended to lock the hubs every now and then to provide ‘splash lubrication’ to the driveshafts.
Despite this, it’s standard practice for drivers to only lock the hubs when they wish to switch to 4WD or when driving on gravel, and they’ll also lock their hubs about one day each week if they’ve been driving on the highway and racking up kilometres in their vehicle.
Don’t have 4WD engaged all the time!
In part-time 4WDs with free wheeling hubs, it’s strongly advised to only use 4WD when needed and not to drive on bitumen with 4WD engaged as it can damage drive line components and wear out tyres.
Considering that the front and rear drive shafts rotates at the same time with part-time 4WDs, the front wheels must rotate faster when making a turn. However, given that the front and rear drive lines are operating at the same rate, ‘driveline binding’ can occur which leads to difficulty steering, jerky movements, spinning tyres and ultimately expensive component failure such as the axles, differential gears, or transfer gears.
If you need any further information relating to free wheeling hubs, or you’re looking some new 4WD products and accessories, get in touch with the professionals at TJM Australia by phoning 07 3865 9999.
