Modern 4X4 vehicles come fitted with a multitude of four wheel drive systems, but all rely upon front hubs to transmit the power from the front axle to the front wheels to drive them, these come in manual and automatic locking hubs. Disconnecting front hubs, to give them their correct title, evolved because of the availability of economically priced 4X4 vehicles to the mass car buying public, and to improve the fuel efficiency and environmental emissions of such vehicles. Prior to this, most people with 4X4 vehicles had them as working vehicles, and knew the mechanics of such vehicles, and how to drive them properly.
Manual hubs operate by the driver getting out and manually operating them, this has benefits and negative aspects, and that is having to stop the vehicle to engage them, and having to stop the vehicle to disengage them. This is fine if a vehicle is working off road, but it means inconvenience to the user, and the risk of getting dirt and mud into the vehicle every time you have to connect or disconnect them.
As 4X4 vehicles became popular with more leisure orientated, rather than pure work related activities, it became more convenient to offer a hub which would engage and disengage automatically as the front axle was engaged by the driver. These auto hubs all follow the same principle of operation, irrespective of which vehicle you drive, most were made to the same design as they were reliable, economical to manufacture, and durable if correctly maintained.
Automatic hubs work in a basic principle that is called relative motion, relative motion is where a stationary axle or drive shaft has a hub with a two way spring loaded mechanism which holds it in a neutral or disengaged position. If the axle or drive shaft moves a few degrees in a pre-determined direction it operates against this spring and this movement operating in a pre-determined manner, engages the hub in its intended direction. On a vehicle this works not in one direction, but in two directions; this means that as soon as 4 wheel drive is engaged and the clutch is released the moving front drive shafts move a few degrees and engages the hub, this also works if the drive shaft rotates backwards. As soon as the drive is disconnected such as reverting back to 2 wheel drive, or the vehicle stops, the spring returns the hub back to its central position and disconnects the front hubs. Many people assume that if a vehicle is travelling downhill the front hubs disconnect, this is a fallacy as relative motion works in two ways that is the drive shafts moving the vehicle, or the vehicle moving the drive shafts. On a downhill slope the weight of the vehicle forces it downhill, the drive shafts oppose this motion, so becomes or remains connected as it is the relative motion between the vehicle and drive shafts.
Automatic hubs have become notorious with unreliability, this is another fallacy as these are durable and reliable if correctly maintained, but many are neglected, this may be a problem if the vehicle is on its second or more owners. If the hubs have not been maintained correctly they may pose problems for the educated of fastidious owner who maintains them, or the owners of working vehicles who undertake more maintenance of their vehicles, and understand automatic hubs.
Operating automatic hubs is relatively simple, but requires a little knowledge, the major problem is when people do not know how to operate them. Connecting the front automatic hubs is as simple as engaging four wheel drive and driving off, disconnecting them means that the vehicle has to be switched back to two wheel drive and reversing the vehicle backwards several feet/metres. So why do we have to do this? If a hub is engaged and the load is leaning on the drive assembly, the spring is not strong enough to disconnect these mating surfaces, reversing relieves the weight on these mating surfaces to a degree where the spring can centralise and free them.
Poorly maintained hubs can suffer other problems, these are normally the ingress of mud and sludge which literally compact inside the hub and prevent it engaging or disengaging, or the ingress of water and sludge, which leads to internal corrosion. Internal corrosion weakens the internal components to the degree that the spring pressure is reduced, so centralising the mechanism becomes difficult for it to do, and in extreme cases the corrosion actually causes internal components to break. This means the hub will not work, and needs replacing. Cold or freezing weather can affect the hub as the ingress of water or wet sludge may freeze and hold the hub in its engaged or disengaged position, as the hub works and heats it will thaw this out, and work correctly.
Maintaining automatic hubs is relatively simple, it can be a part of your annual maintenance schedule and ensure the reliability and durability of the hubs, and involves nothing more than a little oil and grease. Most enthusiast owners have these things lying about in their garage or workshop.
Remove your front hubs by undoing the retaining bolts, the vehicle does not need its wheel removing, but this is recommended as on Independent’s it gives access to the front wheel bearings as the automatic hubs and the bearing use the same grease reservoir. Clean and remove all the grease from the wheel bearing and adjust it correctly to remove any play, repack the front wheel bearings with marine type waterproof grease, and actually overfill the front wheel bearings with waterproof grease. Clean everything from the front hub, the grease, dirt, and any other contaminants, petrol is the preferred cleaner as it evaporates, check for corrosion within the hub, and clean and remove any corrosion. If there is excess corrosion it may warrant replacing the front hub. Once fully cleaned, allow the petrol to evaporate fully.
Place the now cleaned hub onto a flat surface and fill it with clean gearbox oil, this will give it initial lubrication and prevent any wear, leave this and clean out the other hub to the same degree, tip the oil from the first hub, into the second.
Pack grease into the first oiled hub, force this in slowly to fill any crevices or awkward areas, a syringe with a fine end is an ideal way of injecting it in, but tightly packing it will suffice, and overfill the hub in the same way you overfilled the wheel bearing. Locate and align the hub, bolt this back into position and remove any surplus grease which is squeezed out, this will give a full, grease pressurised hub and prevent any ingress of water, sludge, or dirt; this also insulates against the cold in freezing conditions.
Empty the second hub of the oil and follow the same procedure for adjusting the wheel bearing and packing the bearing and hub with grease.
One option for vehicles operating in predominantly sludgy or spending a lot of time immersed in water is to make a thin gasket for the hub, this sits on the hub mounting face and offers a little more protection from penetrating water or sludge. Using the thinnest gasket paper you can purchase, make a gasket using the hub as a template, make at least four so you have two spares when you repack the hubs again, or make as many as the gasket paper will allow.
Remember that the bearing and hub use the same reservoir for grease storage, over time the grease will expand and contract due to the heat from the operating front bearing, this will force it through the seal on the front bearing and release the pressure. Periodic topping up of the grease is recommended, for vehicles working heavily off road, this may be every six months, and annually for all other vehicles; this reinstates the pressure and allows you to see any contamination which may have penetrated into the front hub.
Normal maintenance would simply involve a little contamination around the mounting face of the hub and nothing more, simply scrape this grease away and add a little more to replace it and overfill the assembly to pressurise it again. Many people decide that fitting a grease nipple is a good idea, forget it; the hub is not strong enough to hold a grease nipple, and these protruding often get wiped off while off roading. Many grease nipples can also be a source of water ingress as they are nothing more than a spring and a small ball bearing which seals them, if the spring becomes damaged or corroded, it simply lets water and sludge pour into the hub.
Manual hubs require nothing more than removing every couple of years, then clean and replace the grease.