What maintenance does a 4X4 need?

As with any car servicing requirements, the most relevant requirements will be detailed within your car manufacturer's official maintenance schedule. Yet, because 4x4 transmissions employ more mechanical hardware than a two-wheel-drive vehicle, that tends to need extra attention.

Even so, some 4x4 vehicles require special treatment beyond maintenance. Certain 4x4s have bespoke towing requirements, for example, and can be damaged by being transported at high speed with two wheels raised. Therefore, study your car's handbook carefully and follow any warnings about how to avoid damaging your transmission.

What are my 4x4's servicing requirements?

As a typical 4x4 system possesses more driveshafts than a regular two-wheel-drive vehicle, additional inspections are vital. Propshafts may be fitted with universal joints, which can develop slack, which might cause a ‘clicking’ sound on taking up drive in either first, or reverse, gears. A failing universal joint can be extremely dangerous, due to the shaft’s high rotational speeds. Many propshafts require periodic greasing, a crucial maintenance task that must not be overlooked.

Look also for perished rubber vibration absorbers and centre joint bellows, if fitted. A centre support bearing may also feature, which may be surrounded by a rubber doughnut that can deteriorate and cause vibration. Some cars may possess more than one rubber-supported centre bearing, potentially, with extra hardware.

As an example, the first-generation Land Rover Freelander has a pair of centre bearings, between which is a Viscous Coupling Unit (VCU), a component that fulfils the role of a differential, by compensating for differences in rotational speeds between the front and rear axles.

Unfortunately, it can fail internally, which tends to increase stress and cause failure of other parts of the transmission. Yet, some owners tempt premature VCU failure, by fitting differently sized tyres on each side of an axle, placing the unit under extra stress.

Some 1990s and early 2000s models, other than Land Rovers, also used external viscous couplings (mainly produced by GKN) in their drivelines, before rear differential-mounted couplings became popular.

What are rear couplings?

Mounted to the differential, a rear coupling is an electromagnetic clutch that controls how much power drives the rear wheels. They are used especially on transverse-engined SUVs and Crossover vehicles that are designed to be used mainly on-road. To find out about what this means, consult our earlier blog.

Many vehicles in today’s used car parc utilise a coupling made by the Swedish company, Haldex Traction. Not only are Nordic models thus equipped but Mazda, Ford and Land Rover bought into the technology, as did the Volkswagen Group, therefore adding VW 4Motions (pictured), Skodas, Seats and certain transverse-engined Audi Quattros to the list.

The Haldex unit contains a multi-plate clutch, bathed in oil, to distribute the required drive to the rear wheels. The clutches are engaged hydraulically by a pump, powered by an electric motor that is regulated by a computer (ECU).

The ECU considers inputs from other electrical systems around the car, including the steering, speed sensors and the stability control system. Each car manufacturer can create bespoke software that is optimised for each model, even though the mechanical hardware remains broadly the same. From a maintenance perspective, the oil on earlier Haldex units requires routine renewal, as does the separate filter.

The Haldex coupling’s age also affects maintenance and performance requirements. Generally, the first (introduced in 1998) and the second generation (from 2001) differed from each other by the later system having its clutch plates activated via computer-controlled solenoids. Both of these systems reacted to front wheel slip, before drive was transmitted to the rear wheels.

From 2004, the third generation (called PreX, by Haldex) utilises the electric pump to pre-pressurise the clutch after the engine is started, so that torque could be transferred instantly to the rear wheels, instead of after a significant front wheel slip had occurred. This made it faster-reacting and more effective. Arriving in 2007, the fourth generation incorporated internal changes to make the system less complex. The fifth generation from 2012 took this further, by deleting the accumulator and solenoids.

In the real world, it has been noted that the sealing, within the second and fourth generations Haldex controller permits moisture and road salt to corrode the ECU’s circuits inside, which may cause an ‘ESP’ failure dashboard lamp to illuminate on the dashboard. Fortunately, some aftermarket UK specialists can test and repair corroded boards via mail order.

An alternative to the Haldex coupling is GKN’s Electro Magnetic Control Device (EMCD); a far simpler unit that utilises an electromagnet to apply the required force to the clutch pack, via a smaller pilot clutch and a cam, negating the need for hydraulics.

The main clutch, therefore, is controlled by varying the current supplied to the electromagnet, to a maximum of between three to four amps. Typical models that were fitted with the system included the 2006-on Toyota RAV4, the Dacia Duster and MINI's ALL4 Countryman and Paceman. These systems are less demanding on their oil and are designed with a 150,000 miles lifespan but possess no means of

draining. To get the oil out, the unit will have to be dismantled, or the fluid extracted through the filler plug. As with virtually any mechanical component, replacing old oil is a good idea, because deteriorated lubricant will cause excessive and rapid wear.

Finally, you may come across a Japanese coupling on some Vauxhalls, Chevrolets, Hyundais and Kias. JTEKT’s Intelligent Torque Controlled Coupling (ITCC) also uses an electromagnetically-activated clutch pack, bathed in oil. Technical information on those units seems to be fairly scarce in Europe but examples that GEM has seen possess a fluid level plug but, like GKN’s EMCD, no specified drain intervals appear to exist.

The best advice is to check the individual car’s official service advice first, before considering either sucking out the fluid via the filler plug, or removing the ITCC from the vehicle to drain it.

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