These systems both work in a similar manner by varying torque to the driven wheels via a wet multi-plate clutch. The main control components are the control module, pump and clutch plates.
The control module monitors wheelspin via the ABS sensors. On 4WD cars a basic explanation is the rear wheels are not driven until Haldex sees the front wheels spin. The systems do use more sensors an can pre-empt required torque and later systems can shift up to 100% torque to the rear wheels when required.
Most VW Group Haldex systems are front biased as all the 4WD vehicles are based on their 2WD counterpart, Lamborghini and Bugatti are a reversed system as they use rear wheel drive initially.
The diff lock operates similarly and distributes torque evenly across the front axle by clamping the spinning wheel using cutch discs.
The main problem we see with these systems is with the oil and pump. The clutch discs have to be clamped tightly together to transfer torque to the axles, this is done hydraulicly by the electric pump building oil pressure. We are now at Gen 5 of Haldex systems and they no longer contain a filter, just a strainer on the pump itself. We see a lot that have blocked around 30,000 miles with a grease substance which seems to separate from the oil and worn clutch material. The earlier system Gen 4 has a filter but according to Volkswagen/Audi it’s not replaceable and doesn’t exist on their parts system. Volvo do list it and it is exactly the same differential used on their vehicles so they are available to replace at service. Gen 4 suffers from the same problem with the pump strainer blocking, this usually results in a burnt out Haldex pump on both systems.
Whenever we service Haldex, we remove and clean sludge from the pump strainer and housing and replace the filter on Gen 4. From what we’ve heard the quoted dealer service follows workshop instructions to drain the oil and refill which makes it much more likely the pump will fail.
The GTI front diff is the same design as Gen 5 Haldex and the drain plug sits higher than the base of the sump. If it is not removed and cleaned along with the pump, draining the oil and refilling leaves all the sludge and clutch material in the system, again the pump will fail.
We have had remarks that the dealer can service for the same price. If you called them back and asked for your front differential sump and oil pump to be removed and cleaned then refill the oil the price would be very different.
A genuine pump at the time of writing is £411+VAT. Our Gen 5 Haldex service is £93+VAT.
Gen 1 & 2 systems aren’t as common now but their service intervals were an oil change every 20,000 with a filter every 40,000. Pump failures were nowhere near as common.
Gen 5 systems we recommend 30,000 mile oil change intervals with strainer clean. All other systems 20,000 oil change and filter every 40,000.
If any vehicle with Haldex or locking diff is used on track this will greatly reduce the service interval.
