d If you want to start a fight in a conference room full of
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transport engineers, open a debate about warranty returns. When a component fails prematurely, everybody from the driver to the operator has a suspect, and it's usually the manufacturer. Off goes the warranty claim. When the report comes back from the manufacturers technical department a few weeks later turning down the claim, the result is often the same as lighting the blue touch paper on Bonfire Night. A typical response is: "Change the brand. That will solve the problem!" But it ain't necessarily so.
Take the commercial vehicle clutch. At Sachs we manufacture heavy-duty clutches for OEM and aftermarket fit. The manufacturing procedures are comprehensive. A typical replacement heavy-duty unit can cost hundreds of pounds, so our fault diagnostic process is extremely rigorous, too.
The vast majority of premature clutch failures returned as warranty claims are related to burnout or wearout. Many include amounts to cover vehicle downtime, rescue and hire. To this is added the unit cost, the installation and the labour charges.
It's easy to blame the component, but after a little diagnostic detective work other suspects emerge. For example, the rate of wear of a clutch is influenced by the vehicle's operating environment, It is greater when the terrain is dirty or dusty, or mountainous rather than flat. Is the vehicle used for long hauls or clutch-wearing multi-drop work? Premature clutch wear can be related to the installation procedure. Workshop engineers should check the clutch environment itself carefully before fitting the new unit. Worn flywheels, guide tubes and pivot points in the release mechanism are all likely to cause problems. Access to the vehicle's service history can often be used to corroborate the evidence.
So what are the main reasons for warranty claim rejections in cases of premature clutch failure? Mostly, they are driver-related.
It may seem too easy to blame the driver—but consider the following: the percentage of clutch wear during the gear change is negligible. Most friction lining wear occurs when the vehicle is pulling away from rest. The normal clutch operating temperature is 90-120°C. However, wear MI increase significantly at higher temperatures. For example, overheating is caused by excessive frictional heat after extended periods of clutch slip—such as when a driver regularly slips the clutch to negotiate roundabouts. The wear rate can increase dramatically if the temperature reaches 300-400°C. The friction lining will disintegrate, and failure will occur very rapidly.
The improved soundproofing technology used in today's cabs means some drivers can inadvertently slip the clutch because they cannot hear the tone (and speed) of the engine very clearly. Engines in today's vehicles produce higher torque at lower engine speeds, so it is not necessary to use excessive engine rpm for takeoff. Taking off in a gear that is too high also reduces the life of the clutch. For instance, if the gear selected is too high, the engine rpm has to be increased to prevent stalling. This combination considerably extends the slip time, resulting in high mechanical abrasion and high frictional heat. Tests carried out by the Sachs Development Centre in Germany show that this type of abuse can reduce the life of the clutch to as little as 5% of its original potential life span. In practice, the clutch should be allowed to slip for no longer than 1.5 seconds.
In each of these examples, better use of the rpm indicator will significantly extend the life of the clutch. And let's not forget about reducing fuel consumption. Evidence of premature burnout doesn't necessarily mean the driver is bad, but it can show up a poor driving technique which can be rectified. Address that and the savings in maintenance cost will be significant, not to mention the reduction in vehicle downtime, the increase in the use of the vehicle—and an end to the frustration of warrant/ rejections.