Clutch: Current trends & advice

Power cannot be transmitted from engine to wheels without a decent and well-installed clutch. Working with Sachs, Valeo and First Line, Rob Marshall, provides details of current trends and advice

Last September, my neighbour moved into a care home. With his unused, moss-encrusted and battered Ford Fiesta languishing on the drive, his relatives were astounded by the 'generous' £250 that was offered by the nearest scrappies and asked if I would drive the car to its final resting place. En-route to the crusher, the car drove so nicely that I was convinced that it was not ready to face its final curtain. Instead, I took a gamble and fired the car straight in for an MOT Test. Not only did it pass but it sold fewer than 24 hours later for an extra grand more than the scrap man offered, which was put immediately towards the owner's care costs.

The point is that used cars remain in high demand. With supply and home budgets squeezed, people are holding onto their vehicles for longer. Of more relevance to you, cars are being repaired more, although some reports warn that servicing schedules are being neglected; something that any responsible technician should warn is a false economy. Perhaps this is one reason why Valeo, for instance, told us that its UK clutch sales have risen, although this could be down to a reduction in the availability of replacement clutch parts overall.

Self-adjusting clutches require dedicated installation tools

Taking the strain

Replacing clutches is one of the few remaining tasks on a modern motor car that is dirty and requires both physical and mental strength. It is almost impossible to answer a telephone call, when manipulating a gearbox in, or out, of an engine bay – especially when the task is made easier with another pair of hands. During such a difficult operation, it is very easy to let the transmission's weight hang on the input shaft. While you could damage the gearbox, it is more likely that the clutch plate would be bent – something that may not be discovered until the first test drive and resulting in you removing the gearbox again, while killing the profit opportunity for the business.

Replacing clutches and their related components is not the most pleasant of tasks: so get it right first time

Naturally, decent equipment will make your life easier. These include proper lifting and supporting equipment to facilitate removing subframes, or kit that reduces the human exertion needed when handling the gearbox.

The benefits of a clutch centring tool are well established, especially on engines without a pilot/spigot bush/bearing in the crankshaft, or those with a crankshaft bore (into which the gearbox input shaft positions) larger than that of the clutch friction plate hub.

New Year Resolutions: Clutches

We all make mistakes but here are the top three ones that our partners have found throughout 2022:

1. Friction plate (centre hub) damage, from the gearbox's weight not being supported.

2. Excessive quantity of grease applied to the input shaft splines

3. Friction plate not facing in the correct direction (as pictured). Some non-OE designs do not have markings, so this is an understandable error. Check for any technical bulletins if you are unsure.

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Yet, clutch technology has moved on. An advantage of the self-adjusting clutch is that pedal pressures are kept broadly even, regardless of wear. The technician, however, needs to be careful. One risk involves the pressure plate/clutch cover distorting as the bolts are wound in. You could also pull the threads out of the flywheel. The self-adjusting mechanism could also activate and, in many cases, it cannot be reset. A new clutch assembly is the only answer. The solution is using appropriate tooling to install these clutches properly, which compresses the clutch cover before it is bolted to the flywheel. An example of this is Sachs' clutch tool kit that can be used not just with its XTend self-adjusting clutches but also conventional units, too.

Being familiar with DMF evaluation will permit you to offer more competitive quotations

The stress reliever

Some owners and technicians view the Dual Mass Flywheel (DMF) as an unnecessary source of irritation; others appreciate its value of (primarily) increased passenger comfort and driveline component protection. Yet, a customer may demand that you replace it with a single mass conversion kit to save money. Indeed, you could advise on the merits of doing so, especially if their driving style involves plenty of heavy towing, low-speed urban driving, or long periods of engine idling, which is common for certain emergency vehicles and taxis, for instance. Vehicles with 'chipped' engines can also experience premature DMF failure. However, it is worth informing drivers that there may be downsides, such as increased NVH levels.

Even so, it is worth evaluating the DMF's condition. You may be able to tell just by the clutch's condition if the DMF has been damaged. Bluing from overheating is an obvious example. Not changing the DMF, but checking that its tolerances are within specification, is a potentially useful way of keeping your charges low. Yet, ensure that you are familiar not just with the tooling but also data that details tolerances of the centre bush/ bearing and acceptable free-play between the two masses. Even on new DMFs, bush measurements can be 2-3mm more, compared to those fitted with bearings, so be wary of this difference, especially when assessing a new part.

CNC installation and bleeding errors are the most common causes of clutch drag

Weakness equals leakiness

While many technicians understand the importance of replacing the Concentric clutch Slave Cylinder (CSC), it is easy to compress the unit's piston in error before fitting. This can damage the internal rubber seal. A further common problem occurs when the CSC's top hat seals are not removed before installing a new one, meaning that two seals are in place. The hydraulic fluid, therefore, cannot return as intended and so, when the pedal is depressed again, the CSC becomes overstroked. Consequentially, the clutch will not release properly. Interestingly, incorrect handling and bleeding are responsible for 90% of all CSC leaks.

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Training

As mistakes kill profitability and occupy a ramp needlessly, it is worth spending time planning how and when to enhance your knowledge. At the time of writing (mid-December 2022), most companies were finalising their training plans.

ZF has confirmed that face-to-face training on transmissions will take place not just at its Head Office in Nottingham but also at a new state-of-theart facility in Solihull, West Midlands. Valeo is also planning training events but, until dates are finalised, it encourages AT readers to join its technical team on the company's (excellent, incidentally) online training webinars.