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Automated manual transmission clutches – by Rob Marshall

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Should the clutch arrangement on automated manual gearboxes restrict the aftermarket repairer? Rob Marshall argues that they should not, provided that they are perceived as opportunities, not threats.

Screen Shot 2018-02-19 at 18.09.27For the technically disinterested car buyer, transmission choices rest solely between ‘manual’ and ‘automatic’. This is not the case. Due mainly to shiny-suited new car salesmen being over-keen to seal a deal, rather than explaining how new drivetrain technologies should be treated (something that has generated more than a few complaints), the average customer is unaware that a new and popular transmission type – the automated manual – dictates a slightly different driving technique. Both mechanically unsympathetic driving and disregarded maintenance affect reliability adversely and, ultimately, an abused gearbox will fail. At this point, the informed independent technician can pick-up the baton that was dropped by the salesman and explain the concept of automated manuals to the disenchanted customer, thus providing reassurance that a main dealer visit for repair is not the only option. 

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Screen Shot 2018-02-19 at 18.09.45While other manufacturers have developed their own twin-clutch automated manual iterations, Volkswagen Group’s DSG and Ford’s Powershift (pictured) are the most common types that the aftermarket is experiencing currently. Both types utilise either wet, or dry clutch packs.

 

 

TWIN-CLUTCH AUTOMATED MANUALS

Although development was instigated by a former employee of André Citroën in the 1930s, Volkswagen Group and Borg Warner debuted the first mass production twin-clutch automated manual gearbox in 2003, christening it the Direktschaltgetriebe, or Direct Shift Gearbox (DSG). Unlike the single-clutch unit, twin-clutch automated manuals combine the internals of two manual gearboxes, which are linked together within a single casing by a pair of friction disc clutches. Lightning-fast gear changes are achieved by each input shaft and gear sets possessing their own clutch, each of which operates either the odd (K1), or even (K2) gears. The pre-calculated gear selection is made, prior to its clutch closing as the other one opens, thus effecting the ratio change.

WET CLUTCHES

All early twin-clutch gearboxes contained clutch packs within the gearbox, lubricated by the transmission oil. While reliable generally, most ‘wet clutch’ failures are caused by neglect and encouraging customers to sanction preventative maintenance tasks is critical. As the stressed transmission fluid becomes very hot, periodic renewal (including the filter(s), where necessary) is vital and the intervals tend to be stated in the carmaker’s service schedules. Not renewing engine coolant regularly tends to promote corrosion within the transmission oil cooler, resulting in the transmission fluid and engine coolant mixing. Consequently, the glycol not only strips the friction material from the wet clutches but it also swells the many rubber components, including the piston seals that activate the clutches and those within the gearbox’s inbuilt electro-hydraulic control mechanism (the ‘Mechatronics’). Therefore, should you be faced with a gearbox that has been contaminated with engine coolant, replacing the clutches alone is unlikely to affect a satisfactory long-term solution and it is best to provide a quotation for a reconditioned transmission.

Screen Shot 2018-02-19 at 18.10.01Approach modified cars with caution. Increasing engine torque tends to dictate that the transmission’s internal hydraulic pressure is similarly increased, otherwise the clutches can slip and overheat. Should the engine be tuned (or the car tows heavy weights regularly over long distances), consider recommending that the transmission’s cooling system is upgraded to preserve clutch life. Should oil temperatures exceed a pre-set figure (around 1500 is typical), the gearbox might not select any ratio, until it has cooled.

This ‘wet’ clutch assembly shows clearly the pair of clutch packs, each of which controls a separate input shaft – one input shaft runs inside the other, incidentally.

Screen Shot 2018-02-19 at 18.10.21The LuK dry clutch unit contains the friction, pressure and release mechanisms within a sealed unit.

DRY CLUTCHES

To enhance efficiency, decrease maintenance requirements and lower CO2 emissions further, dry clutch packs were developed for the OEs by LuK (a division of Schaeffler) for lower-powered models initially, although the latest types are featuring on engines that produce torque figures in-excess of 250Nm. Due to not being lubricated by the gearbox, the friction material wears gradually, just as it does with a manual gearbox clutch plate, but the transmission neither runs as hot, nor places its lubricant under as much stress.

Yet, the technique for replacing a dry twin-clutch pack is very different to the conventional methods used to renew the three-part types found in manual and automated manual gearboxes. As the combined clutch friction, pressure and centre plates, plus the release assembly is pressed onto the input shaft and installed in a free state, with no clamping forces applied, investment is required in both training and the appropriate tools to remove, install and ensure that the correct internal running clearances are maintained, before the engine and transmission are reunited.

While LuK established dry clutch replacement procedures for each manufacturer’s dealerships, including designing bespoke tools and removal/installation processes, it is supporting the aftermarket repairer, too. Generic replacement methods have been designed, as well as basic tools that can be used across a variety of makes and models, which are used in conjunction with more cost-effective vehicle-specific kits. These enable the aftermarket technician to remove the clutch unit without damaging the input shaft and both reinstall and adjust the replacement twin- clutch assembly, prior to reuniting the transmission with the gearbox.

Screen Shot 2018-02-19 at 18.10.39Developed specially for the aftermarket professional that repairs a diverse range of cars, LuK has designed a modular tool, which is used in conjunction with a vehicle specific kit. Apart from training, LuK provides immediate technical assistance via its REPXPERT hotline, 01432 264 264.

However, Malcolm Short, Technical Services Manager of Schaeffler UK Ltd., highlights that training is key and, while garages that purchase the company’s tool sets are invited to visit Schaeffler’s HQ for training, on-site visits can also be organised, subject to certain conditions.

He explains that, “With some garages not knowing the difference between an automated manual gearbox and an automatic, it is unsurprising that many of them are choosing to direct the work towards automatic gearbox specialists. We are reaching out to the aftermarket, explaining the differences and the replacement procedures, including visiting fairs and shows, while developing techniques and tools to make replacement easier and more profitable than the more specific OE processes.”

Screen Shot 2018-02-19 at 18.10.54Therefore, if your business advertises clutch repairs, consider that the average customer will presume that this includes those within automated manual gearboxes, too. The investment in providing your technicians with the skills and tools to replace dry clutch packs will be especially beneficial to your bottom line, considering that they have become almost de- rigour for most of today’s production cars.

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