The AMTs retain a conventional friction clutch, although the transmission’s operation is controlled automatically via vehicle electronics. They are now standard equipment on most vehicles across the heavy-duty truck sector.
Analysis using the fleet’s own internal maintenance and repair data, which was designed to evaluate whole life costs of AMTs versus full automatics, revealed a 58% clutch failure rate on one premium make of vehicle equipped with the chassis manufacturer’s own AMT from 2020-2022, with the primary cause being thermal overload. Besides the clutch itself, other components requiring replacement after clutch failure included flywheels and flywheel bolt sets and clutch actuating forks and bearings.
Similar failures and failure rates appear to have occurred on the other makes of trucks in the study equipped with OEM-supplied AMTs.
It was extrapolated that repeat failures were likely to reoccur to the fleet of AMT-equipped vehicles covered by the study during its 10-year working life. The earliest failure recorded was within two years of registration, and failures became more likely as vehicles aged.
While a single repair at a manufacturer’s franchised workshop could cost in the region of £3,000, the true cost, often not considered, is in the region of £7,000 when including recovery costs, a replacement vehicle and all the associated standing costs reported in industry operational cost tables.
NO FAILURES
In contrast, 60 vehicles equipped with Allison fully automatic transmissions used on similar trade waste collections experienced no transmission-related mechanical failures over six years. Just three control modules were replaced during this period. The only maintenance normally required for an Allison transmission is the scheduled replacement of fluid and filter.
Chassis manufacturers normally demand a premium for fitting an Allison automatic transmission in place of their standard equipment on a new vehicle. The study found that this product premium can be repaid by saving the cost of just one clutch failure.
Reliability aside, the Allison transmission is also said to be more productive, thanks to its torque converter technology, which also offers greater acceleration, giving a 14% increase in average speed. Unlike a conventional transmission, there is no power loss between shifts. It has the ability to not only acept greater engine torque and higher revs on take-off without compromising reliability, but also multiply that torque, meaning that in some cases a smaller, lighter, and more economical engine could be specified on new trucks, reducing purchase price, fuel costs and carbon emissions.
The possibility of specifying a higher-ratio drive axle allows the prospect of lower rpm at cruising speed, reducing fuel consumption, noise and emissions.
Installing a single transmission type across a mixed-make fleet may reduce stress on drivers, who can change from one vehicle type to another without having to accustom themselves to operating a new powertrain.