areas, including passenger fittings and the general cab layout, along with other areas wherever possible; Unlike the Class 141, which featured automotive-standard wiring for the traction equipment with resulting poor performance, railway-grade wiring for the traction and braking circuits was mandated by BR for both the Class 142 and Class 143 to yield greater reliability. As originally built, the traction arrangement of the Class 142 consisted of a Leyland TL11 engine, a Self-Changing Gears mechanical automatic gearbox and a Gmeinder final drive unit on each car driving only a single axle. This propulsion arrangement was in part taken from the Leyland National bus, as well as shared with the earlier Class 141. Unlike the Class 141, a microprocessor-based controller for the automatic transmission was used from the onset, allowing the reliability issues posed by defective relay logic and poor earthing present on the predecessor to be entirely avoided. Another improvement was the installation of auto-couplers and auto-connectors that enabled the Class 142 to work in multiple with the Class 150 Sprinter DMUs. The Class 142 is fitted with double-folding external doors, identical to the preceding Class 141. Each car has a fuel capacity of . Both axles (one driving per coach at the inner end) were fitted directly to the chassis rather than being mounted on bogies, unlike traditional DMUs. This uncommon arrangement has been attributed with resulting in the Class 141 units possessing a relatively rough ride, especially when traversing jointed track or points. Their combatively poor ride quality has been said to be a major factor in the type's general unpopularity amongst passengers. As a positive result from BR's experiences with the Class 141, the Class 142 featured an improved suspension arrangement to enhance passenger comfort, this consisted of a wider spring base and double dampers being installed, features that had been deemed necessary by BR to provide sufficient levels of performance, and had been retrofitted onto all of the older Class 141s as well. Excessive flange squeal on tight curves has been a problem on many routes operated by the Class 142. caused by the long wheelbase and lack of bogies. Upgrades and refurbishments Starting in the early 1990s, every member of the class was mechanically upgraded due to the original parts starting to fail. Accordingly, each car was refitted with a more powerful Cummins L10 series engine – 230 bhp per car, which equals per twin-car