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. Starting in the early 1990s, every member of the class was mechanically upgraded due to the original parts being determined to be a major source of unreliability. The most substantial change was the replacement of the Leyland-built engine with a more powerful Cummins LTA10-R as well as the original mechanical transmission being substituted for a Voith hydrokinetic unit. The Class 144 units are equipped with BSI couplers. This allows them to work in multiple with , , , , , , , , and units, as well as units of the same class. As a benefit of their high levels of similarities, Class 144 units were often replaced in service by Class 142 units, and vice versa. Operations British Rail The first Class 144 units were delivered during 1986. They were produced specifically to perform local services sponsored by the West Yorkshire Passenger Transport Executive (since rebranded as Metro). As such, the fleet was painted in the crimson/cream West Yorkshire Metro livery, although three units (nos. 144011–013) were later repainted into Regional Railways livery. During the British Rail era, the type was normally used on services such as the Harrogate Line between York, Harrogate, and Leeds, the Huddersfield Line's Wakefield section between Leeds and Huddersfield, along with the Huddersfield branch of the Calder Vale line. Class 144s were also operated on Hallam Line between Leeds, Barnsley, and Sheffield; the Penistone Line between Huddersfield, Barnsley, and Sheffield; and the Pontefract Line between Wakefield and Pontefract. The Class 144 was also tasked with additional routes, including the Leeds-Morecambe services, services between Scunthorpe and Adwick to Sheffield and Lincoln. More recently from 2008, they have been working between Manchester Victoria and Leeds (usually via Brighouse) amongst others. Prior to 1994, they were also used on Leeds/Bradford-Ilkley and Leeds/Bradford-Skipton services. These lines were electrified in 1994, and passenger services were operated by Class 308 electric multiple units. Early operations of the type were marred by unreliability to the extent where the Class 144 was commonly substituted for at the last minute by either first generation DMUs or locomotive-hauled trains. Their poor serviceability was common to all production Pacer types. According to industry periodical Rail magazine, the Class 144's mechanical