140 uncovered several issues, such as difficulty detecting the type via track circuits, this was reliably resolved by swapping the material of the brake blocks from a composite to iron. Two less easily addressable drawbacks were the high level of noise generated during transit, particularly on older jointed rails, which was a consequence of the railbus's direct connection between the underframe and suspension with the body that transmitted impact forces across the body. It was also observed that the inclusion of strengthening members in the mass-produced bus body added significantly to the overall production cost, which eliminated much of the cost advantage that was the primarily goal of the type. The Class 140 was viewed to be an overall success, and thus BR issued an order for an initial production model, designated Class 141, to British Leyland during 1984 with production commencing thereafter. During its early years of service, the Class 141 experienced numerous issues, particularly with the transmission and ride quality; work undertaken at BR's direct resulted in the quick development of numerous improvements to at least partially address these shortcomings. When it came to ordering more railbuses, however, it was decided that instead of placing these follow-on orders for further Class 141, it would be more desirable to procure improved derivatives of the Class 141. Accordingly, BR placed orders for two new models of the Pacer family with separate manufacturers, these being the Class 142 and Class 143 respectively. Thereafter, another and final Pacer model would be ordered, this being the Class 144. Description A total of 23 Class 144 units were constructed. The units have a maximum speed of and are externally similar to the earlier Class 143 Pacers, sharing a near-identical body built by Walter Alexander. The first thirteen of the classnumbers 144001 to 144013are two-car units, while the remaining ten144014 to 144023have a third vehicle that was added later in 1987. These ten Pacers are the only ones to use intermediate vehicles. Units are formed of two driving motors, one of which contains a toilet. The three-car units have an additional intermediate motor. All vehicles have standard-class seating only. The technical description of the formation is DMS-(MS-)DMSL. Individual vehicles are numbered as follows: DMS: 55801–55823 MS: 55850–55859 (units 144014–144023 only) DMSL: 55824–55846 As originally built, the traction arrangement of the Class 142 consisted of a 200-horsepower Leyland TL11 engine, a Self-Changing Gears mechanical automatic gearbox