The Pacer series was the result of an experiment to see whether the possibilty of using bus parts to create a train was viable. The original two-car prototype class 140 was built in 1984 at the British Rail Engineering (BREL) Derby works using a BREL underframe and a Leyland Motors bus body. The initial prototype was joined by another 18 cars to form the class 141 fleet. The units were used mainly in the North East of England, operating mainly suburban services. They had a capacity of 94 passengers per two-car set and the two Leyland T11 motors gave a total of 410bhp - resulting in a top speed of 75mph (121km/h). The entire class underwent a techincal upgrade in 1988 at the Barclay works in Kilmarnock, and were withdrawn from use in the mid-1990's.
The next and largest pacer class was class 142. Again built by Leyland and BREL in 1985. The train chassis was based on that of Leyland's National bus and many fixtures and fittings of the bus could be found on the train. The new improved class had a greater capacity of 106 passengers per two-car set, but the same motors were used as per class 141 so the speed of the train did not increase. The first sets were used initially on the Devon and Cornwall branch lines and on suburban commuter services around the Manchester PTE area. The units from Cornwall were eventually moved to Manchester and the class 142 has become a common sight on services around the North West of England. The class was upgraded in the early 1990s to include more powerful motors - 460bhp per two-car set - and a number of trains were modified for use on the Merseyside PTE City Lines around Liverpool which included dot-matrix route indicators, improved seating and Mersey PTE paintwork. The class moved into the control of First North Western at privatisation and the majority of the units are still in use.
Around the same time, a Pacer railbus was being developed by the Kilmarnock-based Barclay works, using a Walter Alexander bus body. The first of the new class, class 143, was first used in 1985. Again with 2x205bhp motors and a top speed of 75mph the class originally had a capacity of 122 passengers. The class was used in the North East of England, before transferring to the Welsh lines. The class moved over to Wales & West Trains contol at privatisation. The interior of the class was completely changed in 2000 when the Valley Line service was introduced, with full back, coach-type seating installed throughout along with improved fittings. This reduced capacity down to 106 per set, but improved comfort on the trains. A similar class 144 train, this time a Walter Alexander body on BREL underframe, was introduced in 1987 which as well as the standard two-car sets of 122 seats also saw five three-car sets with a total capacity of 195 passengers and 690bhp of motor force (It could still only do 75mph though!). The 144 class were used in the North East lines, passing over to MTL Trains (now Arriva Northern) at privatisation.
The Pacer railbuses are still in use today and are considered successful by the railway companies. However, there were some limitations to using bus parts for railway use. Instead of the more-usual bogies, the Pacers used basic four wheel wagon axles which, along with the basic bus bench seating lead to an uncomfortable ride. The drivers cab is a lot smaller on Pacers than other multiple units and they lack an area for guards, who usually end up sharing the cab. The two-step entrance makes loading slower especially for the elderly and those in wheelchairs. No more Pacer railbuses have since been produced.