Seddon Diesel Vehicles were, like Atkinson Lorries, ERF and Motor Traction (Rutland), a commercial vehicle producer who bought-in and assembled proprietary components. Robert and Herbert Seddon were sons of a Salford butcher who in 1919 subsequent to World War I demobilisation bought a Commer with charabanc and van bodies, using it during the week for goods transport and at weekends to run excursions from Salford. Initially a further partner was a family-friend, a dairyman by the name of Foster, so the business was initially a partnership. Foster & Seddon also reconditioned vehicles and ran a bus service from Swinton (Lancs.) to Salford, which was subsequently sold to Salford Corporation, and held an agency for Morris Motors vehicles.
In 1937 Robert Seddon spotted a gap in the commercial vehicle market for low-tare diesel-engined lorries and commenced to build his own vehicle out of proprietary units, much of the drawing work being done on his own kitchen table.This was a 6-ton gvw forward-control lorry chassis with a 6-cylinder Perkins indirect-injection diesel engine. It was first shown at the Scottish Motor show at Kelvin Hall, Glasgow in 1938. Since it weighed under 2.5 long tons (2,540 kg) unladen, it was allowed to travel at 30 mph (48 km/h) unlike most other trucks with a comparable payload. Like Maudslay and ERF, Seddon Motors Ltd were allowed to continue producing commercial vehicle chassis for sale during World War II when many more-established makers such as Leyland Motors, the Associated Equipment Company and direct-competitor Albion Motors had all of their productive capacity diverted to the war effort.
In 1948 Seddon Motors Ltd moved to the Woodstock Works, a former shadow factory in Oldham and were able to expand production from one or two a week to more than ten. At this point they introduced their first passenger chassis the Mark IV. The 26 ft mark IV and 27 ft 6in mark VI were sales successes at home and overseas. Coachbuilders for these chassis included Plaxton and a number of smaller concerns, Seddon also built their own coachwork for these models, mainly for export. Subsequently, Seddon also produced (amongst a bewildering range for which Roman numbers were adopted when the firm became Seddon Diesel Vehicles Ltd in 1950) the Mark 7P. This was a short-wheelbase version of the established theme with four-cylinder Perkins engine and up to 28 seats available within a 21 ft overall length.
At the 1952 Earls Court Commercial Motor Show marks 10 and 11 featured vertical Perkins (P6 80 bhp or R6 107 bhp) engines mounted underfloor (when competing underfloor-engined buses used horizontally oriented engines). Although Bedford were to have success with such a layout between 1970 and 1987 the marks 10 and 11 sold poorly, with Seddon, Charles H Roe, Duple and Plaxton bodies on the few known examples. The mid 1950s mark 16 was a 21 ft long bus with a Perkins P4 on the front overhang and the mark 17 was a six-cylinder-engined chassis to similar layout.
The mark 18 of the late 1950s, mainly sold to Australia and New Zealand, with local coachwork. It had a vertically mounted Perkins P6 80 bhp engine on the rear overhang. There was also one mark 20 with a Henry Meadows 550 cubic inch horizontal rear-engine exported to Greece and the mark 25P a normal control 18-seat personnel-carrier based on the mark 25 integral parcel van. The bodybuilding business, not only on Seddon and other manufacturer's buses but building lorry cabs and parcel vans for customers such as Manchester Corporation (who ran a parcel delivery service) was registered in its own right as Pennine Coachcraft Ltd (wholly owned by Seddon) in 1960.
From 1966 (with mark numbers climbing into the high twenties), Seddon decided to simplify its nomenclature, wagons were henceforth to be identified as (for example) 16–4 with the first number being the gross vehicle weight and the second the number of wheels. Bus chassis were to be known as Seddon Pennine Mark (x). The first buses using this system produced were for Bermuda and were Seddon Pennine Mark 3, they are believed to be similar to a short-wheelbase Pennine Mark 4 but with Perkins P6 or 6-304 engines or an integral development of the Mark 17 model of similar layout.
From the middle 1950s, Seddon had been almost absent on the home market for bus & coach concerns. A sole mark 19 using many AEC Reliance components in a Seddon-sourced frame with Harrington body being sold in 1960 to Creamline Coaches in Hampshire. But following the success of the Ford R-Series and the Bedford VAL and VAM, Seddon decided to make a similar product, to a variety of wheelbases with Perkins engines; as on the competitors, these were vertically mounted on the front platform. This was launched in 1967 as the Pennine 4, which thanks to vigorous marketing became a strong seller worldwide, the largest order being from Kowloon Motor Bus of Hong Kong, who took 100 11-metre versions with Perkins 170 bhp V8 engines and Pennine Coachcraft 47 seat + 42 standing dual-door bodies. A rear-engined derivative was the Mark 5 (only one sold in the UK, a 45-seat Van Hool coach) and a version with a turbocharged Perkins 6-cylinder engine mounted at the front but under the passenger floor was the Pennine 6. In 1969 a more concerted effort at the UK bus market resulted in the launch of the Pennine RU.
In 1970, Seddon took over Atkinson Lorries to form Seddon Atkinson. In 1974 International Harvester bought Seddon Atkinson, later Pegaso took over the business until it in turn became part of Iveco, the last lorries under the Seddon Atkinson name were built in Oldham in 2004. Bus and coach production having ceased in 1983 when the last Pennine 7 models were delivered.
Originally the 1 January 1971 merger did not affect the lineup, with Seddon and Atkinson continuing to manufacture their old truck ranges in their respective plants. In 1975, however, a new unified range was presented with modern steel tilt cabs designed by Ogle developed together with Motor Panels.This consisted initially of the 400 series range, followed by the Seddon-based 200 Series in 1976 and then the 3-xle rigid 300 Series - higher numbers corresponding to a higher weight rating.
The Atkinson works manufactured the heavier 400 series while Seddon's Oldham plant built all three lines. The 200 has a lower profile and narrower cab (with a correspondingly lower grille) than do the other two. Meanwhile, the cabin of the 400 is mounted higher up than on the 300, necessitating a bigger front bumper with integrated headlights and different wheelwells. The 200 became the first "Truck of the Year", in 1977. The 200 and 300 both used International diesel engines, with the 300 having a 7.64 L (466 cu in) inline-six with 194 hp (145 kW). The larger 400 was available with a range of diesels from Cummins, Gardner, or Rolls-Royce, with power outputs of up to 320 hp (239 kW). The 400 had a chassis which was mostly Atkinson. In 1981 the range was updated and became 201, 301, and 401. A few early 401s were built in Atkinson's Walton-le-Dale plant but then all production was shifted to Oldham. The 201 originally came equipped with the 200's 135 hp (101 kW) International engine, although this was changed to a 148 hp (110 kW) Perkins motor following the termination of Seddon Atkinson's relationship with International. The 401 also received an improved interior, the changed grille, and a much improved gear linkage. The Motor Panels trucks had severe rust problems, forcing the introduction of a new anti-corrosion package in the mid-eighties. This period also marks the beginning of the recession which killed off many of the companies which had been buying Seddon Atkinson's trucks.