The bus chassis variant of the International S series is a cowled bus chassis (conventional style) that was produced by International Harvester (later Navistar International) from 1979 to 2001. Produced primarily for school bus applications, the chassis was also produced for other applications, including commercial-use buses and cutaway-cab buses. In addition, the cowled chassis formed the basis for front-engine and rear-engine stripped chassis produced for bus applications.
Designed as a replacement for the International Loadstar bus chassis, the S-series bus chassis was produced in two distinct generations. Matching the development of the International S series, during 1989, the model line underwent a major update, becoming the International 3800. The 3800 was also made in a truck variant. In 2004, the International 3800 ended production, replaced by the International 3300 (a cowled-chassis version of the International 4300/DuraStar). In production for over 25 years, the S-series bus chassis was the longest-lived model line ever produced by International and the final Navistar product line developed by International Harvester.
First generation (S series; 1979–1989)
Released during 1979 production, International Harvester introduced the S-series bus chassis alongside its conventional-cab counterpart. Replacing the bus chassis variant of the International Harvester Loadstar, the S-series chassis continued the use of the "Schoolmaster" product name. In a shift from being an adaptation of a truck chassis, the Schoolmaster was designed as a distinct model line intended solely for bus use. Along with completely straight frame rails, the chassis was designed with a flat-back firewall, allowing for body mounting with minimal design adaptations.
During its production, the Schoolmaster changed relatively little. Along with revisions to the powertrain, many changes reflected the manufacturer transition from International Harvester to Navistar International. For 1987, the grille underwent a revision, with the "International" wording moved from the top of the grille to the bottom left, paired with Navistar's famous "Diamond Road" logo (replacing the IH logo on the steering wheel). In another change, Navistar ended the use of gasoline-fuel engines (in all of its vehicles).
Model overview
The Schoolmaster was produced as a variant of the International S1700 and S1800 (Class 6 trucks), with the lighter-duty S1700 and heavier-duty S1800. Along with powertrain configurations, the two model ranges were distinguished largely by suspension weight capacities. Following International traditional model nomenclature, the specific model numbers for the Schoolmasters ended in 3; gasoline-engine examples were given "23" model numbers while diesel-engine examples were given a "53" model number.
Powertrain
At its launch, the Schoolmaster was offered with four gasoline engines and three diesel engines (dependent on the model range specified). The S1723 was powered solely with gasoline engines, with the International 345 V8 as standard, with three optional gasoline V8s (the 392, and the MV404 and MV446). The S1823 was offered solely with the MV-series V8s (which ended production after 1981). The S1853 was powered by diesel engines, with a standard 9.0L V8, along with a DT466 and Caterpillar 3208 as options (the latter, discontinued around 1982, for the Schoolmaster).
For 1983, an S1753 was introduced to introduce diesel engines to the S1700 chassis; in place of the 9.0L V8 and DT466 inline-6, International debuted a 6.9L IDI-series V8. In 1987, the displacement of the IDI V8 was enlarged to 7.3L. A 4-speed manual was standard on the S1700 variants, while S1800 variants were equipped with a 5-speed manual; a 4-speed automatic was optional on all engines. Following the discontinuation of the MV-series engines, the S-1823 was phased out after 1981, while the S-1723 was phased out after 1986, after International withdrew production of gasoline engines entirely.
Second generation (3800; mid-1989–2004)