Used spotlight: International S-Line

The International S-Line was a very popular truck in Australia from its launch in 1979 until production ceased in 1999. The Aussie S-Line was developed from US models that were produced in two cab widths for medium-heavy and line-haul applications.

This is one of a series of reports on used truck models that feature regularly in classified listings on Trucksales. In each we'll examine a specific truck model or family, and provide information on its history, development, and strengths and weaknesses.

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The International S-Line was available in a 4x2 or 6x4 rigid format or as a prime mover, and it was also the base for International's heavier-duty Transtar models.

By the mid-1970s there was a clear need for Inter' to come up with a heavy-duty truck to compete with the extremely successful Ford Louisville range and Kenworth's W-models. International was doing well in the cab-over-engine market with its 3070 and T-Series trucks, but the market was increasingly demanding bonneted trucks. International in Australia was selling the stop-gap Transtar 4270 and 4370 models, but the cab was past its use-by date. An Australianised S-Line was just the ticket…

The Australian-built SF2600 was based on the 'long-bonnet, set-back front axle' US-market model, but used the wide cab instead of the narrow cab, to provide more engine-bay space for its RHD steering position.

The engines available in the S-Line were Cummins L10 and N14, and the International DT466. The decision not to offer GM and Caterpillar engines proved costly, because the L10 and DT466 didn't become anyone's favourite and the Cummins 14-litre six had a series of problems that saw Big Cam I, II and III released in rapid succession. It wasn't until the release of the 86NT in 1986 that faith in the reliability of Cummins engines was restored.

The S-Line also faced tare weight problems when stacked against lighter Louisvilles and Kenworths.

In 1986 the S-Line was given an upgrade and the DT466 was dropped in favour of Detroit Diesel's 6V92. The upgrade included vertical grille bars to replace the horizontal ones while 'International' badging was replaced by the Navistar logo, following the US company's financial crisis that saw the agricultural division and IH logo sold off to Case.

Parallel with the S-Line upgrade was replacement of the Transtar model by the 9000 Series, but this temporary arrangement was superseded by the S-Line-derived Transtar model in 1988. The truck used the S-Line cab, but it was raised 200mm and had a longer, wider bonnet that could house a 50-per cent larger radiator, to cool higher-power N14 and Caterpillar 3406 engines.

The next iteration of the S-Line was in 1991, when streamlined bonnets were fitted to all models and the Transtar version too. That was a tricky design operation, because the rear section of the front mudguards was a steel pressing and part of the cab structure. As a result, the Transtar had a slightly odd mudguard line.

The 1991 Transtar used the S-Line's AYB 6.5-tonne-capacity front axle, but with dual steering boxes in place of the S-Series' one.

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I remember testing some Inter' press evaluation trucks in early 1991 and reckoned they were very competitive with the mainly Kenworth and Western Star opposition. The interiors had been given a makeover in 1990 that improved noise levels and ergonomics, but the quirky, ultra-long gear lever remained.

International had been a bit shy in the late 1980s with press-test trucks, but the company felt sufficiently confident with its latest models to invite truck journos for a spin.

Inter's wide cabs provided more interior space for drivers than the narrow-cab opposition and also a more stable base for rear vision mirrors. They also allowed easy walk-through to an optional integrated sleeper.

Both trucks had revised dashboard layouts that incorporated warning lights and controls for then-new electronically controlled Cummins Celect engines.

The Transtar was powered by a 460hp Cummins Celect 460E, driving through an Eaton RTO15618 18-speed box to Rockwell SSHD diffs, suspended by a Rockwell AC6P lightweight six-rod. The S-Line had a 430E, coupled to an RTO14613 13-speed, with SP40 diffs on International Air System suspension.

Both trucks performed well, once I re-adjusted to the long-throw gear lever action, and they could be stirred along quite happily at 40-tonnes GCM, mostly using the boxes as 9+1s. The 1991 horsepower figures look a tad light on when compared with what's on offer in 2020, but for the early '90s they were cutting edge and 460hp was considered just fine for B-Double work: that's what the 18-speed box was for!

The S-Line/Transtar family was developed and produced in a joint US-Australian effort against a backdrop of financial disaster, so it's a minor miracle that the trucks were as good as they were.

By 1983, the US-based International Harvester Company had placed its Australian subsidiary in court-supervised receivership. In a massive asset sell-off, the US company retained only its truck and engine divisions, and renamed itself Navistar International Corporation.

In Australia, the local company continued trading, but disposed of buildings and assets, including selling the excellent Anglesea Proving Ground (now the Australian Automotive Research Centre) to Linfox.

From 1988 until 1992, David Eagle, one of the few very impressive truck company CEOs I've met, steered International Trucks Australia, while negotiating its sale to IVECO and guaranteeing its future.