Thomas Saf-T-Liner C2

Design and manufacture

As the Thomas Saf-T-Liner C2 marked the first completely new bus body for the company since 1962, Thomas redesigned a number of its manufacturing techniques coinciding with its introduction.

To minimize the number of rivets and welds (a weak point of structural integrity on a bus body), adhesive bonding was used to complete a number of body joints. In the cases where fasteners are needed, self-piercing rivets are used. These engineered fasteners join layers of metal together without punching completely through the bottom layer, thus reducing the likelihood that rivets will become the source of leaks in the future.

To simplify vehicle maintenance, the electrical system of the C2 was redesigned over previous buses. In place of individually wired circuits, the C2 uses multiplexed wiring. With the system, switches on interior control panels can be removed and rearranged to suit the driver without any rewiring or reprogramming.

Chassis

Cummins ISB6.7 in a Saf-T-Liner C2

Although the Freightliner M2 was also developed for use in cutaway applications at its launch in 2002, the use of the M2 chassis for school bus applications paired lead Freightliner subsidiary Thomas Built Buses and Freightliner to develop the Saf-T-Liner C2 as an entire vehicle. Unlike its FS-65 predecessor, the C2 chassis has been paired exclusively with Thomas-manufactured bodies; the Freightliner grille badges are replaced with Thomas badges.

At its launch, Mercedes-Benz MBE diesel engines were the standard engines, with optional Caterpillar C7 and Cummins ISB diesels. In 2008, the Cummins ISB6.7 replaced the MBE900 as the standard engine, with the C7 discontinued. From 2010 to 2018, the sole diesel engine in the Thomas C2 was the Cummins ISB6.7; for 2018 production, the Detroit Diesel DD5 becomes an option.^[5]

The C2 comes standard with an Allison 2500 automatic transmission with an Allison 3000 automatic transmission as an option. The Saf-T-Liner C2 is the only school bus in North America offered with a manual transmission; a rarely-ordered option is a Fuller 6-speed transmission.

Body

Rear view, Thomas Saf-T-Liner C2 (2004-2007)

For the Thomas Saf-T-Liner C2, Thomas Built Buses uses a body designed alongside the Freightliner M2-derived chassis, sharing no parts with either the Saf-T-Liner Conventional or the Type D Saf-T-Liner EF/ER. Although Freightliner has produced M2-derived buses in cutaway-cab form, the Saf-T-Liner C2 is the only vehicle derived from a cowled-chassis variant.

Coinciding with the shift to the Freightliner M2 cowl, several changes were made to improve the aerodynamics of the Thomas school bus body. Most visibly, the windshield underwent a complete redesign. To allow the use of the stock Freightliner dashboard, the traditional multipane vertical windshield was replaced by a sloped single-piece curved piece of glass^[6]; while taller than the stock M2 windshield, the C2 shares the same windshield wipers as the M2. Above the windshield, the front bodywork matches the slope of the windshield; to further improve aerodynamics, the lenses for the lenses for the red and yellow warning lights are faired into the body (where allowed by regulations).

On the rear of the C2, Thomas followed a similar design as the front, fairing in the warning lamp lenses and using flush-mounted glass. While not substantially physically taller than its predecessor, Thomas visually extended the height of the C2 with larger passenger windows than previous school buses, along with larger exit doors.

On the exterior, the Thomas Saf-T-Liner C2 has largely remained the same throughout its production run. In late 2007, the passenger windows saw a minor change, with a shift to equal-size window sashes (previously, the top half was larger). In the rear, the taillights were redesigned and enlarged, later becoming a standard design for all Thomas buses. To improve driver sightlines, the mirror bracket for the passenger-side rear-view mirrors was extended forward.

In the interior of the Thomas Saf-T-Liner C2, Thomas made many advancements in an effort to maximize parts compatibility between the bus body and donor chassis. In previous conventional-style school buses, from the firewall rearward, only the steering column and instrument cluster were used. With the interior of the Thomas C2, the dashboard of Freightliner M2 106 is used in its entirety, with only minor changes (the ignition switch was required to move to the center of the dashboard).

Along with being optimized for aerodynamics, the body of the Thomas C2 was designed to optimize visibility for the driver. With the slope of the windshield, the front entry door was moved several inches back, creating a large window ahead of the main entry door to improve visibility around the loading zone (similar to the Thomas Vista and nearly all small school buses); a similar quarter window was added between the windshield and driver's sliding window. Along with a taller body, the passenger windows were enlarged compared to other Thomas buses. Additionally, the C2 has larger emergency exits compared to the FS-65 and the Thomas Saf-T-Liner Type D buses.^[7]

Along with an air-operated entrance door, in 2012, Thomas added an electrically-operated entrance door as an option. Since 2016, a manually operated passenger entry door was added as an option.

Other uses

Alongside its yellow school bus configuration, Thomas Built Buses produces multiple configurations of the Saf-T-Liner C2, including MFSAB versions (activity/childcare versions), along with the Transit Liner C2 commercial-use bus. Through aftermarket manufacturers, the C2 also serves as a donor vehicle for multiple types of specialty vehicles derived from bus bodies.^[8]

Alternative fuel/hybrid/electric powertrains

In 2007, Thomas introduced a hybrid-electric version of the Saf-T-Liner, named the C2e. Designed as a parallel hybrid, the C2e retains the Cummins ISB engine, adding a lithium-ion battery pack with an electric motor/generator. In the summer of 2013, Thomas removed the C2e product literature from their website, marking its discontinuation.

In May 2014, Thomas Built Buses began production of a propane-fueled version of the Saf-T-Liner C2.^[9] Powered by a 339 hp 8.0L V8, the C2 Propane is paired with the Allison 2300PTS automatic transmission. The engine is designed by Powertrain Integration (an OEM supplier to General Motors) with the 8.0L V8 named the PIthon.^[10]

In 2016, a compressed natural gas (CNG) variant of the Saf-T-Liner C2 was released. The first Type C (conventional-style) school bus produced with a CNG fuel system, the Saf-T-Liner C2 CNG is powered by a version of the Cummins ISB 6.7 engine.^[11]

In late 2017, Thomas unveiled a battery-powered prototype of the Thomas Saf-T-Liner C2; called "Jouley" (after the unit of energy), the prototype previews an all-electric C2 intended for production during 2019.