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Our recent Snapshot number 331 shows, in the words of its makers Mack, ‘America’s first gasoline driven motor bus’ – and its picture was found in their 1925 book Bus Operating Practice.

That book, however, had far more to tell of the company’s products in 1925. A Supplement was dedicated to the technical excellence of their buses and the plants in which they were built; here are some of the highlights. It started with an image of a fine example of the modern Mack bus of 1925, proudly displayed in front of the Capitol in Washington, D.C., that appears in our headline picture.


Manufacturing capabilities

Fig 1 shows the impressive factories; their captions gave a powerful indication of the scope of the company’s resources. The first is the New Brunswick, N.J. plant with its iron, bronze and aluminium foundries, gear shops, bushing shop, main chemical, microscopic and physical laboratories, and the general service department, all in 486,000 square feet of floor space within 17 acres of ground.

The second picture is of the Plainfield, N.J. plant, devoted entirely to Mack engines ’built completely from raw material.’ The caption explains that ‘Here is located the great dynamometer engine test shop.’ The ground area was 8 ½ acres, with 315,000 square feet of floor space.

The final picture shows the enormous Allentown, PA. plant, devoted to main chassis production, body construction and erection, testing and finishing of the final product. The factory covered 132 acres, with 926,000 square feet of floor space.

Fig 1. The New Brunswick, Plainfield and Allentown plants


Some technical features

Mack were at pains to explain the engineering excellence that underpinned their products. Fig 2 shows four examples of Mack bus components and assemblies, with descriptions designed give a message of strength and reliability: the ‘massive case-hardened and counter-balanced crankshaft’; the bus engine, with a ‘remarkable’ manifolding system and accessible cross-shaft pump and magneto drive; the ‘staunch and rigid’ driveshaft brake unit (in other words a heavy-duty transmission brake); and the ‘rugged steering knuckle and its sturdy connecting parts.’

Fig 2. Four examples of rugged components and assemblies: crankshaft; engine; transmission brake; and steering


Two different chassis

The next page reinforced the same message of durability and excellent design. Fig 6 shows firstly a city type Mack bus chassis from the rear; the caption pointed out its ‘clean simplicity.’ Below it is a long-wheelbase sedan chassis with outriggers. This curious specialised type, quite common in the USA at the time, was defined as a luxury bus with multiple side doors and no centre aisle. outriggers therefore carried a long running board to allow passengers to step up to their chosen door. (See Fig 7 later).

Fig 3. Two chassis: city type and sedan


A remarkable rear axle

Fig 4 shows what the book describes as a ‘phantom view’ of the dual reduction rear axle. This type of axle appeared in the Autocar truck described in our earlier Technical Talk 9 (see below on our website) and, just as in the truck, it allowed the bus chassis to be set high – in the case of a bus, to give excellent visibility for passengers. The view clearly shows the initial bevel gear set, then the small and large straight-cut gears that give speed reduction, and finally the normal differential sitting inside the large straight-cut gear. Not mentioned in the text were the massive rear drum brakes; with no brakes on the front wheels, the combination of these drums and the transmission brakes would have had to provide the necessary stopping power.

Interestingly, this exact concept of double reduction rear axle appeared nine years later on the last pre-war Grand Prix Bugatti, the 1934 Type 59 – But upside down, to allow the dry-sump engine to be mounted as low in the chassis as possible, its drive shaft thus being well below the centre-line of the rear axle.

Fig 4. The double reduction rear axle


A modern city bus

Next came three views of a Mack city-bus. Fig 5 firstly shows the interior, ‘designed for mass-transportation.’ Next is the exterior, with the caption ‘Beauty of external appearance need not be sacrificed to gain an efficient bus for city service as the above view depicts.’ A 1925 concept of beauty, perhaps, but a handsome and workmanlike machine nonetheless. Finally is a view of the driver’s workplace. Much was claimed for it: ‘A pleasing instrument-board, adjustable driver-seat and controls conveniently placed make the city-type bus easy to drive.’ This was an effective piece of promotion to bus operators, who needed to look after their drivers.

Fig 5. Three views of the city-bus


Safety and efficient operation combined

Next came more positive features aimed at reassuring operators – this time regarding an effective emergency exit and a rapid loading and unloading in normal service. Fig 6 firstly shows the rear emergency door with ‘a positive lock-bar’ that prevented the door from being accidentally opened while the bus was in motion, but swung ‘quickly out of the way if an emergency arises.’ It then shows two views, closed and open, of the doors on a front-entrance city-type bus. The caption explained yet another advantage for operators – loading and unloading the bus in a minimum of time: ‘A low step, conveniently placed grabhandles, step light and folding door help to reduce running time en route.’ Persuasive words for a cost-conscious operator.

Fig 6. The emergency door and passenger entrance/exit door


The sedan bus described

Finally in this detailed Supplement of the book came a comprehensive description of the features and advantages of the Mack sedan bus. Fig 7 firstly shows two views of the bus, with the caption ‘Luxury, pleasing body lines and mechanical virtue can be combined in a single vehicle as the sedan bus illustrated above so well shows.’ Below these two is a view of the interior. Strikingly, despite the multiplicity of doors, there is an aisle of sorts, winding its way between the staggered seats. Much was made in the caption of the luxurious appointments: ‘The comfort and ease of one’s own private car do not rival the interior appointments of the sedan. Deep cushions of genuine leather, wide windows of polished plate-glass, adequate ventilation and ample warmth in winter make bus riding over long routes a distinct pleasure.’

Fig 7. Exterior and interior of the sedan bus

Fig 8 firstly shows a different sedan bus with only two side doors; the caption makes much of the ‘wide roomy doors, solidly framed, facilitate the entrance and exit of passengers.’ It then illustrates the baggage compartment of the sedan bus: ‘of ample size and unusually accessible.’ Last of all comes a picture of two more features, one for low maintenance and one for convenience of passengers. The caption reads: ‘Readily detachable upholstery on the doors is a factor in reducing body maintenance costs. A close-up of the positive, smooth-operating window regulators is also shown.’

Fig 8. More features of the sedan bus


A convincing message

The main part of the book Bus Operating Practice was dedicated to general information to bus companies on how to gain the maximum of efficiency and customer service from their operations. This Supplement neatly rounded off that information by promoting, in an honest and thorough way, the qualities of the Mack bus – and how it would be a superb choice for an operator seeking such efficiency and service. It was a fine piece of publicity.

Images courtesy of the Richard Roberts Archive

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