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  • 1973 Maxidyne 300 Series Mack Engine

1973 Maxidyne 300 Series Mack Engine

The High-Speed, High-Torque Maxidyne Engine

Bill Senefsky
Jul 11, 2007
Photographers: Courtesy of the manufactures
Photo 2/4   |   New for 1973, the Maxidyne 300-series Mack engine was all about performance and durability. It featured filtration for the coolant, dual oil filters (10 micron), two-stage fuel filtration (down to 2 micron), and a triple-belt alternator drive. Rated at 285 hp and 1,080 lb-ft of torque, this engine also featured the world's first air-to-air intercooler for on-highway truck engines.
The high-speed, high-torque Maxidyne engine
Like many others of his generation, John Mack's first work experience was a turn on the plow. His German parents owned and operated a farm near Scranton, Pennsylvania, where John and his four brothers were expected to row with the lines.
Mack Runs Away from Home
His farming experience was quickly put to rest when he ran away from home in 1878. However, his horse training led to a paid position as a Teamster. Since steam engines were also a part of his farming vocation, John managed to move up as a steam-engine apprentice. Such engines were standard fare in many vocations, so Mack's background took a turn, sending him to sea and work in a variety of locations, including the Panama Canal.
In 1890, John was employed at the Fallesen and Berry Carriage and Wagon Co. Due to his quick success, he convinced his brother Augustus to come on board and purchase the firm located in Brooklyn, New York. A year later, their brother William joined the firm after operating a wagon-building company in Scranton, Pennsylvania. The family's purchase paralleled one of many financial panics that occurred during this period. Undaunted, the brothers quickly adjusted and went into steam-engine maintenance and repair.
Mack Builds a Bus
The upshot of the Macks' new venture was their involvement in the radical development of self-propelled vehicles. Always exacting in their standards, the brothers dabbled with both steam and electric power, and 1900 was the year of their first success. That was the year their first gas-powered vehicle, a four-cylinder, 20-passenger bus, was introduced. This 40hp unit featured a three-speed transmission mated to a cone clutch. Like others of the day, their novel platform was chaindriven. The vehicle, custom-built for the sightseeing firm of Harris and McGuire, operated successfully in Brooklyn's Prospect Park for eight years.
Never ones to be shy, the brothers used this platform in a successful ad campaign, "The first Mack was a bus, and the first bus was a Mack." This successful bus platform was converted into a truck in 1908 and racked up more than a million miles in its long career. Dubbed Old No. 1, this platform marked the beginning of American truck development and forever established Mack as a brand noted for tough, reliable, high-quality trucks. In 1905, the company moved its headquarters to Allentown, Pennsylvania. The Mack Brothers Motor Car Co. was incorporated, and brother Joseph became a stockholder.
Mack Innovations
The new company quickly developed innovations. The brand was one of the first to mount a cab over its powerplant to increase driver visibility, thus improving maneuverability. The Manhattan cabover was introduced in 1905. The constant mesh transmission designed to protect gearing from being crushed and stripped was produced, allowing operators to immediately shift from Low to High and vice versa, skipping intermediate gears when necessary.
Mack also produced a variety of rail cars and locomotives in 1906. The brothers expanded their operations in Brooklyn by setting up the Mack Brothers Manufacturing Co. to continue wagon production and the repair of motorized vehicles.
The Mack Junior brand appeared in 1909. This lightweight, 1 1/2-ton truck platform featured lefthand steering. Of interest is the fact that the heavier Mack Senior-series retained its steering wheel on the righthand side; both platforms utilized chaindrive. The company produced 600 units a year and had 825 employees in 1911. This was also the year in which the young company could claim it was the leading gasoline truck producer in America.
Financial clouds appeared on the horizon by 1913, with decreased truck sales felt by all in the industry. Mack merged with Saurer Motors and quickly thereafter the Hewitt brand. The mergers brought along accompanying board members with conflicting views. Unfortunately, the Mack brothers left their company, never to return.
Mack's new chief engineer, Edward R. Hewitt, however, was responsible for a new medium truck series that many feel was the brand's mainstay from 1914-1936. The Mack AB-series was powered by the company's proven four-cylinder mill backed up with a three-speed transmission and a worm-driven axle. Hewitt's replacement, A.F. Masury, created the equally famous Mack AC, the heavy-duty, chaindriven platform that featured clutch brakes. This platform was solely responsible for the phrase "Built like a Mack truck" because of its ability to haul the heavy artillery pieces to the trenches in World War I.
The '20s were a period of growth and further innovation. Mack was producing 7,000 trucks a year by 1927. The company also added four-speed transmissions, dual-reduction drive, rubber shock insulators, and improved cooling systems.
Inline-Six Engine Debuts
High-speed, inline-six, gasoline engines were introduced by the end of the '20s. Known as the B-series, the lineup included the BJ, BM, BQ, and BX engines. These engines led trucking's transition from established slow four-cylinder platforms to the modern highway-speed models we have today. The first practical off-highway AP dumper was also introduced, and a fleet of these trucks was utilized in the construction of the Hoover Dam.
In the years of the Great Depression that followed, 250 automotive brands disappeared, and truck demand also suffered. At Mack, sales fell by 75 percent from 1929-1932. To answer falling sales and the entrance of new competition, Mack introduced its revolutionary CH- and CJ-series of cabover platforms. Mack survived by cutting costs and benefited from increased acceptance of truck transport and higher demand for bus platforms.
Mack Builds Its First Diesel
In 1938, Mack continued its engineering leadership by introducing the first Mack diesel engine. The new in-house-produced units were the first diesel powerplants made by a truck manufacturer.
As World War II loomed on the horizon, Mack began producing the NR-series truck, a military spec'd six-wheel tank transporter initially sold to Britain. With the opening of hostilities, the MO-series truck was produced to pull a 150mm artillery platform. Military equipment was produced by government mandate until 1946.
Seven years later came the introduction of the Thermodyne END-673 diesel engine. An upgraded diesel unit, the new mill featured direct injection, which produced greater power output, combined with Mack's reliability. Eighty percent of the company's famous B-series trucks were equipped with these powerplants.
The Mack Advantage
In 1966, the company was suffering from a lack of capital, but the new Maxidyne ENDT-675 diesel series was introduced with great fanfare. This novel engine produced 237 hp with peak torque at 1,200 rpm and delivered a usable powerband up to 2,100 rpm. This was a huge innovation because Mack offered a mill with a 52 percent torque rise (torque rise is peak torque divided by torque at rated horsepower). No big deal, you say? Consider the competition offerings of a mere 20 percent, and today's versions have an average of 35 percent. Mack engineering provided the low-end grunt by tweaking the mill's internals, modifying the fuel system, and playing with the turbo pressure.
Mack capitalized on its engine's brute-force advantage by producing a five-speed triple countershaft Maxitorque transmission. The idea was intended to make the driver's job easier (less shifting), compared with the competition's 10-13-speed transmissions. This meant a Mack truck traveling at 50 mph in Fifth gear with a heavy load could climb a 6 percent grade with the driver downshifting only one gear. In Fourth gear, the Maxidyne (Maxis) engine could maintain 1,700 rpm, and the truck would crest the grade at 20-25 mph. Maxis were highly regarded in over-the-road, dump-truck, and mixer applications, where low speeds were common and constant shifting was a pain. In 1973, an intercooled ENDT 676 Maxidyne-series engine was introduced. This new unit featured 1,080 lb-ft of torque with 285 hp.
With current emissions laws, some of the old broad powerband coverage has been lost due to the EPA's exhaust-gas recirculation. The five-speed "tyranny" is history, too, but Mack's new TM-309-M six-speed is available with three extra-low gears. It also features a pushbutton for Reverse, where all six speeds can be utilized as well. The latest Maxidyne series includes the 300-, 335-, and 370hp variants-all are EPA controlled. In 2000, Mack truck became a wholly owned subsidiary of AB Volvo. Mack trucks are currently sold in 45 countries worldwide.