History of the Mack B Series Trucks

by Rob Wagner

Mack Trucks, Inc., originally called the Mack Brothers Company, began producing trucks in 1900. Mack offered heavy-duty commercial trucks, school buses and fire engines. For many years leading up to the 1960s, Mack kept its homely early postwar styling and even continued to produce some chain-driven models through 1950. Mack sold two versions of the B-Series: one offered in 1927 and the other in 1949.

Early B-Series

Mack of Allentown, Pennsylvania, manufactured a wide range of medium-size heavy-duty trucks throughout the 1920s. In 1927, it launched the BJ line of three- and four-ton trucks, powered by a 126-horsepower, six-cylinder gasoline engine. It also featured front wheel brakes in an era in which vehicles only had rear wheel brakes. By 1931, 5 to 8-ton models became available, with optional tractor-trailer models with 10-ton capacities. A BL version featured Lockheed hydraulic brakes and ranged from 1 to 8 tons. The BQ model had a six-wheel chassis for better stability under heavy loads.

Postwar B-Series

From 1940 to 1956, Mack produced its L-Series trucks that employed aluminum engine parts to keep weight down and to provide durability during distance driving. In 1950, the A-Series arrived with gross vehicle weight ratings of 17,000 to 40,000 pounds. However, Mack started phasing out the L- and A-Series vehicles by introducing the B-Series models in 1949. The new B-Series had a wider chassis and front axle to improve handling, especially on dirt roads in logging areas. Mack dropped the truck's boxy look for a rounded cab, hood and fenders for a more streamlined appearance. About 127,000 B-Series trucks left the assembly line before the R-Series models replaced them in 1966. Many B-Series remained on the road in 2011.

Thermodyne Diesel Engine

B-Series Macks initially received a Cummins 220 in-line six-cylinder diesel engine. It shared many characteristics of the L-Series trucks with a Mack five-speed gearbox and Mack Duplexer auxiliary transmission. In 1953, Mack introduced the END 673 Thermodyne in-line six-cylinder diesel, which featured an open-chamber, direct fuel-injection system. The standard Thermodyne generated between 170 and 211 horsepower during its production run, while the turbocharged ENDT 673 developed up to about 220 horsepower. Between 1953 and 1966, about 80 percent of all Macks were equipped with the Thermodyne. However, by the beginning of the 1960s, more Macks began receiving the Cummins engine because it generated more power than the Thermodyne and it matched the advanced Jacobs Engine Brake system.

Fire Apparatus

In 1956, the U.S. Navy awarded a contract to Mack for 33 B-Series fire pumpers. It was the first time since 1942 that the Navy sought a Mack vehicle fleet. Ultimately, Mack supplied 900 B-Series fire trucks to cities, counties, and state and federal government fire agencies from 1954 to 1966. The Navy's Mack B475CF versions featured a 204-horsepower Chrysler V-8 Hemi engine and a five-speed manual transmission. The Mack were the first Navy pumper to have an enclosed cab. It was equipped with a Hale two-stage pump that could generate 750 gallons per minute from a 300-gallon water tank. Its wheelbase was 168.5 inches, with an overall body length of 23.5 inches.

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