Brabham started racing after an American friend, Johnny Schonberg, persuaded him to watch a midget car race.
Midget racing was a category for small open-wheel cars racing on dirt ovals.
It was popular in Australia, attracting crowds of up to 40,000.
Brabham records that he was not taken with the idea of driving, being convinced that the drivers "were all lunatics" but he agreed to build a car with Schonberg.

At first Schonberg drove the homemade device, powered by a modified JAP motorcycle engine built by Brabham in his workshop.
In 1948, Schonberg's wife persuaded him to stop racing and on his suggestion Brabham took over.
He almost immediately found that he had a knack for the sport, winning on his third night's racing.
From there he was a regular competitor and winner in Midgets (known as Speedcars in Australia) at tracks such Sydney's Cumberland Speedway, the Sydney Showground, and the Sydney Sports Ground, as well as interstate tracks such as Adelaide's Kilburn and Rowley Park speedways and the Ekka in Brisbane.
Brabham has since said that it was "terrific driver training.
You had to have quick reflexes: in effect you lived—or possibly died—on them."
 Due to the time required to prepare the car, the sport also became his living.
Brabham won the 1948 Australian Speedcar Championship, the 1949 Australian and South Australian Speedcar championships, and the 1950–1951 Australian championship with the car.

After successfully running the midget at some hillclimbing events in 1951, Brabham became interested in road racing.
He bought and modified a series of racing cars from the Cooper Car Company, a British constructor, and from 1953 concentrated on this form of racing, in which drivers compete on closed tarmac circuits.
He was supported by his father and by the Redex fuel additive company, although his commercially aware approach—including the title RedeX Special painted on the side of his Cooper-Bristol—did not go down well with the Confederation of Australian Motor Sport (CAMS), which banned the advertisement.
Brabham competed in Australia and New Zealand until early 1955, taking "a long succession of victories", including the 1953 Queensland Road Racing championship.
During this time, he picked up the nickname "Black Jack", which has been variously attributed to his dark hair and stubble, to his "ruthless" approach on the track, and to his "propensity for maintaining a shadowy silence".
After the 1954 New Zealand Grand Prix, Brabham was persuaded by Dean Delamont, competitions manager of the Royal Automobile Club in the United Kingdom, to try a season of racing in Europe, then the international centre of road racing.
Brabham started racing after an American friend, Johnny Schonberg, persuaded him to watch a midget car race. Midget racing was a category for small open-wheel cars racing on dirt ovals. It was popular in Australia, attracting crowds of up to 40,000. Brabham records that he was not taken with the idea of driving, being convinced that the drivers "were all lunatics" but he agreed to build a car with Schonberg.
At first Schonberg drove the homemade device, powered by a modified JAP motorcycle engine built by Brabham in his workshop. In 1948, Schonberg's wife persuaded him to stop racing and on his suggestion Brabham took over. He almost immediately found that he had a knack for the sport, winning on his third night's racing. From there he was a regular competitor and winner in Midgets (known as Speedcars in Australia) at tracks such Sydney's Cumberland Speedway, the Sydney Showground, and the Sydney Sports Ground, as well as interstate tracks such as Adelaide's Kilburn and Rowley Park speedways and the Ekka in Brisbane. Brabham has since said that it was "terrific driver training. You had to have quick reflexes: in effect you lived—or possibly died—on them."  Due to the time required to prepare the car, the sport also became his living. Brabham won the 1948 Australian Speedcar Championship, the 1949 Australian and South Australian Speedcar championships, and the 1950–1951 Australian championship with the car.
After successfully running the midget at some hillclimbing events in 1951, Brabham became interested in road racing. He bought and modified a series of racing cars from the Cooper Car Company, a British constructor, and from 1953 concentrated on this form of racing, in which drivers compete on closed tarmac circuits. He was supported by his father and by the Redex fuel additive company, although his commercially aware approach—including the title RedeX Special painted on the side of his Cooper-Bristol—did not go down well with the Confederation of Australian Motor Sport (CAMS), which banned the advertisement. Brabham competed in Australia and New Zealand until early 1955, taking "a long succession of victories", including the 1953 Queensland Road Racing championship. During this time, he picked up the nickname "Black Jack", which has been variously attributed to his dark hair and stubble, to his "ruthless" approach on the track, and to his "propensity for maintaining a shadowy silence". After the 1954 New Zealand Grand Prix, Brabham was persuaded by Dean Delamont, competitions manager of the Royal Automobile Club in the United Kingdom, to try a season of racing in Europe, then the international centre of road racing.
Jack Brabham