Earl (Speedo) Carroll, the lead singer of the 1950s doo-wop group the Cadillacs, who later found contentment, plus a measure of abiding renown, as a New York City school custodian, died on Sunday in Manhattan. He was 75.

The cause was complications of diabetes and a recent stroke, said Vito Picone, the lead singer of the doo-wop group the Elegants and a longtime friend.

One of a cornucopia of street-corner tight-harmony groups formed by young black men in midcentury Harlem, the Cadillacs were among the first to incorporate rigorously choreographed dance moves into their performances.

The group, which flourished for about a decade starting in the early ’50s, had hits with “Gloria” and “Speedoo,” whose title is a variant spelling of Mr. Carroll’s nickname.