This off-the-books economy is, strictly speaking, not legal. But it is crucial to dozens of residents from Inwood and the Bronx, many of them recent immigrants.

Each carwash operates with informal teams of two to four people. When a customer stops, a symphony of tasks begins: One person dunks two large giant sponges into a bucket and soaps down the roof of the car, the doors, hood and the trunk by hand. Another person rinses the car with a hose with a power-washer attached to it. Another pulls out the car mats and hoses them down until they glint in the light. The exterior of the car is usually done in 10 minutes or less.

As reliable as they are, the carwashes are threatened by future development. Mayor Bill de Blasio’s administration has opened this area to rezoning. A 27-story apartment building is part of the proposal being considered.

Until then, there’s not much for the car washers to do but keep washing cars.

In November, on what felt like the coldest day of the fall, there were just a few young men on 201st Street and 9th Avenue washing cars. They were working quickly — a black sedan and a silver S.U.V. were waiting in line. One man wasn’t wearing gloves, and his hands had turned an orangy red. But he was moving too fast to be bothered.