The fourth day of the Long Island Rail Road’s so-called “summer of hell” service disruptions again went fairly smooth, except for an incident that caused heavy crowding on a morning rush-hour Montauk/Babylon train.

After discovering a brake problem Thursday on one car of an eight-car morning train running from Speonk to Penn Station, the LIRR took the car out to be serviced, resulting in the train operating one-car short.

On social media, passengers complained about severe overcrowding on the train, which made 18 stops. In a telephone interview, commuter Sonny Malhotra said he was still able to get a seat when he boarded at Bay Shore, but by the time the “jam-packed” train reached Massapequa, “people were just falling over each other” trying to squeeze into the train, which is making additional stops this summer to accommodate passengers affected by the Amtrak-related service disruptions.

“You’re adding stops, and now you’re going with fewer cars? That’s a recipe for disaster,” said Malhotra, adding that his LIRR commutes this week have been otherwise uneventful. “Of course things happen, but you’ve got to have contingency plans in order. We’re paying 400 bucks a month and people are not getting to sit.”

The LIRR disputed that there were no seats on the train, saying that, even with one fewer car, there were enough seats to accommodate all 1,021 customers on board.

“That train should have all of its scheduled cars tomorrow [Friday],” the LIRR said on Twitter. “We don’t like running trains short either, but equipment issues can make it necessary. Not ideal but it prevents cancellations.”

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The LIRR has been running reduced rush-hour service to Penn Station since Monday — the first weekday of a summerlong Amtrak infrastructure renewal project at Penn Station that requires taking at least three of the Manhattan hub’s 21 tracks out of service until about Labor Day. Gov. Andrew M. Cuomo predicted that period would be a ‘‘summer of hell’’for LIRR commuters.

The fourth day of the revised LIRR schedule also came with a new bus schedule.

In response to three days of low ridership, the Metropolitan Transportation Authority has cut back bus service for LIRR commuters. The agency has reduced departures and discontinued service from three of its eight pickup locations on Long Island: the North Hempstead Beach Park, Roosevelt Field mall and Bethpage State Park locations. Buses serving the five remaining park-and-rides will run every half-hour into and out of Manhattan.