Preservationists are trying to put the brakes on two big Manhattan projects that would take buildings that were once open to the public and convert them into housing for the very rich.

For 35 years, Marvin Schneider came here like clockwork to wind the rare mechanical clock atop this 19th century Tribeca office building.

"I would wind them and it would be good for a week," Schneider said. 

But that stopped in March after the developers, who bought the landmarked building from the city, blocked Schneider and the public from coming in. The clock, now covered in scaffolding, has been stuck in time ever since.

"It stopped working at 10:25 or so," he said.

The El Ad Group and the Peebles Corporation plan to rip out the mechanical clock in order to convert the tower and the rest of the building into luxury condos. The developers declined comment.

The Landmarks Preservation Commission approved the overhaul last year.

"How disposable is our culture?" asked Tom Bernardin with Save America's Clocks. "Is there nothing that is permanent, that is gonna be there to educate people? 

Like many controversial projects, this one is now in court.

"The developer is seeking to violate the landmarks law," said attorney Michael Hiller. "An interior landmark is necessarily open to the public."

The fight over landmarks is going on across the city. Here on the Upper West Side, preservationists are trying to stop a plan to convert this church into luxury condos. 

The landmarks commission approved the project earlier this year, but opponents want the agency to look at it again and block plans to remove religious symbols from the stained glass windows.

Already, the interior of the church, which isn't landmarked and can't be protected, has been gutted. Opponents fear a dangerous trend.

"What we're seeing now on a scale that I've not seen in over 20 years of practice is the privatization of public assets," Hiller said.

The developers of this project didn't return our calls, but supporters say the plan protects the landmarked part of the building.

"In terms of the exterior, I think this is a boon to the majority of the community because this building is being restored," said Ann-Isabel Friedman of The New York Landmarks Conservancy.

As for the Tribeca clock, time may be running out. Work to dismantle it could begin early next year.