The Monongahela Incline was cloaked in the din of transportation as freight trains thundered beneath its twin tracks and cars and trucks roared past its front door on West Carson Street.

But the 139-year-old landmark stayed silent for a seventh day Thursday, awaiting replacement of the steel cables that serve as its lifeline.

The work, set to begin at 7 this morning, will be slow and demanding, said Ken Lockaton, director of facilities and rail management for the Port Authority, which owns the incline.

About 16 crew members trained to work in high places will focus on the two 11/4-inch cables, made of wrapped steel wire, that guide and pull the two passenger cars up and down the 35-degree slope of Mount Washington.

The car on the west track weighs 15,900 pounds and the east car 15,300. "Don't ask me why there's a difference," Mr. Lockaton laughed. The cables are rated to handle at least 125 percent of those weights.

The ends of the cables are attached to the cars and, between them, to a turning electric-powered drum at the upper station. One, called the haul cable, does most of the pulling. The other, the safety cable, is there "to hold onto the car in case there's a catastrophic failure on the other cable," he said. As one car descends, its weight helps to pull the other car toward the top.

A routine annual inspection of the existing cables, using ultrasound-type technology, found deterioration in the core of both. The consultant "recommended that we consider closing it rather than letting it go too far," Mr. Lockaton said. "There was no danger. We were still within our safety parameters."

To replace the worn cables, workers will attach the new ones to the cars and allow them to be pulled slowly up the tracks. Crews will climb the mountain on foot along with the cars, seating the new cables in flywheel-like rollers that are spaced evenly along the tracks. The cables are heavy, covered with lubricant and rough enough to tear skin.

"It's not easy work," Mr. Lockaton said.

Nor is it fast. If all goes as planned, it will take four or five days for the incline cars to make the two round trips necessary to tow the new cables into place. During the work, they will travel 1.5 to 2 mph, much slower than the incline's normal 6-mph cruising speed.

The old cable will be fed into a big dump truck, taken to South Hills Junction, cut up and sold as scrap.

The new cables arrived on spools Thursday from a supplier in Ohio after being prestressed and lubricated.

The crews will work through the weekend if weather permits and hope to have the incline back in service early next week, in plenty of time for its 140th birthday, May 28.

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