SAN FRANCISCO (AP) — San Francisco’s famed cable cars are running again after a 12-day service halt to rehabilitate the gearboxes that help run the 19th century public transportation system.

The wooden cars are slowly climbing San Francisco’s hills Monday, with operators ringing their brass bells.

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The San Francisco Municipal Transportation Agency removed the manually-operated cable cars from streets on Sept. 11.

The gearboxes spin 30-foot (9-meter) tall wheels in a cable car powerhouse that pull the 12 miles (19 kilometers) of steel cables under the cable car tracks that lift the engineless cable cars up the city’s steep hills.

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Officials say the work is part of an upgrade project started in 2017 to repair heavy equipment in service since 1984.

It has an estimated cost of about $6 million.

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