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SF to rebuild underground cable car pulley system

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The “sheaves” that pull cable cars are seen at the San Francisco Cable Car Museum on Sept. 21, 2017. (Mira Laing/Special to S.F. Examiner)

San Francisco’s iconic cable cars are hoisted uphill by 35-year-old wheels called “sheaves,” which pull massive steel cables at 9.5 miles per hour.

Now, those 25 underground sheaves will be rebuilt from the ground up as part of an already-planned replacement of the motorized gearboxes that rotate those pulleys.

The San Francisco County Transportation Authority board, comprised of the Board of Supervisors, approved on Tuesday $280,999 to repair the sheaves. The large wheels were last rebuilt between 1982 and 1984, according to the San Francisco Municipal Transportation Agency.

SEE RELATED: SF’s cable car lines to shut down for historic system overhaul

The new rebuild will be completed in 2020, and the funding approved Tuesday will contribute to the $1.6 million project, along with other funding sources, according to SFCTA documents.

The cable cars’ first power sources were steam engines powered by “enormous amounts of coal each day,” according to the Cable Car Museum website. San Francisco replaced that steam system with electric motors in the decade following the 1906 earthquake and fire, according to the museum, which is still used today.

A request for funding from the SFMTA to the SFCTA outlined dire consequences, should the sheaves not be replaced.

“It is critical to overhaul these components to ensure that the cable cars are running safely and to prevent a catastrophic failure that could result in an out-of-service condition lasting weeks as the SFMTA procures and manufactures replacement parts,” SFMTA staff wrote in their request for funding.

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