Replacement of the equipment that pulls San Francisco’s iconic cable cars will require the shutdown of individual cable car lines at different scheduled times over the next three years.

The San Francisco Municipal Transportation Agency is close to executing a contract that includes to replace all of the gearboxes, four of which are inside the Cable Car Barn on Mason and Washington streets. A fifth gearbox is in storage, said Ed Reiskin, director of transportation.

CLARIFICATION The headline of this story has been updated to clarify that cable car lines will be closed one at a time through 2019. As stated in the story, other lines will remain open as work rotates through the system. SFBay regrets any confusion the original headline may have caused.

During the SFMTA Board of Directors meeting last Tuesday, Reiskin said the cable car system was last overhauled more than 35 years ago:

“The reliability of the system obviously relies entirely on the reliability of the machinery that moves the cable underneath the streets.”

The transit agency anticipates to start the work on replacing the spare gearbox tentatively sometime in the summer, which will not have impact to cable car service, said Reiskin.

Following the overhaul of the spare gearbox, work on the California Street line would in start in the fall followed by the Powell lines in the spring of 2018.

The replacement of the gearbox for the Mason line would start the fall of 2018 and the Hyde line would conclude the replacement process in 2019, said Reiskin.

Reiskin said the work to replace the gearbox for the Hyde line would require the entire shutdown of the system.

While crews are working to replace the gearboxes, the transit agency does plan to run bus shuttles.

It will take about 10 days to replace the gearbox and then conclude with a testing period phase to make sure the equipment is working.

Reiskin said the transit agency is well aware of the impact this would have on the tourists who visit each year to ride on the cable cars:

“We are closely with various stakeholders knowing that the demand for cable car service is different depending on the times of the year, thinking about tourist season.”

He added: