The work will continue until Tuesday morning and begin again Friday through Monday over the following two weekends.
During the first weekend only, passengers will have to board a Muni shuttle bus from Church and Day streets to Balboa Park. Traffic will be diverted over all three weekends along Church Street between 29th and 30th streets and on 30th between Church and Chenery streets.
Muni bus routes will also be affected, including the 24-Divisadero and its Owl service, and the 36-Teresita.
Work on the J line will cost $1 million and is part of an $18 million improvement project that included work on the N-Judah and the L-Taraval.
Most of Muni’s 70 miles of track is more than 30 years old, the agency reported. Regular rehabilitation and replacement on these heavily traveled tracks is required to keep the rail lines safe and operational.
The improvement project also includes new overhead wire poles, new curb ramps and new train signal priority devices.
For more information, visit www.sfmta.com/rail or cal 311.