The upper deck of the 108-year-old bridge will be closed Aug. 2-29 while improved lift joints and locks, new switches and signal equipment are installed.
In addition, crews will replace 9,000 linear feet of rail and expansion rail.
The improvements are necessary to reduce incidents that slow or disrupt bridge access, TriMet officials said in a press release.
The closure will disrupt all MAX lines; shuttle buses will replace some service.