Mercedes introduced the five speed automatic overdrive transmission in the 1989 model year. At a quick glance it looks the same as the four speed 722.3 and 722.4 models. The extension housing is the quickest way to identify the five speed unit, as this is where the overdrive section was added. The 4-5 and the 5-4 shifts are controlled by a computer module. This manual covers the testing, disassembly, inspection and reassembly of the Mercedes 722.5 unit.