On this web site you can find plenty of technical data about various mercedes models, including the w124:
http://macmerc.netium.com.pl
enter the site, click on the english flag in the left menu, scroll down until you find the w124, there are two links at the right - the first is a brief description of that particular chassis an the second contains a list of various engines, the name, the production period and a link which shows you detailed technical information. There is also a "gearbox and performance" link at the bottom of each technical data page.