FYI:
Stock 124 single-diaphragm 10" booster has a boost factor of
3.85
The 190E 2.6 has a dual diaphragm 8"/9" booster with a factor of
4.50
The 400E/500E has a dual diaphragm 8"/9" booster with a factor of
5.60
Although the 190E and 500E boosters look identical externally, they are different internally, and provide different levels of power assist. The 500E booster on a lighweight sedan provides a little
too much assist (pedal effort is too light). But on a heavier car (like Neil's wagon, which weighs almost as much as the 500E) it works fine. I picked up a 190E booster than I plan to install soon, this should correct the pedal feel on my '87 sedan.
Details are in this spreadsheet, look at the "MC & Booster specs" tab:
http://www.w124performance.com/docs/mb/W124/124_brakes.xls
