Mercedes® Vacuum Modulator Valve, Metal, 450SLC/450SL, 1973-1980

Don't be too quick to replace the vacuum modulator valve if you have shifting problems. Most of the time the shifting problem is caused by another component in the vacuum shift control system on your Mercedes. If you test the vacuum modulator with a vacuum tester and it holds vacuum, chances are there is not a problem with it. However, it the modulator won't hold vacuum and there is transmission fluid in the hose connection on it, it needs to be replaced. Most modulators have an adjuster screw on them. If the trans shifts too hard, back out the adjuster screw(counter-clockwise) a half turn or so. If the trans shifts too soft, make the adjustment in the other direction.