This is the new Mercedes O.E.M. replacement for the GREEN transmission vacuum modulator found on most of the models listed above. This unit has been upgraded from the original for better shifting performance (you will note it looks quite different). This new part has a stronger vacuum containment chamber and the thrust pin included has been redesigned with less mass and made with a new material to eliminate fluctuations in pin length during extreme temperature changes. The cap has also been redesigned to reduce leaks and when set up properly you do not need to remove the cap to make fine modulator adjustments! Be wary of cheap aftermarket modulators. We have found a lot of them leak and fail prematurely.
PLEASE NOTE: The vacuum sealing design is different on this newer style. When testing out of the box to see if it holds vacuum, you will note that it leaks down slowly. This DOES NOT mean the modulator is bad. The adjusting cap has to be on TIGHT for it to hold vacuum. A very very slow leak down of vacuum with the cap on is normal and does not mean the modulator is faulty.
Internal spring tension has been increased to improve cold start shifts from 1st to 2nd gear and reduce flaring when shifting between 3rd and 4th gear. WARNING: There are other things that can cause problems with poor shifting, so there is no guarantee this new part will fix them. But due to the cost and ease of installation this is a good place to start. Kent's manual on diesel automatic tuning covers all the other things that could cause shifting problems. See related products below for this advanced transmission tuning manual.
If you can safely jack up your car and get under it with a good light and some basic metric hand tools then replacing the modulator is something you can do yourself! Installation instructions are available separately. These will only explain how to remove and install. For proper modulator pressure adjustment we also recommend Kent's modulator adjustment kit with pressure gauge. See related products below for instructions and pressure set kit:
This is a picture of what the old modulator looks like. Remember, it is the color match you should be concerned about. You will love the features of this new OEM Mercedes modulator.
IMPORTANT: From Kent's garage: "I have found modulators often only last for 12 to 15 years maximum before they start to weaken and eventually fail. Just imagine how many times that diaphragm is moving in and out while you are driving. My recommendation is that you replace it first when troubleshooting transmission shifting problems. Then the modulator can be eliminated as a possible cause of your transmission problems. Proper adjustment is required after installation using a pressure gauge connected to the transmission from under the car. You can not accurately adjust it by guess or by feel. When chasing automatic transmission shift problems you want to start by knowing the modulator is healthy and pressure is set correctly before moving on to vacuum system troubleshooting and fine tuning."
To learn more about fine tuning the vacuum shift controls on your diesel automatic please refer to Kent's transmission tuning manual (look below in related products)
The modulator is located on front left side of transmission body, for 123 and 126 Chassis Turbo diesels from 1981 to 1984 ONLY. This also fits the 190D 2.2 from 1984 to 1986 and the early 190E 2.3 four cylinder gas. Failure of this valve's diaphragm causes hard or abrupt shifting. Please inspect your valve and confirm it is GREEN before ordering this replacement. Modulator pressure should be checked any time you are debugging shift problems. It must be checked and adjusted when installing a new modulator. When the modulator pressure is too high or too low your transmission will suffer. _______________________________________________________________________________