Too much pressure and you will blow the seals. Too little pressure and you will wear out the clutch packs. When installing a new vacuum modulator on your transmission, you most likely will need to adjust it. There are two ways to do this. Many have said you can adjust it by "feel." That means you drive the car, test the shifts, get under the car, adjust the cap, drive the car again, and repeat this process until it "feels right." The other way is to attach a pressure gauge to the transmission pressure test port and adjust it to factory specs. This is the better way, as guessing can cause an "over-pressurization" inside the transmission, leading to fluid and pressure leaks at the critical O-rings and lip seals.
Product Details
Kent has put together this kit with the correct gauge and fitting to attach this to your 722.3 or 722.4 transmission and check pressure with the engine running as you make adjustments. He includes an extra long pressure fuel hose so you can run the gauge inside your Mercedes and test pressure while driving. If you are experiencing abrupt shifts, it could be that your modulator has failed. That is where you should start. Test the modulator with a vacuum hand pump tester to make sure it holds vacuum. If it does not, you need to replace the modulator. IMPORTANT: There is also an upgraded modulator available that INCREASES SHIFTING PERFORMANCE. Unfortunately, you can not tell visibly if a modulator has been replaced with the upgraded unit. If you have no maintenance history, your modulator was updated, and you are not happy with your transmission's shifting performance, I recommend installing a new modulator. Modifications included improvements to the vacuum chambers and thrust pins.
Check out Kent's speed adjuster below if you have the same frustrations he's had over the years trying to adjust the T-pin—especially out on the road, trying to get the pressure right.
PLEASE NOTE: Instructions are included to guide you through attaching this to your transmission and reading the pressure. SPECIFIC FACTORY SETTINGS for your particular model are NOT INCLUDED. Pressure settings vary between models, and it is not possible to include everyone in Kent's instructions, but this information is readily available online if you search for it or refer to a factory manual specific to your car.
TESTING IS DONE WITH THE VACUUM LINE DISCONNECTED and plugged. Golf Tee included for this
The gauge can me mounted inside the car for easy viewing while completing the road test.
The "speed adjusters" that are included with help you easily adjust the tip pin on both types of modulators ( early and upgrade).
The adjuster for the early style prevents the t-pin from falling into the slots while trying to turn it.
The adjuster for the later (upgraded) modulator will allow you to easily turn it by just reaching under the car lying on the ground. (ie road test). Watch the video here for more details.
As of 3/25/26, a new 200 psi gauge is being used, so you can do a line pressure test (full working pressure can approach 190 psi under load). A new video has been added that explains how to do this, as well as a governor pressure test. See the YouTube video above for more details on why this is important.
You can order the MASTER KIT with a new modulator included. See related products below.
Related Products:
1981 to 1995 722.3 722.4 MASTER Transmission Modulation and 3X Pressure Service Kit
This is Kent's master kit for solving a number of transmission-related shifting problems. Please note it will not solve them all - particularly if your transmission is worn out.
1981 to 1995 722.3 722.4 Transmission Vacuum Modulator Valve
9/2025 Update: Green and Red Modulators are NLA, and we have been informed that they will not be remanufactured. But, do not panic! You may have heard that you must replace your 1981 to 1995 transmission modulator with the correct color top.
123 107 126 201 124 722.3x and 722.4x Transmission Modulator O-ring Seal
If your modulator is working ok, but leaking transmission fluid, you may only need to replace the inexpensive oring ( o ring ). You do have to be careful when removing the modulator from the transmission. For instructions (available separately) see related products below.