Automatic Transmission Modulator Valve Replacement - W126 Mercedes 722.3 

Did it solve your late shift?

This modulator allows for fine tuning adjustments. Couple that with adjustments made to the Bowden cable, and yes. There is a high degree of adjustment available and simple replacement alone is just the first step.

Clockwise adjustments of the modulator increase shift firmness. Counter clockwise adjustments make them smoother.

The cap part number is "#" ? Clarify.

From what I understand, the situation you are describing is quite common. Long story short I believe it has to do with the amount of vacuum supplied to the modulator by the VCV (Vacuum Control Valve) under these part throttle conditions. Here is a document detailing the modification of the VCV to help with this situation. I've not done it however. jenniskens.livedsl.nl/Technical/Tips/Files/Mercedes%20722.4%20adjustment%20guide.pdf

@@ImpalamansGarage This article was awesome but I failed to mention, mine's on petrol, not a diesel. I read most of it thinking maybe some parts will overlap but feels like on diesel, the vacuum system is completely different.

No need to drain the ATF to remove the modulator.

@@ImpalamansGarage Thank you!

Clockwise adjustments of the modulator increase shift firmness. Counter clockwise adjustments make them smoother. Going too far either way has obvious repercussions. I'm not sure adjustments to the modulator will address the reverse issue. Here are a couple of links with good discussion on this topic that may help. Regarding Modulator adjustments: www.benzworld.org/threads/i-fixed-my-shift-flair.1314697/#post-2330736 Regarding reverse issues: www.peachparts.com/shopforum/diesel-discussion/376603-only-using-half-springs-722-3-transmission-reverse-piston.html

@@ImpalamansGarage I will try the adjustment tomorrow and will also check the other info. thank you for your time and knowledge.

Here's a vacuum diagram of an OM603 from 1987. It may suffice to help you. www.peachparts.com/shopforum/attachments/diesel-discussion/98874d1326765510-om603-vacuum-parts-vacuum603.jpg

The modulator valve only controls the quality of the shifts. You could remove it entirely from a normal transmission and it would still shift through all of the gears but each shift would be very harsh. There does seem to be a lot of discussion on your problem in the Mercedes forums. www.benzworld.org/threads/722-5-transmission-shift-problem.1549876/

Several annoying issues: Shifts from 1 to 2 and 3 to 4 were hard as nails. Shift from 2 to 3 was way too soon. Also the original modulator has a rubber cap on it that is prone to leaking vacuum. The new modulator is an improved design. Mercedes is not the only car manufacturer that uses vacuum modulators to control shifts. This is an extremely common maintenance item for older auto trans cars.

No sir. It will not. First: Check your fluid. If it all leaked out, then the trans won't do anything. Second: Check your shifter linkage under the car. It may have become disconnected. If it's full of fluid and your shifter linkage is OK then you need to tow it to a transmission shop. If all the fluid leaked out you will need to refill it. Remember that checking trans fluid is done with the engine running at idle and trans in park. Each time you add fluid to the system you should hold your foot on the brake with the engine running and cycle the shifter through all of the gears and then back to park. Check again. Add fluid if needed. Cycle through gears again, etc.....

I cover it in this video. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Wz4_eMrZk9o.html Let me know you need additional info.

Make sure your transmission fluid is new and is full. Usually a transmission which refuses to shift will require a complete rebuild.

Here is the modulator valve for your car. It should not be difficult. www.pelicanparts.com/More_Info/1262709179.htm?pn=126-270-91-79-M22&SVSVSI=3760&DID=13332

You may need to adjust the bowden cable. On my car a clockwise adjustment makes the transmission shift sooner. Counter (anti) clockwise makes the transmission shift later. Do this 1/2 turn at a time and test drive after each adjustment. The bowden cable adjustment determines WHEN the transmission shifts. The QUALITY (how hard or soft) the shifts are is determined by the adjustment of the vacuum modulator on the transmission. A clockwise adjustment of the vacuum modulator will make the transmission shift harder. A counter (anti) clockwise adjustment will make the transmission shift more softly. Both the modulator and bowden cable work in concert with one another. It will take you a while to make the adjustments and get your transmission shifting properly. The Mercedes factory set these adjustments by measuring transmission fluid pressures during the manufacturing process. Lastly, when the transmission is shifting from 3rd to 4th under a heavy throttle condition, you may find it necessary to let up (decrease throttle pressure) to make it shift. In general, under wide open throttle you want the transmission to shift at the shift points noted on the speedometer. There are marks on the speedometer showing about where the car should shift when you floor it.

Here is an excellent document on how to adjust your Mercedes transmission. This document is for a diesel but it may be of help. jenniskens.livedsl.nl/Technical/Tips/Files/Mercedes%20722.4%20adjustment%20guide.pdf

@@ImpalamansGarage the best, thanks very much man. I really appreciate 💪🏽 I’ll let you know if this works 😁

You'll note very early in the video where I show the open port where the modulator resides that there is no transmission fluid which had dripped down over the lip of the pan. It's dry. Thus there is no fluid loss when removing it. If your transmission shifts properly and the only thing wrong is a hard reverse engage then I would say your modulator is not the issue. Without knowing what you consider to be a "hard engage" into reverse, it's tough to say where the problem may reside, however there is a fair amount of discussion on this topic. Here is one example: www.peachparts.com/shopforum/diesel-discussion/376603-only-using-half-springs-722-3-transmission-reverse-piston.html Your issue may be related to the reverse clutches or springs insde the transmission. I would start with the basics however. Does you fluid look good? If it's not red, change it and the filter. Check all vacuum lines.

@@ImpalamansGarage Transmission fluid is bright red and full to correct level. I can get a much less "thunk" by teasing it quickly into reverse, back out, and back in. Wondering if its vacuum. Can the way the Modulator is adjusted have an impact on this "thunk"?

Thanks also for that posting in Peachparts. Interesting that a firm shift to Reverse is less wear.

@@cwmoser I highly doubt it is vacuum. The modulator, whether or it's bad or good, should have no effect on the engagement of reverse gear. The modulator regulates fluid pressure to control firmness of upshifts. I would just hold my foot on the brake and shift it into reverse and wait until it's properly engaged before reversing. I fear moving the shifter around like that might do more harm than good.

The first thing you should do is to make sure you have no broken vacuum lines. Check ALL vacuum lines in the engine bay and to the transmission. Replace any that are cracked or broken. Then adjust the modulator. Clockwise makes the shifts firmer. Counter clockwise makes them softer. The bowden cable on the throttle assembly affects the timing of the shifts - earlier or later. What precisely do you mean by "aggressive shift" when placing it in drive? Any diesel powered car or truck will lunge forward upon putting it into drive because of the torque at idle, although it should not be harsh or loud.

@@ImpalamansGarage fixed some minor vacuum lines before but pretty sure there will be more since they were to brittle. I took out for a spin today to check for some symptoms and this what I found out. - whenever I put it on drive it takes around 7-8 seconds for it to actually click on and start driving (don't know if it's slipping) same with reverse. -when it clicks in to drive it sometimes makes this aggressive shift where you can actually feel the the whole car move. -car only starting in neutral. Rarely in park. - when I get the car to pick up a bit of speed it jerks. Something with the fuel system? I was told to swicth the fuel filter. I have it but never got around to doing it. They told me it's made from cardboard and hope it didn't go bad. -car only starting in neutral. Hardly in park. Any suggestions? The car was driving fine about a month ago.. I parked it to replace the tie rods and since I parked it these symptoms popped up. Thanks for the info!!!

And the engine is the m103 from a w126 300sel

Yes but it required dialing in. The adjustability of the new modulator is nice.

@@ImpalamansGarage Cool!

Yes. The adjustability of this new version of the modulator is nice. Keep in mind the quality of shifts is dictated by the modulator and the timing of the shifts is regulated by the Bowden cable adjustment. They work together so you will need to tweak both of them.

@@ImpalamansGarage great! I'll dig deeper! Great video

The transmission shifts so much better than before. With the updated modulator and adjustments plus new vacuum lines in several areas.... the driving experience is very nice. In some instances, depending on the driving conditions I have noticed a very slight flare from 2 to 3 but this has only happened once or twice. Debating on whether or not to make another small adjustment. Guess I will just have to drive my classic Mercedes some more to determine!

@@ImpalamansGarage Once you put that plastic cap on, can you remove it? I have a new injection pump with bigger elements. The car shifts great except for the 2-1 down shift is rough. I used the fine adjustment and the shift improved slightly. If I could just get that cap off and adjust it more I believe the problem will be solved.

I plan to over the next day or two. Will reply to this video's comments with findings.

Sounds like you've got some troubleshooting to do. Even if the modulator was not working at all, I think your transmission would still shift. I would start with the Bowden Cable. Have you tried adjusting it? Trying screwing the Bowden Cable clockwise (inward) for several turns and see if that has an effect. You are saying your transmission stays in 1st gear no matter what ?

Impalaman's Garage it actually not picking up any gears it I can move it from RD23 but nothing happens the engine just revs

@@joshuapena1314 Have you confirmed that your shift linkage under the car is connected properly? If it is connected properly it sounds like a transmission rebuild is needed.

Impalaman's Garage that’s the first thing o checked and both bushings were missing so I replaced both of the i even went ahead and bought a brand new shifter but still no luck I also flushed transmission fluid out and replaced the filter, Jesus sounds like it’s gonna be an expensive fix

Might be a better option to find a good used one that you know is good to go. Install it. Then buy a rebuild kit for the old one and learn to rebuild one at home.