Tons of write-ups here on tweaking modulators, but I can't find any step by step instructions for replacing the part (Mine leaks, and I suspect it as the cause of my increasingly rough shifts.)

Specifically, how do I remove the old modulator? What tools do I need? And, does the transmission need to be drained first? Torque converter?

Finally, when I order the replacement modulator, will it come complete, or do I need to buy additional seals/gaskets/washers, et al?

Thanks in advance for helping me to do this job right the first time!

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Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Order the right modulator for you car do not rely on the color of the original, it could be the wrong one. ID the transmission first. On the passenger side of the Trans just above the center of the pan is the 722.xxxxx number. Go by that number to order the right modulator, if the transmission was changed use that number. You may get an updated modulator; it comes with a new plastic pin use it at a set. Remove the two 4mm bolts on the bracket and pry the old one out. If you have the up dated mododulator also remove the old plastic push pin that is behind the old one. You are going to use the new plastic pin. A word of caution the old style push pin likes to break. When removed, it should measure around 3 inches. Use a mirror to look into the bore you should only see the modulator valve. Adjust the modulator with a gauge. You do not have too drain anything.

C32AMG--

Thanks for taking the time to reply. Certainly sounds like a straightforward enough job. (I figured that since the old modulator's leaking, it must effectively act as a seal, and that removal would result in tranny fluid oozing out all over the place if not drained first. Delighted to learn that this isn't the case!!!)

Can you (or anyone) provide the correct vacuum specs and procedures for initially "tuning" the new modulator? (i.e. at which points do I need to take readings?) Having these figures in hand will obviously save lots of time...

Thanks again for the fruits of your experience!

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Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

I like this as a help (kinda the "whys" of adjustment)


http://www.continentalimports.com/ser_ic20242.html

and this (more rote):

http://www.mercedesdismantlers.com/AutomaticTransmissionInformation.html

Using a trans pressure gauge:


The modulating pressure for a 722.315 transmission (with transmission at operating temperature of 80 deg C. & vacuum line disconnected) in drive at 50 km/h is 2.9 bar (if the revised pressure transducer is installed 3.3 bar). Working pressure 12.5 +/- 1.0 bar (14.3 +/- 1.0 with revised transducer). Governor pressure should be 1.2 bar at 30 km/h and 2.8 at 90 km/h with either transducer. All of those values are the same for a 722.303 transmission too except the working pressure at 50 km/h with a revised transducer which is a tad higher at 14.7 +/- 1.0 bar.
(I believe this was posted by Marshall Booth and I threw it in a file.)

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Napa has a universal pressure gauge with the right MB fitting. The modulator pressure tap is to the right of the modulator; it is a 12mm bolt. Remove it and attach the gauge. Pull the vacuum hose off the modulator and plug it. You are adjusting the modulator at O vacuum.

USE CAUTION WHEN WORKING ON CARS. BE SAFE



1- Pull the vacuum hose off the modulator and plugs it
2- Raise the rear wheels off the ground
3- Start the car put the lever in D
4- Run the engine up to 31MPH and hold it there
5- Adjust the modulator until it reads 55PSI for your 722.355 transmission
6- Turning the “T ‘handle CW increases the pressure CCW decreases the pressure
7- Install the cap and vacuum hose.

Just guessing, but it sounds like you've done this before! :p

C32AMG, is that target effective speed 31MPH or 31KPH? (The former, I suspect; however your reply has a typo and reads "31HPH", so I figure I should ask just to be safe.)

Also, does the speed sensor read off the speedo? And if so, can't I just engage the cruise control to maintain desired engine speed while I adjust the modulator pressure? If feasible, this would seem to be the easiest way to complete the job on my own.

And as long as I'm badgering you, if you happen to own one of those NAPA universal gauges referred to, would it be possible for you to indicate the correct part number so I can rustle one up?

Thanks to you (and of course to jbaj007) for always being there to help out. It's REALLY appreciated!

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Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Sorry, that is MPH, I will find the part number for you

Okay, I just completed this job successfully and want to add some comments and corrections to this thread while they're still fresh in mind...

First off, C32AMG's guidance was extremely helpful and is accurate for the most part. A few exceptions:

1) The 2 fasteners that need to be removed are 5mm hex heads -- not 4mm. One of mine was very tight and I thought I was in trouble when my hex socket stripped the head of the bolt. Luckily, I was able to get a standard 3/8" to grip the top of the thing (with a few good raps of a ball pein hammer). There ain't much room to maneuver in there...

2) The bolts don't actually secure the modulator directly; rather, they attach a metal strip to the transmission body. This strip, in turn, clamps the modulator in place. Note that there's a groove that runs halfway around the perimeter of the modulator. Since the metal strip must be seated in this groove, you can use this feature to establish the correct orientation for the modulator. In short, the groove has to go on top.

3) Once you pry out the old modulator (I used a screwdriver), there IS indeed some steady oozing of tranny fluid, contrary to comments made above. Given that the fluid flows outward though, I suspect there's little risk of any contaminents being drawn into the transmission... The flow is extremely slow--akin to bleeding brake fluid--so if you're ready with the replacement part, it's a non-issue. But you should be aware that this would not be the best time to leave for lunch!

4) The vacuum connector winds up on the upper left with the modified replacement modulator for my 420SEL. The original part found its connector on the upper right.

5) Though you need to pry the old modulator out with a hand tool, it doesn't take much force to get the new modulator in place. (I kept shoving the thing expecting it to slide in further, but it's not necessary: the aforementioned metal retaining strip clamps it into correct position when you retighten the bolts.)

My old modulator was leaking under the cap, and the device was ineffectual in adjusting my steadily worsening shifts. I noticed an immediate improvement as soon as I took the car out for its test drive. The shifts are MUCH smoother and consistant now--and I haven't even made any of the pressure adjustments C32AMG expertly described yet. (I will probably just manually adjust the new modulator to feel for now. It's getting way too cold here in New York to work outside, so I may not hook the new modulator up to a pressure gauge for "proper" adjustment until the spring... if ever.)

(Also did front rotors, pads, and repacked the bearings as long as the car was off the ground. Bottom Line: She feels like new---How I LOVE this car!!!)

Hope this follow-up proves helpful to others. Thanks again for everyone's support here.

Cheers!

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Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Hi Goldstone,

Did you manage to do this with the gearbox still in the car? Do you know if there would be enough room to complete this with a coupe?


Thanks.

Adam

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Adam
1984 500SEC
1988 560SEC

Answers:

1) Modulator is readily accessible from underside of vehicle--though, as noted in my original post, it's somewhat recessed, so there's not a lot of room to work. It will help to have a good utility light and a small mirror handy to better see what you're doing.

2) I only know my sedan for sure, but I don't know of any structural reason why your SEC's tranny would be any less accessible. (Others may want to weigh-in here...)

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Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Thanks Eric.

I might get down there and have a good look on the weekend.

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Adam
1984 500SEC
1988 560SEC