What kind of job to replace trans modulator on '82 wagon?
 

I have a harsh downshifting wagon. I checked the vac lines and all are good. I have 11 inches of vacuum at the trans vac valve on the inj pump at idle. I put vacuum on the trans modulator line and it won't hold. I pulled the modulator cup off of the modulator and there is trans oil in it.

Do you have to lower the rear of the trans to get to it? If it was a SD then there is lots of room but not so on a 123. I have factory chassis manuals but I couldn't find anything on it.

R u sure
 

The vac is good ? Try with the ccu controls set to off position.

Its not that hard it's just a really tight. So be patient. Make sure you have the correct modulator pin when you put in the new modulator. The new style modulators take a pin with a cup on the end the old modulators use a pin with a point on the end.

I put vacuum directly to the black plastic line that goes to the modulator. Before I did that, I removed the vac line and checked it by its self. The modulator cup is NEW. I also replaced the junction hose between the plastic line and modulator.
I then checked with vacuum and it wouldn't hold. Deffinately trans oil inside the modulator cup and adjustment area where the modulator key is.
Surely someone out there has replaced one??

And if your current pin is the plastic variety, odds are 10:1 that you will break it when removing the modulator.

There is a metal clip with two bolts that hold the modulator in. The modulator will come out once the clip an bolts are out. It fits in tight so it won't just fall out. And the area that all this takes place it in a bout 3" of space.

Is this pin what anchors the modulator to the case? What years did this start?

No. It is essentially a "push rod" that transmits the pressure of the modulator. Some models have a metal rod, some plastic. The plastic one will snap if the modulator is not pulled precisely straight out of its recess. If your modulator is green, you probably have a plastic pin.

Got it! Thanks for the info everyone! I have a great respect for automatic transmissions in that I don't want to screw one up!! :o

Replacing the trans modulator was one of my very first endeavors in working on my old MB. As stated before, it's very tight in there. Although I think I did as well as I am capable, I stripped the head on one of the bolts and the project went from aggravating to totally frustrating. I was advised that lowering the transmission would not work (although later another member of this forum said it would). At any rate I eventually used a small hole saw and cut through the tunnel and had easy access. Did a good patch job after replacing the modulator and all is well. Since my car is more of a daily driver than a showcar, this seems to me a reasonalble fix.

Before you go throught the PIA of changing out the modulator, ensure that this little cap is not the source of your vacuum leak : http://www.allpartsexpress.com/ShopByVehicle.epc?q=1984-MERCEDES--BENZ-300sd--/--L5--998cc--3.0l--Diesel--Fi--Turbo-Transmission&yearid=1984%40%401984&makeid=MERCEDES+BENZ%40%40MERCEDES+BENZ%40%40X&engineid=1194038%4 0%40300SD++%2F+L5%2D2998cc+3%2E0L+DIESEL+FI++Turbo%40%40300SD&catid=Transmission%40%40Transmission&s ubcatid=Modulator+Valve+Cap@@Modulator+Valve+Cap&mode=PA

Because the modulator is not a plug-n-play part. Been there, done that and want to save you a little grief.;)

I appreciate the advice on the cap. I had already replaced it. I keep them in stock in my Mercedes parts stash cabinet when I work on peoples cars.
When you installed yours, how out of adjustment was it???

I've replaced mine on my W126.....not much fun, probably even less so on a W123 since their tunnel is so narrow. At least there's some room to work on the W126.

My old unit's diaphragm had ruptured suddenly one day, so I put in my spare and all was well.

The plastic thrust pin did break (or was broken) and I had to fish it out with tweezers. I had a new spare one though, thankfully. (its always good to have an "inventory" of parts available) :D

Some fluid leaks out too, maybe 1/3 a quart......its gross.

IIRC, it's been a few years ago...before I found this forum, the adjustment wasn't too far out, but enough to cause some flaring 3-4. Due to a vacuum leak in the climate control, I had to block that portion and set it with part of the vacuum system connected. The main PIA was the pressure setting adjustment with banjo bolt, tubing, pressure guage and driving test. I set mine to a firm shift, thinking that when I resolved the climate control issue it would back off a little.

Which was the case for a while. Of course, now I have another vacuum leak in the climate control system, due to another ruptured diaphragm, and now the firm shift is over the edge due to the vacuum loss.:(