So where, exactly, is it? I don't have any jacks right now and am wondering if one will suffice, or if I need two or if ramps would just be better.

My issue is vacuum; I tested much of the system yesterday (Diesel Giant, you would be proud!) and discovered that when I plug the line leading from the blue plastic 'transducer' to the modulator, my vac. reading leading into the white vacuum valve on the IP goes from 5 hg to about 20 hg while the car is idling. With 5 hg there the system doesn't have enough vacuum to shut off with the key, so this is definitely a problem.

I assume I have a vacuum leak in the modulator itself or in the line leading to it. These CA cars have bearish vacuum systems, it would seem, so hopefully my problems will end if I fix this, but who knows.

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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

Left side of the transmission. At the end of the vacuum line. There is a black rubber cap on the modulator which is essential to vacuum integrity. It coud be as simple as replacing the cap or the rubber connector at the modulator. Raise the left side of the car and slide under from just behind the left front tire.

I'm really hoping it's as simple as replacing the cap or line. Knowing my luck it won't be, of course.

Thank you for the info.

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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

If the modulator is original, it's a safe bet that it could stand to be renewed. A simple job, complicated somewhat by access issues with the transmission in the car. If you decide to replace the modulator, I would suggest procuring a new pin (approx $3) at the same time, as it is very easy to break the original one when the old modulator is removed. (This assumes that you have the version with the plastic pin.)

Then, of course, you have to adjust the new modulator. And the procudure for that is subject to substantial debate. I went to the trouble of fabricating a gauge and setting the recommended pressure. The transmission shifted poorly at that pressure, so I adjusted by feel from that point.

My vacuum modulators are on the right side of the trannies [facing front of car] but that's not why I responded to this thread.

I know you are anxious to get to the task of solving your problem, but I strongly recommend that IF you jack up the car rather than driving it up on one or more very sturdy ramp support(s)... when jacking I recommend you always have at least two supports under the car before you go under yourself... and this usually means you jack it up, put a sturdy stand under it, and then you lower the jack but keep it supporting ~50% of the car's weight with the stand supporting the remainder. Then individually grab the jack and the stand and give each a good shake. And after that grab with both hands or put your foot on a bumper and shake to be certain the car is steady!
Best regards,
Sam... yes I'm " MrSafety2@Verizon.Net " !!

Sorry if I got that wrong. I remembered it being on the driver's side. But I am getting old, and they say the memory is the second thing to go.

And maybe one of the reasons that I am getting old is that I never get under a car supported by a jack.

Well I looked for the modulator yesterday but had no luck finding it (this was without the car jacked up). Now if it's on the right side facing the car, that's still the driver's side, I think? I looked on the passenger side, too, but there's so much other stuff over there I don't see how I would get to the modulator even if it were there. I should mention that I did see a metal plate on the driver's side that looked like it was held in place with Allen bolts. It looked like I would probably have to remove the fluid pan to get to it. The modulator isn't under that plate, is it?

There was some good news yesterday. I realized the line to the transmission wasn't even connected to the modulator! It could be that it was knocked loose very recently while I was working under the hood, but the elbow joint that would connect to the modulator was filled with so much oily gunk that it doesn't seem like the disconnection could have been recent. OTOH, I wouldn't have thought that all my shifts except the first two upshifts would be smooth if I had no vacuum at all. On the other other hand, I'm far from being an expert.

I'm thinking that the buildup of gunk is the reason I had some vacuum in the system as opposed to none like you would expect with the line completely disconnected.

The fact that the line may have been disconnected since I've owned the car (Jan. 6 of this year) makes me wonder about the tranny rebuild that was done last July by the PO. It also makes me wonder whether re-conecting the vacuum line will make the shifting worse.

Thanks for the warnings about supporting the car. I'm not too keen on having it fall on me so I definitely plan on taking the proper precautions. I'm still not sure exactly how I will do it, though, as I can't really afford to buy too many car accessories right now.

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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

I was under my 1985 300D yesterday looking for this same thing. Mine is the federal version, so the modulator is green, making it a bit easier to find. I believe the California model has a black modulator, so you have that to add to the difficulty. I, too, couldn't find the thing, but eventually did. I put the car on ramps and found the easiet access was to get under the car, just below the front driver's side wheel. By below, I mean between the two wheels on the drivers side. The modulator is indeed on the driver's side. It's located between the transmission and the transmission fluid pan, so it's in a fiarly tight place. Also be sure your care is cool or else you'll most likely burn your hand due to the tight quarters in which the modulator resides.

The rubber cap on mine is torn. I'm hoping that's the problem. I don't know where to get a real reaplacement one, but am guessing a hardware store will have an adequate cap that'll do the job.

The cap must fit correctly to provide a good seal. PM me if you can't find one.

The cap is available here at Fastlane for a whopping $2.16!
You will spend more than that driving around trying to find something that may/won't work.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Excellent. I looked though the "transmission" section and all I could find was the valve and the seals, but no cap. I don't suppose you could supply me with the part number?

Thanks,

JL

Mine is an '85 300D Cali Ver. but the trans. modulator is green with a black rubber cap, and i believe it is still stock and original from the day she was born. Located on the driver side of the tranny. The question is: What's the difference between the black trans. modulator and the green one aside from the shade of color??? Is it calibrated differently??? but we can always adjust it by feel, right?

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'85 300D Turbo - CA Version

The difference is unknown to me, but I could only speculate is has something to do with emissions control. At what level and how, I have no clue.

Well, I looked it up and for some reason it was listed for my car (W126) but not yours (W123). I double checked and it is the same modulator. Try here:http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1TK0N72XS1U00MAPX9&year=1984&make=MB&model=300-SD-002&category=J&part=AT+Modulator+Cap

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Sam

84 300SD 350K+ miles ( Blue Belle )

My mechanic sold me one for $2. Sadly, I still have the flare. Before I got the new cap, I'd turn that key on the modulator clockwise one notch, but was not thrilled with the stiffer, harsher shifts. I returned the setting back to the orignal position and put on the new cap. I may try adjusting again one notch clockwise with the new cap to see how it acts. I'd much rather have smoother shifting and the occassional flare than continually annoying shifts.

Is adjusting the position of that key a legitimate way to solve/troubleshoot the flaring or is more of a work around? My next step may be to test the vaccuum to the modulator to determine if the issue is there. Did I read correctly that another possible issue may be a broken spring, which the K1 Kit replaces?

JL