I just took my '83 300D into a shop (that I thought was good) for an unrelated repair when I asked them to also look at the transmission adjustment because of extreme 2-3 and 3-4 flaring. They came back and said the transmission is just shot and needs replacement. I just purchased the car from the original owner (my uncle) and it has only 165k miles on it, so I'm surprised to hear that a new tranny is necessary. I changed the fluid/filter after I got the car from him and the fluid and pan was clean.

After doing alot of reading on here, I'm hoping that this is only an adjustment problem so I've done the following today with limited success.

1)Checked that modulator holds vacuum.
2)Checked vacuum at primary line orifice (good vacuum)
3)Adjusted the vacuum regulating valve linkage. (.020" from stop at FT)
4)Adjusted control pressure "kickdown" cable.
5)Adjusted vacuum regulating valve to give 10 in Hg to 0 in Hg range. (I actually test drove the car at various settings at idle from 7 in Hg to 13 in Hg and it would flare some amount at all settings.)

I don't have the correct fitting or gauge to adjust the modulator valve correctly so I've stayed away from it so far. Does anyone have any idea where I should proceed next? Or does this indeed sound like the transmission needs replacing?

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'83 300D
'85 300D
'01 VW TDI

You've done an admirable job in covering all bases. Once the vacuum level to the trans is somewhere in the range of 10-12" at idle and properly falls toward zero as you open the rack, you've done all you can with the vacuum system.

To reduce the flare with the proper vacuum levels, some members have increased the pressure at the modulator. It has a T handle that folds down and allow you to increase pressure by turning the handle clockwise.

As a test, turn the handle three complete turns clockwise and drive the vehicle again. Report back with results.

Also, be sure that the transmission vacuum is properly dropping down when the rack is opened. Flaring will occur if it fails to do this.

It's highly unlikely that you need a new transmission.........just a need to get it properly adjusted. BTW, your experience with the transmission shop is typical. Their diagnostic capabilities are just about nil.

Thanks Brian, yes, I had already checked the regulating valve function and it does drop to zero when the rack is fully opened.

I just adjusted the modulator 3 full turns as you suggested. Much better!! It flared on me once, but I couldn't get it to do it again after lots of starts and stops. However now when the car slows below 20 mph it downshifts hard. The 4-3 downshift though is really smooth when I step on it.

Should I adjust further? I've hesitated adjusting the modulator without the correct pressure gauge attached. What is a sign that I've increased it too much?

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'83 300D
'85 300D
'01 VW TDI

The pressure gauge is of limited value on a transmission that is not fairly new or recently overhauled.

Responses:
Q - First am I correct that your 1983 MBZ is a W123 300D Turbodiesel?
[1] The vacuum regulating [bleeding] valve is more commonly called the Vacuum Control Valve (VCV),
[3] Yes, I would recommend that you continue the adjustments... but now you adjust only ~2 increments of the adjusting key... two "clicks" to the right and carefully observe how it shifts and report back to this, YOUR, THREAD.
[4] The upshifts will become more and more firm.
I also recommend that you remove and double check the green plastic "dashpot" chamber on top of the VCV and make sure it holds vacuum off the car. Inspect it closely to make certain it does not have a crack that might heat up and leak.
See: http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1WH11JXAQ1ZE03W25C&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1983&product=J5050-116224&application=000500211
Regards,

You've got it close to what you want. Don't make any more adjustments for a few weeks. You've got to drive it under various operating modes to be sure of what it will do. Travelling on a slight uphill grade with moderate pedal (1/2 pedal) at low speeds on an accel is a killer for the flare. If it will flare, that's when it's going to do it. So, seek out some small upgrades and test for flare.........you don't need a steep hill...........and you don't need full acceleration...........just a slight grade and moderate accel..........and it will flare badly on the 2-3 if it's prone to do that.

If the flare is eliminated in that condition, we can tweak the vacuum to cut the hard downshift. If not, some additional modulator pressure is required.

As TF mentioned, a gauge is practically useless on a machine with 200K on the clock.

After driving it when it was cold, the 2-3 flare was still there, just not nearly as bad as it was before. So I started turning up the modulator again. Ended up turning it up another 4 full turns before I got it to not flare (but of course by that time things were warmed up so we'll see how it does tomorrow). Right now it seems to shift pretty nicely going up.. 1-2 is firm as always, but 2-3 and 3-4 are very nice and smooth.

What "clicks" are you referring to when adjusting the modulator? Mine has a large plastic cover over the T-handle, once the cover removed the T-handle rotates smoothly, no detents or anything. Maybe I have an older or newer style?

The downshift is still hard though, and I can't seem to ease that. It seems that it must be a 3-1 or 4-1 downshift because if I only get it into 2nd gear then stop it's fine. What controls this downshift? Is this controlled by the 3/2 way valves on the valvecover? The levers on them look worn, but aren't broken off.

The vacuum dashpot appears intact, no cracks or heat damage. How can you check it? What is it's purpose?

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'83 300D
'85 300D
'01 VW TDI

By clicks I think Sam just means positions on the modulator itself. A 'click' would just be the next position you can put it in. It does not click when moving the T handle.

I do not know for sure, I think the Bowden wire thats on top of the valve cover controls it, along with a kickdown switch underneath the accelerator pedal. I *do* know that the 3/2 valves on your car only control the EGR operation. You can remove them if you do not need to pass an emissions underhood inspection. They will however cause vacuum leaks and make the trans shift wrong. It sounds like you are OK - your vacuum specs look right.

You're in good hands, Brian and Sam helped me bring my vacuum system/transmission *way* back from the dead. I'm now at the same stage you are - tweaking. I am surprised at how many turns it takes on the modulator to make a big difference - mine acts the same way.

Good luck.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

You can ease it by adjusting the Bowden cable so it has a bit of additional length. This means that you turn the nut counterclockwise. This will cause the upshifts to happen sooner, so, you'll need to balance your efforts here. Don't go overboard.

You can also try to increase the vacuum level to the transmission at idle. This runs directly counterproductive to the flaring issue, so, use this bit of advice with extreme caution.

... you are correct DDan in your suposition about my meaning of "click" Dan. After writing that, I had reservations and just this a.m. I almost went back to the POST to edit out that term. Yes, I should have said something like "adjustment key detents"!!!
Ian [ " IanJ " ] - I'm a little surprised it took that many more turns to finally get the tranny to shift more normal. " DD " is right, you will likely go through a period of "tweaking" her until you are accepting. I actually still manually shift to the "S" position in my 240D because otherwise it wants to shift back-and-forth too much for my preferences. I have also added a "dashpot" chamber which acts mostly to soften the 1-2 shift. I suppose IF you had a newer model that shifted well EXCEPT for the 1-2 shift... I suppose a fix worth trying might be to add a second "dashpot"... something I'll have to try some day just to see what happens.
Regards,

Regards,

I must have a different model modulator... mine has no discrete positions. I can turn the key smoothly in either direction without having to pull the key out at all. Mine does look a bit different from some of the other pictures I've seen posted on here.

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'83 300D
'85 300D
'01 VW TDI

Doesn't your modulator valve look like this one... maybe black instead of green?
http://img.eautopartscatalog.com/live/J5020102310.JPG
Regards,

No, mine has a different style cap and a shoulder around the cap that comes up flush with the top of the key. No detents at all around my key. The inside of my cap is splined which keeps the key from rotating once the cap is on. (It is green though )

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'83 300D
'85 300D
'01 VW TDI

Thanks Brian, That seems to have helped a bit. I've got the vacuum level to the tranny turned up to about 13" at idle and backed off on the Bowden cable. Now it only seems to downshift hard on quick stops, but doesn't seem to be as noticeable on calmer stops. We'll drive it around for a few days and see how it does before I start adjusting much more.

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'83 300D
'85 300D
'01 VW TDI

Okay, the results now that I've been driving it a few days. I still have a 2-3 flare when she is cold first thing in the morning. Once I've been driving it a bit, and in the afternoon it's fine. Doesn't flare 3-4 anymore. It still downshifts a bit hard though, but I can live with that. I hesitate to turn the modulator up anymore since I've already cranked it up quite a bit. At this point I was thinking that maybe the K1 spring kit that I've read about may eliminate the cold 2-3 flare. Any thoughts?

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'83 300D
'85 300D
'01 VW TDI