My mechanic replaced my vacuum controlled shift valve on the top of the vavle cover last week. He checked each component in the transmission shifting with a vac pump. My modulator checked out fine as did the valve on the injection pump. Until friday it was shifting the best it ever has done. The first vavle he put on was defective and he said he hoped the batch his parts guy got was not totally bad or he would have to do to the Mercedes dealer and get one. He installed a second vavle. Friday my car started reving up before shifting into gear. Everyone on forum said check the Bowdin cable. It is fine. No vac lines broken or unhooked or leaking But that valve on top of the cover is what works the Bowdin cable. If it is bad, then maybe it would cause this? (Engine revving to 4000 RPM before shifting into 2nd and 3rd gears. Can't call mechanic back until Monday.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

try adjusting the bowden cable clockwise for earlier shifts

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

The valves don't do much for the transmission, mainly there for the EGR. The problem is WAY to much vacuum to the modulator, or a modulator thats not set correctly for it to be slipping that much. Check the vac at the line going to the transmission, it should read 12-15" at idle and down to about 0" at full throttle. If that's what your getting, the modulator is not adjusted correctly, you can do it on feel, but to do it "by the numbers", you need a special tool that hooks to the transmission fluid pressure port and on to the vaccum supply (not a Mity-Vac).

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Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

If you remove the black cover over that shift valve and look at the cam on the valve, it does two things. It conrols EGR and it has a cam that directly affects the movement of the bowden cable. In fact, the bowden cable is moved by that cam. The throttle is part of the entire setup, but that cam is what moves the bowden cable. Take yours off and look sometime. If this valve is bad, then you won't get correct pressure on your mityvac at the modulator. It definitely does more than EGR.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

If your 82 300SD has original equipment throttle linkage like mine and all the cars used for pictures in the Mercedes factory shop manual I bought from mercedes, then the transmission "shift cable" is a cable which travels from the right side of the transmission, is attached midway to the transmission filler tube, and is then connected to the THROTTLE linkage. The original equipment vacuum valves on the valve cover control vacuum to the EGR only. However, they affect shift to the degree that they (or the connecting hoses or the EGR)leak. For example, air leaking through those valves would reduce vacuum at the modulator. But maybe you have some unique, mickey mouse arrangement put there by a previous owner or mechanic who didn't understand how the system works. If that's the case, we can show you pictures of how it's supposed to be. Good luck!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Ok - I think you are right - the leaking valve was affecting my modulator. I just called the mechanic and he said the revving up before shift means the transmission is slipping. He told me there is a tab on the other part of the linkage with the lever that pulls the shift cable that might have gotten knocked the wrong way.

He also said that I needed to check the fluid level which he topped off. I asked why since I have no visible leaks. He said I could have a bad modulator that was sucking it up into the vacuum line and burning it. I checked the level before he worked on it, and I didn't think it was low enough to add any.

I reminded him that he had checked the modulator and said it was ok. How could that have gone bad so quickly if he checked it last week?

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

If the modulator was sucking up trans fluid it would be all over the inside of the vacuum line. If the modulator holds vacuum it's probably fine. I think these get replaced a lot more often than they need to be. The "vacuum control valve" that controls vacuum bleed is on top of the IP. Make sure that operates properly too.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I am almost ashamed to tell you guys this, but I turned my truck in on lease and the MB is all I have to drive, so I had to get it right. I took the car to the dealer today. They have a mechanic who only works on the older models. He called me within an hour and said the problem with my transmission slipping and revving up before a shift was that one of the valves on top of the valve cover that the other mechanic put on was defective and leaking. There are two valves - one does affect the shift charateristics and how much vacuum goes to the modulator. This is from the dealer tech at Leith Mercedes Benz - Raleigh NC. Once replaced, my shifting should go back to normal. The reason the shift characteristics changed so drastically, was that when the other mechanic put on the new valve, he also adjusted my modulator 2 turns to soften the shifts. When the new valve went bad and threw off the vac to the modulator - WHAM! It was worse that before it was fixed. The mechanic who originally did the work will replace the part at no cost and use a factory MB part this time.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup