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Old 04-25-2012, 07:01 PM
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Join Date: Apr 2012
Location: Baltimore Maryland
Posts: 18
Kickdown solenoid works but no kickdown

Greetings,
I'm hoping someone in here knows how the solenoid valve operates on my 83 240D (Automatic).
I haven't found a thread dealing with what I'm finding.
I have an 83 240D which has vacuum controlled AT ( Has no mechanical linkage to trans.).
I've recently restored vacuum to the 2-3 way valves, VCV, and modulator. It was all a mess from previous owner.
The car is shifting smooth and at appropriate shift points I believe. But there is no kick down shift at all. It used to when the vacuum was still obstructed.
So far I've checked
-The kickdown switch-- has continuity and pedal does activate it.
-The wires too the switch-- shorted when car is off. when ignition is on one lead is +12v and the other is 20 Ohms to ground.
-I can hear the solenoid clicking when I work the switch. Also checked it with a hot wire
-Removed the solenoid, tried to clean it... not sure how it works really, can't find much info.

My question is, does the clicking tell me that the solenoid is working and if so is there something else preventing it from shifting down when the switch is depressed? Could I have adjusted part of the linkage or the modulator in such a way as to prevent the kickdown? ((I believe the modulator was adjusted far CCW to smooth the shifting as when I cleared the vacuum line the car started shifting through the gears too soon and too soft, So I turned the mod. CW to tighten it up))

Or, would this indicate the "inner" part of the solenoid is bad and needs replacing.

All help appreciated!

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  #2  
Old 04-26-2012, 06:24 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
Here is a great post with transmission adjustment information:
It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...

As per the thread, it is very important to get the correct vacuum diagram for your vehicle to ensure that correct vacuum is applied to the transmission through a special orifice (If the vacuum lines have been "modified" this orifice may even be missing).

On the MB diesel engines, the vacuum modulator is set by internal pressure of the transmission, which is checked by a test port and pressure guage, and is specific to your model.

The problem we run into with the MB diesels, is that unknowing mechanics try to adjust them the way you would a gasser. A typical scenario is someone gets an oil change and then complains of hard shifts. Rather than find the vacuum leak caused by messing around in the oil filter area, they dive in and swap lines around or adjust the modulator. Once the modulator is set per the pressure requirements, rarely should it ever need another adjustment.

If the transmission kicks down with no vacuum applied to the modulator, then I would tend to lean towards a problem with the vacuum system. I know that the link provided is a long post but well worth studying.
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Sam

84 300SD 350K+ miles ( Blue Belle )
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  #3  
Old 04-26-2012, 11:56 PM
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Join Date: Apr 2012
Location: Baltimore Maryland
Posts: 18
Thanks I'll read it. My vacuum meter broke so I'll have to get a new one.

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