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Old 04-04-2000, 02:57 PM
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My 1983 240D is shifting really late. Going from 3rd to 4th gear is only achieved when I hit 60 MPH. All of the other gears are shifting late as well. I was adjusting the 'key' in the modulator on the transmission, but was told that it only controls for controls how smooth it shifts, not when. Any help would be great. I am ruining my engine by the higher RPM's. Fluid is good; red. Problem started when I had both the valves adjusted and the key lock assembly replaced.

1983 240D 220K
1988 260E 198K
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Old 04-04-2000, 06:39 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The 83 240D is one of the few trannies MB built without some form of control pressure link or cable.

To adjust the shift timing you will have to alter the relationship of the conditioned vacuum curve. The vauum is modified by a proportioned controlled leak (the white plastic device on the rear of the injection pump.

The first thing you must do is verify that the system is working by teeing into the black line that goes to the modulator. The vacuum lines are complicated but look at the modulator end and follow forward. I think I tee that model at the valves on the Valve cover.

What you are looking for is high vac at idle 20in or more. At this point the leak isn't in the system and full vacuum goes to the modulator. When you take up the slack in the linkage and engage the valve cover micro switch the leak is hooked up by the depressed micro switch. All this is to be done with the motor running. At this moment with the switch engaged the engine is still at idle (the linkage movement and switch activity happens before you get pump movement. At this point you should drop to 10-15in of vacuum.

A quick full throttle rev of the motor should drop the vacuum to close to zero. This is the activity that you need to verify before you make the adjustment. High vac - dropping to 10-15in after microswitch closes and then a smooth transition to around zero inches at full throttle.

The adjustment to this is the link between the valve (white plastic) and the throttle. If you view from the top the link goes vertically down the inside of the pump. Where the link is attached at the bottom is a adjustable ball stud that the link hooks to. The nut is 8mm (fairly hard to get to). You will need to move the ball dowm about an eighth of an inch. The easiest way to tell how much you are moving it is by turning OFF the motor and pulling the throttle to full throttle. The valve's metal lever will approach a full throttle stop. Pay close attention top this position and when your done the lever should be 1/8in further away from the stop than it was when you started.

All of this was based upon the proper vacuum curve when you started. We just rearranged the relationship between the throttle and the vacuum curve. If you have a severe drop in vacuum after the microswicth is engaged (one of the first step)then you have encured an extra leak probably when the valve cover was off. The micro swith is highly suspect here. What you will see on the vacuum gauge is high vac 20in and then a drop to 5 or less before the engine leaves idle (when the microswitch hooks the rest of the system up.

It actualy gets complicated from there.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 04-06-2000, 10:56 PM
fz500sel's Avatar
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Join Date: Nov 1999
Location: Venice, FL - "sharktooth capital of the world"
Posts: 712

I have a '85 300D. It seems to shift slowly (as in not having alot of pull,not really slipping) when its cold. After driving awhile it seems to run better. Also it doesn't seem to shift from 3rd to 4th as easily as it does in the other shifts (1-2, 2-3). It seems that I will have to be at about 40mph and at about 3200 rpm when it finally shifts to 4th. Sometimes it won't shift until I reach about 50-55 mph. The lower gears will shift right at around 2000 to 2500 rpm.

Do I have to go thru this same vacuum control curve adjustment?


84 500SEL EURO 87K
85 300D 267K (and still goin' strong)
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