I need some help troubleshooting a shifting problem in my '84 300TD. This is a federal car but the vacuum system matches the '84 california / '85 federal vacuum system as shown in the attached vacuum diagram. There is no blue flying saucer style vacuum amplifier (or switches on top of the valve cover).

The car shifts firmly when the accelerator is down 3/4 to all the way. I get some flare when the accelerator is pressed a more lightly (1/4 to 1/2 down). Because of this I think I'm dealing with a vacuum problem rather than transmission problem.

I've resolved quite a few vacuum issues within the car... rear hatch lock leak, vacuum pod leaks in the climate control. In addition I found that the switchover valve was leaking vacuum... I resolved this by plugging both vacuum lines attached to the switchover valve (hence also disabling the ARV). I also plugged all lines going to the vacuum coverter to disable the EGR and simplify the vacuum system. Can anyone help to verify that this is ok? The vacuum converter is a bit of a mystery to me... I'm not sure that its function is entirely EGR related...

Also, if anyone can tell me what proper vacuum levels are on the vacuum control valve side of the vacuum damper, this would be helpful. Likewise, any info on the transmission vacuum levels would be useful. I've done some research on this but all the different vacuum designs have me a bit confused. Again, this is an '84 calif / '85 federal style vacuum system.

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

I had been chasing a transmission shifting issue that I finally fixed today.
The condition was a firm 1-2, soft 2-3, and slightly firm 3-4. After reviewing many posts as I am a MB Newbie, I replaced the old and brittle vacuum lines. I experienced only a slight improvement...basically the same firm 1-2, soft 2-3, and slightly firm 3-4. Next, I adjusted the Modulator and Bowden cable. The adjustments improved the soft 2-3...but firmed the 1-2 even more. I ordered a K1 spring kit as that seemed like the next step to fix. I stumbled across another post that recommended replacing the plastic valve levers as they wear to the point that the valve is not functioning properly. I removed the plastic black box on the valve cover and sure enough they were shot. I had seen a DIY on DieselGiant.com so I ordered the plastic valve levers and replaced today. I wish I checked the valve levers first as the Bowden cable and Modulator adjustments were not necessary. However, I am very happy now, the transmission is shifting like new!

http://www.dieselgiant.com/trannyleverreplace.htm

These are not present in the '85 style system...

I may try adjusting the vacuum control valve as per http://articles.mbz.org/transmission/adjust/ but I'm still not sure about plugging all lines to the vacuum converter.

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon