Since 2 days, my '93 300D 2.5 auto transmission was shifting really bad: I found this little white tubing to be disconnected :-(

I have to admit I probably disconnected it accidentally when I changed my 5 glows plugs last saturday...

Also, what is the purpose of this green part on the vaccum line? Is it a filter?

Thanks,

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W126 1985 300SD TurboDiesel
W164 2009 ML320 BlueTEC (Sold)
W123 1983 240D Stick (Sold)
W210 1998 E300D TurboDiesel (sold)
W124 1993 300D 2.5 Turbo (sold)
2012 GMC 2500 Duramax PickUp
2015 Ram 1500 EcoDiesel PickUp

Just taking a guess, I would say its a valve (one-way air flow).

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I read that hard shifting may be helped by drilling the
orifice of the plastic tee fitting between the vacuum
pump and brake booster. The port that goes to the
trans is small by comparison. I was trying to
make this a little oversize, when it cracked.
At Home Depot I bought a plastic tee that was 3/8"
on all three sides. It fit perfect into the big lines
and a bigger hose was rigged to the three way rubber
connector that joins vacuum to the bleeder valve.
My hard shifting has definately improved. I still have
a problem with going through to gears too soon,
but that is not a new problem. I tend to think this
modification may compensate for soot in the vac lines
and a weakening vacuum pump. It worked for me,
Mark 82' 300SD