Something is wrong here. Hard shifts are caused by a low vacuum condition, while soft shifts (flaring) are caused by high vacuum. If you plugged the line correctly, it would be impossible for you to have less vacuum than with the 2/3 valves connected. You see the vacuum line coming out of the IP? Somewhere between the IP and its source (the brake booster supply line), you'll see a 3 way rubber connector with a line going to the 2/3 valves on the valve cover. Disconnect that line at the source and plug the fresh hole in the 3 way connector with something suitable. Whatever you use, it must fit VERY snugly, or you will have a vacuum leak. You are leaking vacuum somewhere, and I strongly advise you to get a Mitey-Vac if you're going to be troubleshooting vacuum issues. It's MUCH easier than trial and error.
That's just a piece of vacuum/emissions hose, readily available at your local Craptastic Auto Parts store. I don't remember the size, but I just brought in a piece of hard plastic vacuum line to find the size that fit. Again, it must fit VERY snugly! You may want to buy at least a foot, because there are other pieces of hose just like it that are probably just as old. If you're worried about breaking something when removing the old rubber line, slice the end of it with a razor blade. I do this whenever I replace old heater and radiator hoses that don't want to come off easily.

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K

Replaced subject hose and promptly broke nipple off the T in the line from the pump to the brake booster - so I'm down again....

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Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

Epoxy time?
JB weld actually doesn't look at all unattractive in its grey form on black or white parts

Yeah expoxy or JB weld (my personal favorite) will fix you right up. Put a nail through the broken nipple to hold it in place on the tube.. smear some glue around the fitting and leave it a few hours.

the xmission modulator will not hold vacuum from the mighty vac. I found a used one and it leaks down slower than the one currently installed.

My question: should the modulator hold vacuum indefinetly?

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

......

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

Yes, it should hold vac. They are fairly cheap from the dealer or cheaper from fastlane. I would just buy a new one and make sure to get an extra seal. It comes with one but it's easy to rip.

Fastlane AT Modulator

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

yes, it should hold vacuum for a long time. It's OK too if it leaks just a tiny, tiny bit, but a good one will be real obvious - it will hold for a long time. Go ahead and replace the rubber line right at the modulator. It's too cheap to worry about and is one less thing to factor in.

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

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

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