1981 300 SD 1-2 Hard Shifting

I've been reading a lot on this topic and based on what I can comprehend, one, if not the main reason, is low or no vacuum. Since I am not a mechanic and do not have the tools to test the vacuum and from
what I can tell everything in the car works fine, other than the 1-2 hard shifts, am I being too simplistic by just replacing the hose leading to the transmission? My rationale is either there is a crack or obstruction in the hose resulting into no or low vacuum. Also, I was looking at the engine today and it appears that the hose (about 1/4" round) just "snaps" and there are no clamps at the connections. Am I looking at the right thing?
As always, any advice will be greatly appreciated.
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If only the 1 - 2 shift is hard but not the subsequent shifts, then the vacuum modulator is working as it should.
Some M-B shifts ARE hardER than those found in modern cars that have electronic engine and transmission controls which briefly retard the ignition to depower their engines at the instant of a shift. We're spoiled by these new fangled cars!
Back to your car. It could be that the transmission is not shifting WHEN it should be; that can be easily checked, even by a non mechanic.
At the top back of the engine, on its right side is a rod or cable that links the throttle linkage on the top of the motor to the right side of the transmission. Its purpose is to "tell" the transmission what's going on with the throttle so the transmission will "know" when to shift. It could be that this rod or cable is not correctly adjusted. To check its adjustment (motor shut off) one pries the ball at the upper end of the rod or cable off its pin on the throttle linkage. Gently pull the rod or cable as far as it will go (gently) and allow it to return to is own natural position. It's correctly adjusted if you can reattach its ball to its pin WITHOUT pushing or pulling the rod or cable. If you can't reattach it then lengthen or shorten the rod or cable so it CAN be reattached as described. Any adjustment should be minor but may improve the 1 - 2 shift.
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As far as I can tell, it's only the 1-2 shift that is hard. It is more pronounced when I step on the accelerator gradually and almost smooth when I rapidly step on the accelerator. Again, thank you very much for your advice. I will check the rod/cable and let you know what happens.
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The transmission design is to shift harder (slip less) as the throttle is opened: i.e. full throttle will have the firmest shifts and light throttle openings should have smooth shifts.
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