I just bought a 1985 300D. I have noticed that the transmission shifts hard when going from 1st to 2nd and 2nd to 3rd at low RPM's (between 2000 & 2500) but at higher RPM's(2500 and up), it shifts smooth. Any advise would be appreciated. Thanks

Mine did that. I considered it a quirk of the transmission and drove it like that from the time I bought it until the front seal of the tranny started to go (@ 310,000 miles) and I swapped in a manual.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Harshness of shifts is controlled by vacuum level. Low vacuum=harsh shift. You could have a vacuum leak. You can use a MityVac to monitor the level of vacuum going frm the vacuum control valve on top of the back of the IP to the transmission modulator at various accelerator positions. You can then compare those numbers to the info on the transmission vacuum thread.
85's have an additional componenet in the transmission vacuum system--it's the blue flying saucer type thing on the left inner fender. It's called a vacuum amplifier I think.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Search for the valve body spring kit, if the vacuum turns out okay.