I've read many of the threads on vacuum leaks creating hard shifting. But I'm experiencing different symptoms. I just started noticing my car shifting very hard between
2nd and 3rd only at low speeds, some times with a loud clunk. If I step on the rack and drive it hard, the car still shifts smoothly and without any noises. I checked the trans. fluid level, and it was fine.

Any ideas on what might be happening? Am I looking at a new transmission within the next few thousand miles?

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1987 300TD; 166,000 mi/267151 Km - had to make room for the dog
1973 220D; mileage ??????
1978 300D; 178,000

Check yer Vacuum, matey.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Do a search on the K1 spring, I think that is related to the 2-3 shift.
This is assuming your other gears change just fine and there are no vax leaks. I'd definately check the vacuum first though.

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

Hey i seem to have the same problem with my 87 300sdl. Let me know what you find out. I have checked the tranny fluid too, but not sure if it's a vacuum issue too.

http://www.peachparts.com/shopforum/showthread.php?t=237249

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1987 Mercedes 300sdl, 280k mi (daily driver)
1982 Mercedes 300sd, 205k (occupying driveway)
1985 Mercedes 300d, CA, 148+ mi.
1986 Chevrolet suburban, 50k? or 150k? mi, diesel
1998 BMW 740il, 120k mi (for sale)
1999 Honda CBR900RR, 42k
1997 Jeep Wrangler Sport, 103k miles (sold)

It doesn't shift any smoother at higher power levels.........you simply don't notice the "clunk" because it's over too quickly.

The problem is low vacuum. 99% of the time there is a vacuum leak somewhere in the system. You'll need a Mityvac and some time to find it.

If it's plumbed like the SDL's, you can eliminate all the vacuum components on the right side of the vehicle. The EGR and ARV systems are prone to leaks and you'll get a resulting hard shift.

Additionally, if the transmission is more than 1 pint low on fluid, the shift will dramatically firm. So, that's the very first thing to check..........hot.........and at idle in neutral.

Add more vacuum to smooth the shift.
If the others start to flare, look into a Superior shift kit.

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1982 300CD Petrol/Black Leather

how do you add 'more vacuum'? i just had my transmission rebuilt and it shifts much harder than before it went out.

Search for "vacuum control valve"
This is what controls the firmness of the shifts, as it regulates how much vacuum to send.

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

Brian, could the loud clunk he speaks of be some kind of driveshaft bushing that is worn? A 300D I looked at before I bought mine had similar problems- at light throttle something clunked, but at higher power it was not present (like you explained)
Or is it more likely that the hard shift itself is causing something in the chassis to make the clunk?

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

.........my money is on this.

Why are you posting on this thread when you failed to answer my questions on your own thread???

Thanks for all the feedback. I guess I'll buy the mity vac and start tackling the vacuum gremlins.

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1987 300TD; 166,000 mi/267151 Km - had to make room for the dog
1973 220D; mileage ??????
1978 300D; 178,000

I posted this and it got deleted. Not sure why. I think it is relevant and something to check.

I had a similar problem with my 123 and is was getting 0 vacuum to the transmission. The problem was a plugged orifice in the T coming off the main vacuum line. Cleaned it out with a small drill bit (my hand). Be careful not to enlarge the orifice beyond the size stamped on the T. Mine was 0.6 mm.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

So I've been preparing to go after the vacuum system this weekend in the hopes of smoothing out the shifting. But this morning I was parked on a slant and the oil light came on. I checked the oil - after finding a flat spot - and was down maybe 2/3 of a quart. i added a pint of oil and the shifting issue disappeared. Am i crazy? Can't see how this would have any effect.

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1987 300TD; 166,000 mi/267151 Km - had to make room for the dog
1973 220D; mileage ??????
1978 300D; 178,000

You're not crazy.

When the trans on the 603 is low on fluid (even 1 pint low), the shifts firm up. You were more than 1 pint low............