I have an 82 300sd. I bought it knowing about this issue so I don't know how long it has been going on.

When I first got it a couple months ago it had a bad flare from 2-3 and from 3-4. 1st gear was always firm and 2-3 and 3-4 is firm at fairly hard throttle(2-3 only flares at light throttle, 3-4 will shift normal at hard throttle but soft when cold)

Then I installed superior spring kit, I only used the k1 and k2 springs. transmission shift timing is fine. I also have checked the modulator valve and it does leak. HOWEVER disconnecting it does not change the flare. From what I understand if the modulator valve is disconnected(no vacuum going to it) it should eliminate this as the current problem correct?

So after the superior kit I noticed much improvement. 2-3 only flares when cold for the first few miles, then is normal and very firm at harder throttle. 3-4 flares all the time but does flare less when tranny gets warm, it also does not flare at all if the transmission gets very warm, like after driving the car harder.

Since my flare problem goes away when the car warms up and shifts are firm at harder throttle levels does this mean it is not necessarily worn? I would think if this was the case it would flare and slip under hard throttle worse then at very light throttle. I get NO tranny slippage.

Also transmission fluid and filter has been changed and is at correct level.

So what to do or check next? I know I need a new modulator valve cap but I suspect there is something else that needs replaced first. Or maybe it is a sign of a worn out transmission.

I know this goes against conventional wisdom on this site, but if your car has a bowden cable to the tranny, I believe you need to tighten it. Most of the time here, people say that the bowden cable just controls shift RPM. But on my w124, I was able to alleviate symptoms very similar to what you describe by simply tightening the bowden cable.

You pointed out that many of the shifts are fine at hard throttle. You need to simulate that condition all the time by unscrewing the tensioner on the bowden cable (to make the housing longer and tightening the inner cable). That fools the car into thinking your are pressing down on the throttle more than under your current set up.

My car did the poor shifting at light throttle on slight declines. By tightening the cable, it now shifts perfectly all the time.

If your car does not have a bowden calble, sorry for wasting your time.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

if you get no difference in shift quality when disconnecting the modulator, there could very well be a vacuum problem further up the line. could be a leak somewhere, could be the vacuum control valve on top of the IP is malfunctioning, if you've got the 3/2 switches on top of the valve cover those are prone to going bad and causing many problems!

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1981 NA 300D 310k miles

Bowdon cable is adjusted so that at full throttle it's pulled out all the way. It was like that and haven't changed it. I've tested vacuum going to modulator valve and it's fine. Also I do not have the 3 2 switches. But by disconnecting vacuum from modulator valve doesn't this eliminate the possibility? Since at 0 vacuum the modulator valve should be shifting as firm as possible

What leads you to believe that the cable should be so adjusted?

I suspect that you would get better results making the adjustment so that initial take-up occurs in conjunction with initial movement of the accelerator linkage.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Also confirm the linkage is set to the fsm. Make sure the rod from the injection pump to the stop lever is adjusted so there is a 5mm gap between the ball and socket when the stop lever is pushed towards the valve cover.

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I know it is not FSM recommendations on the cable. It was like that when I got the car. I don't want the shift points to be any lower. I didn't think that could cause the problems I'm having but I guess I'll change it. I'll also check the shift linkage. I'm confused about the gap check but I'm sure I'll find it in the manual.