Good morning everyone. A few weeks ago I posted on here about my 85 300SD having issues with shifting after sitting for the better part of a year. It would only shift after hitting 4500RPM at 25 and 45MPH. I was able to get that issue resolved by replacing the kickdown switch and she's worked fine since, at least until before this past Thursday.

On my way back down to VA Beach going through the Chesapeake Bay Bridge Tunnel, I engaged my kickdown switch going upgrade in the last tunnel. After getting through the tunnel, I noticed that going back above 50MPH, my RPMs would peg at 5k, but this was only for a moment as the car shifted at drove fine and was able to get to my destination. Since then after driving the car around town for an extended period of time, I'd loose the ability to shift up at 50MPH and line out at 5k RPM. The revving sound is similar to max revving the engine while in park (makes like a "wonwonwonwon" sound - I should probably have recorded it and attached it to the post) Once this happens, I downshift to 3rd manually in order "unstuck" the shift. Even then, the car is still driving at around 3300RPM, which it at this speed it should have shifted down to at least 2k-2300RPM (I shouldn't be driving at 3k RPM until at least 70MPH after this shift point). If she sits for a while (like overnight as I juts did prior to posting this), it will shift up fine and not peg out.

Another thing I tried doing is to see if I could downshift with the kickdown switch. I'm hearing the click, but it's not downshifting which makes me thing that maybe something happened to the solenoid when it downshifted in the tunnel. I might put the old switch back in to test to see if the solenoid works. It's been a bit since I've had a transmission flush, so I'm going to go ahead and have that done regardless. Bowden Cable also looks and moves fine (my past issue I was playing with this a bit and had to readjust it for shifting)

So, my questions are:
1 - what could have happened to cause this issue?
2 - could I have blown the solenoid and if so how do I check it (I know I need 12VDC going to the solenoid from the kickdown switch but what else do I need to do to check it)?
3 - Should I go ahead and mess with the Bowden Cable again?
4 - Could this be the start of more transmission issues that could lead to a possible rebuild?

Hope I gave enough information here that someone is able to guide me in the right direction. Thanks in advance!

Since you say it shifts fine again if it shifts overnight, I would think the Bowden cable adjustment is ok. I would first check the fluid (level, color, burnt smell. etc) I would also recommend a fluid AND filter change if it has not been done in some time. If the car was sitting for a long time, the fluid might have collected some water in it.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Personally I would not do a transmission flush on an older automatic transmission. It is a gamble in my opinion. Also might be a waste of money in your case.

Fluid and filter change not nearly as much if any. There is a plug to drain the torque converter. So you can get the vast majority of the transmission fluid with a normal change. Also read how to read the transmission dipstick on these models.

don't do a flush. just drain the fluid and put in a few filter.

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1981 NA 300D 310k miles

What has been said is good.

Besides the Kick Down Switch there is also a Kick Down Solenoid on the Transmission itself. It is not common for it to stick but I guess it can happen.

The Transmission also has a Governor but I have never read of what symptoms it causes if it does not work correctly.

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84 300D, 82 Volvo 244Gl Diesel