W126 transmission question re. kick-down and safety overide?

[donbryce]

Yesterday I had an interesting experience, tooling down the highway at about 3000RPM when I decided to punch the kick-down button (under the gas pedal) to pass. The transmission did indeed gear down like it's supposed to, but then I looked down and the RPM's were at 5000 and climbing! I immediately moved to right lane and let off the gas to pull over, but had to keep going for a bit before finding a suitable spot.
I was able to slow down, and still could feel the gas pedal accelerate the car while I was doing so. As this was happening, I was still in gear (D), I then noticed that pressing the gas had no effect on the transmission, as if it was sitting in P at idle, just revving with no actual power getting to the driveshaft. All pushing on the pedal did was blip the tach reading. Ohmygod, I thought, I've blown the tranny!
At that point I slowed enough to stop by the roadside, which I did, putting it in P and leaving the engine idling while I struggled to disconnect the kickdown switch, which was stuck, as I suspected.
End of story, it went right back into D and accelerated, shifted up/down like nothing had happened. I'll replace that damn switch soon.
My question: Is there some sort of fail-safe mechanism in the transmission that disengages the drive gears when the unit is over-revved in a lower gear than high? I'm wondering why the transmission 'cut-out' just before I actually coasted to a top, still in D.

[C32AMG]

If the kick down solenoid is activated, power supply to the kick down solenoid is interrupted at about 200/ 250 rpm before the engine reaches its governed speed/ red line.

Depending on model, the KD solenoid is controlled by a cutoff valve relay, a kick down limiter relay or the fuel pump relay. When power is interrupted, the transmission will
Up SHIFT into a higher gear, lowering the engines rpm to a safe range

If the engine over revs, again depending on its strategy and model, the engine control module or fuel control module will interrupt power to the fuel pump relay, until it sees a safe RPM reading.


Base on your description it sound like the transmission neutralized/ slip, I would check the Transmission level.