I had catastrophic clutch plate spring failure and it sounds about the same as what you're describing. I Shifted from 4th to 3rd coming off the freeway, pushed in the clutch to go into 2nd and there was nothing. The springs came apart and then did battle with the flywheel bolts. That was the noise I heard at the time.

When the springs break, you get a no-go situation.

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"