Mechanical Auto-shifting

[asid61]

After seeing 971's friction clutch this year, I was wondering if any teams have made a mechanical auto-shifter in the past.
I'm not talking about code to shift when the current spikes or something like that, something more like a friction clutch that would automatically shift back into higher gear once load lets up. 971 definitely had a good design, but they were still using a pneumatic cylinder in place of something like a spring.