Nothing....I just replaced this pod....

The LOCK vacuum moves the pin into the locked position. There is a spring that moves the pin back to the unlock position when the vacuum is released out of the other (open) nipple.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT