I assume you are working on a 616/617.

Put a wrench on the central nut/bolt and turn clockwise.
You should be able to turn the shaft a few degree.
When you release the wrench, the shaft should go back to its old position under spring pressure.
The visible part of the TD should stay put because it is held by the chain.

You also can remove the front plate of the TD by removing the two 8mm bolts, this will give you access to the springs.

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76 240 D.
60 Unimog 404.
67 250 SE.