Why doesn't the cassette rotate when I backpedal?

Question

I have an old bicycle where backpedaling causes the cassette to not rotate. Instead, the cassette stays still and the rear derailleur bends, providing new chain to go around the backpedaled chainring. When releasing the crank, the rear derailleur spring causes the crank to rotate again forwards, negating the backpedaling effect. This is very annoying because I want the ability to backpedal in a permanent manner to cause the pedals to be in a position to easily resume riding.

It's almost as if the rear derailleur spring is too weak, or the freehub body is poorly lubricated for free rotation.

How can I solve the problem, causing the bicycle to behave like an ordinary bicycle when backpedaling?

Answer 1

The cause was neither poor lubrication at the freehub nor a weak rear derailleur spring.

I investigated the bicycle carefully and noticed that mud at the rear derailleur pulley wheels was hindering the rotation of the pulley wheels. When riding the bicycle forwards, this probably caused slight power losses, only so slight that the effect was not apparent. However, when backpedaling, the power losses were great enough that they caused the pulley wheels (and thus the cassette and freehub body) to not rotate but rather offer new length of chain by bending the derailleur.

Cleaning the rear derailleur pulley wheels with a flat blade screwdriver negated the effect. The pulley wheels were in pristine condition, albeit coated with thickened mud.