I took it to the bi-annual checkup that is required in Norway. There was lots to fix, and it all got fixed, but this one problem still stands: The rear brakes brake equally strong at first. Then the left side doesn't get any stronger, and the right side continues normally, to about 40% more than the left side.

I've changed both cylinders and shoes, greased the contact points on the back plate, and washed the drums thoroughly with de-greaser, but there is no change.

Any ideas?