Took the belt out and released the cover on the mechanism side.(Do not open the "springside" tilt the belt back and forth and you can feel the weight moving around tahat is the mechanism side). Inside the mechanism is the "movable weight" which does lift a little arm when the car is accelerating or slowing down. The arm had "jumped" off it's right place and jammed the weight. Just put the arm in it's right place, it's pritty easy to figure out, and the belt worked fine again. It is really a very simple/smart mechanism and worth while looking into.

When you disassemble the cover there might be different screw's. On the spring side there were two "three winged screw's. Don't touch those. On the mechanism side there are two plastic tensioners. Don't take pliers and try to turn those. There is a hole in the middle. In the hole there's a little, 5 mm long plastic rod that tightens the plastic tensioner. Put a nail in the hole and knock the plastic rod out. Be shure not to loose them, they are small. When they are out you can pry the lid off. Good luck!