I have three sets of MTH Premier Madison passenger cars. All have six wheel, identical (I believe) trucks. Two of the sets run fine around my O42 curves (minimum for these cars) but one does not. The wheels on all five cars bind on the curves. Three of them roll through the curves without too much resistance, but the other two bind a lot.
When I roll a car by hand, I can feel the friction when it enters the curve. If I push a car and release it, it stops on the curve.
All axles have been oiled and roll freely. All the couplers swing to the limit of their travel and the trucks swivel freely. The only thing that is different is the "bad" cars are about ten years older than the others.
Has anyone else encountered this problem?