MTH Challenger on 0-72 Ross switches.

Are you saying that this switch is NOT laying flat but is in fact on a grade?

Ron

No the switch is not on a grade Im unsure if its perfectly flat and it looks to me as if the pilot trucks and the first set of drive wheels derail right at the frog. Its almost like it cant make the curve but it runs fine on the same switch going the other direction. I have a class a that makes it fine.

Check the locomotive to make sure that nothing is impeding the movement of the front engine. I've seen it happen that something gets out of line and keeps the front drivers from swinging all the way in one direction. It could be a misrouted wire or something loose or incorrectly assembled in the guide mechanism for the front drivers. A wire in particular would only cause a problem in one direction. 

I have the same derailing problem with our MTH Challenger.  The spring which makes the pilot truck press down gets weak and causes a derailing problem on our curved 072 ROSS switches ... it doesn't like it.

Replacing the spring with a slightly stronger one helped a lot.

The switch is on a grade but is level to the grade, i.e. flat as measured with a straight-edge.  The tracks entering and leaving the switch are flat to the switch for at least 14" each side.

Other large locomotives don't have a problem, except one turbine which doesn't like it either. 

Worked on it for weeks trying to make it work and it does now, ... sorta.  The Challenger will make it through at one speed and one speed only.  Any faster or slower and it derails.

Is the track in the shape of Gargraves tubular or Lionel post war tubular track?

I have found that my MTH Reading Lines T-1 don't like Gargraves switches but works better with post war style tubular track switches, like K-Line 042. Something about the style of the track, rectangular verses rounded, seems that my MTH T-1 prefers a rounded style of track.

Lee Fritz