OK I am stumped. I dug out my old trains, my 5 year old is getting into the hobby early! So I have an older bachmann santa fe chief. When i pit it on the track I was getting no responce or so I thought. Thought cleaning so i did. Put it back on the track if i jostled it a bit it got some power but only for a short zap no movement, when I went to take it off i licted the the rear trucks from the track and only have the fronts on it it ran like a champ but as soon as the rears hit the track its dead? Thoughts?

Thanks