When I first put together my Lego Roller Coaster, the cars ran on it very smoothly. After about a week or so of use, I noticed that momentum was being lost. At first, it started by barely not making it to the lift chain, then got so bad, it couldn't make it around the curve that was over the ticket booth. It got so bad to the point where one of the trains couldn't even make past the first curve after the giant drop. I took off the cars and cleaned them thoroughly with a q-tip and noticed that helped a bit, but they'd just lose momentum again and I even experimented with Teflon grease which helped, but then left residue behind (which has all since been wiped away).
I ordered parts for another six cars because I wanted to run two trains of six cars at once and when they finally came in a couple nights ago, I put them on and those new ones worked beautifully, just like with my original cars when I first used them. I took the wheels out of one of the new cars and swapped them with an old car, and the old car ran smoothly, so this tells me there's nothing wrong with the track or the chassis; there's something wrong with the wheels. I inspected the old and new wheels and there is no perceptible difference between them so for the life of me, I can't figure out what to do here. I cleaned and cleaned and cleaned them, but to no avail.
I'm hoping against hope that someone here has this set and experienced this exact problem and came up with a solution.
