I am new to N scale. I am really an O gauge guy but decided to try my hand at N. Anyhow, I converted a bunch of my rapido couplers to micro trains coplers. The kind that come pre-assembled attatched to the trucks. Anyway, I recently purchsed a new bachman engine (ns gp-9). The new engine comes with the claw shaped couplers not rapido. They attach to the micro trains couplers fine but when I go around certain curves I notice the engines coupler moves higher than the freights and they become un-coupled. I figured if I could shim it somehow to adjust the height, this might work. What would I use to shim them or is there another way o adjust coupler height? Is this a common problem in Nscale? If I buy all the same brand will I not have this problem?