Ive used a few of these things now, weedkiller train, some NSE coaches and an engineers tool coach. Take the bogies off, and smooth out the section where the coupling cam acts. Theres a bit of a rough section that stops the bogies mooving freely. Secondly, remove the couplings, and file down the top of the 'crank', it rubs on the back of the buffer beam. Thirdly, take the wheels out and throw tham as far away from the model as you can. Theyre split axle, so b2b's cant be adjusted, and theyre really badly machined. I've replaced mine with some 14mm sets from Peters Spares. After that, they run as sweetly as the Bachmann coaches they were copied from