I bought a Bowser RTR covered hopper from MB KLIEN. I have never been able to make it reliable.
I have changed the trucks,installed kaydee couplers and added weight to total 4 OZ .It will still derail everytime I add it to a consist. The height is right and everything seems normal what have I missed?
Check the underframe for an angle brace running from the truck bolster to the outside corners of the frame. This may hit the flange of the wheelset on curves. Shave the downward side of the angle off or remove the whole angle. Another solution is to add a washer between the truck and the bolster to raise the frame. This will require using the correct offset shank coupler to correct the coupler height.
Edit: In later runs I beleive Bowser corrected the problem.
I have several of those hoppers from the days when they were in kit form. The wheel flanges rubbed on the bottom of the hopper body. The cure was to put washers between the trucks and bolsters to raise the car body. This may be the problem with the RTR versions.
A couple of the Kadee red fiber washers between the body and each truck should solve the problem. I don’t remember needing to change the couplers to correct their height after adding washers.