I have 3 Class 66's and they all "complain" on my 2nd radius tail chaser test track.
They don't derail but you can hear clicks as the bogie turn round the tight curves.
This could be due to 2 of them having No.36 Kadee's fitted directly to the body and the fairing fitted. But the 3rd doesn't have this yet and it's much the same.

They don't derail but you can hear clicks as the bogie turn round the tight curves.
This could be due to 2 of them having No.36 Kadee's fitted directly to the body and the fairing fitted. But the 3rd doesn't have this yet and it's much the same.