Tested on O-36 Fastrack.
i know it says O54 but can it run on smaller radius?
Dave
I just tested my Lionel UP 1943 (6-85315) and it went right around O-36 with a car coupled up. No kinematic couples. Ran same as all my UP Heritage SD-70ACes. I think the O-54 is a typo.
Which brand? Not all 036 are the same.
Lionel Fastrack
From above, check if the coupler swings (too) far outside of the center rail. Two couplers of varied size could also compound any issue there.
Can the trucks/coupler swing tighter than 36"? (not hard to tell)
Wiring slack tension may be an issue over time ??