Hello, I'm looking for advice on how to get reliable action from the bobbing head gimmick on a Lionel 6-26726 T-Rex Transport boxcar. I typically run this car on the layout, but it's Christmas time so it is getting a turn under the tree. On the layout, I feel I get reasonable action from the bobbing head feature while running on tubular track with several straight track sections in the loop. The Christmas tree loop is different, as it uses FasTrack and is all curve track sections - the bobbing head gimmick does not seem to activate.
I assume this boxcar is similar to others with the bobbing head feature - there are extra gears attached to one of the trucks, and as the wheels turn, those gears are supposed to engage and transfer that movement to the internal mechanism in the car, which causes the head to bob up and down periodically. No electronics are involved in the function of the car.
I can get the desired action by removing the car from the track and manually turning the geared axle. I've tried running the car pointing both directions, but that doesn't appear to help. I've tried various running speeds on the Christmas tree loop, but that does not get the feature to work. I've also added 4 straight sections of track, turning the loop into an oval, with the thought that maybe the gears engage better on straight sections - after doing this the feature worked once, but after running the train another 3 minutes there was no further action. If I manually engage the gears and get the bobbing head into the "up" position and then run it in the train, the head will go "down" very reliably automatically, but it doesn't come up again on its own.
Normally I'd just swap out a finicky car when dealing with a temporary layout, but my 3-year old is enamored with his T-Rex car, so it is worth querying the collective wisdom/antics of the OGR Forum. 
Thank you kindly for any tips/tricks you can send my way.
