Framebuilders - Trek Pedal Trailer won't trail true

I own two Trek Mt. Train 206 (http://www2.trekbikes.com/bikes/bike.php?bikeid=80766&f=38) pedal trailers. One of them just won't trail right. I know, because I spend a lot of miles riding behind it while my wife tows it (and I tow two other kids in a conventional two wheeled buggy). It appears that the wheel is set where it is not vertical as I look from the back. I don't think it is a matter of the wheel axel being set crooked in the dropouts (to track to the left or right). If vertical is 0 degrees, I'd estimage the wheel runs at about 10 deg. The pedal trailer is made of steel (and not cro-moly at that, I think).

Q. -- Is there a way to scientifically determine if this is real or an illusion?

Q. -- If it is cockeyed, is there a way to fix this? At a cost which is not out of line to the value of the pedal trailer?

Have your dealer take a look. I can't visual the problem you are describing. When I first got a Trek "Tail-A-Bike, it would wobble from side to side, even with a skilled rider on it.

I bought a second mounting kit, and that kit including more sizes of shims than the original kit. After experimenting with different combinations of shims, I found a combination that enabled the hitch to snuggly fit around the seatpost of the lead bike, yet pivot smoothly and easily when going around corners.

I had told the dealer about the side-to-side sway, and he used a rubber shim. That shim did not allow the hitch to pivot freely. Replacing his rubber shim with a smooth plastic shim from the Trek "fit kit" solved the problem.

When I mentioned the fact that the original "fit kit" was missing the "key" shim, the dealer said "I've noticed that too...some kits have more shims than others". I e-mailed Trek about the problem, and got a "thanks", but NOT what I wanted: a "refund" for the second fit kit, and an assurance that future trail-a-bikes would be shipped with all of the various shim sizes.

I'll take the both to the dealer so he can compare. Thanks for the suggestion.

FWIW, the first one I bought had NO shims at all. I could not hook it up at all. I did eventually get a set or three or four shims/collars for each unit. They are identical. They let you use it with different size seatposts. I still wonder what you do if your seat is so far down that you can't attache the collar.