At times I pull an 18' 2,200 lb. car hauler. Especially when there's a car on board, I'll pick-up a vibration at about 55 or so. It makes no difference if the OD is on or off. My friendly Ford dealer says it's not the truck. (He didn't look at anything!) Anyway, how could he test it unless I drove in with the loaded trailer? A friend that's towed for years told me that this sort of thing is common, and that it happens all the time. I didn't check the balance on the trailer wheels...in fact there's no weights on them. People have told me that if a trailer wheel is out of balance I wouldn't feel it in the truck anyway. Is it just harmonics? Could a trailer brake be dragging? This has seemed to have gotten slightly worse, and at times I can just barely pick the vibration up with the trailer empty. I sware that when I bought the trailer new a year ago there was no vibration.

Anybody got any ideas?

 

I would guess that the problem was the trailer, unless you use a weight distribution hitch, then it could possibly be your truck. You need to do things to rule out what it isn't. Check tire pressure in your trailer tires, check trailer tire size to make sure they're all the same size. check bearings on your trailer. Borrow someone's trailer and see if you pull it with no problem. Have someone follow you while you tow and see if the trailer looks normal. If you do use a weight dist hitch, you might have a problem with your front suspension, try varying how much tension you put on the hitch. Just a few ideas, I would just try to vary things until I found something that changed the problem. Good Luck!
J.J.