Vibration when towing at Highway speeds
 

My new 2018 F-150 super cab four wheel drive, vibrates at highway speeds when pulling a 16 ft utility trailer with my 51 willies jeep on it. Trailer has two 3500# axles and is not heavy jeep weighs about 2400 lbs.
The truck is a 5 liter with 10 speed and 145 inch wheel base. I believe the max weight on the sticker was 7050 lbs for the truck. I purchase the truck with trailer options, receiver, 7 pin plug, and break controller. The dealer tells me that the newer trucks have softer springs and this causes the pinion angle to change when a load is applied to the rear bumper. This change in angle causes the vibration you feel in the seat. I never felt this when pulling the trailer with any other truck. I feel it when ever i pull a trailer with this truck. Is this dealer pulling my leg?

Are you using a weight distributing hitch? If not, it _might_ help since it will bring the rear of the truck back closer to the non-towing height.

There have been a couple threads on vibration problems where the trailer was the problem. As I recall, one was a harmonic issue with the length of the tongue. I think the other turned out to be an issue with the tires (balance, out of round, etc) or the alignment of the axle. Try different tire pressures on the trailer to see if that changes the vibration. Mainly a lower pressure, not a higher one as that would be likely to exaggerate the issue. Some tire shops will send you on your way with new tires without balancing. I've had that happen. They need to be balanced.

There have also been a few Superduty trucks with towing vibrations where the dealer added shims to keep the driveline at better angles. So yeah, your dealer may not be taking you seriously and doing their due diligence to try and resolve the issue.

Yeah, have the trailer tires balanced first. I have had tire stores give me funny looks when I ask to have my trailer tires balanced. "Nobody balances trailer tires. There's no reason." Bzzt. Wrong. I always balance my trailer tires. The trailer pulls/rides better and the tires will last longer. Of course I regularly tow long distances at interstate speeds. YMMV.

I have been saying this for about 20 years. I agree, I prefer to balance trailer tires. I haven't done it. It is a good idea.

I've used Balance Beads in all of my Trailer Tires for many years .. it works ..

Might be a pinion angle vibration. The weight of your trailer is changing the angle.

I'm having a similar problem with my ATV trailer. It's a single axle trailer with a 1,500 lb ATV on it. No issues with my much heavier bumper pull toy hauler.

I am experiencing this same issue, with 2 different trailers, where you able to get it remedied? Mine starts at about 62mph and starts to lessen around 75, more often on hills. truck seems to ride smooth no trailer. Just had tires balanced and rotated, same results.