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Old 09-03-2013, 07:43 PM   #1
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2007 30' Classic S/O
Somewhere , South Carolina
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Trailer Sway, Observed, Someone else's "trailer"

This is just a report on an observation on the road today. I have no hands on info, only visual.

An SUV was passing me and it was pulling an empty car tow dolly. But the dolly was rhythmically swaying L-R-L-R.

As it finally passed me still swaying and actually making the SUV sway a bit, I got a look at the hitch. Nothing special except for the stinger or shank wiggling back and forth in the receiver. It just appeared that the loose fit might have been allowing the uncontrolled dolly sway.

Here's the commentary. We have pretty sophisticated hitch systems and the final link TT to TV has a fairly loose fit of the shank to the receiver. While I have never tried any of the commercial shank clamps a couple of years ago I fabricated full length stainless steel shim plates. One a 90 DEG shim and the other just one side. This covers three sides. Both are secured via the pin. The shank is a pretty nice sliding fit. It was after I did this that the steering wheel really settled down and it has stayed that way. I wish I had a video of the rhythmic swaying and loose shank/receiver. I have no idea how new or worn the components of the SUV were.

If you want to demonstrate your fit, if you can insert the hitch head and in my case attach the bars, then pivot them out parallel to the bumper, now lift up and push down on the end of the bar, moves up and down? Shank is allowing the rotation?

I know hitches are one of our most controversial topics and I have hesitated reporting on my shim plates, until this AM's observation of a wiggling shank dance. If something is loose and beating around, it surely must lead to more clearance and it just gets sloppier.

Fire away..

Gary
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Old 09-03-2013, 08:07 PM   #2
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An empty car dolly is notoriously unstable to tow.

The axle pivots like a steer axle to allow the a four wheel car to be loaded and have the front axle off the ground. One axle of a four wheel trailer must pivot, or it will have to slide in a corner. This "loose" axle easily sets up an oscillation that can only be stopped by slowing down.

When loaded, the sway is dampened by not only the weight of the car, but the rear wheels of the car, too.


We had 4 wheeled hay wagons that exhibited the same behavior, one fix was to set the front axle with a more-than-normal amount of toe-in. It was ok in the hay field, but ate tires on the highway. But, it ended the sway.

I doubt the slack in the receiver had much effect.


Regards,

JD
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Old 09-03-2013, 08:09 PM   #3
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I'm sure you're right about the last part, that a trailer wagging back and forth will at least eventually "wallow out" the receiver. I doubt that the slight looseness in the receiver was really contributing much to the sway of the dolly, it's just an issue of a poorly damped system. The only damping it gets is when the tires are so far from the line of travel of the TV that friction pushes the other way... and then the trailer goes "over center" until the opposite tire pushes it back, etc. Even a cheap friction sway bar would reduce a lot of that.

Side-to-side looseness in a receiver is going to allow a little "wiggle" but with WD set, there won't be much up-and-down motion and the shank transferring that force through the receiver will reduce the side-to-side motion a little bit, as well. With some form of sway control, it'll be better still.

Yes, a big sloppy worn-out receiver is not going to be a good thing, but a little clearance is probably not going to be noticeable when everything else is set right.
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Old 09-04-2013, 10:15 AM   #4
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The only thing I disliked more than towing with a car on the dolly was towing the dolly empty, for the reasons mentioned above. I was following one the other day and watching it bounce around like nothing else. I always disconnected my brake controller - having the dolly's brakes activate made the situation that much worse; even turning them down pretty far didn't help (and the motorhome didn't need the extra help slowing down an empty dolly).

In mine, the axle didn't steer; the tray the front wheels of the car sat on would rotate as necessary.

Geez, I don't miss that dolly. Not one bit. When I needed to tow a car recently, I rented a full car trailer from U-Haul and had zero problems with sway or anything else.
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Old 09-04-2013, 10:50 AM   #5
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Quote:
Originally Posted by Skater View Post
Geez, I don't miss that dolly. Not one bit. When I needed to tow a car recently, I rented a full car trailer from U-Haul and had zero problems with sway or anything else.
This is good to know. I had been considering getting a tow dolly to move our project car around (to the painter and back, etc). Sounds like I'll just go with the full size UHaul car trailer. We rented the car trailer before when we fetched the car from Eastern WA in the first place. Driving slow and easy it gave us no troubles hauling it home.

Seems to me like if the receiver was so wallowed out you could see it moving on the road, that's just an unsafe condition. Not to mention the guy was passing which indicates he was probably going faster than he should have been. Recipe for disaster!
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