Tail wagging the dog.

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Mustang1964s
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Tail wagging the dog.

Post by Mustang1964s » Wed Apr 28, 2021 1:48 pm

The other day my wife and I were driving down the highway.
We came upon an F150 pulling a little trailer. It looked like it was for a ATV.
It was swaying from side to side.
I pull my T on a trailer and this got me thinking as to why the swaying back and forth.
The only thing I can think of is the axle was not on Square.

Am I way off or could there be another reason?

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David N
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Re: Tail wagging the dog.

Post by David N » Wed Apr 28, 2021 2:46 pm

If the load is heavier behind the axle this could cause the swaying. Always put the heavier portion of the load in front of the axle, toward the tongue of the trailer.
Last edited by David N on Wed Apr 28, 2021 5:26 pm, edited 1 time in total.

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Fordwright
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Re: Tail wagging the dog.

Post by Fordwright » Wed Apr 28, 2021 3:23 pm

One morning, for no reason that makes sense at all, I pulled onto a freeway going against one-way traffic. I had gone a few miles before I was head-on to a pickup pulling a trailer. That was the microsecond I realized my error, and the pickup was a bit slow to respond but eventually swerved out of my way. I still remember seeing the trailer swaying back and forth in my rear-view mirror. It was another mile or two before i was able to cross over to the proper side of the divided highway. Good thing there wasn't much traffic that morning.

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Oldav8tor
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Re: Tail wagging the dog.

Post by Oldav8tor » Wed Apr 28, 2021 3:30 pm

Reminds me when I made a trip to the city a few years ago. My wife called and warned me that she heard on the TV that some nut was going the wrong way on the freeway.... "One, I said...there are hundreds of them!"
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Re: Tail wagging the dog.

Post by Norman Kling » Wed Apr 28, 2021 4:22 pm

Another think which could cause a problem is a trailer without brakes. It will work fine when you are pulling, but if you have to stop fast, the trailer will try to push the truck. This would be worse with a light truck or car pulling the trailer. It could jackknife and push the truck to one side and then when you try to straighten it, could push the other way.
Norm

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Fordwright
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Re: Tail wagging the dog.

Post by Fordwright » Wed Apr 28, 2021 5:01 pm

I don't suppose it's legal anymore, but I saw a brake system that applied the brakes on the trailer when the towing vehicle decelerated, by compressing a piston in the hitch, which applied the trailer brakes.


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Re: Tail wagging the dog.

Post by Wayne Sheldon » Thu Apr 29, 2021 3:30 am

Called a 'surge brake'. I don't know for sure, but as far as I know, they are still legal.
The most common reason for trailers swaying or oscillating is improper weight distribution. Weight either too high or too far back relative to the axle and hitch geometry.
I once was going up a steep hill, with a steep going down the other side, when near the top I saw an improperly loaded trailer swaying a bit while still going uphill. As close to the top as we were. I slowed down and kept a ways back. Going down the other side, the idiot (I am being kind here) sped way up to well above the speed limit. What made it worse, was anyone with half a brain could see traffic backing up and nearly stopped at the bottom of the hill! As soon as the idiot hit the brakes, the trailer broke into oscillation swinging from jackknife right to jackknife left and back again and again and again! On top of everything else the idiot did wrong, he wasn't in the right hand lane! Cars on the right of him and the left of him got hit multiple times! He clobbered at least three cars before he got stopped. And I wasn't sure, but I thought one of the cars he hit also hit a car in the next lane over when he in turn swerved as well.
I have seen way too many bad trailer accidents as they happened caused by people that have no clue how to load or pull a trailer!


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Re: Tail wagging the dog.

Post by Rich Bingham » Thu Apr 29, 2021 12:13 pm

Besides load distribution, height of the hitch point is a factor. Tongue pointing downward causes oscillation.
"Get a horse !"

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Re: Tail wagging the dog.

Post by Kaiser » Thu Apr 29, 2021 12:19 pm

This is a short, simple and informative video about why a trailer starts to sway and takes over the car

https://www.youtube.com/watch?v=w9Dgxe584Ss
When in trouble, do not fear, blame the second engineer ! 8-)
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Re: Tail wagging the dog.

Post by Duey_C » Fri Apr 30, 2021 12:53 am

Neat video find Leo! We've all Been There Done That (BTDT).
A level trailer loaded to the rear isn't any fun. I can believe it about a downward pointing trailer being naughty too.
Thought I had it about right one day with a 6500 pound load of an old tractor, some pressure on the rear bumper of the truck but nope.
About 35 mph was all I was comfy with and very gentle corrections. :oops:
Then other times when we get it right, 65-70 and it's smooth as glass. :)
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Re: Tail wagging the dog.

Post by ironhorse » Thu May 06, 2021 7:32 am

Surge brakes are still legal if you want to see for yourself rent a heavy U-Haul trailer. they are all equipped with them because most trucks don't have a trailer brake controller installed.
Do it right or do it over,your choice. Drive like everyone is out to get you!

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Re: Tail wagging the dog.

Post by Kaiser » Mon May 10, 2021 5:12 am

Here's a more elaborate video about weight distribution in the car and the trailer and it's effects, the comments are in dutch but watch closely and it is self-explanatory
It is quite obvious what is going on as the demonstrator puts on and takes away weight at different places of the pulling vehicle and the trailer :

https://m.youtube.com/watch?v=KlD7THCoypk
When in trouble, do not fear, blame the second engineer ! 8-)
Leo van Stirum, Netherlands
'23 Huckster, '66 CJ5 daily driver

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