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The mechanics of fishtailing

Post in 'The Gear' started by SolarAndWood, Feb 27, 2012.

  1. SolarAndWood

    SolarAndWood Minister of Fire

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    This trailer is usually pretty docile but was all over the place last night and I'm not sure why. On the flat it would start about 55 and on a decent downgrade it was out of hand at 50. I think the weight was pretty equally distributed, trailer pretty level, etc. Any idea what am I missing other than a Duramax and a gooseneck?

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  2. MasterMech

    MasterMech Guest

    How's the tire pressures? Brake dragging? Dry wheel bearing?
  3. blades

    blades Minister of Fire

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    Alignment of axles, or possibly one or both are bent, bad spring, or shackle. As others mentioned breaks ,bearings. one more Bent tongue.
  4. SolarAndWood

    SolarAndWood Minister of Fire

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    Tire pressure was good when I left. I'll go out and check it again with the load off it. It is about 45 miles out to the farm through the hills and I didn't notice it dragging or moving around on the way out even at higher speeds. But given my recent experience with the little trailer, I should probably have this one serviced.
  5. ironpony

    ironpony Minister of Fire

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    Actually it is probably to balanced
    it wants to float around
    more tongue weight usually helps
    or it has to much tongue weight
    lightening the back axle
  6. bioman

    bioman Burning Hunk

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    just a little more tongue weight. make that truck squat just a little !
    ditchrider likes this.
  7. Jags

    Jags Moderate Moderator Staff Member

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    If tire pressure is even, it appears in your pic that the back tire squats a bit more than the front leading me to believe that you might be rear heavy. That WILL cause a trailer with that much weight on it to start the mambo dance on ya.

    I don't know, looking at it again, I might just be "seeing" things.
  8. lukem

    lukem Minister of Fire

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    I think you probably have it a little too light in the tongue. That will cause it to get unruly. I would rather have too much tongue weight that not enough. Sudden breaking with a back-heavy trailer can be an unforgettable experience...and not in a good way.

    If you have a bent/broken/worn/damaged/unbalanced something in the axle or suspension of the trailer, my experience tells me that those will be more apparent when the trailer is unloaded. For example, I have a trailer I borrow off my BIL every so often. It is a 10K lb dovetail flatbed, and unloaded it will shake my teeth out at 35MPH and 55MPH because one axle is jacked. When I load it down it rides like a dream (other than being too heavy for my 1/2 ton truck!). I've noticed this in a couple other trailers too.
  9. smokinj

    smokinj Minister of Fire

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    +1 Thats kinda of a short tounge! ;-P Compaired to mine! :cheese:
  10. zzr7ky

    zzr7ky Minister of Fire

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    +1 on the tongue wieght.

    I left mine unattended for a couple hours once. Since it was known I gathered wood, a friend with a loader full of wood filled it. I had to stop and shift wirght forward by hand, and it straightened up quickly.
  11. Adabiviak

    Adabiviak Feeling the Heat

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    ^
    That's awesome! Small price to pay for a free load of (presumably good) wood.
  12. clemsonfor

    clemsonfor Minister of Fire

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    Yep the usuall cause it to light of touge weight. Even if that is a 3/4 ton suburban or tahoe it should be squatting more than that with that load unless its bone dry!
  13. SolarAndWood

    SolarAndWood Minister of Fire

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    I'm buying the tongue weight explanation. I noticed as I was unloading it that I kind of ramped up the pile against the tailgate and the bigger stuff was in the back compared to the front. I'll have to put some sideboards on it to make sure I get enough in the front of the trailer. It's a 3/4 ton burb. Doesn't squat much at all especially compared to my old half ton even with tongue weight on it.
  14. lukem

    lukem Minister of Fire

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    Ideally you want 10% - 15% of the trailer's weight on the tongue. Once you know you have a properly loaded trailer (truck scale is your friend here), it is always a good idea to get a reference on how much the truck "looks" like it is squatting or by taking a measurement (i.e. where does the draw bar land when measured against your boot or leg). Nothing too scientific...just the if it passes the look test.
  15. SolarAndWood

    SolarAndWood Minister of Fire

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    I kind of assumed that would happen naturally with a dump trailer loaded with relatively uniform material. The front axle is 42% back on the box, the rear axle is 67% (~5 ft and ~8 ft from the lead edge of the 12' box). Looking closer at my picture, I am pretty sure what got me in trouble is the back half getting stacked higher against the tailgate than the front. The tailgate isn't light either. This loading distribution probably more than negated the bias of the axle locations. I'm thinking if I run a 2x12 around the sides and make sure the front gets loaded with the extra instead of the back, I should be in good shape and still right around the towing capacity of the truck.
    ditchrider likes this.
  16. clemsonfor

    clemsonfor Minister of Fire

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    Your probly right. Or either just dont fill the back to the top. Or run the 2x12 in the front and halfway down the sides to discourage the loading high on the tailgate urge.
  17. SolarAndWood

    SolarAndWood Minister of Fire

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    lol, have we met? I can only run a single 2x12 for similar reasons. Probably end up with 6 or 7 ton in there if I justified higher sides on it for mulch :)
  18. SolarAndWood

    SolarAndWood Minister of Fire

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    So, one other question for the mechanically inclined, why does this problem seem to be so much worse on extended significant downhill grades? Is this because of the difference in control from the ball pulling on the flat or up versus being pushed on going down? Or is this the weight effectively moving back on the trailer on the downhill which I can't see but it's been a while since I took or used mechanics?
  19. smokinj

    smokinj Minister of Fire

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    Weight pushing you hard and your light in the rear.....
  20. Brogan007

    Brogan007 Member

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    Had the same thing happen to me while pulling my dump trailer with ~4tons of logs...on a downgrade, at 50 mph, the fishtailing started & got real scary, real quick.
    My take is the "tail starts to wag the dog"....the momentum of the trailer overpowers the truck. If we'd had trailer brakes...or had them & adjusted them to work right...so when applied, they held the trailer back....it'd have fixed it. Breaking the truck, only causes a jack-knife effect, as the trailer keeps pushing. All this imho only...ymmv.
  21. SolarAndWood

    SolarAndWood Minister of Fire

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    Gotcha, so kick up the gain so the trailer brakes are slowing the train down instead of the truck? Alternatively, stay off the Interstate through those sections with heavy loads so you don't have as much momentum at the top of a long descent. Seems like the Interstates are graded with much longer runs like that than the 2 lane roads where you can mange your momentum a little better.
  22. SolarAndWood

    SolarAndWood Minister of Fire

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    Looking at the topo maps, the section that really scared the chit out of me drops 400' in a mile with a pretty good bend towards the bottom.
  23. Brogan007

    Brogan007 Member

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    Lordy....you could ski down that slope!!!
  24. SolarAndWood

    SolarAndWood Minister of Fire

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    Kind of felt like I was snowboarding through the trees for a little while there...
  25. 711mhw

    711mhw Feeling the Heat

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    Sway always = not enough tongue wt. no matter the tire cond, equal psi, one, two or three axles, etc. That 3/4 Sub can take it, and you would have to "squat" it very badly before you would ever need to wory about being too light in the front for proper steering/braking. This "too balanced" condition is pretty std. on all of the dump trlrs that I've seen, as is a short tongue. A crude trick that I'll do when loading is, when empty, measure the bumper or hitch, tailgate or what ever against your knee or belt or maybe your arm and hand hanging down by your side. After loading be sure that what ever you "measured" against is now 3" above the vehicle.

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