Can I Dangle My Car in the Air from the Quick Jacks Alone?

[1795]

Originally Posted by Argess

Doesn't a flatbed have the winch in the center, so the pull won't be straight if that's the case. Gets worse the farther up the flatbed you are. Honestly, I never really noticed if a flatbed winch can be moved laterally.

And any side load would be doubled with only one strap....

Also, there will be a twisting torque on the whole car when you pull it from one side, so there will be side-loads even if it is a straight pull. If the whole business is beefy enough, everything will be OK.

But is it? Patrick's ERA looks different than my older one, if I remember correctly. I wouldn't trust the threaded rods in mine for this purpose as I think they would bend quite easily.

Mind you, Patrick is committed now as he's drilled the hole, so he might as well try it and see what happens.

Good point about the winch typical being in the center. When I installed the winch on my trailer it was offset to the side that the strap was attached to the quick jack, so it is more of a straight line pull.

[patrickt]

Originally Posted by 1795

Good point about the winch typical being in the center. When I installed the winch on my trailer it was offset to the side that the strap was attached to the quick jack, so it is more of a straight line pull.

Wait a minute, this is just high school trig. You know, the horizontal and vertical components of a force that acts at an angle measured from the x-axis? I asked Ellie and she says that if the quick jack tow hook is one foot away from the exact middle of the car, and the tow winch is lined up with the exact middle of the car, and the winch is ten feet away from the car, the angle is just over 5 degrees to that quick jack hook from the winch. The sine of 5 degrees is about .087, so if the winch is pulling a thousand pounds worth of force to get the car up the ramp, you've got 87 pounds pulling sideways on that hook. That ain't much. Ellie says she can muster up that amount of force with one paw and that we're dumb for having to ask a dog to solve a simple trig problem.

[rodneym]

Yes.
Indeed, Ellie is the smartest one here

[patrickt]

Beefing up the horizontal strength of the linkage. Here is the before picture:



And here is the upgrade. The sleeve around the lower boss and aluminum tube is 4130 Chromoly, with a wall thickness of .120", just measure it, cut it, grind it at an angle for a perfect fit, and tap it on to the boss for a snug press fit. I used an ID of .76", as the aluminum tube is .75" and the boss was a few thousandths above that. With the grommets out you can test for any lateral play with the aluminum tube and threaded rod installed -- if you did it right there will be next to none.



To get to the bottom linkage ERA was kind enough to include a removable plug in the fender well.



Part two will be the replacement of the threaded rods, nut, and acorns with Grade 8 stuff. Then, not only can I dangle her from a crane, but I can drag her sideways across asphalt without ripping the front end off.

[patrickt]

This part's easy. The advantage of using this double ended stud is that I get 40% more strength from the increased tensile stress area, since it's not threaded, over all thread. This little gem has 120,000 psi yield strength, for those sideways pulls. Plus I'll trim it down so the quick jack is actually on the shank, instead of the threads, for increased shear strength. The acorn, stover nut, and washer are all Grade 8. And that's the heavy-up.