Mount High-Lift to rack towers, need some help.

[DaveM]

I am going to mount my high lift jack to the rack towers of my Thule lumber rack. The jack will be mounted with 3 quick fists per the directions from the manufacturer (pic below), on a steel or aluminum flat bar that will be bolted through each tower. Only the bar will be bolted to the towers, the jack is mounted to the bar. My question is, what size bar will be strong enough for this application? I was going to use aluminum flat bar 1/4" x 4" x 4'. But I may use steel instead since the aluminum is pretty expensive. What size steel sheet or bar would work here?

The towers are about 43" apart on center. They are 1.5" deep and 2.75" wide.

 

[granitex1]

I would use 1 inch square steel stock, with as thin a wall as I could find. You could also use the perforated square stock and not have to drill any holes in it. Also looking at the design for the quick fist, why not just use a couple of 1/2 inch grade 8 bolts with ss wing nuts and be done with it. You can even throw a padlock throught the beam of the jack and the square tubing for when you are in unsavory places. I have seen equipment lost when trees reach out and grab quick fists, but have yet to see anything lost with the wing nuts, or regular ones you just need a wrench to take the high lift down.

 

[madizell]

I tend to agree that the bar is superfluous. Two bolts directly through the towers will suffice, or if the holes won't line up, two brackets bolted to the towers, and two bolts through the brackets. Two quick fists might not be sufficient, which may be why the diagram shows three, and I agree that mounted with quick fists and facing the rear of the vehicle, the jack might be knocked off if it strikes an object, whether you use two or three quick fists. Mounted down inside the bed where it is protected, the quick fists would be fine. Looking at your photo, if you mounted the quick fists to the bed rail supports instead of the towers, quick fists would work well and be better protected from the elements, IMHO.

 

[DaveM]

I've mocked up the flat bar setup with QFs and the jack sits inboard enough that I wouldn't worry about snags too much ( I don't drive in really rough conditions, just back-country camping) . I want it outside of the bed because it's an always on item and with that small short bed I don't have a lot of real estate left for the stuff I take camping with me. The other side of the towers will get a similar set up for the axe and shovel.

I want to use the flat bar instead square tube to keep the jack as close in as possible. Check the diagram for the QF set up for the jack and you will see that they use an outward facing bolt that helps hold the jack in place and can be topped off with a wing nut if desired.

Its the design I'm going with, I just need to know if 1/4" bar will be strong enough. Or what the right dimensions would be for steel flat bar?

 

[madizell]

Considering what you intend, 1/4 aluminum should be strong enough. Certainly it will take the weight, and if you are not concerned about striking objects, you also don't need to be concerned about the bar taking a hit or bending if the jack takes a strike. For steel, probably anything 10ga or thicker is going to work (roughly 1/8 inch), and if flex on such a bar is also a concern, a perpendicular brace, say a half inch high, on the back of the bar would solve any flex issues. I really don't see a need to over-engineer the mounting bar, as the jack itself is quite stout, and so long as the quick fists hold, if the jack does not flex, the mounting bar won't either.

For what it is worth, I have carried a hi-lift jack bolted to the floor of my CJ-7 behind the front seats, for the past 6 years, and have used it exactly once. I find that it won't lift a tire off the ground on my Jeep without chaining the suspension to the frame, and on most surfaces, it is so unstable as to be useful only as a last resort. Seems that no matter how I block the tires, the vehicle always wants to roll off the jack, usually to the detriment of the sheet metal or someone's foot. I would never use one to get unstuck, as I believe that trying to use if for that purpose is just asking for broken bones. Since it is almost mandatory to find firm flat ground to use the jack safely, I find that once on firm ground, a small bottle jack under the axle tube or frame rail will lift the vehicle more reliably than the hi-lift, and in the past 9 years, all trail repairs on our club rides but one or two have been accomplished with a bottle jack instead of a hi-lift, even though nearly all of us carry the hi-lift as well. So, having it handy has never been high on my list of priorities.

 

[DaveM]

I really don't see a need to over-engineer the mounting bar, as the jack itself is quite stout, and so long as the quick fists hold, if the jack does not flex, the mounting bar won't either.

Thats what I was imagining but I wasn't sure.

So you think 10ga (1/8") at about 4" wide would be strong enough? I guess I just need to give it a try. The steel is cheap enough compared to the aluminum that I can afford to make a mistake with it.

Thanks for the help.

 

[madizell]

I do think 4" wide is sufficient. If you have a sheet metal fab shop handy, if they can bend one inch of the 4 into a 90 degree bend for you, 1/8 inch steel would be hell for stout.