Four-post lift on uneven slab

[Skyman]

Hi, all.


Here's a question that I don't recall ever seeing addressed here where four-post lifts have been discussed. On a slab that was not finished perfectly flat, is the open-channel design that has the adjustable lock ladders preferred? I'm guessing that would be the case, although from just a structural design perspective, I like the enclosed sleeve-type that is found on Advantage, BYB, and a few others. I will probably move the lift at least a time or two while determining exactly the ideal placement, and having to level it by shimming the posts even once doesn't sound the appealing, let alone having to do it any time the lift is relocated in the garage. The slab was finished to what I regard as "builder-grade" quality -- looks good enough, but measurements reveal high and low spots.

An additional -- just how much slope will be okay with a four-post. To ask it another way, how far out of plumb is it acceptable for the posts to be? This will be placed on a slab that has a slope of a couple of inches back-to-front.


TIA for all insights.

 

[Farmall450]

I would ask the manufacturer(s) for this information.

 

[wssix99]

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[racecougar]

Yes, and the manufacturers provide the max "out of plumb" spec.

 

[Skyman]

Thanks, guys.

 

[J-Man22]

I have an Atlas EXT-L four post lift, which has the lock ladders. My garage floor slopes 2.5" from the front posts to the back posts. I didn't want to anchor the lift to the concrete, so I came up with a different plan that still allowed me to shim the posts. I had some plates cut that are the same size as the post bases, two 3/4" plates for the rear posts (total of 1.5") and one 1/2" plate for the front posts. For the two 3/4" plates for the rear, the top plate has through holes and the bottom plate has threaded holes. The one 1/2" plate for the front posts has threaded holes. I also had some thin shims cut in both 1/16" and 1/8" thickness, the same width as the post base with notches to go around the bolt holes, and a few smaller shims in the same thicknesses. I was fortunate that I had someone with a plasma table that could cut all this for me.

After I assembled the lift, I lifted it up on the wheels that came with it. I set the steel plates on the floor then lowered the lift onto them. I added some of the thin shims at the back edge of each post to get them plumb front to back, and there were a couple posts that I had to add some of the smaller shims to plumb them side to side. Once happy with everything, I used 5/8" bolts and bolted the post bases to the steel plates, essentially making the rear posts 1" taller and everything plumb on my sloped floor. For the rear posts with the two plates, the bolts pass through the top plate and thread into the bottom plate. Before I put the plates on the concrete I also glued rubber to the underside to help keep them from sliding. It has been a couple years and the lift hasn't moved at all, though it is used for storage so not driven on and off very often. And even with the 1.5" of plates added on the rear post bases they will still lift off the floor with the wheels so I could move the lift around if I wanted to.

After all this was done, I adjusted the cables so the runways lifted level, and adjusted the lock ladders so the runways were level when sitting on the locks. The lock ladders have 2" of adjustment, so between the 1" extra height of the rear post and approximately 1.5" of adjustment of the ladders I was able to account for the 2.5" slope of my floor. One issue I found is that because the runways were level and the floor was not, when the lift was all the way down the rear crossbar did not rest all the way down on the post bases, and the rear of the runway would hang from the cables when the lift was down and when I was driving on and off the lift and I noticed the cables had stretched as a result. So I just made up a couple blocks of wood that I set on the post bases and tucked into the post channels, so that the crossbar would sit on them when the lift was down. One other thing to keep in mind is when you level the runways on a sloped floor the approach ramps will be at a steeper angle than if the lift was installed on a level floor. For my lowered classic truck this is not an issue (barely), but for my daily driver I cannot get it on the lift to do maintenance because of the angle of the approach ramps so I have to build or buy extension ramps.

 

[Skyman]

Thanks much for the detailed response, J-man. Muchly appreciated.