Lift options for less than 4" thick pad

[DanWheeler]

My conractor says my pad has a minimum thickness of 3.5". He thinks it's probably more than that in most places but it's too risky to trust. What are my options for a 2 pole lift?

is the concern that the bolts dont have any purchase if the pad is too thin? Can epoxy help with that?

I'm sure I could cut out parts of the pad and re-fill. Does anyone know the general guidelines of how much to cut and how deep to re-fill? I wish I would have made my mind up where the lift was going to be before they poured the slab so i could dig it out a bit.

I was wondering if I could weld up some "guy poles" to support the lifts?

of course I could only do this on 3 sides of each pole and I would prefer to only do it on 2 sides of each pole.

with a 2 pole lift in which direction is a majority of the force/leverage applied? Do the 2 poles want to lean towards each other? Or is there more risk of them leaning side to side (i.e. car would nose dive)

For lifts that have a bar across the top, does that bar provide any strength to keep the 2 poles from caving in towards each other?

I would be lifting about 5000lbs max.

thanks for any help or suggestions.

dan

 

[Lloydthumper]

There are a few varibles with it I have also thought about putting the bracing on mine if I get one just for safety sake and I know my concrete is 4" of 4000psi concrete. But if the base under the floor was not compacted really good the concrete can crack under the load. The braces them selves would provide alot of support for back and forth movement and that is the main concern. I am not sure if I would use and asymetrical lift to where the load may be more to one end or the other than with a symetrical lift. If there is a real concern with this and what I would do myself is just purchase a 4 post lift and learn to live with it. the load is evenly disributed and should never have a problem.

 

[gesoffen]

I think the real concern would be the shear strength of the concrete. Concrete itself has little/no strength in shear or tension. Rebar and other reinforcement structures allow concrete to bear a shear or tension load without failing. With 5k+ weight under the small foot print of lift pads, you run the risk of the concrete cracking through shear.

The fore/aft moment on the lift will depend on the weight distribution of the car on it. I'd imagine that Dodge Ram you have pictured there would load the lift such that if it failed in the fore/aft direction, the truck would do a face plant. If you had a rear engined car (Porsche 911 for example), depending on the lift points on the car, you could have the same problem in the other direction.

For lifts without the overhead crossmember, there is a significant concern of the lift towers "caving in" on an insufficient floor or insufficient connection to the floor. With a vehicle on the lift, this is probably one of the more dangerous forms of failure since the concrete could fail or the bolts could pull out and cause the car and lift to fall suddenly.

An overhead crossmember should significantly reduce this risk assuming it is structural (i.e. not just a sheetmetal wire/hydraulic conduit). But this won't protect you from the concrete failing in shear, driving the lift pads through the concrete floor.

Bottomline is go with what the manufacturer suggests. I'd even solicit some help from a structural engineer. Also, if you're in doubt about the floor thickness, you'd best cut the lift pad areas out and repour. Keep in mind that you're repoured floor should be a monolithic slab that is poured as a unit across the entire width of the lift. If not, you run the risk of the individual "piers" or blocks shifting under the leverage of the lift.

 

[CraigFL]

The other alternative you have is to try to spread the base load out over a larger area. One way to do this would be to put an additional pad under the lift base, say 1" thick by twice the length and width dimensions of the pad-centered on the existing pad. This would spread the load out over 4 times the area and should be OK. I realize these are trip points and you may have to taper some edges to drive over if they interfere.

 

[jimval]

I am a structural engineer. You are playing with fire if you install a two post lift in an unapproved manner.

You have a little more leeway on the 4-post lifts....

 

[rsanter]

have you contacted the manufacruter for recomendations

bob

 

[3bay]

Your pad should be at least 6" thick with rebar for it to be safe. If it was me I would cut out a 4'x4' section where the pad will set and drill holes into the old slab at least 6" and epoxy in rebar across the hole in both directions before you re-pour it with 4000lb mix. The area should be well compacted also, I prefer a lime and gravel mix instead of sand. I once worked for a company named Complete Lift and thats how we did it. Its better to be safe when working with something that could kill you very easily. I have seen 2 lifts that did fail and its not a pretty site when a heavy vehicle comes crashing to the ground.

 

[UnSub45]

I consulted with Bendpak when I was having my slab poured. They referred me to a few docs to answer my questions. I recall reading slab repair instructions in one of them if the slab was cracked within **" of the posts. It was what you are looking for. I don't recall where I saw it. Give them a call they will tell you what you need to do.

 

[JRGSPE73]

Here's another option...not as convenient, but much less hassle. No concrete to pour or holes to drill...

Sorry...couldn't resist...

 

[DanWheeler]

funny.

those don't work very well when the frame of your truck already sits 3 feet off the ground.

i also need to put a 4 link kit on a Suzuki Samurai which means the frame is going to need to be suspended at least 3 feet so I dont know how I'm going to do this without a 2 pole lift.

 

[JOHNMAN]

The lift manufacturer will have minimum specs for your floor. Don't cheat. You will be sorry.

You could always call them and ask them if they could install much larger column base plates as a special order (and for more money). The lift manufacturer is the only one I would trust as they are the ones who know the reactions that their lift will have on the floor. (A structural engineer could also make some recommendations, but they wouldn't be real familiar with the exact lift you are looking for information on, and would more than likely go far beyond what is really required due to the liability involved.


Just my $0.02.

 

[Vicegrip]

Drill a test hole and see how thick the concrete is. 3.5 min might be 5 inch real life. While talking to a lift maker rep we discused the needs and how they are determined. The PSI and thickness ratings are for anchor retention more so than anything. More likely to pull the anchors than crush the concrete.

From memory, my 2 post Bend-Pac called for 4 inch of 4000 psi.

X2 on don't cheat but you don't need to go overboard ether.

 

[Vicegrip]

funny.

those don't work very well when the frame of your truck already sits 3 feet off the ground.

i also need to put a 4 link kit on a Suzuki Samurai which means the frame is going to need to be suspended at least 3 feet so I dont know how I'm going to do this without a 2 pole lift.

Samurai? Have a buddy hold the frame up one end at a time. He can use the other hand for his beer.

 

[turbojimmy]

I definitely wouldn't cheat on the specs. Make sure your mounting surface conforms to the manufacturer's specs 100%. This is important both from a safety and warranty perspective. Safety aside, the lift is a fairly big investment. If you have a failure that damages or destroys it you're going to want to make sure you have warranty coverage.

It's already been stated, but unlike a 4-post lift, the tops of the columns on a 2-post lift are going to want to touch each other. If there's a bar installed across the top that helps, but you need to have it sitting on the right type of pad to make sure that the anchors don't pull out. You also are concentrating a lot more weight over a smaller area with 2 posts so you're going to want to make sure you have a solid pad that's properly compacted underneath.

Anchors could pull out quite suddenly causing you to have to hold your truck up over your head Superman-style. However if the concrete were sinking under the weight you'd have evidence of that before you had a real problem. It would crack first, you could see rebar poking through. I doubt it would shear in a manner that would cause a sudden failure. It would still **** to have to take the lift out, pour new pads and put it back in. My Rotary manual has a list of what to look for and when you need to replace the mounting surface. You should probably just have the pads cut and poured into the floor now and be done with it.

I installed a 4-post lift in my garage a few weeks ago. Even though I followed the manufacturer's specs completely, it is still scary to look at and work under. I'm getting used to it but if there was any aspect of the installation that was questionable I'd be a nervous wreck all the time. I bolted it down as a precaution but I was told it wasn't necessary by Rotary.

Jim

 

[Yotaforce]

I spoke with an engineer about ny similar plans and he told me that I could easily cut out 24"x24" under each post leg, dig down atleast 24", install rebar, pour concrete "piers" with atleast 10" anchor bolts and that it sould be enough. I did not know where I would eventually install a lift and did not need to spend the money to have the whole slab at 5", so this is what I plan to do later down the road.

 

[3bay]

It would probably be safe to say this was a properly installed lift, lol.

 

[bluesman2a]

It would probably be safe to say this was a properly installed lift, lol.

THAT is how I built my slab.
X3 or 4 or whatever... Don't cheap-out on the mounting surface.

Read this, it's rotary's specs for concrete. If you do not have the minimum, they recommend:
http://www.rotarylift.com/Service_a..._Questions/FAQPages/Concrete Requirements.pdf

On all Two post models; If anchors do not tighten to specified torque, replace concrete under each column base with a 4’ X 4’ X 6” thick 3,000psi minimum concrete pad keyed under and flush with top of existing floor.

 

[6768rogues]

Jimval, best advice I have seen yet on this topic. I agree completely.

 

[oiler]

I work under a 12K Rotary lift everyday in a GM dealer
We've got 6 hoists in a row and some of them were working the bolts loose
We cut out a 6x6 hole where the hoists mount and poured a pad 12 inches thick to mount the hoists too.
To my suprise the floor was around 3.5 inches thick where we were mounting the hoist to.
My hoist has never worked loose and it is still in the original 3.5 slab.
Doesn't bother me at all
Jeff

 

[DanWheeler]

I work under a 12K Rotary lift everyday in a GM dealer
We've got 6 hoists in a row and some of them were working the bolts loose
We cut out a 6x6 hole where the hoists mount and poured a pad 12 inches thick to mount the hoists too.
To my suprise the floor was around 3.5 inches thick where we were mounting the hoist to.
My hoist has never worked loose and it is still in the original 3.5 slab.
Doesn't bother me at all
Jeff

thanks Jeff, it's funny the range of opinions you get on something like this. Some people will swear up and down a car WILL fall on you and you WILL die if your pad is 3.99999" thick. "Right or wrong only" people. no in-between.

I tend to think that if 4" works, then 3.5" and a little common sense will too. Plus, i'm really quick - i could jump out of the way of a falling car

but what it might come down to is that a 2 post lift is just too wide for my 24' wide garage and even though a 3.5" pad would probably work fine especially for the intended purpose of lifting a Suzuki Samurai that weighs a whopping 2000lbs.

The reason I really want a 2 post lift is so I can install a 4-link kit on a Samurai and I need the truck raised off the wheels while still having the frame between the wheels be completely clear. A 4 post or scissors lift doesn't accomplish either of these requirements.

but... what I was just thinking is what if I got a low-rise scissors lift to get the wheels off the ground and used tall jack stands at the front and rear frame rails and then let the car down on those jack stands? That way the wheels would be off the ground and the frame rails between the wheels would be even more clear than if i had lifted with a 2 post lift.

anyone ever done this? When you let the scissors lift down does it have a lot of front to back movement that would want to slide the jackstands back? or should I be able to safely transfer the weight from the scissors lift to the jack stands?

check out this awesome drawing i made to explain what i'm talking about

 

[DanWheeler]

holy smokes, forget about a 2 post lift, these midrise lifts keep the frame rails just as clear as a 2 post lift and they are completely portable and tiny relative to a 2 post.

http://www.gregsmithequipment.com/PhotoGallery.asp?ProductCode=TPPRO%2D6M

 

[Mapleshade]

Dan, don't skimp on the weight of the hoist either. You should go at least 9000 pounds. I had a 7000 at my garage and it just wasn't enough. You are spec'n it for your 2 jobs but whats down the road? We do lifts all the time and one of my techs prefers jack stands to a hoist on these jobs. Buy heavy, good quality jack stands and they will last a lifetime. Cheap out on a hoist or stands and there may be no lifetime.
Cheers,
Barry

 

[rsanter]

how about 2 high lift jacks or the old bumper type jacks from an old garage and then some tall jack stands

bob

 

[DanWheeler]

I would certainly get a decent set of 4 tall jack stands:

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200318711_200318711

and yes I totally agree about going big even though I dont plan on using it unfortunately i can't find a mid-rise lift over 6000lbs so i think that would have to suffice.

I assume when they say 6000lbs, it means it really can lift 6000lbs? or is that not the way that works? I dont know of any trucks i'd be working on that realistically weigh over 6000lbs. Even my friend's full size 91 Landcruiser is under 5000lbs.

90% of my work would be basic wheel and axle work and I guess if I have to use jackstands on the 4 corners of the frame rails to drop a ****** once a year or do some 4-link suspension work then i can deal with that. at least the mid-rise lift will make it easier and safer to put on the tall jackstands than doing one side at a time with a floor jack.

 

[bofus]

I believe that there are two things to consider here. First is the vertical loading. To decrease the vertical loading, you need to increase the footprint of the posts. In other words, the larger the base plate is (and thick enough to be essentially rigid) the more effectively it distributes the weight over a larger area...in effect reducing the pounds per square inch of loading on your concrete slab. The other factor is the resistance to tipping over (or pulling out the anchors). The larger base plates should also help in this respect because of the ability to place anchor bolts further from the posts and also possible to increase the number of anchors. This should also be sufficient for either symmetrical or asymmetrical lifting. Whatever solution you decide to go with, I also agree with the earlier recommendations for having your installation plans reviewed by a licensed professional engineer. Such an evaluation should not take very long or cost too much.

 

[Ironcrow]

Twin post lift installation in 3.5 inch floor:

1) Post punch through the concrete floor as it fails in shear: Increase perimeter of post pad by a factor of, 4 / 3.5 = 1.14, 14 percent.

2) Anchor pull out: Instead of upside down 'Y' as pictured, buy about 6 feet of substantial 6" angle iron. Cut it into two 3 foot pieces and weld to each post making upside down 'T'.

3) Posts tipping toward each other: Cross-brace supports this load.

Note that adding item 2 will solve item 1. There - no need to call an engineer.

 

[DanWheeler]

Twin post lift installation in 3.5 inch floor:

1) Post punch through the concrete floor as it fails in shear: Increase perimeter of post pad by a factor of, 4 / 3.5 = 1.14, 14 percent.

2) Anchor pull out: Instead of upside down 'Y' as pictured, buy about 6 feet of substantial 6" angle iron. Cut it into two 3 foot pieces and weld to each post making upside down 'T'.

3) Posts tipping toward each other: Cross-brace supports this load.

Note that adding item 2 will solve item 1. There - no need to call an engineer.

oh man, I love idea 2 - brilliant! thanks!

 

[bkg]

funny.

those don't work very well when the frame of your truck already sits 3 feet off the ground.

i also need to put a 4 link kit on a Suzuki Samurai which means the frame is going to need to be suspended at least 3 feet so I dont know how I'm going to do this without a 2 pole lift.

Not sure why you "need" a lift for working on the sami... I've done a number of solid axle swaps on toyota's, lift kit installs, and the like with only a 2.5 ton jack and a few jack stands... A lift might be more convenient, but definitely not necessary...

Though there were times in the middle of Winter that I wish I wasn't lying on my back on the slab.

 

[DanWheeler]

Not sure why you "need" a lift for working on the sami... I've done a number of solid axle swaps on toyota's, lift kit installs, and the like with only a 2.5 ton jack and a few jack stands... A lift might be more convenient, but definitely not necessary...

Though there were times in the middle of Winter that I wish I wasn't lying on my back on the slab.

no, i dont NEED a lift i've done all that stuff without one for years now but thats part of getting older and wiser isn't it? Having better tools to do the job faster and easier. I just would like to avoid using the floor jack if possible. It would be nice to have something that I could quickly get all 4 off the ground to change a set of tires without having to do a few at a time.

i'm liking the idea of the mid-rise lift supplemented with some tall jack stands. thats probably the way i'll go but a 2 post is so tempting. it really limits re-configuring my garage though if I ever wanted to change things around.

 

[brownbagg]

I,m a foundation concrete inspector and I also have that same bend pak lift.

two answer and only two, either cut a footer under the lift or buy a four post, no other answer.

 

[Berg]

A Bend pak spx7 would spread the load out IMO

 

[hypnotoad]

funny.

those don't work very well when the frame of your truck already sits 3 feet off the ground.

i also need to put a 4 link kit on a Suzuki Samurai which means the frame is going to need to be suspended at least 3 feet so I dont know how I'm going to do this without a 2 pole lift.

Ahh, you don't know about stacking 2x4's? j/k