Special car jack stand for sloped grades

[lortech]

I do mobile mechanical work on customers cars. If the car needs under car work, I always ask "Is the car on a slopped grade?". It is very unsafe to jack up a car on a sloped grade and rest it on jack stands with the possibility of the jack stands tipping over if the grade is to slopped.

I was thinking, why not design and build a jack stand that works on uneven grade driveways and roads. I am not sure how safe a stand like this could be. I imagine its base dimensions would be much larger. Also, the main support column would be on pivot at its base and it could be up righted so it pushes the vehicle strait up at 0 degrees, rather then road grade angle which could make it topple.

The slope side of the jack would be much further from the jack point. Or is that even necessary?

Gravity obviously would be pulling strait down on the jack. At the same time, the coefficient of friction would want to make the jack slide down hill. I would have a rubber pad riveted to the base of the jack so this does not happen.

Is there a way to mathematically calculate the brake away coefficient of friction on a rubber mat for given weight and angle ?

Thanks a bunch. Given the typical weight of a car, 2,500 bls. Road grade angle 10-15 degrees maximum.

Not sure what the typical road coefficient of friction number is.

Also, the jack head would pinch onto a part of the body so it does not slip off or, tie down with a tie strap.

 

[RevMatcher]

Great idea. You'll be able to do all the static force balance calculations by hand. But, it's not mathematically possible to calculate coefficients of friction between surfaces. They are determined experimentally.

 

[AtomicJoe]

Problems come when the first person gets killed using the jack and you get sued.

Working under a jack is pretty dangerous on a flat surface, the problems are multiplied on a sloped surface because the car is likely to roll.

Anyhow one other point what is a 'sloped grade' I have never heard that expression before.

 

[lortech]

sloped grade means any surface of road that has a slope to it.

Now, if the car is in the air on both ends, all its weight is pressing down on top of the jacks.

think of it this way, if the jacks pad was large enough, there is no way for it to slide "think of a tire contact patch as a jack stand pad" and it won't topple over. Also, the jack stand would also have a pinch clamp to pinch the welded seams or, a deep grove where the axle would settle into it so it does not slide off the jack it self. The key here, is large base, Jack shaft that is 0 degrees to Earth's surface Pinting strait up, and a high friction rubber pad.

What does a person do when walking down steep grade? he is still standing upright, but has his feet pointed down the road, and has a much wider stance with a lower center of gravity.

I can model something like this in rhino3d and it will give you a idea what I am talking about.

 

[pallidin]

It's certainly possible... after all, all cars can resist a fairly steep downward slope(dry, solid and rough surface)
in "park" or "emergency brake" or such.
But, I don't think a jack stand of that nature would be approved for common use; nor any insurance carrier likely to cover it.

After all, a slope-enabled jack stand must have sufficient friction with the ground, else disaster.
So, sand surface is out, yard surface is out. What about dry, rough asphalt or concrete? Maybe, but what if in that position oil or antifreeze leaks from the car and gets underneath even just one jack stand?! Disaster.

Too many safety problems for public use, in my opinion.

 

[lortech]

IF the jack stand was locked to the frame or axle, it would be as safe as tires on the vehicle.

After all, isn't a tire like a jack stand? Axle resting on wheels resting on tires? If a center of gravity was REALLY low because of its massive pad footprint, I would think it was just as safe.

I think a nylon tie down strap pulled over a axle and winched down would work really well.

I used nylone tie down straps in the millitary and thay are STRONG! A chain would be the strongest but it could crush the axle. I used 10 and 20 ton chains to strap a fuel tanker truck onto the floor of a c-130 once.

One really good way to know, is put a load meter on a cars rear frame, and attempt to pull it with another car. Measure its friction and break away torqe. Then do the same with these jack stands..see what happens. It would be a ultimate test! these jacks would be for my own use. There is one possible problem with this setup, using a floor jack and putting the corner, or end in the air. Car could roll. In this case, it could be a different car jack/floor jack combination design.

 

[pallidin]

IF the jack stand was locked to the frame or axle, it would be as safe as tires on the vehicle.

Yes it would, but we are talkng about a sloped surface and with that surface having, very likely in the real world, non-ideal conditions.

How safe is a car on a sloped surface covered with ice, water, grass, sand, dust or oil, etc?
Lock the tires, fine, but the vehicle might still "slip and slide"
Understand?

Too many variables that would need to be controlled for a safe experience.

As such, you will always see in public: "Jacks Stands MUST be Level with the Ground"

 

[KingNothing]

Of course it's possible, you will just need a wider base for stability. I think at some point it might be easier having a very long jack which simply lifts the whole side of the car. Imagine taking two jack, separating them about 5 feet, and welding some metal beams onto them to keep them in line.

[STRIKE]/\ /\[/STRIKE]

 

[newzbarron]

A pivoting jack is good idea that addresses a vexing problem but perhaps the solution is not so much in the base of jack as preventing the load from moving. You might consider a device that can stabilize a load on a slope while it's being lifted by a jack. From the posts above it seems your already half way there with the pinch on the jack head. In other words, you need to increase the "friction" on the load as opposed to the jack base.