Using four jackstands

[SHOZ]

When using a floor jack and jacking from the side be sure you are on level ground or the jack will tip over.

Sometimes you have to angle the jack so the jack handle is pointing towards the down slope.

Same goes for an engine crane......

 

[stephen9666]

Originally Posted By: B20z
My thing with pushing or rocking the car to check your stands is that if the car falls during your "test" how's that going to help you? Now your brake rotor has hit the ground or your jack stand has spiked something attached to the underbody. I mean sure, you saved yourself from being crushed but you're going to wish you had been.


Well, that's a little exaggerated.

Mostly, you're checking to see if it's rocking and to make sure all four stands are secure. The goal is not to push so hard that you push the car off that stands, which would take quite a lot of force. Even if one of the stands isn't supporting the load properly, the car will likely rock well before you push it over.

 

[rationull]

I do this at every oil change in order to rotate the tires, as well as when the car needs to be lifted and level for diff or transmission oil changes. Never had a problem.

I don't like doing it though. I'm not worried about the safety, it's just a PITA. Matter of time before I buy some kind of lift!

 

[Kiwi_ME]

I would not use four jack stands because the lateral stability of either end of the vehicle is only provided by the width of the stance of the legs of two jack stands, worst for those 3-legged types or taller ones. If everything is perfect, knowing the car's weight you could calculate the tipping force required from a lateral push at one end of the vehicle.
But if there are imperfections in the geometry, the stability only gets worst, never better.
The geometry could be compromised by a number of factors that are not easily noticeable and can add up - poorly-centered placement of load, bending or flexing of the welded seam (if used,) soft, slightly uneven or sloped concrete base, and of course clearances and tolerances in the jack stand design that affect the load being centered perfectly over the feet. Never mind the additional loads from wrenching and opening doors, etc.

I get the creeps driving by houses with a car on four jack stands in the driveway, knowing that a small lapse in judgement could be fatal. If you're going to do this and work underneath, have a Plan B.

 

[Vikas]

I presume it also depends up on the base of the jack-stands and the height of them. With wider base and its is minimal height, the should be lot more stable than when they are extended and have narrower base.

 

[Kiwi_ME]

Certainly right, the shorter the better ... tip-over force would be something like (0.5 x vehicle weight x shortest jack stand base radius)/(jack stand height)

Mine are 16.5" high at the top setting with the shortest base radius at 3". That's the center of the loading pad to the closest edge looking straight down. The post is offset to accommodate the lock bar.

So that's about 118 kg under ideal loading conditions for my 1300 kg car, probably quite acceptable for changing tires and brakes as long as the surface is flat and stable, but I would be adverse to crawling underneath.

 

[SHOZ]

Somehow I had a car sitting on 4 jack stands for over 2 years and it never fell over......