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"If a jack can lift a load, surely it can withstand the load for extended periods of time?!"

I've come across some conflicting ideas regarding this subject:

  • The user guide for my low-profile hydraulic jack warns against using it as a stand for static load-bearing duty. Paraphrased, it says that the jack should be used for no longer than necessary and should not be used for extended periods of time.

  • I frequently see roadside mechanics using these jacks to raise vehicles while they work on them (not that I deem them to uphold standards of safety, but it seems to work for them).

  • These jacks are typically designed such that it is difficult to release them accidentally.

  • Unless the seals in the jack are shot, I don't see how the load would cause the jack to "sag" over time.

Is there some unbeknownst-to-me reason which explains why a jack makes for a poor stand?

  • 2
    Based on that logic you should be able to lay down beneath the weights of a strongman's 1000 lb dead-lift for extended periods of time. It's really a question of "where will you be when disaster strikes?" – MonkeyZeus Feb 7 '18 at 14:58
  • 18
    The work done using a jack (especially on the roadside) is limited to tasks that don't involve getting under the car, such as changing a flat tire. For anything else, use stands -- they're cheap insurance! – Dave Tweed Feb 7 '18 at 15:27
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    A person who makes a living in that way is not necessarily a "professional". A professional would use stands even in that scenario. – Dave Tweed Feb 7 '18 at 15:35
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    Beyond the failure information provided by Adam and Paulster, hydraulics are never a safe form of support. I regularly skip the jack stands if I know I will be under the car for only a moment but I regularly inspect my jack. Commercial style four post hydraulic lifts have mechanical locks for the same reason. Relying on some seals is why the Space Shuttle Challenger crashed. I've watched $30k lifts have hoses pop or internal seals fail, if you have the lift on it's safety locks... nothing happens. When you don't, the car falls... and fast. – finleyarcher Feb 7 '18 at 21:49
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    "Unless the seals in the jack are shot" - yeeeaaaah. Tell me - do you want to trust your life to the maintenance status of a seal which was made by the lowest-cost producer in Godonlyknowswhereistan by someone with a sixth grade education whose dedication to turning out a quality product might be charitably described as "dodgy"? I sure as hell don't. Hydraulic jacks have many failure modes that a jack stand simply doesn't have because it's a remarkably simple device. Fewer ways to break means fewer ways for it to let you down - or to let a heavy load down on you. Still, it's your life... – Bob Jarvis Feb 8 '18 at 13:09

10 Answers 10

50

There is no such thing as "absolutely, perfectly, 100% safe."

Each tool has its proper and improper uses, and each works either in parallel with other tools to increase safety and dependability, or in series with other tools ultimately reducing safety and reliability.

Will a hydraulic jack hold up a car safely? That depends on the level of risk you're willing to take. In a hydraulic jack there are several failure modes:

  1. Structural failure (metal fatigue, fastener failure, weld failure)
  2. Slipping, falling
  3. Seal
  4. Valves (3 - release, and two one way valves)
  5. Improper assembly/maintenance/fluid

Further, some of these are slow, almost imperceptible failure modes. If the seal or a valve leaks slow enough that you don't notice, you might start work, not discovering until too late that the vehicle is lowering and finding yourself unable to extract your body from the slowly lowering vehicle. If you're lucky you can call for help. If not...

If you have confidence that all of these are acceptable risks, then sure, for your definition of safe perhaps a hydraulic jack is "safe". I wouldn't trust my life with it, I wouldn't recommend it to any others, but if it's just you then not even the government can force you to employ better safety practices.

Let's look at the jack stand failure modes:

  1. Structural failure (metal fatigue, pin/ratchet failure, weld failure)
  2. Slipping, falling

There's simply not too much that's safer than a jack stand in terms of supporting a vehicle... except more jack stands.

For me, though, this still isn't safe enough. One jack stand means one failure - thought perhaps unlikely - could result in injury or death. So at minimum I continue to use the hydraulic jack and a jack stand, but more often than not I'll use two jack stands for each lifting point and remove the hydraulic jack simply because it takes up so much room.

What you really need to determine to answer your question is what is your level of acceptable risk, and what's the cost. If you experience a failure, what's the cost of the failure? Given that your life and limb are involved, the cost of failure is so high that, for me, the extra time and cost of setting up a jack stand is always worth it.

  • 4
    @Ruslan Falling poses many hazards, and the underside of a vehicle doesn't provide as stable a surface as you might suppose... ;) – Adam Davis Feb 7 '18 at 21:17
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    @Ruslan Don't some lead batteries spill acid when flipped upside-down? – BlueRaja - Danny Pflughoeft Feb 7 '18 at 21:37
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    @BlueRaja-DannyPflughoeft Thanks, you've convinced me that flipping my car upside down for repairs was impractical just moments before I attempted it – wedstrom Feb 8 '18 at 18:58
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    @jpmc26 If you want a risk analysis with hard numbers, you hire a professional engineering firm, you don't ask random strangers on the internet. – barbecue Feb 9 '18 at 14:33
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    May want to add the risk of tipping. As the jack lifts the car the center of mass changes, and can cause the jack to tilt. This is especially true for bottle jacks. Floor jacks mitigate the risk somewhat by moving the base of the jack as it lifts, but can still tilt in two directions. – barbecue Feb 9 '18 at 14:36
25

TL DR: Nope, I'd say not.

When I was a young man, my Dad always told me, "Use the tool which is designed for the job." For instance, if you are trying to remove a bolt out of your suspension holding an A-Arm, you wouldn't use a body hammer to move it out, you'd use something with a little more heft, like a 5lb sledge or something similar. I'm sure if you used the body hammer, you could eventually get it out, but it's really not meant for this type of work.

Just like the hammer, the jack is the same. It's intended purpose is to lift the car when you need it. Just as you stated, a jack can have a catastrophic failure when you expect it least. Whether it's a seal or what have you, the consequences would be devastating if you were under the vehicle. Things would happen so fast, you'd not be able to get out of the way. Then most likely you'd be trapped. The proper tool for the job is the jack stand, which is meant to keep the vehicle lifted after the hydraulic jack has lifted it.

Another thing to think about is not accidental release, but improper closure of the release valve. I've used jacks before which when I started jacking it, realize the release valve was not fully closed. These, while lifting the vehicle, would also start lowering at a very slow rate as the pressure was released through the valve. I can imagine a situation where the person doing the jacking might not close it enough, then it start lowering at a very slow rate which may be imperceptible. The person then gets under the car as it starts lowering every so slowly. If the person didn't realize it soon enough, they would then be trapped under the vehicle suffering a very slow painful death. Along the same lines, if the release valve was slightly damaged or worn. In either scenario, the jack would lift the vehicle, but wouldn't be holding it in place.

  • 4
    I had forgotten about the release valve, I'm happy you mentioned it – Zaid Feb 7 '18 at 13:19
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    I've seen similar behaviour to your last paragraph with industrial lifting gear that's designed for gentle lowering -- a nut caught in the release lever and preventing it fully returning can lead to very gentle lowering. – Chris H Feb 7 '18 at 16:20
  • Gentle lowering is a dangerous thing. I was trying to get a stand under a car that I was working on a few years ago and had to tighten the valve nut and re-jack the car. It dropped a few inches in between me leaving the jack, pulling the stand out from under the car because it was too low, adjusting its height and putting it back under the car. Had I been under the car faffing with the stand I could've been in serious trouble. – Miller86 Feb 9 '18 at 9:37
  • @Miller86 that's certainly true. With the stuff I had in mind, lowering at the rate of a typical trolley-jack could easily break something very expensive, so being able to lower gently is important -- and that's why you support it with something solid of course – Chris H Feb 9 '18 at 14:43
  • "Proper tool" is key here. – Peter A. Schneider Feb 12 '18 at 11:00
16

No, I thought it could as well. One time I had a Corolla up in the air while I battled with a speedometer cable (which meant I was going in from the top of the car, underneath, and through the wheel arch). I walked away from the car to get a spanner, I came back and I was looking at where to remove a bolt. I then noticed the car was very low down.

The jack had collapsed, and neither me nor my friend heard it.

It's just not worth it. Axle stands aren't expensive, and they're a whole lot cheaper than your life.

EDIT: To clarify what I meant by "collapse", when I jacked the car up the arm was totally in the air. When I noticed it had collapsed, the arm had moved down to the normal default position. I then started to jack the car up, and as I pumped it up, it would stay up for a few seconds, then slowly sink back down. Internally a seal had popped so it wasn't maintaining pressure.

  • Can you elaborate how it collapsed? Failure to close the valve, or a mechanical collapse? – Sean Houlihane Feb 7 '18 at 17:25
  • @SeanHoulihane I've edited my answer – mickburkejnr Feb 7 '18 at 17:27
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    I know collapse still works in the way you are using it, but when i first read it, i imagined a violent and sudden collapse. The edit really helps, and the seal definitely seems like the main point of failure to me. – user31794 Feb 8 '18 at 2:34
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    I can't really tell you how quick or violent the first collapse/fall was, because neither my friend or I noticed it or noticed any sound. So it could've been rapid, it could've been a slow fall. But either way neither of us heard it, which I think adds to the danger of such a failure. – mickburkejnr Feb 8 '18 at 9:01
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    If you're under the vehicle when the hydraulics fail, even coming down smoothly at a few centimeters per second can easily be too quick for you to take any meaningful action and while you don't go ::splat:: you still get crushed and asphixiated. – dmckee Feb 8 '18 at 17:37
13

NO, and I don’t understand why you don’t refer to standard workshop practise which is to lift the vehicle and then put proper stands under it.

Sadly there are too many accidents of either vehicles or tipper trailers falling due to the failure of hydraulics and injuring or killing people.

Don’t rely on hydraulics to keep the mass in the air: stands or chocks or a physical blocking device...

  • 1
    The reason I brought up the "non-standard" practice was to show that it is something done in the real world. I am curious as to how the hydraulics could fail catastrophically in this context (i.e. the mechanics of the failure). – Zaid Feb 7 '18 at 8:53
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    Catastrophic failures can be due to prolonged loading on a seal with a weak point or temperature effects etc etc - the issue is hydraulucs can fail and most of the accidents can be prevented... – Solar Mike Feb 7 '18 at 9:15
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    Here is a link to one example, but slightly different as it was bing worked on : dmp.wa.gov.au/Documents/Safety/MSH_SIR_151.pdf – Solar Mike Feb 7 '18 at 12:11
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    I'm just wondering how this answers the question at large: Explain why a jack makes for a poor stand" You give good reasons not to use one, but nothing as to what the failure modes might be. – Pᴀᴜʟsᴛᴇʀ2 Feb 7 '18 at 15:02
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    @SolarMike - No, the title states that, but not the question. – Pᴀᴜʟsᴛᴇʀ2 Feb 7 '18 at 17:22
10

Stands are simple mechanical devices in the sense that typical failures (cracks, bends) are easily observable by a simple visual inspection. That's what makes them inherently safe.

A hydraulic jack on the other hand is sophisticated enough to have hidden failure modes (leaky seals / valves, etc.) which are not instantly obvious and can be easily overlooked.

In the end, it's the amount of risk that you take that matters. If you do DIY repairs on your car, you can afford the risk of accidentally breaking it down (if you don't, you should know that you're taking it anyway). So, if the additional risk of the jack failure will result in damage only to your car, you may be willing to take it. The problem starts when you're also risking your life by not using the stands, perhaps without even realizing it.

9

No it's not the same as a jack stand or even a brick or a tire on its side.

My primary fear/experience is that a jack will tip. Adam Davis explains the risk of slow leakage, which is a thing, but your more direct risk is of the jack toppling over. Look at the design of a jack stand: it's wide at the bottom and has no wheels. Now look at a jack. Other than 4+ ton floor jacks most of the rest of them are proportionally very narrow and even wide floor jacks have wheels, which means they're not made to sit still.

To the point of it lowering accidentally, jacks and jack stands both move up and down, but a jack stand has a physical catch that must be moved out of the way in order to let it lower. The same is true of hydraulic lifts in shops too. They typically -- if not all -- have physical catches that must be moved in order for the lift to lower. Jacks do not have this safety.

If your jack does have physical catches and it's also not narrow and therefore prone to tipping over then I'd say SURE use it.

But I'd put a jack stand under it too ;)

  • 2
    A brick is similar. Geometrically unsound, and transitions from the right shape to powder with no warning. – Sean Houlihane Feb 8 '18 at 17:30
  • @SeanHoulihane correct - a brick is baked sand. Its not a rock even though looks similar. – Criggie Feb 10 '18 at 21:27
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    I would like to add the issue with it tipping is the fact that a jack is only designed to resist downward forces. This is the crux of the issue and is only hinted at in the other answers which say the jack is not designed for this, but do not say why. The amount of sideways force required to tip the jack over is much smaller than the amount of weight that is being held up because the jack is not designed to resist much sideways force. – Michael Feb 11 '18 at 21:02
8

Hydraulic jack seals blow.

Because hydraulic jack seals blow one should never put body parts under a load (vehicle) raised with a hydraulic jack.

Let me state that again so that it sinks in: Hydraulic jack seals blow.

Using jack stands is like wearing seat belts. It might take years until you get into a car accident or see a jack seal blow. But after it happens once, you'll make sure that you're prepared next time. And next time will happen.

  • 3
    'But after it happens once, you'll make sure that you're prepared next time.' I've read this entire thread thinking that this is one of those questions you ask yourself until the day it happens to you. I had a jack fail while lifting a car - it just stopped lifting and then gently went back down. With the wheels still on and nobody underneath it was no drama, but I'd hate to find myself stuck under a brake disc... – Dan Feb 9 '18 at 14:36
6

It's not safe.

The probability for a jack to lose pressure slowly and even rapidly due to extreme failure is exponentially higher than a welded jackstand coming apart.

Also there's the argument that jacks do not have a equal footprint meaning they are more susceptible to tipping over one way over another. Jackstands don't have this issue, as the base is uniform.

You are also relying on one piece of equipment that wasn't designed to SUPPORT the vehicle for extended periods of time, instead of a piece of equipment (JACKSTAND) that is designed to HOLD the vehicle for extended periods of time.

Jackstands have less failure points, are better designed to prevent tipping, and using multiple jackstands provides the safest and lowest risk possible of being crushed by a vehicle.

Now if you are just changing a tire on the side of the road and aren't getting under the car, sure.....jack away. If the car falls there's rarely any damage done which is why manufacturers supply jackscrew type jacks and it says not to get under the vehicle even with those.

4

You'll see it done. It's not as safe as using a stand. There are more ways for a jack to fail than for a stand to.

You'll also see cars propped up on a pile of bricks. That isn't as safe as a stand either.

But stands can fail too. Nothing is 100% safe, other than not being under the car at all. But I expect you're under there to fix something that will make driving it safer? Best not go near the car at all!

"If a jack can lift a load, surely it can withstand the load for extended periods of time?!" is very flawed reasoning. Might as well say "If a man can lift it, he can hold it up for ever." Patently untrue.

-2

NO!_Not Safe_very Unsafe! Wonderful detailed explanations in this thread. If the work you're doing on your vehicle requires you to get under the chassis then you Need a Jacks-stand. Borrow or buy 2 of them and use them. Don't let you life become a statistical data point proving the everyone should use jack-stands when doing anything at all under a car that has been jacked up by any kind of jack! Would you let your daughter or son under that car without jack-stands? I would sincerely hope not.

protected by Pᴀᴜʟsᴛᴇʀ2 Feb 9 '18 at 11:30

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