Stabilizing vs. Lifting Scissor Jacks

[jives]

Scissor jacks for stabilizing trailers generally have a greater lift range (e.g., 24-30") and load capacity (5000 lbs +) than your typical car scissor jack, but come with a warning they are for stabilizing and not lifting. Can someone educate me on why a 5000 lb rated stabilizing scissor jack should not be used to raise a 5000 lb load (okay, more likely a 2-4,000 lb load)?

 

[richfinn]

The greater lift range/height would make it way too precarious and unbalanced for lifting.

Car scissor Jack's are only for emergency tyre changes at best, they still scare the cr@p out of me and I've been doing roadside assistance for almost 20 years

I can't tell you how many times I have had to rescue somebody who got halfway through swapping a tyre at roadside before the scissor jack collapsed (soft ground/improper jacking points/faulty parking brakes/wheels stuck on the spigot and too much force used).

No serious injuries (yet)!!!

Invest in a decent jack, it might save you a lot of aggravation or worse

 

[jives]

The scissor jack is not for normal lifting. I am looking to devise a sort of jack stand or cribbing that can also serve as a lift jack that can raise the car and hold it at higher than my standard floor jacks. Just pondering ideas at the moment. My current jack is a typical 3T floor jack.

 

[whateg01]

I guess we're going to need more details. If you are able to stabilize it so that it can't get spit out, it might be usable. Depending on how you intend to use it, remember that it has almost no lifting power until it's part way open, and even then the mechanical advantage increases until it's maxed out. I don't know how those are rated but it might be fully open when it is out of travel and gradually less as it closes.

 

[richfinn]

The scissor jack is not for normal lifting. I am looking to devise a sort of jack stand or cribbing that can also serve as a lift jack that can raise the car and hold it at higher than my standard floor jacks. Just pondering ideas at the moment. My current jack is a typical 3T floor jack.

I use plastic ramps to get the car/jack points high enough to use an extension between the trolley jack and the jack point/chassis, then sit the car on larger jack stands, that's what the WRC Rally car mechanics do during service.

 

[zendriver]

My guess is since they state stabilizing trailer capacity, not load capacity,

Two different animals

 

[jives]

I guess we're going to need more details. If you are able to stabilize it so that it can't get spit out, it might be usable. Depending on how you intend to use it, remember that it has almost no lifting power until it's part way open, and even then the mechanical advantage increases until it's maxed out. I don't know how those are rated but it might be fully open when it is out of travel and gradually less as it closes.

Yeah, that makes some sense about the the mechanical advantage.

 

[toolenthusiast]

remember that it has almost no lifting power until it's part way open, and even then the mechanical advantage increases until it's maxed out.

Can you explain this further? Your assertions do not align with my intuition, my experience with jacks, or my understanding of worm screws. (But I have little training in physics and I’ve never deeply contemplated pantograph jacks.)

 

[Dalez]

Might have something to do with twisting the frame of the trailer.

 

[mogandave]

Look at it and think about it.



As the jack gets taller, each turn of the screw raises the jack less, correct?

If each turn of the raises the jack less, less force work is being done by the screw, yes?

 

[Bigblue&Goldie]

I'm not sure if the base and pad are the difference in how they're designated? Obviously they are different in that one has a base made to be mounted to a frame and lift against the ground, while the other is meant to sit on the ground and have a pad designed to lift a car. Personally, I'd be far more inclined to get a high lifting floor jack. Having a 2nd floor jack is really handy. Scissor jacks are a pain in the *** and not something I'd ever use at home.

 

[jives]

Below are two commercially available jack stands with built-in jacks. A google search will reveal some homemade devices using wood cribbing and scissor jacks. I'd like to give that a try, but want to make the lift higher.

 

[mogandave]

Using a floor-jack, I would just raise it the car and put it on stands. Then let the jack down, put a GOOD block on it and raise the car higher.

Same with the bottle-jack, but put the GOOD block under the jack.

 

[jives]

Using a floor-jack, I would just raise it the car and put it on stands. Then let the jack down, put a GOOD block on it and raise the car higher.

Same with the bottle-jack, but put the GOOD block under the jack.

Yup, this is the common way. Looking to figure out a less time-intensive way, without a lift.

 

[nh_yota]

My guess is since they state stabilizing trailer capacity, not load capacity,

Two different animals

Probably...and probably because if it fails you trailer will just drop back onto its suspension instead of hit the ground.

 

[zendriver]

Probably...and probably because if it fails you trailer will just drop back onto its suspension instead of hit the ground.

I would think with stabilizer jacks, the trailer wheels never leave the ground. No reason to, that I can see and have never done that with stabilizer jacks.

Apparently the load capacity is based on the weight of the trailer, since using one with a 40,000 trailer probably would not work well.

 

[mogandave]

I would think with stabilizer jacks, the trailer wheels never leave the ground. No reason to, that I can see and have never done that with stabilizer jacks.

Apparently the load capacity is based on the weight of the trailer, since using one with a 40,000 trailer probably would not work well.

Could also be a safety factor thing.

 

[mogandave]

It's not likely the "lift" mechanism on a stabilizer is robust enough to move raise a significant amount of weight from it's "lowered" position.

A 24-30" stabilizer is designed to run down quickly, it's only designed to "lift" the last few inches of the screw. To provide lift through the entire range would require a larger screw with a much finer pitch.

 

[mogandave]

Yup, this is the common way. Looking to figure out a less time-intensive way, without a lift.

Having purpose-built blocks speeds things up a good bit.

 

[RTM]

Just to bring back up a slightly dormant thread. Walked thru the local RV park today. Guy was stabilizing a big 5th wheel trailer with a pair of onboard scissors jacks on the **** end. I saw how skinny the threaded screw was, and then looked at the body of the jack. Both looked much skinnier than the jack on my Acura TSX.

So yeah, I would be very concerned about lifting vs stabilizing capacity.