Adding scissor jacks for side to side leveling

[vtraudt]

My Forest River Salem has electric 'stabilizer' jacks (pivot, won't work for side/side leveling even IF they were strong enough). And the usual front A frame jack.

I do NOT like to drive onto (2x6, lego blocks, curvy plastic thingies, etc). I rather put the trailer exactly where I want it, THEN do all the leveling.

Front/back leveling with the front A frame jack is no issue.

For side to side, I would like to add scissor jacks on (or near, 3/4 points, else) the main frame at each corner. From this weeks stay, it seems that most (all?) not so new trailers have just that. I watched dozens setting up (some with hand crank, some with power drill/impact).

My trailer has a max weight of 7000 lbs.
The main rails are one piece, going from front to back (no welds, no steps).

a) is it ok to 'lift' at the ends or near the ends of the main rails?
b) with theoretically 1/2 of the weight (3500 lbs) on one jack, should I pick 3500 lbs jacks, or go even higher?

I am not sure yet if I will permanently mount (if it works, I likely will), either weld on or bolt on (only reason not to would be weight/inertia added to the rear.

Also, if it works, I would REMOVE the electric stabilizers (the jacks will level AND stabilize) and maybe use the MOTORS (2 on hand. would by 2 more) and add 2 more switches for 'electric' leveling (not AUTO leveling).

Does someone have experience with this modification?
Concerns, suggestions, ideas?

[ajriding]

Thinking in theory is fine, but as for bending....
In reality, the bending from jacking at the rear corner is bad. It can even cause the door to jam.
There is no pot hole that puts upward pressure on the rear corner.
I know because I had a camper n tried to jack at the rear and all these bending issues discussed became harsh reality.
Stabilizers at the corners are fine, they do not bend things.
Jacks at the corners is not good unless the trailer frame is massive, or has steel walls that can help support the stresses.
The reason to jack at or near the axle is because that is where the trailer is supported to begin with and lifting here will not stress anything.
I see stabilizer lifts on motor homes, but those have axles at the ends, not in the middle, so is different.

I almost never use jacks. Trailers are easy, just drive one side up on blocks, rocks, or drive one side into a hole. Then use the tongue jack for front/rear level.
When I use rocks then I can just drive off and not even retrieve the rocks as I would my blocks.

[vtraudt]

JRscooby wrote:


What is wrong with that simple view point? Doesn’t need a discussion of gravity.

There is nothgin wrong per se with the simple few: the rear overhang when on wheels is bending the frame down under its weight/mass (gravity does it, and in addition, acceleration (from bumps) does it too.

Bend lifting up, it is bending the frame up by (simplified) the same amount.

Regarding uneven "twisting". If you drive through a pothole with one side of camper only, the same 'twisting' of the frame will occurs as if you lift on one corner only.

How much (in accurate terms and amounts) bending down (gravity, acceleration from bumps) and up (lifting, bumps) takes place is difficult to calculate (too many unknown variables).

Fact is: our trailers bend A LOT already (mostly down)

[vtraudt]

JRscooby wrote:

I can't stand under the "potentially several times".

You don't have to stand under anything if you don't want to.

But if 'back/forth' is not an option (as stated), it simply IS not an option.

Hence, an alternative way is needed.

[JRscooby]

vtraudt wrote:

I will use this method when 'driving back/forth' (potentially several times) is not an option. And certainly in my driveway (car/trailer under angle, incline and more than 4 inches to level sideways.

I can't stand under the "potentially several times". Once to see how much lift is needed, the 2nd time to put it on the ramp. You're done.
If I needed ramp in my drive, I would bolt it together, and leave it home. Of course, if I need 4 inches when I get home from last trip, I assume I will need 4 this time.
(I have a pair of rubber mud flaps, with a 4X4 bolted to 1 end, and a 2X4 spaced right, and bolted to other side. They stay in the thinly graveled drive. I back in until trailer goes over the 2X and stops against 4X. Chocks on both sides of both wheels, the jack goes down on the 6 inch long 2X6. With the tires sitting on rubber, no need to get weedeater close to tires.

BB_TX wrote:
My simple brain looks at the whole frame bending thing in a much more simple way. An RV trailer sitting on dual axles is going to have 6-8-10’ hanging out past the rear axle. The weight supported by and spread over four suspension points on each side. And the weight of the RV is going to cause that rear cantilevered overhang portion to sag downward.

Now put jacks near the rear of the trailer and raise those jacks to level the trailer and that new upward force at the rear is going to start taking weigh off the suspension, and instead transfer that weight to the rear of the frame. Now the center of the frame with less support will tend to sag downward due to the transfer of points supporting that weight.

Lift at one rear corner more than the other and the frame will tend to twist.

What is wrong with that simple view point? Doesn’t need a discussion of gravity.

Thank you.

[BB_TX]

My simple brain looks at the whole frame bending thing in a much more simple way. An RV trailer sitting on dual axles is going to have 6-8-10’ hanging out past the rear axle. The weight supported by and spread over four suspension points on each side. And the weight of the RV is going to cause that rear cantilevered overhang portion to sag downward.

Now put jacks near the rear of the trailer and raise those jacks to level the trailer and that new upward force at the rear is going to start taking weigh off the suspension, and instead transfer that weight to the rear of the frame. Now the center of the frame with less support will tend to sag downward due to the transfer of points supporting that weight.

Lift at one rear corner more than the other and the frame will tend to twist.

What is wrong with that simple view point? Doesn’t need a discussion of gravity.

[vtraudt]

ajriding wrote:
Assuming you have a twin axle trailer?

You also said jacks, not stabilizers. Jacks can and will and are made to lift the trailer. We are not talking about stabilizers.

I lift the frame at the axle point. I used a bottle neck hydro jack, not scissors jack. For a dual axle I put the jack between the axles under the frame if possible, or as close to the axle as I can get if in front or behind the axles. This does not put any new stresses on the frame and lifts the frame at about where the axles hold the frame anyway. Or easier to just lift the axle, not the frame. One axle is fine and will not damage the frame, body, or door or bend anything. Your trailer goes on one axle all the time driving it around (one of 4 wheels unloaded anyway).

I do this only in extreme situations if I have to park off level and my other leveling method is too short.

Parking on ramps or boards or rocks is much preferred to me. It is easier than crawling around with a jack.

I was under there yesterday; the process is certainly easy (lifted one axle at a time, but board under. But it is combersome.
If planning to keep trailer ON WHEELS, then lifting axle is easier.

If NOT using wheels, I would lift the FRAME and put jackstand under frame.

I will use this method when 'driving back/forth' (potentially several times) is not an option. And certainly in my driveway (car/trailer under angle, incline and more than 4 inches to level sideways.

For axle lifting, I am planning to make a "U" shaped top for my bottle jack. For the 'frame lifting', a square platform (with replaceable wood on top).

[Grit_dog]

ajriding wrote:
Assuming you have a twin axle trailer?

You also said jacks, not stabilizers. Jacks can and will and are made to lift the trailer. We are not talking about stabilizers.

I lift the frame at the axle point. I used a bottle neck hydro jack, not scissors jack. For a dual axle I put the jack between the axles under the frame if possible, or as close to the axle as I can get if in front or behind the axles. This does not put any new stresses on the frame and lifts the frame at about where the axles hold the frame anyway. Or easier to just lift the axle, not the frame. One axle is fine and will not damage the frame, body, or door or bend anything. Your trailer goes on one axle all the time driving it around (one of 4 wheels unloaded anyway).

I do this only in extreme situations if I have to park off level and my other leveling method is too short.

Parking on ramps or boards or rocks is much preferred to me. It is easier than crawling around with a jack.

OP is talking about installing a leveler system, not mucking around with a bottle jack every time he parks the camper.

[ajriding]

Assuming you have a twin axle trailer?

You also said jacks, not stabilizers. Jacks can and will and are made to lift the trailer. We are not talking about stabilizers.

I lift the frame at the axle point. I used a bottle neck hydro jack, not scissors jack. For a dual axle I put the jack between the axles under the frame if possible, or as close to the axle as I can get if in front or behind the axles. This does not put any new stresses on the frame and lifts the frame at about where the axles hold the frame anyway. Or easier to just lift the axle, not the frame. One axle is fine and will not damage the frame, body, or door or bend anything. Your trailer goes on one axle all the time driving it around (one of 4 wheels unloaded anyway).

I do this only in extreme situations if I have to park off level and my other leveling method is too short.

Parking on ramps or boards or rocks is much preferred to me. It is easier than crawling around with a jack.

[Boon_Docker]

Be sure you bend your beam carefully or suffer the gravitational consequences. :B :B

[Grit_dog]

So have you tried jacking up your trailer or is this just a theoretical discussion on steel beam design?

[vtraudt]

JRscooby wrote:

vtraudt wrote:


You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).

This sounds like somebody educated beyond their intelligence, or acting stupid. Over the years I have bent a lot of steel, (most, but not all on purpose). I have had some sag under own weight when lifting 1 end.
But even a super light duty, like a garden cart, when loaded to capacity, you lift the tongue, the back goes down, but nothing bends. (If it did, you could not tow it without it bending.)

Who is talking about raising the tonque? if you raise or lower the tonque, the bending does not change (yes, it is bent if a load is applied). But if gravity is present, your tonque is actually pushing UP the A frame. If you want to test it (the amount of bend), balance out the trailer (for example put a lot of weight on the rear until the tonque just lifts up. Now check how much your rear has gone down. That is about the amount your front is sagging. Note: you would need to put jacks under the center (axles) to prevent your suspension to go down.

But the concept of a beam bending, the force that act upon the beam, bending stiffness, moment of inertia, forces from acceleration, etc is very much beyond the grasp of the most of the members of this forum, and not (I realize it finally) suited for discussion here.

[JRscooby]

vtraudt wrote:


You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).

This sounds like somebody educated beyond their intelligence, or acting stupid. Over the years I have bent a lot of steel, (most, but not all on purpose). I have had some sag under own weight when lifting 1 end.
But even a super light duty, like a garden cart, when loaded to capacity, you lift the tongue, the back goes down, but nothing bends. (If it did, you could not tow it without it bending.)

[vtraudt]

Huntindog wrote:

As for it not adding any strength, see the exerpt from my previous google quote:
Cambering beams allow smaller beams to be used in place of larger beams to support the same load.May 29, 2016.
(that is a very cost effective way of making an RV lighter.)

Yes, allow smaller beams to be used in place of a larger beam so support the same load. Reason: the beam was BENT UP, adding load flattens it to be used with the 'house'. It was BENT DOWN by the load of the house to be flat again. It did NOT make the beam STIFFER. It did NOT (and your article nowhere states it since it is NOT true) reduce the bending. The beam was just crooked to start ("cambered") and then flexed down (bent) by the weight. The amount would have been teh same if they had started with a straight beem, the beam would then flex down by the weight of the house, by the same amount. Quite simple physics (here: stiffness of a beam as calculated by moment of inertial (simple example: rectangle shape beam: https://wesbeam.com/Wesbeam/media/Images/Blog%20images/2019-08-27_14-10-28.png).

[vtraudt]

JRscooby wrote:

vtraudt wrote:

Lifting at the 2 rear corners (the front is already lifted at the corner, the A frame (front jack) lifts the 2 front corners, and all the static bending is/has taken place every time you put your front jack down, or hook up your trailer to the car)

You must have some weird trailer. Other than the ones with floating tongue, any of the hundreds, if not thousands of trailers I have been around, jack the front up, the rear goes down. When pivot on the suspension, there is no force to flex the frame.

You are correct (if you put your trailer into a no gravity zone (like outer space). You are my first alien contact on RV.Net.

If you would bring your trailer here on earth, gravity does do its bending thing, if you like it or not. In fact EVERYTHING on earth is bent (past tense), sometimes just bent into a straight line (I know, this will bend (present tense) your brain; double pun intended (yes, gravity bends even the stiffes brain on earth!).