Interesting problem with outside storage drawer.

This weekend I was parked in an area where the passenger side of the 2552 was low.  I used my levelers and all was fine - so I thought.  I could NOT get the outside drawer to open.  I was afraid I was going to break it if I pulled any harder.  I emptied the top portion, lifted the floor and was able to get what I needed in the drawer so I managed ok.  When I got home and was parked on a fairly level area (no levelers), the drawer opened just fine.  What is happening?  Could the rear leveler be jamming against the drawer somehow?

Do you have Liquid Springs?  It is possible to twist the frame if you do not not turn off the LS before leveling.

Did you by any chance have the levelers raised so much the right rear duals were off the ground?  Likewise with the right front?

No liquid springs and the back tires were on the ground.

Try replicating. Use your levelers and try diff Scenarios. Stop at diff points and try the drawer. Even better if you have a second person to help along the way.  Also pull the drawer all the way out and take a look at the slides the best you can. Has one of them come loose or one of the mounting screws backed out .

Levelers have been known to apply a slight twist to the frame, especially in the longer lengths.  I have never heard of it causing any such issue, but it is conceivable.  Keep in mind that the frame twists a tad bit while driving too, so don't be alarmed.

It's possible something shifted in the drawer while driving and jammed it. By going in from the top you may have moved the offending item and fixed the problem without realizing it.

As a reminder if you have HWH leveling jacks remember for the non auto leveling option the proper sequence is shown on this.  As I understand this is to minimize racking or twisting of the frame.  I would expect this should load the four corners more evenly than the use of leveling blocks under the wheels.

Good info.  A bit hard to read.  I transcribed it into a Word Document to make it easier to read.  Attached.

As a reminder if you have HWH leveling jacks remember for the non auto leveling option the proper sequence is shown on this.  As I understand this is to minimize racking or twisting of the frame.  I would expect this should load the four corners more evenly than the use of leveling blocks under the wheels.

I'm confused...how could the four corners be loaded more evenly than if the rig was parked on the level?

If the site is level you would not add leveling blocks under any wheels neither would you need the HWH system to level.  The HWH jacks could be deployed to add stabiliy whereas blocks under the wheels do not.


In a worst case site condition you could add leveling blocks to two diagonal corners to establish level to the point the remaining two wheels were not carrying any weight.  This would result in worst case racking.  At the same out of level site the HWH system would balance out hydraulic pressure to minimize racking and also provide stability.


To understand the impact on systems I often find it helpful to imagine worst case conditions.  In reality I doubt you would ever encounter a site as I described above but I think frame racking would be somewhere between a perfectly level site and a worst case site condition.


If I am looking at this wrong I am certainly interested in any counter views.

Thanks JSanford. Much appreciated.

If the site is level you would not add leveling blocks under any wheels neither would you need the HWH system to level.  The HWH jacks could be deployed to add stabiliy whereas blocks under the wheels do not.


In a worst case site condition you could add leveling blocks to two diagonal corners to establish level to the point the remaining two wheels were not carrying any weight.  This would result in worst case racking.  At the same out of level site the HWH system would balance out hydraulic pressure to minimize racking and also provide stability.


To understand the impact on systems I often find it helpful to imagine worst case conditions.  In reality I doubt you would ever encounter a site as I described above but I think frame racking would be somewhere between a perfectly level site and a worst case site condition.


If I am looking at this wrong I am certainly interested in any counter views.

I read this a few times, as I have had a history of misreading posts... 


OK, first off as far as stabilizing, no contest. Jacks do, wheel supports dont.

But on frame 'racking' or twisting, I dont feel the jacks are superior. Certainly more convenient!  No question.

In your worst case, lets imagine an old paved slot. There are high spots under the drivers front, and passenger rear. Low spots happen to be under the drivers rear and passenger front.

 As observed from the front to the back, the frame is absorbing a clockwise twist. And to make it worse, the entire slot is lower on the front than back.

We need numbers, and without pictures this could get eye-glazing complex. 

So JUST for an example, lets say the high spots are 2" high, and the lows spots 2" low. The entire slot is lower by 3" in the front than the back.

So... our drivers rear needs 4" of block under it to make it level with the passenger rear. The passenger front needs 4" of block to be level with the driver front. BUT...

The front sill being low means both the front need an additional 3" of lift.

So this would result in Passenger rear with no block.
The drivers rear has a 4" block.
The Drivers front needs 3" of block to overcome the slope of the slot.
The passenger front now needs 7" of block. ( to overcome the 3" of slot slope, the 2" low spot under it, and the 2" high spot under the drivers front).


Now we have level. The wheels are all equally loaded, as they are all on the same height when measured to the bottom of the tire. The coach is level. No frame twist, or racking.

To unload the opposing wheels, we would have to add even more blocks....But why would we? We have achieved 4 level spots under our tires, and so the coach is level.

The same would apply with the jacks. Lets assume auto leveling, so the computer does its thing, the jacks have enough travel, and the proper amount of lift is provided at the jack mounting points to make the coach level.

The difference is WHERE the force is applied to the frame. 

The wheels are the designed point of weight support from the factory. 

The rear distributes the forces through 4 points on the frame, as shown below. (2017 chassis, similar to all)



The forces enter the frame through the 4 leaf spring mounts. (red arrows)
The frame is braced against twisting due to uneven forces via the crossmembers. (blue arrows)
The yellow box shows the primary affected area, note how much bracing is in there. One can make a big "X" between the corners of that box, and the crossmembers inside contribute great torsional (Twisting) strength. 3 inside the box, one close by.

Now lets see how the jacks compare. They are mounted with two points of contact, indicated by the red arrows below. (as the instructions for my E350 showed, models may vary)



There is only one crossmember nearby, two others further away. There is no yellow box, as there is only two points of contact. You can see the torsional rigidity is much less. And the frame is taking an upward point load where it was not designed to, unlike the leaf spring mounts that are purpose designed for it.

Why is it designed like this? 

The engineers for the frame started with a 'blank sheet' and could design around the points where the force enters. You can see they took full advantage of bracing, and allowing for a box around the fuel tank.

The engineers for the jacks are under MANY restraints. They have to use whatever space they find, and cant be cost competitive designing and adding more frame crossmembers. And there night be no room for them anyway. So they start with a considerable handicap trying to avoid putting twisting stresses on the frame that will be resisted by a crossmember. This results in a point load on the frame in a place that the original designers did not plan for.


Likewise with the front. (Ebay picture fo a 99-07 front half of a frame, I couldnt find a good factory pic that showed the front well)  If you look at the factory pic above, the mounts just to the rear of the steering wheel are the two round holes by the green arrow below.



The 6 red arrows show where the forces enter the frame through the A arms and spring perch. Note the blue arrow - That crossmember is the beefiest on the entire chassis, and is designed to resist the torsional forces.

The green arrows show where the jacks put their point load onto the chassis. (again, from the instructions for my E350. Models may vary)
This is an area that was never designed to accept these forces, it is boxed but no crossmembers. AND... the body mount is above, and the frame was intended to only get 'downward' force. The jacks exert upward force here, and cause the frame to support the weight of the engine, transmission (partly) and wheels in a spot it was never intended to by the original designers.


So... I hope this clarifies why the jacks may cause unnatural bending and flexing in the chassis that wheel levelling blocks would not. The drawer binding is a good example of the result.

This flexing problem, and the added weight of the system, is why I chose not to add levelling jacks. Too 'high a price' for the convenience for me. May be fine for others, but understand the limitations of an add-on system.

 

Thanks Volkemon for sharing your thoughts and in depth descriptions.  You have provided valid arguments when it comes to the detail frame design which must be done once all the loads are determined. Even then there is a lot of back and forth between members of the design engineering team as each member has their own negotiable and non negotiable constraints while focusing on things such as safety, reliability, cost, marketability, etc.  Your comments as it relates to the magnitude, direction, and location of forces and how it applies to the design of frame member section modulus in handling stress and strain (flexure) in all 3 axis is of paramount importance.


I was looking at the potential for and magnitude of torsion loads that causes longitudinal frame twisting,  By minimizing these loads with a given frame design it appears the Bi-Axial operating strategy utilized by HWH on their 725M (Phoenix specified system in 2016) would minimize torsional loading about the front to rear longitudinal axis.  This then should minimize shear and ultimately reduce relative displacement between adjoining body components such as windshield, front and rear end caps, etc.  The old designs which allowed a single Jack (rather than current control strategy of using Jack pairs to be moved) was notorious for cracked windshields.  This link describes Bi-Axial operation in greater detail.  https://www.hwhcorp.com/ml23032.pdf


As in most decisions there certainly are numerous pros and cons.  The leveler system on our Phoenix units is no different.  For our style of camping when on  6 - 8,000 mile road trips over the last 5 years has made us fans of the HWH leveling system.  Along our travels there would be many one night stays and in all sorts of weather.  Many stays occurred  in a National Forest, State Park, and National Parks.  During inclement weather setup was achieved with hardly any need to get out while assuring we were level enough and were not doing damage to our absorption refrigerator.  Unfortunately I don’t have too many fond setup memories when towing a camping trailer and getting outside in the rain unhooking and leveling.
This photo shows to an extreme what happens when frames are subjected to huge differences in loading between front two wheel and huge but opposite loads on the rear wheels.

Slightly off the original subject, but the first time I tried to use my jacks after driving home from purchase, the previous owners had installed a full length mirror on the partition next to the refer(2552).

It SHATTERED from the frame twisting.  Because of all the glue holding the mirror, I had to replace the whole wood panel.  Played with some stain mixing and got the new wood almost exactly to match the old.  Still a little apprehensive about the mirror on the other wall by the sink.  But it is not full length.