Jacking ribs to fix mid trailer floor sag

[CA_Tallguy]

Hey folks - really need some advice on how to safely jack up the shell on the forward side of my curbside wheels. It appears I have failing and/or badly repairs outrigger(s) in this area. My current theory is that the outrigger was sagging and it was just welded to stabilize it without correcting the sag.

I discusses what led to this conclusion with photos here...
http://www.airforums.com/forums/f36/...ge-112346.html

Hopefully some of you have some advice on the best way to jack this up, and what I can expect for a reaction from the rest of the shell. Jacking seems drastic and if there are signs to watch for in the process before any catastrophe I want to be on the lookout.

Some of the main questions are...

(1) how much realignment can the shell take from localized jacking? I think it may need to go up at least an inch, maybe 2 in this area.

(2) Should I localize the jacking to a single rib at a time or try to stabilize a few with interior bracing and then jack the bracing?

The main drawback in bracing, I theorize, is the bracing could lock in bad alignment rather than letting the trailer start to (hopefully) relax into more of its factory alignment. Maybe a closer inspection of the ribs forward of this area will help decide... Seeing how far off they are. My feeling is that the rib next to the wheel well needs substantially more jacking than those forward of it.

Thanks in advance for any and all responses! I'm very nervous about this.

[barts]

Off the top of my head, I'd find a level concrete pad to park on, and then:

* establish datum lines w/ a water level (or laser for you techies).
* pull the belly pan
* level the frame wrt the datum line. It will have a bend for & aft.
* check frame for issues - corrosion/cracking, etc. plan repairs if
needed.
* inspect the outriggers and get/fab. replacements for any that are
badly rusted.
* using screw jacks (can be homebuilt) and blocking, support the
floor around the perimeter between the failed outriggers so that
shell is properly supported. Replace any failed outriggers at this
time. check floor inside for level. You may need to grind welds
on badly repaired out riggers.
* weld any replaced/detached outriggers; watch out for fire issues
w/ plywood floor.
* replace belly pan....

Note that shell weight is pretty much uniformly distributed over the
perimeter and pushes down on all the outriggers. Axles in poor condition can lead to high loads and damage to outriggers near axles; check for this as well.


- Bart

[CA_Tallguy]

Thanks Bart! That makes a lot of sense.

We got the section of banana wrap off and got our first good look. Don't like what I see as there is a hole in the frame!! Unfortunately the water tank is right behind it so I don't know of it can be repaired without taking it out. Well, it is dropped already so all the way out may not be too bad.

[barts]

Hmmm. It looks to me like that axle plate more than makes up for that hole... not sure where that hole came from, though.

Take your time and make a sketch with measurements from the floor down to your flat surface/datum, and you'll get an idea of how bad things are....
and poke around that frame with a chipping hammer looking for rusted out sections.

- Bart

[perryg114]

Get some string and tie from one end of the frame to the other and maybe you can see what is happening. Alot of floor sag issues are the result of rear end separation. The rear end of the shell is no longer attached to the frame and the outriggers start taking up the load and sagging. The shell and the frame are weakly attached at the front and rear of the trailer and when one of those connections fail then you have problems. It looks like someone has tried to patch that outrigger already. I would pull the belly skins and get a total picture of what the frame looks like. Is your trailer a rear bath and what do things look like at the very back?


Perry

[CA_Tallguy]

It appears the frame rail is splitting open at a seam. The little tac welds seem to have broken. So, we think most of the sag is coming from the frame rail vertical bending outward where the outriggers are attached. That magnifies to 3/4 to 1 inch sag at the outside. In addition, the outrigger at the forward side of the wheel well should be replaced. I hunk the other outriggers look pretty good and the sag they are showing is coming from the bending rail.

I started a new thread to discuss the frame rail split and outrigger issues here...
http://www.airforums.com/forums/f36/...ge-112346.html

For this thread, I'm hoping to concentrate on the jacking and stabilization of the shell and how safely to go about that. But beggars can't be choosers so pleas post your wisdom on whatever subject wherever you like! All the advice I can get is much needed and appreciated.

I have some screw jacks being delivered today to assist in trying to precisely jack things up. I guess that I need to watch out for skewing of door and window openings as well as hatches. And any weird stress dents or ripples in the skin?

We have good access to three outriggers on the side we are working on, so I guess I will position the jacks under each of those, perhaps with some additional bracing around and between them.

[CA_Tallguy]

Originally Posted by perryg114

Get some string and tie from one end of the frame to the other and maybe you can see what is happening. Alot of floor sag issues are the result of rear end separation. The rear end of the shell is no longer attached to the frame and the outriggers start taking up the load and sagging. The shell and the frame are weakly attached at the front and rear of the trailer and when one of those connections fail then you have problems. It looks like someone has tried to patch that outrigger already. I would pull the belly skins and get a total picture of what the frame looks like. Is your trailer a rear bath and what do things look like at the very back? Perry

I have a mid bath, 31 feet. The front seemed to look good as we just last couple of weeks replaced the skin below the front window, going into the hold down plate etc. I will check the back for any obvious distress.

I'm a little hesitant to rip open the rest of the belly right now as I was just getting ready to head to Texas when this arose. I do think that is a good idea and will plan to do that very soon. I am going to carefully inspect flooring and the banana wrap for any other clues around the trailer. This bulge in the flooring raised my eyebrows as out a big issue so hopefully I'll be lucky and find other clues if there is anything major in other areas. If I do, then I might have to go open the whole thing up and postpone the trip.

[CA_Tallguy]

Originally Posted by barts

Hmmm. It looks to me like that axle plate more than makes up for that hole... not sure where that hole came from, though. Take your time and make a sketch with measurements from the floor down to your flat surface/datum, and you'll get an idea of how bad things are.... and poke around that frame with a chipping hammer looking for rusted out sections. - Bart

I'm having a hard time with precision and finding level on the trailer front to back and side to side, amount that needs to be jacked, etc. especially since we are talking about such small measurements. I'm a but frustrated in this regard at the moment but am trying to figure it out.

As I said, my best guess right now is that the frame rail is splitting a quarter inch or maybe less and that is magnified out so we are talking really small amounts... But amounts that seem to matter quite a lot!

[perryg114]

Once you take the belly pan out, you will probably find some more corrosion issues. It sounds like your trailer is the same as my 31 ft 81 Center bath. The wet insulation really messes up the frame. My frame rails were two channels welded facing each other to form a box.

Perry

[CA_Tallguy]

The main thing that worries me about the skin and ribs with this sag is that in the sag area, the normal curve of the airstream goes flat. It kind of seems like a dent but I think it just seems that way since it is recesses from the normal gentle outward curvature. I think that even jacking up this area is going to just push hone distortion since my guess is that the rib has flattened and extended to accommodate the sag.

Anyone experience anything like this before? Recommended actions to take? Not sure how much to try to level the floor considering this section. Will I have to leave the floor slightly off level? Or should I still shoot for level and hope the ribs settle back, maybe over time?

[CA_Tallguy]

I bought these camco screw jacks marketed for rv leveling to help jack up the ribs. Under $30 for 4 with free delivery! They are rated to 6000 lbs each so they should work well. I wasn't looking for rv leveling jacks per se but they came up hin in my search for screw jacks and they seem great!

http://amzn.to/19FaOJk