Pin Box Movement

[hhh]

I have an update. When to Crossroads and met with the Lippert rep. They had removed the bottom skin and the front cap. There are no broken welds, all the welds looked good and could see no physical damage. Once that was all removed and the trailer was lifted you could see where the frame was flexing. This is not some lightweight frame, the walls are 4 gauge steel making the walls of the frame tubes about 1/4" thick and from what I was told is heavier then most manufacturers use. The side walls bolt to the frame in two places behind the rear pin box crossmembers. The walls do not attach in front of this crossmember because of the frame design is not a box but an angled or notched design so there is nothing to bolt to. The frame flex starts just about where the forward most sidewall bolt is. See the picture below.

the front of the trailer is on the left.



The frame is designed like this because the front cap is curved or rounded so a square front frame would not work. As you can see from the above picture there is about 9" of wall in front of the frame rail. To reduce the flex they are going to extend the frame rails as far forward as possible and then run a new crossmember to the pin box area plus add a couple extra braces and gussets between the new framing and existing framing. The side wall will then be bolted to this new framing.

All in all it appears they have a solution for it. This will not get rid of all of the flex and some is desirable as being too rigid would just transfer the shock to other parts. I won't put the blame for this on anyone, it's just something that was not foreseen when designed. Below are a few more pictures for your enjoyment.








Edited by: hhh

[Lloyd]

Hank, tell us which way you were pointed when you took those pics. It will make it easier to get the jistof it.

[hhh]

The picture at the top, the front of the trailer is on the left.

3rd pic front is on the left, last pic the front is on the right.

Once the work is done I'll post pictures of the added framing.

Sometimes it's hard to explain things in words




Edited by: hhh

[Lloyd]

Thanks

[GaPete]

Hank,

Thanks for keeping the info flowing. This is good info to have.

[gtoguy1967]

I looked at ours after seeing this and I didn't see any changes. Hooke vrs unhooked. I will watch this though. Nice post and great pics and follow up.

[hhh]

After thinking about this excess movement I believe that my lowering of the pin box in the mount is contributing to the movement. I had to lower my pin box 2 holes (about 4") because I have a 2WD truck and the front of the trailer was way low. I could not raise my hitch any further. Lowering the pin box increases the leverage it applies to the frame.... this is one reason most manufacturers do not recommend using a goose neck adapter.

[Dayle1]

Originally Posted by hhh

After thinking about this excess movement I believe that my lowering of the pin box in the mount is contributing to the movement. I had to lower my pin box 2 holes (about 4") because I have a 2WD truck and the front of the trailer was way low. I could not raise my hitch any further. Lowering the pin box increases the leverage it applies to the frame.... this is one reason most manufacturers do not recommend using a goose neck adapter.

Hank,



While I agree that lowering the pin box increases the leverage, that only applies when you are towing and I don't think you have many miles on your unit. The movement you are measuing when standing still is dead weight and position of the pin box will not affect the amount of movement you are seeing.

[hhh]

I am far from a structural engineer but I would think if there is increased leverage it would apply static or moving. What caught my attention while at Crossroads was the Lippert engineer calling the point where the frame started to flex the "pivot point". I made the crude drawing below to maybe illustrate what I mean.

Since the pin is not below the mounting bolts it has to apply a lever action to the frame when it is loaded. The point where that lever action intersects the frame I would call the pivot point. In the upper pin box mounting position this pivot point is closer to the front of the frame then the lower mounting position.

My observations was this pivot point was located right around the front sidewall mounting bolt. This sidewall bolt is about 4" behind the frame crossmember. 4" is about the same amount the pin box was lowered so I would think the pivot point for the higher pin box mounting position would be right where the front crossmember would be. Also, since the lever is now effectively longer it applies more force to the frame.

Much like a teeter totter, if you have two people the same weight, you want both sides the same. One weighs more you have to made the heavier side shorter so it lifts less weight on the other side. This applies even when the teeter totter is static.

Not sure if this makes sense or even if this is taken into consideration when designing a frame. It is just something my little brain thought of while sitting around with nothing else to do




Edited by: hhh

[Dayle1]

Hank,



Leverage is basically distance times force. In the static case, all that matters is the horizontal distance and the vertical force (gravity). This is the force vector acting on the weak point of the frame. Moving, you have this plus the forward power from the tow vehicle, so now, the vertical distance and horizontal force become a second factor. Combined, you have two force vectors acting on the pivot point instead of a single force vector. Now replace your 4 inch drop with a longer gooseneck adaptor. The original force vector due to gravity remains unchanged, while the other one is increased due to the increased distance, and of course, the total force or leverage applied to the weakest point in the frame also increases.

[Texas1949]

Thank you for all the information.
I am looking at an 05 29MK and that is something that I did not look at.
I am going back to look at the unit again and I will check that out.
How many bolts should be in the pin box. If my memory is right. I think the unit I am looking had 2 on each side.

Thanks
Mike

[Hunter11]

You should not have this issue on an 05 model. We had an 05 Cruiser 29RK and never had this issue. Seems to be a problem on some of the newer models and floor plans.

[wenzdong]

You might also wish to go to Lippert Componets website below and pull up LIP Sheet - 0170. It has info and torque on this hitch:

http://www.lci1.com/index.php?option=com_content&view=article& id=61&Itemid=68

[hhh]

I got word that the modifications to my coach is complete. It is not all put back together yet but I do have some pictures of the work that was done. While I have not seen it yet Randy claims the changes reduced the movement from 1 1/4" at the front of the pin box down to 3/8" or less. If that is the case I'll be happy. Here are some pictures.

Here you can see where they extended the frame. C channel was used to extend the frame and then tie it in with the pin box mounting area. You can see where they bolted the sidewall to this new piece that was added. The front of the trailer is to the left.



In this photo as a front view of the added extension. The sidewall is to the left and the front of the trailer would be behind you. Note that they added angle iron to the new sidebeam so the sidewall rest on it and then bolted the sidewall to the angle iron.



This photo shows they also added the angle iron to the existing sidebeam and bolted the sidewall to the angle iron. Sidewall is on the left, front of trailer behind you.


Here you can see they welded the two crossmembers together and then added two gussets between the crossmembers and the bedroom subfloor. The front of the trailer is to your right.



Here is another view of the added frame extension on the other side. Note the added angle iron sidewall supports. The sidewall is to your right, front of the trailer behind you.



One last photo of the added sidewall angle iron support added to the existing frame.



So that's it! I should be going back next week to pick it up and will report back what my final findings are once I have a chance to tow it home. Hope this is helpful.

[Hunter11]

Hank, so they tied the walls into the frame to take more stress/flex off the frame/pin area? I would be concerned about that as a long term fix and what it might do to the aluminum walls but I guess they know more than I do. As for the looks or appearance of the repairs, well I will hold that comment to myself....

[BipeFlier]

I don't know who the welder was, but I wouldn't let him build a sand box. Welds are very poor, didn't grind the paint or rust off prior to welding and some of the joints look as if they were cut out with a torch. Poor joint gaps and while it appears they used a stick welder, they didn't chip the sl*g off to inspect the welds.



I hope it works but good luck.Edited by: BipeFlier

[hhh]

The sidewalls were already bolted to the sidebeams. They just added more support and fasteners.

I post 'em as I got 'em. Not sugar coating anything. I will be calling on Tuesday, hopefully before the button it up so ask about the weld job.








Edited by: hhh

[Dayle1]

Here is my sketch showing one side of the front frame. This is based on measurements I made and some of the pictures that have been posted. While not totally accurate, it is a fair representation. I assume there are gussets where the braces meet the front crossmember that are identical to those at the rear crossmember, but I don't know for sure.







From what I have seen of older square frame designs, this seems more robust than the others, even on heavier units. There are a total of eight fore-aft brace points, all are full height. The two where the notch begins are doubles, the outer ones are short doubles with a plate between them and of course the inner ones also have the pin box mounting brackets. Most I have seen on any other frame was six and some were not full height.I really don't think that this part of the structure is flexing much. I have no idea how this compares to other new frames that also notch the front crossmember.

[martinstwopopfarm]

[martinstwopopfarm]

I noticed on our Cruiser we have about 2/3" flex movement in the pin box when we are hooked up.