Hi Folks
Rick and Larry I’m still looking at your pics.
Rick trying to figure yours out. If you lay a 2 to 3 foot straight edge on top of the A frame by the snap ups and then drop down with the combo square “I think” if there is any permanent twist in the channel it would show up and the vertical surface is no longer square to the straight edge.
I had today off from work cleaning up the big camper to go camping on Thursday. And this is still on my mind so I did some fiddling trying to see if I can reproduce the channel torsional forces in some fashion. I still cannot find the direction of another force that will bend up the battery bracket or buckle the header the way it is so the channel has to be twisting to allow the header to buckle. I do however feel it is both a torsional twisting combined with the downward vertical weight of the TT at the same time. It is not just this twisting action from WD. The twist is there, how much it adds to the failure, will only come out in calculations or stress testing.
Larry’s header now shows signs of the outer ends of the header that are outside the channel being bent down. His header is also shot. BUT this shows that the header is stressed at the A frame so when the I beam is pressing down on the header normally, it can impart high stress in a rotational direction towards the Channel. The A frame acts as a pivot point. The I beam is sort of held up by a cantilevered arm. That loading combined with the WD twist and extra downward loading on the A frame might be what breaks the camel back. The header and the A frame cannot the handle those forces the way it is made
Sunline moved the A frame up into the middle. This then “might” have been to minimize this cantilevered effect. The header is more of a beam then acting like a full length beam. Cutting a hole in the middle of a beam is not as bad as cutting a hole in the bottom edge of it that has high torsional forces going on with a small lower flanged header to stop the buckle.
See here on Larrys left side. The string tells all. That end of the camper is pressing down on the I beam wanting to twist the A frame and buckle the middle of the header. The right side is the same too.
Larry’s right side.
If we had a trailer frame designer on the forum it would help as they deal with this every day for a living. I know I’m not one, but figuring out why machines break I do dabble with so this has really peaked my interest to make sure I myself do not create a problem on any of my TT’s.
Hopefully some of this will spark others and possibly a frame engineer following along silently in the back ground. I really hope Lippert can assist, but if they do not, then trailer frame shops will do the repair. There is nothing here that cannot be fixed.
Now to my fiddling. My first problem was finding a piece of 4” channel with the right web thickness. No have. But I did have a piece of 3” channel with 0.180 thick web. This would at least get me a rough feel of how much twist can occur in a channel shape. It twisted more then I had thought. For this shape, a thicker web will help the twisting resistance., Width also adds resistance. The 2004 and older models using 5” channel, 0.200 thick webs have greater resistance to twisting on top of more load carrying rating. Not that 4” channel will not work, but the older A frame was stronger. Do not know if on the final Sunline fix that GoodoleBob, KathyH and Eman have has a thicker channel.
If either of you can measure that it will be helpful. HenryJ yours is the older model and we can compare to it if you have a set of calipers. Rick’s and Larry’s may or may not be different.
Since I did not have these shots on the 2005 and forward model, I used my 2004 T2499 to show the point I was trying to figure out if it means anything. This is where I see forces acting in certain directions that at least add up to how some of this “might” bend things.
The WD adds a lot of point load in the chain snap up area. When you are towing straight, both left and right WD bars have equal loading. When you have a high back flex of the WD hitch, like coming off a high up set of RR tracks or a high up driveway as long as you are straight, both sides get more load equally. While the loads go up this back flex may not be as bad as a turn.
On the back flex of the hitch, the WD bar loads goes up high, but then the back of the truck lifts too. So it then takes some of the load off and finds a new equilibrium. This is for sure is a high loading condition and it too may break the header if the tongue weight and the truck bed weight was high enough. Point is, the loading in the A frame is equal if straight. And if a turn occurs while back flexed, well that one side of the TT A frame really gets jolt of load.
I'm not saying that a high WD hitch back flex will not break the header right in the middle this may be a 2nd cause. If the header is weak enough, if you push down on the A frame even equally on both sides, the frame I beam rails can still twist the header pivoting on the A frame and buckle it in the middle. If the forces are high enough, this "might" happen.
Now to the side loading going around a turn. First off lets say the T2499 was loaded to have a 1,000# tongue weight using 1,000# WD bars. Each bar can hold up 1,000#. When the TT and TV is straight each bar is only lifting ½ the weight. So they may only have 500 to 600# on them.
There is also extra load that the WD bar works on and that is the weight inside the TV aft of the rear axle. If there is 200 to 300# of gear in the back of the TV aft of the axle, well to the WD hitch, it has to lift that up along with the TT tongue. 2, 1,000# bars will lift 1,300# of weight going straight. And again when straight each side takes ½ the load.
Until a turn with a slight angle to the ground or road.
See this turn. This is by far not a jackknife. It is only 50 degrees.
Here is looking at the truck. I’m sure we have all made a turn like this just driving across town pulling out of a gas station with the TT on the back.
Now see the hitch
The outside WD is holding up the entire TT. The inside turn WD bar is doing nothing to hold up the TT. I rattled it with my foot to prove this. Now that 1,300# of WD force is all on one side of the TT frame. It is pushing down on the 1 A frame rail only and that high force is delivering a twisting action in the A frame along with only 1 side of the A frame holding up the entire TT. This is with only a 1,000# tongue. A 1,200# tongue or 400 # of gear in the truck bed create large loads in these cases.
One may think well how much does stuff weigh there is no way we have that much weight in the truck?. Well stuff adds up. See here for 250.8# worth of camping stuff that use to ride in my K2500 Suburban in the back.
And lastly the WD frame twisting.
See here for a WD snap up bracket. It hangs on the top of the frame. Even if you have the Equal-I-zer brand hitch it too has some of this same effect. The chain pulling on the WD bar hangs off the one side. This puts both a downward load on the frame and a level of twisting motion.
So when during that turn, we get a high downward load in the frame and some twist. The A frame twists until it finds something to try and stop the twist. In this case the frame header and the ball coupler. Since the snap up is closer to the header, the header gets more of the twisting.
See here for the 3” channel twist test. I was only pulling about 75# on that 3 foot handle or 225 ft lb of torque. On a snap where the chain is 1 ½” away on say 1,300# of force that is 163 ft # of torque. So by the numbers even though this looks bad, that is not a lot of torque for what this should be able to hold up. But the I beam twisting around the A frame is hugh.
The test. A fixed end on one end, a wrench 22 inches away and a square to see vertical
Now with no load the square is vertical
Now with 225 ft lb of torque
The twist looks bad and is. But putting 163 or 225 ft lb of torque in the Channel held by the header, should not affect this that much. So I sort of talked my way out of this being a smoking gun.
Bink68's fix was to adde the 1 x 2 tube. Well when both I beams are pressing down, the 1 x 2 tube keeps the middle from compressing and twisting. I have not figuired out if this is the final fix and it sure will not fix Larry's, However Bink reports an improvement in WD loading. So we may be getting 1 step closer to what the actual cause is.
In summary here are my thoughts on this.
The T2499 loads tongue heavy. That floor plan just does. 900 to 1200# is not unheard of especially if fresh water is carried.
Any weight in the truck bed Aft of the axle can add to the WD bar force.
When a turn is encountered the 1 side of the A frame is holding up the entire TT while also having high downward loads of the WD effect on it. With the way the header is built and the loads involved holding up the TT, 1 A frame rail can’t take it.
The main I beam frame rail has to take the load and it presses down on the main header impacting both a large downward force in the header and a large torsion load pivoting on the A frame trying to bend up the main header in the middle.
The header might be able to handle the load in a pure vertical loading but the lower flange being so small allows the header to buckle.
When you throw in the dynamic loading of towing down the road the shock impact of bumps increases the loading even more.
When the header buckling actions start, it starts ripping apart the joint where the A frame goes thru the header.
After a few of these cycles this, the header starts failing and then it is down hill from there.
There are still a few holes in my thought process yet to be ironed out, but this was what I “think” I seeing going on as of right now until new info comes in. I’m open to any Sunline Club member questioning anything as the more we talk the more clear this comes. And being open minded, it is easy to come to a wrong conclusion.
Hope this helps
John