Hi Tod,
Here are my thoughts on the back of the frame cracks. I will talk to the axle area in a separate reply. I will explain a little about what I “think” is going on. Consider it an opinion only at this point, not an absolute. You are up close to it and may see something I cannot see from the pics.
Having been through this unique rear frame flexing issue on my 2004 T1950, I can see by your cracking how the cracks may have come to be. First off, Sunline made a lot of T1950’s, and we will call this failure mode low at this point. There is not a significant issue with the system, but it does have weak points. The cracks you found now are not new. I would say they may have started a few years ago, could be two to maybe even four years ago unless you had better knowledge when they started. But the length of the cracks was a lot less, only minor and hard to tell when they first started unless you were intensely looking for them. The cracks were tiny when they started, and as time went on, they grew in size. The cracks exhibit a somewhat standard low cycle fatigue crack. The camper frame twists back and forth over time. All frames do, just there are factors to turn that twisting into exsessive twisting and an actual crack.
The black tank set up on the T1950 uses an approx. 4’ long piece of 3”. C Channel in the left rear corner to pass over the top of the black tank dump pipe. That 3” Channel iron has an offset jog outward from the main trailer frame. The frame jog creates a pivot point where the 3” channel meets the main frame rail behind the rear axle. My 2004 used 4” Channel main frame rails, and your 2006 uses 6” tall I beam shape. Technically your main frame rail is more robust than mine, in certain lengthwise loading directions. It is weaker in a few other side loading directions.
This rear joint behind the rear axle hanger creates the flex. This picture is from my 2004 camper.
When that left hand 4 ft long frame rail is unbolted from the camper floor, that joint has a high degree of flexing. Two paint cans hanging on the end will cause it to bend down 1/8”. While an 1/8” is not a lot, the right side has zero movements with many times that weight.
Here is a left-hand side video of my foot wiggling it showing a lot of movement with about 10 to maybe 30# of push. This link will take you to my Flicker site and should run the MOV file. Just click the pic to run the movie when it loads up.
https://www.flickr.com/photos/camper...posted-public/
Here is a right-hand side video of my foot wiggling it. Minimal movement, it is much more substantial compared to the left side. This link will take you to my Flicker site and should run the MOV file after you click it. I am doing more wiggling then the frame.
https://www.flickr.com/photos/camper...posted-public/
The left side frame does get significantly more rigid when the camper gets bolted to the floor. The floor and walls make the structure stable enough to use as a camper. But my point is when large dynamic forces act on the camper frame, the left side is much weaker than the right side regardless if the floor is bolted to it our not.
See here for more on this bending joint if wanted.
https://www.sunlineclub.com/forums/f...tml#post151090
Now to your frame cracks. Based on how I have seen the left rear side of the camper flexing, the left side is for sure flexing at the frame jog joint to cause this crack. A needed understanding is, which direction is the force to create the crack and continued ripping of the main frame rail? The substantial forces to develop the crack comes when the back of the camper raises “up”. Yes, up, not down. A downward force on the end of the camper creates compression where the crack started. That crack is the result of the bottom of the 3” channel being forced up, not down. Cracks in steel like this only happen when the steel is being pulled apart in tension. The weak spot in the joint is when the camper comes up out of a large bump and upward flex. When the back of the camper flexes down, the top of the joint is strong enough to handle those forces. See here.
To help show how this happens, I used my T1950 in the rebuild process as an example. I rotated the picture of the camper picture 5 degrees in both directions to show what is going on when you are driving over a single bump in the road with the camper, the bigger the bump, the more rotation. And multiple bumps in a row are even worse.
The camper level at rest or riding down a smooth highway. The yellow line is horizontal. You can see it on the siding.
Now you hit a bump. We will pick a pothole, and the left tire drops in the hole first. The back of the camper is going to drop down first on the way into the hole. As the camper hits the bottom of the hole, a massive jolt goes into the frame joint that flexes it hard. Remember, this side of the camper is weaker than the right. While the right side will also bend and twist, it is at a much less amount. The frame is not balanced left to right.
As you keep driving forward, that hard down jolt force goes in the opposite direction and upward. This picture is the same 5 degrees rotation but in the opposite direction. This upward direction is causing the main frame jog joint to start the crack and continue to rip it apart a little at a time as the flexing cycles continue to repeat.
Your cross country trips, and then you said you ran into several rough patches, do you recall how many miles this was over the last 14 years? Trust me. I know all about an interstate loaded with land mine potholes that bent my T310SR frame. Same problem, just larger camper weights and rear overhang. The lack of shock absorbers on campers just makes all this that much worse. Even somewhat normal small bumps over many thousands of miles constantly flexes the back of the camper frame, back and forth at that frame joint for every bump. It just needs to be strong enough to take what our highways throw at it. Or get better roads.
OK a little sarcasm there.
Now to the right side main frame rail web crack, that comes from the camper flexing from the left side going up and down. As the left side goes down, it pulls down hard to the left on the web of the main frame rail. When the left side rear frame goes up, a complete reversal of the bending forces pushes the right side frame rail back to center of the web and beyond center over to the right side. This constant significant push and pull starts a fatigue crack in the I beam web just about on the centerline of the unsupported web steel. The 3” C channel is rigid halfway down the 6” main frame rail in this pulling direction. The bottom of the main frame rail has the I beam bottom flange to reinforce it. The weak spot is halfway between the two. In this case, the 3” left to right C channel is about 6’ long. That is a good-sized lever flexing up and down with the left side flexing up and down.
I needed to convince myself somewhat, I understood where the forces were coming from before suggesting a repair. Here are some thoughts to talk to your welder about. See what he says.
On the left side,
1. Drill a 3/16” to 1/4” hole in the end of the web crack. Center the drill right at the end of the crack. This is nicknamed a stop drill hole, which is standard practice on these kinds of repairs.
2. Grind out a weld prep and full penetration weld the crack closed.
3. Grind the outside of the main frame smooth, where you will add reinforcement.
4. Add between a 2” x 2” up to a 3 x 3” x 3/16 to 1/4" thick angle in the joint on the outside of the frame. The length should be from the top inside flange to bottom inside the flange of the I beam. Chamfer out the corners of the angle to fit into the I beam radius and the original channel weld to the I beam. Do not grind the I beam radii or the original channel weld to fit the angle iron.
5. Stitch weld in the angle.
6. I picked the outside of the main frame on the left as it will be easier to weld in the angle.
Some general guidelines on these thin I beam welds. Heat shrink can be your enemy when welding these frames if you are not thinking about the weld sequence. For every weld, the metal will shrink less than it was before the welding. That shrink will bend the metal as the fibers are shorter in that local area. Welding above the centerline of the I beam will shrink the upper part and bend (camber) the frame rail upward (positive). Welding below the center of the main frame rail will bend camber it down (negative). Use short stitches, let it cool to the touch before putting the next weld on. Yes, it will take a long time. Go back up to the header area and work as a weld is cooling down and come back to it. The goal is to balance the top of center welds with the bottom ones. And do not over weld the joint, short stitches put less heat in I beam. If you overheat the frame, it will twist in the direction of the most heat. Be extra careful welding across the face of the upper or lower I beam flange that area will camber the beam the fastest. The frame makers put positive camber in the frames by just putting down weld beads on the top flange while the frame is being made. Do not put a lot of heat on the lower flange, it will bend down from the shrink.
Have the welder bring a few pieces of sheet metal to shove above the frame to shield the heat from melting the Darco. A few 2ft x 2 ft pieces will work.
Odds may be they use high strength low carbon steel on the I beam which is 56 ksi yield strength steel. My T310SR camper I beam is like that. He will need 7014 or 70XX weld rod if he is using stick. If MIG, he needs the right wire to get up in the right range for 56ksi steel.
On the right side,
1. Do the same stop drill (yes at each crack end, use 3/16" bit) and grind out weld prep both inside and out for a full penetration weld of the crack.
2. Grind the inside of the main frame smooth, where you will add reinforcement.
3. Add between a 2” x 2” up to a 3 x 3” x 3/16 to 1/4" thick angle in the joint on the outside of the frame. The length should be from the top inside flange to bottom inside the flange of the I beam. Chamfer out the corners of the angle to fit into the I beam radius and the original channel weld. Do not grind the I beam radii or the original channel weld top fit the alge iron.
4. Stitch weld in the angle
5. I picked the inside of the main frame on the right side as the heat on the right side will be partly on the channel iron and help make that side stronger.
I agree, get the spare tire off the left side rear bumper area. Your 2nd spare tire on a pivot mount frame on the right side frame rail area is a good idea. I had not yet figured out what I was going to do as I have to move one too. I will look into that. May just have to pivot the tire down if you use the gas water heat option.
Hope this helps
John
Linear Mode
