RV Frame Extension

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New to the forum but after readng some posts here regarding frame welding, thought maybe you guys could give me some advice. I only he a 90 amp mig so I know I cannot do this weld myself. I will be finding someone to weld it up, but I am trying to design and buy the metal myself.My 32' Class A RV's hitch has been pulled down through the flimsy frame extension installed by the manufacturer. Hard to believe is came with a 5k rating. I am pulling a 20' enclosed trailer with offroad toys.Weight of fully loaded trailer ranges between 4k and 5k. the tongue weighs in at 500lbs give or take.The extension is 3"x5"x1/8" by 12" in length, 1/8" fish plating to back side of frame and extension with I believe a small butt weld attempted. The extension is tied into the bumper and supports a small section of the coach rearend. The hitch is a class III with 2 bolts into the bottom of the extension. (No damage to the hitch)I would like to remove the bottom portion of the extension to the fish plate and the top portion to the outside edge. I then want to weld in a 3"x5"x1/4" by 3' extension in it's place. A bolt in the frame and one in the fish plate. Then weld a 1.5"x1.5" piece below the new extension to tie in the bottom of the existing frame. I will then install a new Curt class IV I got, bolted and welded to the new extension.Then weld a 2.5"x 2.5"x1/4" by 34" between the inside of the 2 extensions just inside where the existing frame ends. Then same type metal from cross tube to back of hitch receiver for extra tongue support.Picture attached for clarification.Any help is appreciated,     Kevin Attached Images
Reply:Not quite envisioning what exactly you are removing from the existing extension with your explanation. I think I have an idea what you want to do for the replacement however. A few things I think you need to alter at a minimum.You probably need more than just one bolt into the existing frame. Probably at least 3 on each side, if not more. With 3' of new extension you should be able to find enough areas to do this no problem. I'd probably also redesign the idea to remove the added tube under the new extension. First thought is see if you can't simply carry the size of the main frame straight back. It would lower your hitch about 1 1/2" from your drawing. Not sure if that will work with your rig or not. Second, I'd think about cutting some plate to match the same idea you have now, and then weld top and bottom flanges to this instead. ( the fabricator could cut the unit out as one piece of plate and then bend the top and bottom flanges if he has a heavy press instead. My 1st choice if I had to do a raised extension. ) Or I'd use material that matches the inside shape of the frame and then cut out the material needed to shorten the back end and weld in the new bottom flange.I would not try welding anything to the existing frame rails. All of this could be done with a bolt on "kit" if done properly. There is a reason most hitches and so on are bolted on not welded on.I'm hoping Jason ( Black Wolf) chimes in on this. I know he could easily fab up something along this line and make it work right. He can probably describe better what I'm trying to say.You need to be sure who ever you get to do this has a good understanding about what is involved. I'd be looking for someone who does heavy truck hitch installations and is used to doing this sort of work, not just the average "welder" of the street. It's not that the welds are all that complicated, just that getting all the parts to fit up right will make a big difference in the strength of this. A few pieces tossed together,  even though they may be heavier than the original, may not gain you much, if who ever is doing the work has no clue..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Thank you for the reply,I attached a picture with the yellow circles showing where I would remove the existing extension at and then put the new extension in its place and weld whats left of the old extension to the new one.You suggest bolting the new extension to the existing frame and fish plate instead of welding? Picture shows 5 bolts on each side, would that do? Can you explain the reason for not welding to the existing frame.I already have the necessary metal to do what I was laying out. I was hoping that I could do this with what I have and be strong and safe enough with subtle changes if need be. I thought that the 1/4", 3' rectangle section would have plenty of strength if incorperated into the existing setup. I don't quite understand the part where you talked about using plating and welding flanges. How would that tie into the existing frame?You did not address the 2.5"x1/4" square tube that would go between the new extension and tee'd to the receiver for additional support for the tongue and frame. Is that not necessary or should that be done differently as well.What is a bolt on kit?Sorry for so many questions, but this is a learning curve for me. I am not discounting any of your ideas, just looking at all possible solutions to this fix.Please keep the info coming.Kevin Attached Fileshitch4.doc (137.5 KB, 133 views)
Reply:I wasn't thinking tube, but "channel".   Tube to channel will probably work, but I do see some issues getting all the parts to line up with that preformed frame channel. That's why I was thinking getting the new pieces formed in a press to match the existing channel. Just slapping a tube to the side of the existing frame is not going about this the right way. The loads will not transfer well and you will loose a lot of strength because of this. If I was going to go this route, I'd make sure I could get tube that would fit the original channel, and the alter the rear end as needed by cutting out the lower section and welding in a new lower flange to match the cut shape.The square tube underneath is probably redundant and unneeded, if the hitch is strong enough as is.Take a look at Black Wolf's and Wello's examples in this thread. (I reposted Blackwolfs pict from another thread there) It sort of shows how you could do this as one unit rather than using a premade hitch. The only difference would be with yours, you'd have to add a length of channel to the top running back as a frame extension. If you look real close at Wello's picts you can see the doubled channel in his frame picts. That's sort of the way I envision your new frame extension fitting into the original frame. His pict sort of looks like what your whole new assembly would end up looking like if you looked at the new frame extension and hitch from the front rather than the rear. I hope this makes sense. http://weldingweb.com/vbb/showthread.php?t=60674Both of these guys do this for a living. If anyone here can explain it they can. If they don't respond, you can PM them and ask that they look at this thread and give their opinions.It will take me awhile to try and draw up my idea to make it clear. I'll try latter tonight if I have time.The reason I wouldn't suggest welding to the frame is that many frames are made of high tensile steel or are heat treated. Many specifically say not to weld on them. It's not that they can't be welded, only that they require special procedures to ensure that you don't damage the base steel. These are not "normal" procedures most welders are familiar with. Just throwing weld on a heat treated frame will case issues and frequently cracking. Not the best thing where you are attaching a hitch. Some of this is covered near the end of the linked thread.As far as a "kit" I was thinking more the guy could fab up all the parts and then it would just bolt on "like a premade kit". Very much like Black Wolf and Wello's do in that  linked thread..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:This is a common problem on class A gas motor homes, even from the factory the coach builders just scabbed stuff onto the base frames. You could go to glamisdunes.com and search in the RV section of the forum for several examples of fixes that have been done to the hitch installations. You should also check to see if the main frame rails have sagged and not just the extension. This can occur on coaches that have a lot of overhang from the rear axle back to the hitch area.