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Message: [QUOTE="me2, post: 437579, member: 3825"] I received a bunch of questions. "Why do you have to grind the frame flat after you weld it ?" I was told that because cracks will develop wherever there are big changes in stress and having the frame go from its normal thickness to the weld thickness and back to normal puts 3 areas of different stress close together. Grinding the weld reduces that. "Why can't you just weld a plate in/on the side (web) of the C section ?" Because adding material to the web doesn't increase the frame strength that much. Material needs to be added to the flange, because that is where a C section gets its strength from. "Why don't they weld diamond plate over the frame splice on the inside ?" I don't know. "Why isn't the flange of the brace welded to the flange of the frame ?" If you did that it would create stress changes in the frame flange. I'm guessing that adding the brace to the frame by welding it to the web is like making it an I beam without messing up the stress in the existing flange. I'll trust that Ford knows how best to extend its own frames. "Why is the web of the preferred frame brace angled in the Ford document ?" Probably to better distribute stress to the original frame. "Why doesn't the brace have a flange above the frame ?" I suspect that the top flange is in compression and already strong enough. "Why doesn't the list of trucks include short box trucks ?" (156 inches for CCSB) Because there isn't enough room between the cross member behind the cab and the front leaf spring hanger. Ford doesn't want mods done in that area. And Ford probaby thinks you should start with a long box frame if you want a longer frame. I'm guessing here. "Why do you want to buy a short box truck then ?" Because my splice will be under the cab, not behind the cab. I'll be splicing in a piece of frame section or grafting on another entire frame to lengthen it. I don't have to touch anything back by the leaf mounts. And if you start with a long box frame you need to add length under the cab as well as shorten it under the box, essentially making it a short box frame. And that shortening would be in the area by the front spring mounts, where Ford doesn't want it to be messed with. The Ford document doesn't contemplate the owner stretching the cab. Only the box. My frame shop tells me its fine to stretch under the cab. "Why is the brace stitch welded ?" I don't know, probably some stress distribution strategy. But the shop told me to do it that way and the Ford manual says to do it that way, so I'm not going to argue. They know what they are doing. "Do you really have to get it inspected ?" Actually, the frame shop told me I didn't if it wasn't going to be used for commercial use. But my insurance company asks me to list the modifications and enhancements on my truck when I renew and I think it would be a bit of a fib if I didn't tell them it had 6 doors instead of 4. And then they want it inspected. I think the government only wants it inspected if you sell it. I'm not sure and I don't really care. Mine is getting inspected. "Does it matter how you cut the frame ?" I don't know. "Why doesn't Ford use higher strength steel ?" I don't know. I think that stronger steel has less resistance to fatigue from flexing. And its probably cheaper. "Have you ever worked on a frame before ?" Yep. My dad and I extended 2 MDT frames about 15 years ago. No problems with them that I know of. But I'm told that MDTs and pickup truck frames are different and need different techniques. "Are you a certified welder ?" Nope. "If you buy a short box truck are you going to splice on a 2nd frame or just lengthen the current frame ?" I don't know. Prior to seeing the Ford document I was going to graft on a new frame. They are about $400 to buy used. However, the Ford document seems to indicate it would be fine to just add a section using the right C section. "How do I stretch the frame on my XYZ truck ?" I don't know. Get help like I did. I'm not a frame expert. I'm just relaying the information that I got to try to answer the questions. Someone who does Finite Element Analysis could answer these much better than I can. I know that this isn't the way one would stretch a frame on an HDT. I'm just following what I've been told works for a pickup truck. I hope this helps. [/QUOTE]