What alloy steel are the frame rails made from?

[ramdough]

Anyone know the alloy and temper for the frame rails used on FMTV?

If not, do you know the material properties?

Looking to weld a frame extension. Would like to have info to evaluate options.

Thanks!


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[snowtrac nome]

I welded on my bumper extentions with 6010 and 7018 towed up to 35 k with it you shouldn't have to worry about the frame just butting to it, proper welding would have to be done when welding forward of the rear spring mound or aft of the front spring mount.

 

[Jbulach]

Most modern frames are proprietary alloy and heat treatments giving you a min yield at the very least of 100ksi. Welding is best left to a professional, with frame repair knowledge and experience. 11018 is a decent rod choice. A lot of people will tell you to cut the web on a 45, but my belief is a straight cut is just as strong in the end, and a 45 causes most people improper fit and prep issues. Frame cleaned and beveled properly, mild preheat, weld from the outside of the flanges toward the web, vertical up on the web. Keep heat and mixing of base and filler to a minimum, light post heating and blanketing to control cool down as necessary. Do not fish plate, instead bolt in liners of the same thickness, at very least 2’ long if possible.

 

[simp5782]

Welding has to be done to the "manufacturer specifications" eh. Whatever they want to tell you.

Member profo welded to his LMTV frame a 4ft extension from a m939 series truck. Works best for double channel overlap of inner and outer so it can be welded and riveted/bolted

 

[snowtrac nome]

Most modern frames are proprietary alloy and heat treatments giving you a min yield at the very least of 100ksi. Welding is best left to a professional, with frame repair knowledge and experience. 70110 is a decent rod choice. A lot of people will tell you to cut the web on a 45, but my belief is a straight cut is just as strong in the end, and a 45 causes most people improper fit and prep issues. Frame cleaned and beveled properly, mild preheat, weld from the outside of the flanges toward the web, vertical up on the web. Keep heat and mixing of base and filler to a minimum, light post heating and blanketing to control cool down as necessary. Do not fish plate, instead bolt in liners of the same thickness, at very least 2’ long if possible.

proper fish plating at the end of an lmtv frame would be near impossible one thing I aim to do but haven't yet is to build a link to go between the old pintle mount and the new one I added to my frame extenion

 

[Jbulach]

Ever better reason not to fish plate...

 

[ramdough]

Most modern frames are proprietary alloy and heat treatments giving you a min yield at the very least of 100ksi. Welding is best left to a professional, with frame repair knowledge and experience. 70110 is a decent rod choice. A lot of people will tell you to cut the web on a 45, but my belief is a straight cut is just as strong in the end, and a 45 causes most people improper fit and prep issues. Frame cleaned and beveled properly, mild preheat, weld from the outside of the flanges toward the web, vertical up on the web. Keep heat and mixing of base and filler to a minimum, light post heating and blanketing to control cool down as necessary. Do not fish plate, instead bolt in liners of the same thickness, at very least 2’ long if possible.

I have multiple friends that are certified professional welders. I will definitely get help. I am doing background research. I plan to have the upper frame rail and lower frame rail seam staggered so they do not line up. Then have vertical joints so I can easily square it off. The extension is going to be aft of the rear suspension. After full penetration welding, I plan to grind and then add sandwich plates on both sides with a bunch of through bolts. This is just to maintain the towing capacity. Should not see much load ever.

Thoughts? Thanks!


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[Jbulach]

Yes, staggering the upper and lowers at least a foot would be ideal. I doubt your sandwich plates would even be necessary, although I believe those frames do already have a ton of bolt holes in the very rear that you could utilize. Use grade 8 hardware that fits the holes nicely, and have a shoulder long enough to get past the shear points between plates. Don’t forget to do a good job painting before assembly to help prevent rust between layers. Also, I edited my first post. Welding rod type should have been 11018, not 70110

 

[ramdough]

Thanks for the help everyone!


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[ramdough]

Prepping to weld on my frame extensions. Planning on using ER70S-6.

I have the back 6 feet of a 1078A1R. Planning to use 3.5 feet of it to extend the frame.

I attached two pictures showing two options for how I could cut the frame. I am leaving the rear frame cross piece (that the hitch connects to) so I do not have much frame to shape on the truck. The square cut would be easier. This is behind the rear tires so torsion is limited to towing or my camper box.

I plan to plate the inside and outside. Thinking of thru bolts.

Do you see any concerns?