I have my frame stripped for the 36 and I took it to the car wash to ridd it from the years of grease etc. Now I built this thing back in the 80's, so it has been on the road quite a while. After degreasing I noticed a crack in the front crossmember, where the locating hole is for the front leaf spring. It is cracked in both directions coming out of the hole. So I thought , "I'll weld that up real quick"....but, then I started wondering if it might just crack again in the same area. What can I do to relieve some of the fatique? If I heat it before welding would this somewhat anneal the area and make it soft if I let it cool slowly?
I don't know about the annealing but you may want to stop drill the crack. Just drill a small hole at the very end of the crack to relieve the stress crack and then weld it.
best bet is to drill an 1/8 hole at the end of the crack then make a plate with 1/8 over sized holes and weld around the hole thing and holes.
common area for cracking, the entire load of the front end... all kinds of dynamic stresses are imposed under... blah blah blah.. I seen it a bunch, on my last build the A frame's front cross member was one cranky little crack baby I said cut it out! so I did. and welded a nice well behaved piece of mild steel in it's place
Yes drill a hole at the end of the crack. For a little more insurance v out the crack with a grinder then weld it up. I did this to a buddies A 8 years ago and it is still running strong.
Root, The problem you describe is very common to these old ford cdoss members and should more properly be called stress relief cracks rather than "metal fatiuqe" Those locating holes are square and all the stresses to the cross member are concentrated at the corner of the hole thus causing the cracks . The term "annealed" really refers to softening hardened high carbon steel and doesn't really apply to mild steel used in the cross member. It won't hurt to heat and cool the steel be for welding but it probably won't do any good eighther. When steel is welded the molten weld metal shrinks when it cools and shrinks more than the surounding parent metal thus causing stress to the parent metal just outside the weld zone which can be several thousand pounds per square inch. This tress can be relieved by peening the weld bead while still hot, preferably whike still red, similar to hammer welding sheet metal. Now to answer your original question. If I were doing your repair I would, as others have suggested, drill a 1/4" hole just beyond the crack, "v" out the crack, weld it up, peen the weld ,grind it smooth and you should be good for another 60 years. Ted
What is often thought of as mild steel nowadays- is not what Henry made his frames and bumpers from......not certain of exact alloy but not soft by any standards. They had a degree of hardness or spring to them .-all you have to do to convince yourself of this quality is get yourself some repro frame rails and crossmembers-Now those ARE made from mild steel!!
I did this on my Deuce frame. I did it to lower the car but I think it makes sense to replace the fatigued metal with new. Out with old and in with the new.
Ditto, and since using a later frontend with wider spring, I made the slot wider. I believe the cracking is mainly from loose Ubolts, along with extremely bad road conditions early in life. I don't think it will re-occur after it's fixed as long as the woven pad is in there and it's tighter than shit. http://directimagehost.com/is.php?i=60151&img=Dsc00961.jpg Then re-check occasionally, I changed my truck springs, carried the breaker and cheater, reefed on them every day til I couldn't get anymore. Just do them the first time, leaves will start to break.
The cracks are there because the metal work hardened and became brittle. Repeatedly straining steel causes it to become brittle through work hardening and it eventually cracks. The whole area around the crack has been work hardened, and needs to be repaired. I think the most effective and easy way to properly repair the damage is to totally remove the affected metal and replace it with new, thicker mild steel. Once you are done welding, run the torch over the whole area and get it do a dull red glow to stress relieve it. And it will be better than new.
I'd just bevel the cracks and weld them. Start on the downward facing end of the cracks and weld to the hole. Maybe, even weld a quick pass around the hole. Then, plate the top. I doubt if you can plate the sides, as the U-bolts won't fit over them. Just weld the sides of the plate... NOT the ends which go crossways on the crossmember... If you bevel the cracks and take care when welding, you won't even need to grind much of the bead. That's just me.... JOE
Wow, lots of info, some accurate and some not. As the official HAMB metallurgist, those cracks are fatigue cracks most likely. The metal is not any weaker than the day it was made. Fatigue is cracking below the yield point under cyclic stress. You can stop drill the crack, grind out the crack and weld it shut. You do not have to anneal the metal, it is not work hardening that causes the cracks. The cracks are from tens of thousands of cycles of the suspension loading and unloading against the crossmember. That is fatigue cracking. Fatigue is NOT the metal getting weaker, as your muscles do when you do significant work and you can not lift the same amount. The metal is the same strength. Work hardening can cause cracks, but those require bending the metal past yield. Your situation is not bending past yield, if it was the part would be very distorted in shape, which it is not.
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