Welding tubes on AMC20 - question - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-10-2001, 10:13 AM
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Welding tubes on AMC20 - question

I'm getting set to weld the tubes to the housing and have a stupid question. Does the gear-lube have to be drained? I will need to drive to a buddies shop to weld, so I need lube in it. I understand that 3-4 1" welds are better than all the way around the tube, anything else to be aware of?

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post #2 of (permalink) Old 05-10-2001, 11:22 AM
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Re: Welding tubes on AMC20 - question

I think have heard from many offroad magazines that welding the tubes on a model 20 is not the thing to do and actually makes the diff weaker. But if you are set on doing it I would not think that you need to drain the fluid unless you cook it when you make the welds.

post #3 of (permalink) Old 05-10-2001, 11:23 AM
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Re: Welding tubes on AMC20 - question

You do know about the housing being cast and need to be preheated to around 500F, don't you? The lube could stay if you go slow I guess as long as the breather hole is open.


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post #4 of (permalink) Old 05-10-2001, 12:19 PM
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Re: Welding tubes on AMC20 - question

I have to agree with Spike. If you look at the way they are made, It would take a lot to spin a tube. I have no doubt that something else would break before the tube spun.

John...southern CA
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post #5 of (permalink) Old 05-10-2001, 02:04 PM
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Re: Welding tubes on AMC20 - question

I'll jump in on this one. I am still of the opinion that it is not good to weld your tubes to the housing. OzarkJeep and I went back and forth on this a little bit, and I was going to build a finite element model on my computer to see what kind of stresses develop, but I haven't had time to do it yet[img]/wwwthreads_images/icons/frown.gif[/img](Ozark, if you are reading this, I haven't forgotten). Ozark was going to take a 10-bolt and weld it and do some abuse testing, but I haven't heard the results yet. The reason I don't think that it is a good idea, is because of the differences in the materials between the housing and the tube. The tube is probably not a real high alloy steel, and the housing is probably a maleable cast. The housing is a lot more rigid that the tube, and has to be to keep gears in tolerance. Even though the housing is maleable cast, it is still more brittle than the tube. With the tubes pressed into the housing and plug welded, it allows the tube to flex, and even move a little in the housing (we are talking maybe less than a thousanth of an inch, nothing big). Also, by welding on the top and bottom of the tube you create what is called a stress concentration in the tube. A stress concentration is a spot of weakness. Think about taking a paper clip, and putting it in a pair of side cuts and just denting the clip. When you bend this paper clip it will fail at the notch just created. A weld can have the same effect. The problem will be more pronounced in the welds on the bottom. A good way to illustrate this is with a block eraser (like the pink ones used in grade school). Draw a box on the top and bottom of the eraser and then bend it. You will notice that one box gets shorter and the other gets longer. The longer box would be on the bottom of the axle, which means that in essence your axle tubes actually stretch a little on the bottom and compress on the top. The weld against the housing will limit some of this bending and transfer the load into the housing. This would be fine, but the housing is designed to not bend. Plus, the cast does not behave as well when it is loaded in tension. With the tubes welded either the housing or the tube will fail prematurely, even if it is a series of short welds. I would bet that the housing will crack around the weld. If you are looking for a stronger axle, I would recommend a truss. Just my two cents, actually as long as this was, I guess it is probably closer to $2.50[img]/wwwthreads_images/icons/wink.gif[/img].

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post #6 of (permalink) Old 05-10-2001, 02:29 PM
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Re: Welding tubes on AMC20 - question

That's what I like - a completely scientific answer.
Who knows the best place for an AMC20 truss? Or, better yet, the best way to build one?

post #7 of (permalink) Old 05-10-2001, 03:54 PM
 
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Re: Welding tubes on AMC20 - question

I havent had time to stress test the 10 bolt housing yet jeepfiend.

I think your right htough, a well designed truss is better than welding the tubes.


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post #8 of (permalink) Old 05-10-2001, 04:26 PM
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Re: Welding tubes on AMC20 - question

Jeepfiend, that was one of the best answers I've ever read.

post #9 of (permalink) Old 05-10-2001, 05:26 PM
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Re: Welding tubes on AMC20 - question

Kutyafal, You can weld cast to mild useing a low hydrogen rod and backstep method without heating the housing. You can also weld cast with a high nickel rod useing the same method without preheating. I have to agree with Jeepfiend that the axle should not be welded.

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post #10 of (permalink) Old 05-10-2001, 08:30 PM
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Re: Welding tubes on AMC20 - question

As I understand it, the problem with welding the tubes is that it weakens them in the area of the weld. The best solution I have heard of is not to weld the tubes but to weld to the tubs through the locator hole and fill the hole with metal. It is possible to toque the diff with one peice axles installed. My friend did so and broke a u joint. It was kind of funny to drive behind him with the pumpkin pointedup one minute and at the ground the next.

Welding in a circle around the tubes creats a heat stress in a ring all the way around while welding only the locator hole prevents torquing while not forming a convenient stress to break on.

bandhmo

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