Welding Tips and Tricks

Welding a cast iron differential housing from a car, and I had to make a special steel mount for it. The mount has to be welded onto it, and no matter what I tried the Ni55 rod would break under stress (I would pound the mount with a 5lb sledge and the weld would break clean in half)
I had some 308L and my god, it held wonderfully. I beat the part really good and no cracks anywhere.

Is this going to fail on me down the road? High stress area. I peened the welds a bunch as well
No preheat, I just welded small sections at a time and it
It worked....but for how long?

Akraczek86 wrote:Welding a cast iron differential housing from a car, and I had to make a special steel mount for it. The mount has to be welded onto it, and no matter what I tried the Ni55 rod would break under stress (I would pound the mount with a 5lb sledge and the weld would break clean in half)
I had some 308L and my god, it held wonderfully. I beat the part really good and no cracks anywhere.

Is this going to fail on me down the road? High stress area. I peened the welds a bunch as well
No preheat, I just welded small sections at a time and it
It worked....but for how long?

There is no gaurentee with cast. 309 probably would have worked better. And is normally the go to when the ni55 will not suffice .


Personally I would never weld anything to cast iron and trust it in a drivetrain especially high stress areas .

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So should I cut it out and try ni55 again? Its very strong but I will cut it out if necessary. Theres two sides, and I believe I was welding at a better angle on the side that held. Should I order some 309L to be on the safe side? Already ordered some 1/8" ni55, I believe that the gap is a tad too large to cover up on the side that keeps cracking, I was using 3/32nd filler.

Akraczek86 wrote:So should I cut it out and try ni55 again? Its very strong but I will cut it out if necessary. Theres two sides, and I believe I was welding at a better angle on the side that held. Should I order some 309L to be on the safe side? Already ordered some 1/8" ni55, I believe that the gap is a tad too large to cover up on the side that keeps cracking, I was using 3/32nd filler.

What exactly is being mounted to the differential if I might ask. May help me to better answer your questions . I understand a tab of some sort . But what will be connected to the tab.

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If you look theres a mild steel "box" that you weld together, then weld it to the housing. Its for the torque arm that attaches to it from the transmission, and butts up to the housing (in most areas)
It sees flex forsure, but Im not sure how much

It is also reinfornced by steel thats actually bolted to the housing (look in 3 areas) which Im sure takes stress off of the welds.

I believe I had success. I welded the area again with the 308L that I had, and the results arent pretty, but I beat the area repeatedly with a 5lb sledge and no cracks whatsoever.

Dont laugh, but heres the weld (after I ground it down)
Look at the fusion between the housing and the square bracket. How does it look?

It may well have good impact strength now but the real test will be repeated in-service thermal expansion and contraction.
Obviously your choice of rod could have been better but take heart, we were always taught if you have different metals and you don't know what they are, use a stainless rod to get the job done at a pinch.

Thanks man. Im really embarassed to say I did that, but Im learning and I worked for HOURS to achieve that, seriously. Luckily that mount doesnt get that hot, so I should be in good shape

I've read Hastelloy-W/Super Missileweld/ER312 work great for applications such as this (dissimilar metals)

Washing Alloys ER312
Pinnacle Alloys ER312
Lincoln Electric ER312
Harris 03SMW Super Missileweld Rod
Hastelloy-W

Well, the problem is its a little late for that. This sucker is not coming out LOL. this filler is tough stuff! And I beaded up pretty good, its not going anywhere. I just really wanted to know what the torsional strength is on a weld like this?
It will see some strain, as the torque arm coming from the transmission will be pushing down on the mount.

Should have asked first, lol. Good luck with the project.

Once a weld has cooled and has not cracked, is it good? Or do I still need to worry about thermal expansion and contraction cracking the weld under load?

I'da peened it with s noodle gun while it was hot but you'll be ok. I use 312 also for that application. Good running electrodes for that app

I peened them with a bolt (yes, a bolt) that had a small OD and peened the welds using my 5 pounder, hitting the bolt while they were still hot.

Time for a peening hammer!

Thermal expansion cracking is always a problem. It has more to do with the extreme range of temperature swings it will see and the frequency of the thermal cycling. IE something that’s going to get hot and stay hot for days or weeks at a time even if it’s seeing a 300-500 F temp rise will be less likely to crack then something that only sees a 200 F temp rise but cycles temp changes several times a day. Temp range of the swing depends on the material welded. Dissimilar metals are more prone to cracking then a base metal welded with an identical filler. It’s more a question of is it good enough for what your using it for.

I know it's a little late but I guess I'll ask , did you by any chance spark test the housing to be sure its cast iron and not cast steel ?

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As a general rule and from what i've seen.

Thermal stress, expansion & contraction and so forth IS the main concern in things like this.

I've done some automotive stuff, stuff for motorcycles, hot water, boilers, etc. Down the road it COULD be a problem and it could not. Stainless is notorius for it's flex which is why it's such a good choice for cast because it allows the cast to do what it needs to do and the Stainless just goes along with it.

Once the 2 heat and expand, we can only hope they do it at the same rate or it will crack and that's where the concern is, same for when it cools and contracts.