Another brake question. It never ends…. But at least I’m learning as I go. The Pullman I’ve been working on broke a brake rigging rod. Apparently cracked sometime and finally broke. Is there a specific alloy for the round bar? Rod is slightly bent so weld-on splice likely won’t do, at least in my book.

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Well, we had an old brake rod in our scrap pile, and I cut a slice of it off for what I don't remember. I put it in the lathe, and started turning it, and found a hidden fissure right through the middle!

So I wouldn't put too much confidence in the quality of brake rod material.

In my infinite wisdom, I suggest 4140 heat treated...

This rod looked like it had a longitudinal crack that corroded into some kind of occlusion in the middle. The break didn’t look like a normal break you’d see when steel fractures like that under tension. It was kind of lumpy, almost crystalline. Acquiring a bend in that area didn’t help much, either. So yeah, not a quality piece.

It’s a 1921 vintage car. Don’t know the vintage of the rod.

The design requirements assume the material will be A-33, wrought iron. The yield strength used in design is 10,000 psi, giving a safety factor of about three. But actual construction these days uses A-36.

That explains the look of the broken ends. My brain didn’t even think “wrought iron”. If I recall somewhat correctly, it doesn’t like getting bent so that could ultimately explain the failure.

Expanding on Sammy's post, a major locomotive builder also listed 4140H as being a suitable material for this type of application.

PC

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After looking up the properties, I’m going to agree with David and Kelly. A36 is common, easy to work with and with the size of these rods - they’re huge compared to freight cars - I don’t see breaking it again unless the welds on the jaws are poor.

Thanks for your responses.