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300M Alloy Stub Axle


BRAD D

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I was wondering if I just got some new stub axles machined of 300M exactly the same as stock 280Z. How strong would they be and how much it would cost? I have a machinist buddy that works at Bristol Aero Space, I wonder if he would make me some. What do you guys think?

 

 

300M is a low alloy, vacuum melted, steel of very high strength. Essentially it is a modified AISI 4340 steel with silicon, vanadium and slightly greater carbon and molybdenum content than 4340. 300M has a very good combination of strength (280 to 305 ksi), toughness, fatigue strength and good ductility. It is a through hardening alloy.

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You would also need to machine a matching set of companion flanges. Generally the metallurgy of the 27 spline stub axles are fine. They fail at stress risers (usually in the splines) or at the fusion weld of the axle to the wheel stud flange.

 

300M would be a good material choice although its probably a little overkill. You would also need to surface treat the areas where the bearings ride. I would be interested in a set with matching companion flanges if the splines were shot peened and polished after machining.

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Road racers break the wheel stud flange off the shaft. If youi're lucky that just means a trashed brake drum and a big spin. If you're unlucky, it means a rollover at speed as the wheel and drum go flying away from the car. 240/280 stub axles generally last about two years in a road racing environment before you'll start seeing cracks in the fusion weld. Companion flanges fail almost as frequently.

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