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In addition to that, the hardness you end up with must still be somewhat similar to the hardness of the mating components, otherwise hard part chews up soft part eventually. If you can't get much stronger while still in the same hardness range, then a stronger base material (at lower hardness) is needed. If the OEM shaft is already harder than the mating components, there's probably no room to increase.




Sorry man, not true. Nearly every planetary carrier on the planet is aluminum with steel shafts. Nowhere near the same hardness.


If they have a tight spline fit the impact loading is reduced and hardness matching becomes less of an issue.

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Also, its necessary to run a bronze gear (soft material) on a billet cam core (hard material). As I understand it, it's important that the two components actually DO NOT have the same hardness.


Keep in mind, bronze usually contains lead, which is a lubricant, so on a distributor gear that's a whole different ballgame.

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I wouldn't be afraid to try it. If the stock shaft may already break, what do you have to loose if this one breaks? I've been thinking of sending mine out for cryo treatment. I know some of the 4-cyl turbo guys do it...

You know the other thing I'm really surprised is that the 904 output shaft is weaker then the aluminum splines on the front planetary. I would have thought for sure that planetary would have stripped before breaking the output shaft...




As I don't deal with this every day, I reviewed the question with a guy that has been designing planetary components for at least 25 years, and there's truth in what both of us said. There's a lot of science (and a little magic) to material type, spline fit and hardness matches, and depending on a bunch of little details, sometimes hardness helps, sometimes it causes other problems -- and you won't know until afterward.

I stand behind my original line of thought, that possible failure of a 'home-brewed' shaft is a big gamble compared to the cost of an aftermarket shaft that has some real-world testing under its belt.