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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.

If I had the type of car that needed a stronger shaft, I wouldn't risk saving $600 on a shaft against the colateral damage if an 'experimental' shaft had a problem whilst under power.



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

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.

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...