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Discussion Starter · #1 ·
So i went down to a local metals engineering shop to get my input shaft cryo treated...The guy was asking me what it was made of and all this other stuff and he was like well i can test it for you to see how hard it is and then you can make a decision.


Im guessing this on a rockwell scale but it was 49/50 he said it is about as hard as your going to get. no need to get it treated, so if these shafts are so hard why have they been breaking?

Also how can places be selling the input shaft for the 4500 and say
"YOU BREAK IT (TWIST IT OFF), WE'LL BUY IT!
*GUARANTEE DOES NOT COVER BROKEN OR DAMAGED GEARS. ONLY A TWISTED OFF SHAFT. "

from Pure Diesel Power why cant we get one for our transmission?
 

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They break because you put more torque and abuse through them, then they can stand.
 

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If your breaking an nv5600 input shaft then you are really getting abusive. Those shafts are wicked strong and can put up with a lot of beatings but eventually everything has a breaking point. Even billet shafts for autos can snap after repeated abuse.
 

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The early shafts where known to break under heavy loads. Dodge did it in 150k miles with 20k lbs. However the early NV5600 had the same size input shaft as the NV4500. Later NV5600's have stronger shafts.

The Rockwell test is only part of the equation. Hard metals tend to be brittle and snap rather than bending or twisting. The overall design of the input shaft is the deciding factor. Re-engineering and removing as many stress risers as possible would be the best route it sounds.

Personally I can't even see why anyone would want a billet shaft unless the shaft was re-designed to improve the high stress areas.

However I think if you don't excessively abuse this one it should last some time.
 

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What NV should have done was made it into a stock 1 3/8 with a 40 spline. I sure as hell doubt people will break it then...oh and made out of 300M.
 

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Discussion Starter · #7 ·
thats the thing i really havent abused my truck i have done a few truck pulls and what not no launches at all and i was just passing a car when it let go
 

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When the shaft broke and when it started failing are separate occasions. A week or two months ago during a FUN event is when it was failed. Hardening is probablly of no assistance. Cleaning stress areas of sharp edges will perhaps help. JMHO
 
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