After my experiences, and reading other's experiences, I will never recommend anything besides billet shafts. "Hardened" shafts break all the time, and it doesn't only happen on high hp vehicles. I'm pretty sure the weight of the truck has alot to do with it.

 

I totally agree, especially with as much power as lot of folks here are putting through their transmissions and there are many more reasons to why a shaft may break than just sheer size and length, like has the shaft been drilled for oiling passages, how many machined steps are on the shaft and how large of a radius do they (have if any), is the shaft necked down after the splines, metallurgy and so on. Most of the time when we talk about necking down a shaft after the splines, it’s in a derogatory manor, but in all reality the end of where the splines are cut ideally should never end directly into the shaft. The major deal with necking down is that most manufactures pick a spline size and then neck down the shaft afterwards, when actually is should be performed in the opposite manor, the shaft should be of X size and then the splined end increased to the necessary diameter to machine them properly. I would imagine cost and machining complexity becomes more of a factor than top strength though. The bottom line though, is for a lot of applications the 4L60/65's as a whole are just not strong enough for the abuse we put them through in a full size truck.

 

<<<<<<<<<<<<<<<< Doesn't have a Billet shaft...

 

1Bear, after I posted, I thought I shoulda said torsional (or twist) whereas ductility is more likened to stretch or elastic properties. But u had my back. U posted before I could correct my error.

I'm w/. Roger, I believe the weight of our trucks has alot to do with it. But usu. some other factors weigh in too.