[gtobird]

Originally Posted by RAJ7395

He's my take on this.

One 3/8-24 fine thread grade 8 bolt dry torqued to 50 ft.lbs produces a clamping force of 7900 lbs. Torquing a 3/8-24 grade 8 bolt higher than 50 ft.lbs causes plastic deformation of the bolt. Plastic deformation causes the bolt to grow in length and shrink in diameter.

My guess is that reusing an already plastically deformed bolt is not recommended as the longer length may cause it to bottom out in the blind ring gear bolt hole and the bolt is weaken due to the decreased cross section.

You are on to something, but I don't think the issue is reusing a bolt that is plastically deformed from use or factory torquing. Rather, it may be because you can no longer torque it reliably after it's been used. Please allow me to explain.

Being a geek who did all sorts of physics experiments in college I had the opportunity to test the tensile strength of bolts and actually did the elastic to plastic deformation tests. Your point helped me remember that lubricating a bolt lowers the amount of torque you can apply to it. The theory is the bolt will turn easier with lubrication, but is still stretching at the same rate as it would without the lubrication. So, in essence you will reach the point of "plasticity" at a lower torque level. It's not a small amount either. It could be anywhere from 10% up to 50% depending on the type of lubricant that's used. Seeing that used carrier bolts would have been continuously soaked in one form or another of lubricant and likely some form of posi additive, it would be hard to predict just how much the applied torque would change on a used bolt. Even if you clean them well, they can still retain quite a bit of oil on them (and for that matter, so can the ring gear threads). All this to say, a given torque on a dry bolt will have a lower load than on a well oiled bolt and that could be yet another reason not to rely on "used" bolts.

[RAJ7395]

Originally Posted by gtobird

You are on to something, but I don't think the issue is reusing a bolt that is plastically deformed from use or factory torquing. Rather, it may be because you can no longer torque it reliably after it's been used. Please allow me to explain.

Being a geek who did all sorts of physics experiments in college I had the opportunity to test the tensile strength of bolts and actually did the elastic to plastic deformation tests. Your point helped me remember that lubricating a bolt lowers the amount of torque you can apply to it. The theory is the bolt will turn easier with lubrication, but is still stretching at the same rate as it would without the lubrication. So, in essence you will reach the point of "plasticity" at a lower torque level. It's not a small amount either. It could be anywhere from 10% up to 50% depending on the type of lubricant that's used. Seeing that used carrier bolts would have been continuously soaked in one form or another of lubricant and likely some form of posi additive, it would be hard to predict just how much the applied torque would change on a used bolt. Even if you clean them well, they can still retain quite a bit of oil on them (and for that matter, so can the ring gear threads). All this to say, a given torque on a dry bolt will have a lower load than on a well oiled bolt and that could be yet another reason not to rely on "used" bolts.

Sounds like the best answer yet! It only takes 30 ft.lbs of torque with a lubricated 3/8-24 bolt to achieve the same 7900 lbs of clamping force. 65 ft.lbs on an oiled bolt could very well pop the bolt head off.