Has anyone had a 4340 stub axle break off at the theads?
I have attempted to contact Joe from Chequered Flag Racing / Modern Motorsport as this is the stub axle he sells, but I have not heard back, I know he is on this forum so I hope to responds.
The stub axle was purchased this year and has only done 30 miles
The failure point is not under load with engine torque or torque forces caused by sticky tires. The only failures I have had with standard stub axles is the wheel flanges failing.
The nut was not over torqued and CV axle is not too short and pulled the threads off, there is more than 1.5 inches of plunge extension left and my suspension has very little droop
My analysis of the failure.
1. Design. The threads are machined all the way to the step causing a large stress riser at the failure point, I have included a picture of the Modern Motorsport theads next to standard theads, You will see on the standard stub axle the threads stop well short of the step and have a nice radius
2. Hardness. I had the 4340 stub axle hardness tested, result was more than 51 HRC (Hardness Rockwell C scale)
Carroll Smith's book 'Engineer to Win' states 42-44 HRC range for E4340 hubs, axles and torsion bars, Aircraft landing gear are also made from 4340 and need to be in this range too.
Did I get an incorrectly machined and heat treated stub axle set?
If there are any Metallurgists out there I would like their opinion too and looking forward to hearing from Joe.