Disaster!!!!!

[RC-Monster Mike]

Snapped shafts happen from time to time, especially with a high torque motor and a heavy truck with a 1/8" shaft. You are also probably a bit unlucky! :)
To minimize this issue, make sure the pinion is as close to the motor can as possible when you mount it up. To eliminate the problem, run a 5mm shaft (although I have never heard of a lehner shaft breaking - they are hardened 1/8").