EDIT: The linked question does not address any of the three subquestions listed below. This question is about the mechanical repercussions of a car rolling the wrong way, the linked question is a discussion on parking techniques for manual vehicles. Parking techniques are mentioned here only as motivation for the question.
A car's engine is turned off, and the engine, transmission, and wheels are all connected because the clutch is engaged and the transmission is in gear. The car is forced to roll in a direction opposite of the intended direction of the gearing, for example by being allowed to roll down a hill that is steep enough that gravity overcomes the compression of the engine.
- How would this affect the engine?
- How would this affect the transmission?
- Do modern manual transmissions resist movement in the wrong direction in some way, or is the resistance entirely a function of the engine compression?
This question was motivated by often conflicting advice I hear about parking a vehicle with a manual transmission. Some advice recommends using the first or reverse gear depending on the direction of the incline, some recommends only using the gear with the highest ratio.
It seems to me that selecting a gear depending on the direction of the incline would be done with the safety of the internals of the vehicle in mind in the case of an absolute worst-case scenario, which got me wondering just how much damage rolling in the wrong direction could cause (ignoring the devastation a runaway vehicle rolling down a hill would likely already cause).