When can slippage occur in a manual transmission?

Slippage in a manual transmission is most likely to occur when the pedal free play is not adjusted properly. Free play is the distance the clutch pedal moves before it actually starts to disengage the clutch. If there is either too much or too little free play, it can cause issues with clutch disengagement.

If the free play is not adjusted, it can lead to situations where the clutch does not fully engage or disengage as needed. This incomplete engagement can result in slippage, where the clutch disc will not fully press against the flywheel when the clutch pedal is engaged, allowing the engine to rev higher without corresponding acceleration in the vehicle. Properly adjusting pedal free play is crucial for ensuring that the clutch operates effectively and prevents slippage during operation.

In the other scenarios presented, shoeing full engagement of the clutch, using gear oil that may be too thick, or the car being in neutral does not directly lead to clutch slippage the way improper free play does. These situations typically involve either functioning normally or engaging/disengaging the transmission as designed.