How do I diagnose a gear problem?

My car won't engage the reverse gear. What could be the problem? - Aloise N 

If the gearbox is manual and all the other gears operate well, the most likely problem is maladjustment of the reverse gear linkage (a rod between the base of the gear lever and the gearbox) which might be easily rectified.

Otherwise it could be a problem with a hard component inside the gearbox, which would require the gearbox to be removed and opened for repair. A badly worn clutch can also have a jamming effect. 

If the gearbox is automatic, the likely cause could be low fluid level or dirty fluid. If those are okay, then a faulty sensor or valve could be the problem, and again repair could require dismantling of the box.

The shift levers on automatics can also jam…because of a safety feature!

When the shift is in the Park (P) position, the vehicle is very effectively immobilised – the engine is disengaged and the drive wheels are locked. For safety, the car cannot start to roll – whether the engine is running or not and whether the handbrake is applied or not – when the lever is in P.

There is an additional safety feature to reduce the chances of the gear lever being accidentally knocked/bumped out of the Park setting into a Reverse or Drive position.    

When P is engaged, a lock pin (not unlike the bolt on the bottom of a door) drops into a slot and the lever cannot be moved unless a “release button” on the gear knob is purposely pressed and held in to lift the pin out of the slot. If the release button is faulty, you could be stuck in P. 

The remedy is to burrow through the plastic console at the base of the gear lever, and either repair or remove the pin mechanism. It is small, light and easy to disengage and can be tied in an “unlocked” position using a thin piece of wire.

In an emergency (e.g. you are on a railway line and a train is coming) you could “bypass/smash” the lock with sheer force on the lever, drive out of danger, and worry about the repair later.