In the 5MX65 five-speed manual an internal defect can mean that first gear or reverse will not engage: the lever goes across but the gear does not take, or the lever will not move that way at all.
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The defect is inside the gearbox, so the repair means removing and opening the unit.
What to check
- With the car stationary and the engine running, select first and reverse: both must engage without snagging
- Pull away in first and reverse as well: the gear must not jump out under load
- Try it from cold too: the shifting fault is more obvious then