Renault JB / JC / PK / UN-1

Renault's transverse manual gearboxes — the JB, JC, PK and UN-1 families, and the M-coded variants of them.

⚑ Renault names one gearbox several ways — a family code, a variant code and a fitment code — so M5P and JB1 can be the same unit described from different catalogues. Establishing which system a code belongs to comes before any parts search, and it is the commonest reason a Renault gearbox order goes wrong.

These are light cable-shifted units and the linkage is the first suspect in almost every complaint: worn cables and a perished gearbox mount produce a change that feels like synchroniser wear and is not.

The UN-1 is the odd one — a longitudinal transaxle used in mid-engined and rear-engined cars, sharing its name with the transverse boxes and almost nothing else.

Fifth-gear and reverse selection problems are the pattern that recurs, and on the higher-mileage units they are usually the selector mechanism rather than the gears.