Chrysler NSG370

The six-speed manual in the Jeep Wrangler TJ and JK, the Liberty, and the Chrysler Crossfire.

It is a Mercedes-Benz gearbox, which is what the DaimlerChrysler years left behind and what nothing on a Wrangler tells its owner. So the useful literature is split across two worlds — Jeep forums and Mercedes parts catalogues — and a search in only one finds half of it.

Its recurring complaint is noise rather than failure. These are known for a gear rattle at idle in neutral with the clutch out, which is normal for the design and not a fault; and for a whine in fifth and sixth that owners find alarming and which is usually the gearbox behaving as built. The tell for a genuine bearing problem is that it rises with road speed in every gear, not only in the tall ones.

Where it genuinely wears it is the shift tower and the synchros for second and third, producing a crunch on a fast cold change. A crunch in every gear is the clutch not releasing — hydraulic, outside the gearbox, and much cheaper.

It takes a specific fluid. These want a synthetic manual-transmission oil to the Chrysler specification; a conventional gear oil makes the change notchy when cold and is often mistaken for synchro wear.