Honda H5

Honda's first five-speed automatic, built from 2000 to 2015 and fitted to almost everything the company sold with two pedals — Accord, Odyssey, Pilot, Civic, CR-V, Ridgeline, Fit, the Acura MDX and RDX, and even the Saturn Vue.

It is the one transmission on this site that is not built like the others, and everything else about it follows from that. Every other automatic here — the ZF units, the Aisins, the Toyota U-series, the Mercedes — turns power through planetary gearsets. Honda's does not. It uses gears on parallel shafts, permanently meshed, each engaged by its own hydraulic clutch — the layout of a manual gearbox, with clutches doing the work synchros and a driver would otherwise do.

The reason is a patent. Honda could not license the planetary designs, so it built something else, and what began as a constraint turned into a set of genuine advantages: the ratios work independently, so a failure in one gear does not necessarily disable the whole gearbox; the unit is compact; and first gear can be reached from outside the case, which makes some repairs far cheaper than they would otherwise be.

The same architecture also set a ceiling, and Honda hit it. Because each ratio needs its own pair of gears and its own clutch, adding a speed adds length and weight rather than being absorbed by a cleverer gearset. Five is as far as the design goes. That is why the story of this gearbox ends where it does: Honda went to planetary designs and to bought-in units afterwards, and the ZF 9HP on this site carries the later Pilot, Odyssey and Acura applications that this one used to have. The handover is visible in the two pages' car lists, and it falls exactly on a change of generation.

There are effectively two H5s and the difference matters when buying one. The early units run three shafts. They were later redesigned around a stronger case and four shafts, arriving with the 2005 Acura RL, and the four-shaft version is markedly more durable — the three-shaft ones carry the failure rate this family is remembered for.

What actually goes wrong, in the order the trade meets it:

• The third-gear clutch pack, which wears early. This is the defining failure. The friction material it sheds does not stay put — it circulates, blocks fluid passages and turns a worn clutch into erratic shifting throughout the gearbox. Honda's own improvement was to add an oil jet to feed that area better.
• Second gear overheating, which in the worst cases seizes the transmission outright rather than degrading gently.
• The one-way clutch between first and second, which is vulnerable to hard, aggressive shifting in a way the rest of the unit is not.
• Pressure switches and blocked solenoid screens, which produce shift faults that read as mechanical and are not.

The honest summary for somebody looking at a used one: the reputation is real, it belongs to the earlier three-shaft units and to the third-gear clutch above all, and the later four-shaft cars are a different proposition. Fluid is the whole of the preventable half — Honda's own ATF, changed rather than left, because the failure that defines this gearbox works by putting debris into the fluid and letting the fluid carry it everywhere else.