4-speed manual (4MT)
A four-speed manual gearbox — the simplest transmission ever fitted to a kei truck, found on the oldest eligible models.
How it works
A conventional four-speed manual gearbox with a clutch pedal. The driver selects gears through a floor-mounted or column-mounted lever. Found in older kei truck generations from the late 1980s through mid-1990s.
Pros and cons
Advantages
- ✓ Simplest, most reliable transmission type
- ✓ Full driver control — no parasitic power losses
- ✓ Cheap and straightforward to rebuild
- ✓ No fluid change schedule beyond gear oil
Disadvantages
- ✗ Only four forward gears — wider ratio gaps mean the engine spends more time outside its optimal RPM range
- ✗ Older technology — less common in newer trucks
- ✗ Top gear is shorter than a 5MT, so highway cruising is noisier
Maintenance schedule
| Item | Specification |
|---|---|
| Service interval | Inspect gear oil at every oil change; replace every 40,000–60,000 km or if dark/contaminated |
| Fluid specification | GL-4 75W-90 gear oil |
Common issues
| Issue | Severity | Notes |
|---|---|---|
| Synchromesh wear on 2nd gear | Minor | Common on high-mileage examples. Symptom: grinding when shifting into 2nd. Synchro rings are replaceable; catch it early. |
| Gear oil leaks | Minor | Check the output shaft seals and drain plug. Low gear oil causes accelerated wear on all internal components. |
Recommended for
Buyers targeting the oldest eligible trucks (DC51T, DD51T, early Acty) who want maximum simplicity
How the 4MT compares — and who should choose it
The 4MT is not a modern choice. It exists on the oldest kei trucks — the DC51T, DD51T, and early Acty — because those trucks predate the 5MT becoming universal. If you are targeting one of these older models specifically for its age (and therefore eligibility), and you want manual-transmission simplicity, the 4MT is what you get.
Compared to a 5MT, the 4MT has wider ratio gaps and a shorter top gear. In practice this means the engine spends more time near the top of its power band between shifts, and highway driving is noisier. Neither is a serious problem on a farm or trail truck that rarely exceeds 80 km/h.
Choose the 4MT if you want the oldest eligible trucks and manual simplicity. Do not choose it over a 5MT if both are available on the model you are buying — the 5MT is objectively better in every metric. On the DC51T and DD51T the 4MT is your manual option; that is the only context in which it should be your first choice.