Manual Gearbox
A torque-trading machine
An engine only makes useful power in a narrow rpm band, but the car needs everything from crawling to highway speed. The gearbox trades speed for torque using pairs of meshed gears: low gears multiply torque for acceleration, high gears reduce engine rpm for cruising. In a manual box, you choose the pair.
What it does
Matches engine speed and torque to road speed by selecting between fixed gear ratios.
Bolted to the engine, under the floor just ahead of the cabin.
How it works
- The input shaft, driven through the clutch, spins a countershaft via a constantly meshed gear pair.
- The countershaft carries several gears of different sizes, each meshed with a partner gear that freewheels on the output shaft.
- Moving the shift lever slides a fork, which pushes a synchronizer sleeve to lock one freewheeling gear to the output shaft — that pair is now “in gear”.
- Synchronizer rings act like tiny cone clutches, matching shaft speeds before the teeth engage so the shift is silent.
- A small gear ratio (e.g. 3.5:1 in 1st) means the output turns slower than the engine but with 3.5× the torque.
Key numbers
| Typical ratios | 1st ~3.5:1 → 6th ~0.7:1 |
| Gear type | Helical (quiet, angled teeth) |
| Lubrication | Gear oil (75W-90 typical) |
| Efficiency | ~96–98% per mesh |
Warning signs of trouble
- Grinding on shifts — worn synchronizers or dragging clutch.
- Whining that changes with road speed — worn gear teeth or bearings.
- Popping out of gear — worn detents or fork wear.
- Stiff shifting when cold — wrong or degraded gear oil.
Maintenance & care
- Change gear oil at the specified interval (often 60–100k km).
- Don’t rest your hand on the shifter — it preloads the forks.
- Always fully press the clutch when shifting.
Frequently asked questions
What does the manual gearbox do?
Matches engine speed and torque to road speed by selecting between fixed gear ratios.
How does a manual gearbox work?
An engine only makes useful power in a narrow rpm band, but the car needs everything from crawling to highway speed. The gearbox trades speed for torque using pairs of meshed gears: low gears multiply torque for acceleration, high gears reduce engine rpm for cruising. In a manual box, you choose the pair.
What are the signs of a failing manual gearbox?
Grinding on shifts — worn synchronizers or dragging clutch. Whining that changes with road speed — worn gear teeth or bearings. Popping out of gear — worn detents or fork wear. Stiff shifting when cold — wrong or degraded gear oil.
How do you maintain a manual gearbox?
Change gear oil at the specified interval (often 60–100k km). Don’t rest your hand on the shifter — it preloads the forks. Always fully press the clutch when shifting.