Manual Transmissions: Do They Use Fluid? Manual transmissions rely on gear or motor oil to lubricate gears, synchronizers, and clutches. Most use 5W‑30 motor oil or 75W‑90 GL‑4 gear oil, ensuring smooth shifting and protection against wear. It is essential for longevity. Now.! Definition of Transmission Fluid in Manual Systems In a manual gearbox, the fluid is not a single […]