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A vehicle gear shift

What Kind of Transmission Fluid Should I Use?

Automatic transmissions provide a more convenient driving experience, which makes them far more popular than manual transmissions in the U.S. According to research by CarMax, 96% of Americans drive cars with automatic transmissions. This means that fewer drivers and mechanics are familiar with manual transmissions. When your vehicle needs maintenance, you have to know which transmission fluid to use.


Manual Transmission Fluid

Traditionally, manual transmission fluid is much thicker than automatic fluid. The main differences between the fluids used for manual transmissions align with their intended functions. Here are the responsibilities of manual transmission fluid:

  • Facilitating smooth shifts: Manual transmissions have built-in synchronizers that equalize the speed of the gears that are being engaged, which makes for an effortless shift. The two main components of the synchronizer, the sleeve and the synchronizer (blocker) ring, work together to ensure a successful gear shift. The friction between the synchronizer ring and a cone on the face of the gear matches their speed. The smoothness, or feel, of the gear shift is related to the lubricant's viscosity.
  • Minimizing wear: Quality transmission fluid should actively fight against damage to the synchronizers and the unit as a whole. Synchronizers are typically made of brass, which isn't compatible with certain lubricant additives. The thickness of manual transmission fluid helps reduce friction and heat, which can cause deterioration.

Automatic Transmission Fluid

Automatic transmissions and their fluids are a little more complicated⁠. Automatic transmission fluid performs several functions that include managing friction levels and preventing wear. Additional duties of the fluid include:

  • Functioning as a hydraulic fluid: Automatic transmissions use pressurized fluid during gear shifts by sending an electric signal to the correct shift solenoid. The solenoid sends fluid through passages in the valve body to engage the selected gear. This fluid squeezes a set of plates inside a clutch pack to direct the engine to the transmission output shaft and send power to the wheels.
  • Reducing heat: High temperatures can be severely damaging to automatic transmission fluid. It breaks down the substance and creates a sludge that can clog passages and make shifting difficult.

Selecting the Right Transmission Fluid for Your Vehicle


Sometimes, automatic transmission fluid can be used in manual transmissions, but you should consult a transmission professional and the car's manual before purchasing transmission fluid to service your vehicle. A professional can provide maintenance tips to ensure that your vehicle's transmission is functioning properly and help extend its lifespan.


Not everyone feels confident performing maintenance on their own transmissions, and that's why Best Transmission offers automotive support for drivers in Jacksonville. We perform transmission maintenance on cars, trucks, 18-wheelers, and more while offering a 12-month guarantee on our work. Contact our expert technicians today by calling 904.783.4980.


Best Transmission

8139 Nevada Street Jacksonville, FL 32220


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