How to Shift a Fuller 13-Speed Transmission

Written by kelvin hayes
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How to Shift a Fuller 13-Speed Transmission
Truck transmissions use auxilliary-style transmissions to allow for overlapping shift patterns. (line of trucks 1 image by Aaron Kohr from

The 13-speed Eaton-Fuller heavy-duty truck transmission is designed to pull heavy loads while conserving fuel via an overdrive gear splitter. Like many other truck transmissions, the Fuller 13 has a splitter valve that allows the driver to place the transmission in "low" for starting off the line, "Dir" (direct) for high-gear (mid-range speeds) and "OD" for overdrive for fuel conservation at highway speeds. While it seems confusing, shifting a 13-speed splitter is simple once you've mastered the shift pattern.

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  1. 1

    Start the engine with the transmission in neutral and bring the air pressure to normal, a process that is done automatically as the vehicle idles.

  2. 2

    Set the splitter valve to low range by pulling the valve switch on the gear lever nob to the rearward Low position.

  3. 3

    Depress the clutch pedal with your foot and pull the gear lever to the left and down. This far left and rearward position is your Low gear. Note that you only use the Low gear position when your splitter valve switch is in the Low range position as well.

  4. 4

    Release the clutch pedal gradually while simultaneously depressing the accelerator and until the truck RPM requires the next gear to avoid reaching the RPM red line.

  5. 5

    Depress the clutch halfway and shift from low position into neutral, releasing the clutch again. Then immediately depress the clutch again and shift upward into first gear, releasing the clutch as the shift movement is complete. This technique is called double-clutching, and it helps to match the speed of the transmission gears with the engine for improved transmission longevity. Again, as the engine RPM rises, depress the clutch pedal halfway, shift down (straight back) into neutral, release the clutch, depress the clutch quickly and pull straight back again to second gear. Release the clutch once the movement is complete. Repeat this double-clutch process while pushing up, to the right and up again into third gear. From there, pull straight back into fourth gear. You're still in low range at this point.

  6. 6

    Move the splitter valve (selector valve) on the gear lever nob to the "Dir" position, which will engage the high-gear range of the transmission. This is done just prior to your shift from low fourth to the next gear, high fifth.

  7. 7

    Double-clutch while moving the gear lever forward (neutral) over one slot and up, reaching fifth gear. This is the same position as first gear when you were in Low range. Shift straight back for sixth, up/over/up for seventh, and straight back for eighth gear ensuring that you double-clutch each time. Note that you may place the transmission in "OD" (overdrive) while you're in fifth, sixth, seventh or eighth gear, without use of the clutch, by simply moving the splitter valve from the "Dir" to the "OD" position. You don't have to use "OD."

  8. 8

    Flip the splitter valve to "Dir," and downshift from your current gear to the next lower gear. As you downshift, ensure that you continue to employ the double-clutch technique. It's important that you gear lever the positions of each gear, noting that first gear is found in the same position as fifth gear, second as sixth, third as seventh and fourth as eighth.

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