The basic form of a motorcycle's manual transmission is to change gear combinations by rotating the shift shaft with the force of the shift pedal. Whether or not there is a link between the shift shaft and shift pedal depends on the model, but if there is a link, the pedal height may be adjustable within a slight range. The adjustability is convenient, but be aware that exceeding the proper range may cause problems.
Even a shift pedal with a direct shift shaft connection requires caution.
In some models, the height of the brake pedal, as well as the change pedal, can be fine-tuned. For this model, remove the heel guard that protects the master cylinder.
The pedal height is changed by the master cylinder pushrod locknut. Be careful not to lower the locknut too far (raise the brake pedal height too high) or the pedal and rod will come off. The adjustment range is a few millimeters.
If the brake switch is built into the brake pedal itself, the timing of the switch activation should be adjusted to match the change in pedal height. If the pedal is lowered, the switch position is lowered, and if the pedal is raised, the switch is raised as well, thereby optimizing the timing of the brake light illumination.
Shifting gears in a manual transmission is done by turning the shift shaft, which comes out of the engine, clockwise and semi-clockwise at a fixed angle to rotate the shift drum. When the clutch is held and the shift pedal is depressed, the shift shaft rotates, turning the shift drum at the end of it, and the shift fork, which operates along a groove on the outer circumference of the shift drum, changes the transmission gear combination as desired.
The relationship between the shift pedal and the shift shaft is important in converting the force of moving the shift pedal to the upper limit into rotation of the shift drum, like a seesaw. If the shift shaft cannot rotate the shift drum, either clockwise or counterclockwise, the gearshift cannot shift.
When the shift shaft is activated, the pawl on the end of the shift shaft hangs on the pin of the shift drum and pulls or pushes the pin to rotate the drum. Therefore, if the angle of rotation of the shaft is insufficient for the amount of shift pedal operation, the shift drum will not rotate enough, and the transmission gear combination cannot be changed, i.e., gear shifting will not be possible.
The shift pedal, on the other hand, influences the operability and comfort of the rider. The height of the footpeg and shift pedal is set to the greatest common denominator for most riders, but the toe may be too high or too low, depending on the rider's build.
When combining the shift pedal and shift shaft, some models have a built-in link mechanism between the two, while others are directly connected. In either case, the shift shaft and shift pedal may be shifted to a different position in order to prioritize pedal operability.
What we need to pay attention to here is the relationship between the amount of pedal pressure and the rotation angle of the shift shaft. Have you ever had a problem where you lowered the pedal because the toe was too high in the normal position, and now you have more room in the position but it is harder to shift? In this case, the pedals may be interfering with the chassis or engine, or the height of the footpeg and pedals may have changed, making it impossible to stepped on the pedals firmly.
Adjusting the shift pedal is important to reduce discomfort when riding, but the positional relationship between the seemingly simple shift shaft and shift pedal is surprisingly delicate and requires attention.
- Point 1: Set the shift pedal so that the shift shaft rotates at the same angle each time when shifting up and down.
Pedals with links should be adjusted so that the shift lever and shift rod are at 90 degrees
When changing the pedal height in a link-type shift mechanism, in which the shift shaft and change pedal are connected by a shift rod, the first step is to loosen the lock nuts on both ends of the shift rod. Since one side has a right-hand thread and the other side has a left-hand thread, the direction in which the nuts are turned is opposite to each other.
Since the shift shaft and shift lever remain in the same position, it will be understood that the shift pedal will gradually lower as the distance between the rods widens. If you keep turning the rod more than the threaded part of the rod, it will come off from the ball joint. When removing the shift lever from the shift shaft, the shift rod angle can be correctly restored by marking the set position of both in advance.
A shift mechanism that incorporates a link is useful for adjusting the positional relationship between the shift shaft and shift pedal, especially in terms of height. In models where the shaft and pedal are directly connected, the distance from the footpeg to the pedal is naturally limited. Placing a long pedal between a wide distance between the shaft and the footpeg will inevitably increase the stroke of the pedal.
If a shift rod with sufficient stiffness is placed here between the shift shaft and the shift pedal, the distance between the shaft and pedal can be separated without increasing the pedal stroke. It is easy to imagine a rearset for adjusting the riding position.
Linked pedals with a shift lever built into the shift shaft and a shift rod connecting the shift lever to the change pedal often incorporate ball joints at both ends of the rod as well as an adjuster to adjust the overall length. By increasing or decreasing the rod length with the adjuster, the height of the change pedal can be changed, which is useful for adjusting the riding position.
However, it should be noted that overconfidence in the adjustment mechanism may adversely affect the operability. Specifically, it is important to keep the angle between the shift lever and shift rod at 90 degrees. As explained earlier, the shift shaft rotates clockwise and counterclockwise at a fixed angle to turn the shift drum and change gear combinations. The shift lever, which is actuated by the shift rod, must also operate at a certain angular width, like a fan.
At this time, if the angle between the shift lever and shift rod is 90 degrees, the angle of rotation of the lever will be within a certain range regardless of whether the rod is pushed or pulled. However, if the angle between the two is outside of 90 degrees, the shift lever angle caused by pushing and pulling the rod will not match, and either shifting up or down may not work properly.
However, the adjustment range of the shift rod may not be able to absorb the problem and the angle may become incorrect depending on the set position of the shift shaft and shift lever, so we cannot be optimistic.
If the height of the footpeg and shift pedal is given too much priority and the angle of the shift lever and shift rod is overlooked, the driver may find it difficult to shift gears after starting to drive. It is important to confirm not only the style but also the functional feasibility in advance when installing custom parts.
As a side note, I would like to mention the threads on both ends of the shift rod. Some riders may have seen how the shift pedal height goes up and down by loosening the lock nuts on both ends and rotating the rod itself, but have you ever wondered why it goes up and down? However, if both ends are right-hand threaded, turning the rod only moves the threaded part of the shift lever and shift pedal ball joint in parallel, and the distance between them does not change, so the height of the pedal does not change.
The reason the shift pedal height changes by turning the shift rod is that the direction of the screws is opposite at both ends of the rod. The general screw is called a right-hand thread, and turning it clockwise moves the screw to the back. In contrast, the left-hand thread is counterclockwise and the screw goes in the back.
By placing screws with opposite directions of rotation at both ends of the rod, when the rod is turned in a certain direction, the screw on one side goes in the back, the other side also goes in the back, and when the screw on one side is pulled out in the front, the other side also moves out in the front. This changes the length of the rod and the height of the shift pedal.
Therefore, when loosening the shift rod lock nut, pay attention to the direction of rotation. The nut on the right-hand thread side can be loosened by turning it counterclockwise, but turning the nut on the left-hand thread side counterclockwise in the same direction will only tighten it tighter and tighter and will not loosen it. The lock nut for the left-hand thread may have an identification mark, so it is a good idea to check it before making adjustments.
- Point 1: In the case of a shift mechanism with a link, set the shift rod and shift lever so that the angle between the shift rod and the shift lever is 90 degrees.
