by TJ Hinton
Jupiterimages / Stockbyte / Getty Images
Motorcycle transmissions share many common design characteristics across the spectrum of manufacturers. With few exceptions, most are constant mesh manual transmissions that use a hand or foot actuated clutch. These common design features make it possible to perform basic troubleshooting procedures to diagnose certain problems without disassembling the transmission. If troubleshooting identifies a transmission problem and you don’t have the tools, resources, and experience to fix the problem, have a professional repair it for you. It’s very easy to skip a spacer or put a part upside down if you’re unfamiliar with the job, and any transmission failure can cause a dangerous driving condition if you fail at high speed. Make sure the transmission lubricant is fresh and in good condition before troubleshooting to avoid creating or aggravating symptoms.
Change mechanism problems
The shift mechanism translates the movement of the shift lever into a movement of the shift slider within the transmission. Typically the shift mechanism is a spring loaded cam or drum shaped device that operates the sliders through the shift forks. Friction caused by wear, damage, or corrosion can cause shifting problems, such as rough shifting, inability to locate the neutral seal, and worst case, the inability to shift at all. A bad mechanism of change will manifest itself with these symptoms. You will feel them through the gear stick. The gearshift ratchet return springs can fail, causing a loose gear lever and a moody or non-functioning gear lever.
Dogs, Pockets, Shift Forks and Sliders
The shift forks connect the shift mechanism to the sliders. A bent shift fork will cause your corresponding slip gear group to jam in one gear and then have insufficient dog-to-pocket engagement in the other gear in the group, with the other gears performing as expected. Use on dogs and pockets will allow the slider to activate, but may allow it to slip out of gear when subjected to the heavy loads of rapid acceleration or compression braking. Indecisive shifting, a worn shift mechanism, bent or worn forks, and worn gear spacers can all cause wear on dogs and pockets. If you determine that your dogs and pockets are used, then you should modify your shifting technique or look at the other components mentioned above to avoid further damage.
Gears and bearings
A solid diagnosis can help determine if bearings or gears are worn beyond service specifications. As the gears wear, the gap between the teeth or the gear set increases. If gear backlash becomes excessive, you will hear gear crash sounds, particularly when shifting and initially releasing the clutch, or when momentum changes during compression braking. Bad bearings, on the other hand, will produce a grunt when the transmission is spinning. You can tell which heading is bad by the other conditions present when you hear the sound. If you hear it when the clutch lever is out, but the transmission is in neutral, then one of the main shaft bearings is damaged. If you hear the noise only when the transmission is in gear with the clutch out, then one of the countershaft bearings is bad. If you hear the noise all the time, regardless of the clutch position with the engine running, the clutch hub bearing is damaged. Motorcycles equipped with a primary drive chain between the engine output sprocket and the clutch hub can make this noise if the chain is too tight and loads the clutch hub bearing. Be sure to check the chain tensioner adjustment according to the manufacturer’s instructions before breaking it to inspect the clutch hub bearing.
Some other conditions can cause the same symptoms as the problems described above. For example, clutch resistance can cause jerky shifts and excessive gear shock. The solution for this can be as simple as a bad adjustment of the clutch or the cable of the …