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Thumper · 10-20-2023, 02:13 PM

During downshift coming to a stop, even with the clutch pulled, if the part of the transmission connected to the spinning crankshaft which is idling (the input shaftcounter shaft-counterspinning shaft, or main shaft in the transmission) is spinning much slower than the forward spinning side (connected to the rear sprocket/wheel), the dogs on the side of the gear has to abruptly change the speed of the input shaft to go into the next gear as you downshift. This is the situation when the engine is idling, and the motorcycle is rolling to a stop. This shocks the transmission bearings, seals, dogs, and even the contact between the gears and the shafts. The input shaft spins even with the clutch pulled, and it is spinning slowly at idle.

It is not possible to precisely match the rpm of the engine to exactly the speed of the output shaft for a given gear every time, but the farther away it is, the more shock the transmission experiences. OK, you say it is worst going down to first, but that is the lowest gear so it makes some sense.

Ever seen someone rev the engine, pull the clutch, then slam it into first without waiting for it to return to idle. Yeah. LOUD crack. This is because even with the clutch pulled, the main shaft (counter spinning shaft) is spinning FAST since the clutch has some friction even with the clutch pulled, turning the main shaft/counter shaft, and the output shaft is NOT TURNING at all since it is connected to the rear sprocket and the wheel is not turning. Putting it in gear instantly stops the input shaft (breaks the clutch loose). That is a major shock to the transmission. Downshifting at speed with the clutch pulled is the same thing, but with reversed forces.

You have to shift! I know

But try to wait until the difference in the countershaft and output shaft (for the gear you will shift into) is as close as possible. It WILL get better as the transmission is broken in, or worse if the transmission is subjected to repetitive shock. The quieter the shift, the closer you came to matching the speed of these two shafts, for a given transition.

I usually put the engine in first gear, pull the clutch and break loose the clutch (rolling forward/back) BEFORE I start the bike (after warm up). Yes, I will actually turn it off after warm up and do this. So my transmission experiences NO shock at all when I do that. It is much gentler on the entire transmission. When you pull the clutch, the input shaft (main shaft/coutershaft) keeps spinning! Putting it in gear stops it from spinning, abruptly!

10-20-2023, 02:13 PM	#7
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,380	During downshift coming to a stop, even with the clutch pulled, if the part of the transmission connected to the spinning crankshaft which is idling (the input shaftcounter shaft-counterspinning shaft, or main shaft in the transmission) is spinning much slower than the forward spinning side (connected to the rear sprocket/wheel), the dogs on the side of the gear has to abruptly change the speed of the input shaft to go into the next gear as you downshift. This is the situation when the engine is idling, and the motorcycle is rolling to a stop. This shocks the transmission bearings, seals, dogs, and even the contact between the gears and the shafts. The input shaft spins even with the clutch pulled, and it is spinning slowly at idle. It is not possible to precisely match the rpm of the engine to exactly the speed of the output shaft for a given gear every time, but the farther away it is, the more shock the transmission experiences. OK, you say it is worst going down to first, but that is the lowest gear so it makes some sense. Ever seen someone rev the engine, pull the clutch, then slam it into first without waiting for it to return to idle. Yeah. LOUD crack. This is because even with the clutch pulled, the main shaft (counter spinning shaft) is spinning FAST since the clutch has some friction even with the clutch pulled, turning the main shaft/counter shaft, and the output shaft is NOT TURNING at all since it is connected to the rear sprocket and the wheel is not turning. Putting it in gear instantly stops the input shaft (breaks the clutch loose). That is a major shock to the transmission. Downshifting at speed with the clutch pulled is the same thing, but with reversed forces. You have to shift! I know But try to wait until the difference in the countershaft and output shaft (for the gear you will shift into) is as close as possible. It WILL get better as the transmission is broken in, or worse if the transmission is subjected to repetitive shock. The quieter the shift, the closer you came to matching the speed of these two shafts, for a given transition. I usually put the engine in first gear, pull the clutch and break loose the clutch (rolling forward/back) BEFORE I start the bike (after warm up). Yes, I will actually turn it off after warm up and do this. So my transmission experiences NO shock at all when I do that. It is much gentler on the entire transmission. When you pull the clutch, the input shaft (main shaft/coutershaft) keeps spinning! Putting it in gear stops it from spinning, abruptly! __________________ -2022 5 speed Templar X Orange, OEM 51T rear sprocket, 14T front sprocket -NOS 2020 KTM 250SX (2-stroke motocross), less than 10 hours on it Last edited by Thumper; 10-21-2023 at 08:22 AM.
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