Quote:
Originally Posted by wparsons
No, no, no. Read what I said. When the gearbox oil is really cold if you're shifting slow the input shaft will slow down faster (or fully stop) than the shift so double clutching can actually help. When it's really cold it doesn't take much time at all for the input shaft to stop spinning with the clutch in.
You're not slowing down the input shaft, you're speeding it back up after it slowed down too fast during the first part of the shift.
Like I said originally, it's not something you would need to do often, but in certain situations it can be handy.
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Transmission is always turning at road speed. Inertia of the clutch and input shaft spinning in neutral is insignificant compared to the inertia of the entire assembly of gear clusters. That's why you don't need to double clutch the shift from neutral into any gear while stationary, it will always go in because any upshift from neutral only needs to match the speed of the input shaft. Conversely, just about any shift into any gear from neutral when rolling is a downshift and double clutching can help the synchronizers if done accurately.
What you describe, where the shift takes so long it is in effect a downshift, isn't an upshift of any description. Whether you're shifting up or down depends on the road speed relative to the desired gear ratio engine rpm, not which gear you were in when you selected neutral. Only road speed matters in a constant mesh transmission.
These transmissions are baulky when cold when shifting from first to second. This disappears within a few miles of driving. I expect this will disappear completely well within 20,000 km but some transmissions can take longer to fully bed in the synchros. If this fault doesn't disappear I expect Aisin will issue revised lubricant specification for cold climates. I know Mazda tried this on their transverse gearbox, blending in some automatic transmission fluid for winter. However, they decided it made shift quality unacceptable when hot so went back to the lubricant originally specified. In line manual gearbox lubricants are tricky to make because of the friction requirements of synchronizers.