Quote:
Originally Posted by sweetfrs
(Post 1888736)
I would think it would put more stress :popcorn:
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Understanding how the transmission actually works internally will help you understand why more power doesn't equate to synchro wear. Other parts of the tranny can wear faster and/or fail from additional power/torque, such as gear teeth, bearings, and cause other problems like shaft deflection, etc. Higher RPM causes more wear because there's a larger delta between each gear, so the synchros need to do more work to engage a gear.
Synchronizers are like little clutches between each gear. They create friction when you try to select a gear, and it won't allow the gear to engage until the speeds of the chosen gear and the input shaft are matched. The only
wear they see is when these speeds are different.
Upshifting can be timed so there's almost no difference in speed when you click into the next higher gear, because the input shaft naturally slows down from oil friction when you clutch in and are in neutral (between gears). This is why you can time your shifts to be buttery smooth, catch the engine at just the perfect RPM as it falls, and not lurch at all. Do this well enough and a passenger can't even tell you've changed gear beyond the sound of lower engine RPM.
Downshifting can put more strain on the synchro because the synchro is being used to force the input shaft up to a higher speed. This is why rev-matching is important, it speeds the engine up to a higher RPM so the clutch engagement is done at match-speed. Double clutching bypasses the synchro function entirely and revs the input shaft along with the engine via rev match while in neutral. Do this smooth enough and a passenger can't even tell you've changed gear beyond the sound of higher engine RPM.
Engine power/torque numbers are irrelevant to synchro wear because it's function is during shifts, not power delivery. Hard shifting however is relevant, as is fluid choice and component tolerances from the part manufacturer.
Make sure you can tell the difference from a true grind and an occasional notchy shift. Many of the complaints I see IMHO are related more to the fact that first, second, and third use triple cone synchros which are much more durable, but don't feel as smooth with that nice single bump of resistance. At low rpm you can feel a few extra bumps as it engages, which can be misinterpreted as a grind.
