Quote:
Originally posted by DARISC
This will also extend the life of your synchro rings as well. Think I'm nuts? Not so- and I'm sure a lot of you older guys out there know it.
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The Porsche gearbox has a slip synchro design that uses friction surfaces to match the speed of the gears within the transmission (connected to the wheels) to the speed of the engine. If you shift the car at exactly the correct RPM for the speed that you are traveling, then you indeed experience no wear.
However, I do not know anyone that can do this in real life. If you shift without putting in the clutch, then you are using the friction of the synchro rings of the transmission to mesh and align the two speeds together (assuming you're not "perfect" in your shifting). This will inevitably cause your synchro rings to wear out sooner.
When you push in the clutch, you disconnect the engine from the transmission. This allows you to shift gears as the internal components of the transmission slow down or speed up to match the speed of the car. If the engine is still connected, you are fighting the momentum / power of the engine when you engage the gear (all assuming that the shift is not "perfectly aligned"). In this manner, you will definitely increase wear on the synchros in your transmission.
The simple way of thinking about it is that you need friction to align the speed of the engine with the speed of the car. By not using the clutch, you are then using the internal components of the transmission to accomplish this task instead (the synchros), and will thus increase wear on the synchros. One of the principles behind this design is that the clutch is meant to be the wear part of the assembly - not the synchros. It's far, far cheaper to replace a clutch, than it is to replace synchros in your transmission.
Of course, if you can shift perfectly 100% of the time and match the speed of the car with the engine, then there will be almost no wear. But again, I don't know anyone who can shift like this 100% of the time.
This is how it is for the Porsche 911 transmissions - I know that other cars have different synchro designs that may or may not be more amicable to clutch-less shifting.
-Wayne