rs8001

dimbulb,

As far as simply pulling a manual gearbox out of gear when you let off the gas you should be able to shift out of gear into neatral no problem. What is happening is the at some point in time very soon after you lift the drive-line including transmission goes from transmitting power from the engine to the road to transmitting power from the road to the engine. At some point in time during this transition there is no load on the drive-line (i.e. no power is being transmitted in either direction). It should make sense that to go from one transferring power in one direction to the other there has to be an instant when power not is being transferred in either direction. At this point (or in practice very near it when the drive line is lightly loaded) you can simply move the tranny into neutral. This is because the mechanism that engages the gear is not 'held' in place by the power that is being transmitted through the tranny.

Try this: drive at a steady speed with the tranny in any gear. Rest your hand on the shifter adding only a slight pressure. Lift off the gas and the shifter (with the slight pressure you have on it) will move easily into neutral. Once you feel the shifter start to move get it into neutral. If you go really slow at that point you may wind up with a grind. It really isn't that hard. Do not ride along for long stretches pushing on the gear lever: this can result in transmission wear. Doing so for the second or two it will take for the tranny to fall into neutral shouldn't be a problem. With a little practice you will get the feel and be able to simply move the tranny into neutral at the right time without the constant pressure.

You will also find that when leaving the car in gear as you slow down transmission will slip easily slip into neutral as you reach idle speed. At the point where you slow down enough to reach what would be engine idle speed the power situation reverses again (from road to engine to engine to road) and you have a point where no power being transmitted. You'll be able to pull the gearshift into neatral.

That part is easy. Shifting back into gear from neutral (either up or down) is a little different for a normal manual tranny like you'd find on a street car. What you need to do is make the engine speed (RPM) match whatever it needs to be to the gear you are trying to engage. If you are shifting to a lower gear the engine must be turning faster than it was in the higher gear. This is accomplished by simply giving the car enough gas momentarily to create this matching condition. Blip the throttle just right and you'll be able to engage the gear you want. This takes a lot more pratice to do properly. Others have already pointed this out. If the next gear you want is a higher gear you must wait for the engine speed to slow down before you can engage the higher gear. On a street car as DE137, points out it is simply faster to use the clutch.

***edit: after re-reading spyder's and others posts, I admit I don't understand exactly how clutchless upshifting can be faster on a normal street car tranny. Three possible reasons for this occur to me. First, the spacing between gears typically gets smaller and smaller in the higher gears (this is true both for road cars and race cars) so the engine speed drop needed to engage the next higher gear is less. Second, is that when shifting close to red-line or at least at high engine speeds the engine speed will slow rapidly anyway. i.e. it will take less time for the engine to fall from 6000 to 5000 RPM than it will take to fall from 3000 to 2000 RPM. Third, my guess would be that worn synchros will be less and less effective and result in easier engagment under these conditions. ***

That isn't the whole story though. DE137 is on to something about the racing transmission but he is wrong about the straight cut gears being the reason. Straight cut gears are used in racing applications mostly becuase they are strong. They are also more effecient than helical cut gears (they generate less heat). The downside is that they are noisy. Ever hear a car whine when it is in reverse? This is because reverse gears are typically straight cut gears. Helical gear run much quieter, this is the reason (I believe) they are used on street cars.

Any modern gearbox either for street or race cars are what is known as a constant-mesh gearbox. In a constant-mesh gear box each gear set (in a five speed tranny there are five gear sets - i.e there are five pairs of gears matched to eachother) is always engaged (meshing). The gear sets, how many ever there are are mounted on two adjacent shafts. When you "engage" a gear you are not meshing one gear with another; they are already meshing with eachother. What you are really doing is "engaging" one set of already meshed gears to the input shaft of the transmission thus creating a path from input shaft to output shaft. (Each of the gear set are always engaged to the output shaft - the sets that aren't engaged still rotate with the output shaft.)

In a racing gearbox this mechanism will disengage the gear very easily and quickly and is fundamentally the same operation as the street type gearbox. It is the process of engaging a gear that is different. In a racing gearbox you do not have to perform the engine speed to road speed matching. Under most circumstances you can simply jam the box into gear. This can result in the driven wheels (typically rear, but the same would apply to a front wheel drive car) that want to lock up and other braking considerations that have already been touched on in this thread. I am not that familiar with motorcycles but I believe they operate in the same fashion as a typical racing gearbox.

In a street car the gear box will incorporate synchronizers. There is a synchro associated with each gear set. They are devices which through the use of friction will not engage the gear until the input shaft and the gear (and therefore output shaft and everything connected to it) speed are roughly matched. It is due to the synchro that you have to wait for the engine speed to slow when attempting a clutchless upshift on your road car. The lack of a synchro is the reason why the motorcycle guys and easily upshift without using the clutch. It is also due to the synchros that you must match engine revs on a downshift. One point here, it is still generally a good thing to match engine speeds on a downshift on a racing box in order not to upset the whole car when the gear engages. The major difference is that it is not necessary to do so to get the gear engaged in the case of the race type gearbox.

Synchros were developed and are used in transmissions simply so the driver doesn't have to perform the engine speed/road speed matching in order to shift gears without a grind or even at all. Ever notice that you can't even engage one of the lower gears like first when the car is still moving at a high rate of speed. Ever notice the whine the gearbox can make if you try to jam the gear in under these conditions. That is the sychros doing their work. I suppose it is as much a safety consideration as anything now. We've all probably changed from fourth to third instead of fifth accidently. It is propable a good thing first is near impossible to engage at this time because people would be over-reving engines and so forth by accidently putting the car in a gear that is way to low at that moment. I'm sure we'd also have people accidently engage a low gear followed by rear wheels locking and accidents because of this too. Synchros are not used on race cars because they create lots of heat and also as pointed out slow shifting down.

I know it was a simple questions and I've written a very long answer. I enjoyed typing all this in and also wanted to make it clear that the manual gearbox on a street car and the manual box on a race car and motorcyle operate differently. That is why there are some conflicting posts above. Also, it sounds like spyder_venon must race some sort of production based car since he mentions synchros in one of his posts.