In the case of shifting your sequential transaxle, I'll try to give a little insight into how your sequential gearbox operates. Then you, as the informed consumer, can decide what is best for your application.
General understanding:
The modern transaxle, gearbox or transmission is a "constant mesh" design. The name comes from the fact that all of the gears in the transmission are in constant engagement with one another. The gears are arranged so that you have a drive gear, coupled to the engine, and a driven gear coupled to the rear wheel. They are arranged on shafts, the drive gear on the main shaft and the driven gear on the countershaft a.k.a. pinion shaft. The main shaft is driven directly by the clutch. The clutch is driven off the engines crankshaft on the flywheel. The countershaft (a.k.a. pinion shaft) drives the pinion gear that in turn drives the ring gear. This is called the final drive or secondary drive a.k.a. ring and pinion gear. The ring gear transfers power to the drive flanges through the planetary gears in the differential. Which make your axles turn.
http://science.howstuffworks.com/gear1.htm
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http://science.howstuffworks.com/gear8.htm
http://science.howstuffworks.com/framed.ht...ntroduction.cfm
http://science.howstuffworks.com/framed.ht...nformation.html
Gear engagement:
One of the gears in a pair of gear sets, will be coupled to its shaft, main or counter, at all times. The other gear in the pair will rotate or spin freely on its shaft on bearings. In between the free rotating gears and splined to the main or counter shaft, are the engagement dogs, or at least half of them. The other half is built into the face of the gears themselves. Each free-spinning gear is then coupled to its shaft by the engagement dog. The engagement dogs are typically one of a few designs, but all of them work basically the same way. To move the engagement dogs back and forth along the countershaft, the shift forks are moved by the shift drum that is rotated by a selector mechanism, typically a ramp and pawl design. The shift drum is designed to select only one gear pair and engagement dog at a time.
http://auto.howstuffworks.com/transmission.htm
Basic shifting:
Starting out in neutral, the driver disengages the clutch and pulls on the cockpit shift handle. This moves the selector to engage the 1st ratio gear pair by sliding the shift fork on that engagement dog into the side of the driven gear on the counter shaft. Letting the clutch out (engaging it) couples the engine's output through the transmission and on to the rear wheels. As speed picks up, the driver rolls off the throttle, disengages the clutch and pulls on the cockpit shift handle. The transmission selector slides the 1st gear engagement dog out of 1st gear and then engages the 2nd gear ratio pair. The clutch is engaged again, the throttle opened and acceleration resumes. The same mechanism applies for each higher gear ratio and then the reverse order on shifting back down through the gears. This is how your transmission was designed to operate.
http://auto.howstuffworks.com/clutch.htm
A note:
Your transaxle has what's called a "sequential" shifting arrangement. This means that each gear ratio from lowest to highest and back again has to be selected before the next desired ratio could be obtained. Contrast this with your typical car or truck where any gear ratio in the pattern can be directly obtained. In other words, with the latter you can shift directly from 1st to 4th and skip 2nd and 3rd along the way. Not on a "sequential" as it's one at a time up and down.
States of driving:
There are three states (four if you include being stopped) in your drive train that we need to discuss. They are acceleration where the engine is turning the rear wheel; deceleration where the rear wheel is turning against the engine; and a neutral condition between the first two that we'll call "coasting" During acceleration or deceleration, torque is being applied through the transaxle. In turn, this applies a load against the shafts, engaged gear sets, engaged dogs, the clutch, and the primary and final drives. Any effort to shift the transmission when the vehicle is in one of these two states will impart moving thrust and shear forces against the parts in question. If the load is light, it's still possible to change gears but it also causes some wear. Under a heavier load such as hard acceleration it may or may not be possible and any gear changes run the risk of damaging parts.
The next way to shift gears is to simply roll off the throttle so that the vehicle is neither accelerating nor decelerating momentarily; it's coasting! All of you dirt bike riders and others who have shifted a lot without using the clutch know you momentarily roll the throttle off on an up shift, select the next gear and roll it back on. If the bike is decelerating, we have to roll the throttle on a bit, again to achieve the coasting state, and then make our shift. If it's a downshift, we should give the engine a little throttle right before the next gear engages whether we're using the clutch or not to smoothly match road speed to engine speed.
How does F1, Dragracers, Super bikes, shift gears under a full throttle load?
Actually, they don't. For a time, even a very brief one, the transmission is in a coasting condition where little to no torque is being transmitted through it. There are several ways to accomplish this little trick. The first, most obvious and most commonly used method is to disengage the clutch. This decouples the engine to the transmission which is then left free spinning from whatever drive is coming through the countershaft from the rear wheels. We can then up shift or downshift with relative ease. If we pick too low a gear ratio for the road speed we're at, the transmission will start over speeding and apply some torque as well, but it's next to nothing compared to what we'll experience when we let out the clutch! In other words, it's best not to shift into low at 60 mph and let out the clutch!
So how does an electric shifter work? Simple really. As you start to push on the shift lever, it engages a micro switch that momentarily kills the ignition. Add a control switch and you now have a shifter where you just hit a button on the steering wheel under full throttle and it's instant up shift.
Timing:
Now, as with so much else in life, timing is everything. Using the clutch ensures the most timing tolerance ( i.e. the most time you have to make a smooth shift) and the latter electric shifter example is the most critical. This is where everything has to be set up perfectly. In between, we have the driver who likes to shift without the clutch. Some have mastered the timing of having no load on the transmission and perfectly matching the engine speed to the road speed by chopping and blipping the throttle at appropriate times. It should also be observed that the timing is both longer and more critical for changes between the lower gears, and quicker and less critical for the higher ranges. There are lots of reasons as to why this is but we don't need to go into them here.
So, what happens when we shift poorly? Parts get worn or worse. The first ones to suffer are usually the engagement dogs and the shift forks. It can also include the counter or main shaft splines and shift selector. Why does the transmission start jumping out of gear? Typically it's a bent or worn shift fork, or, it can also be worn engagement dogs. This is where the fingers or blades are worn on the ends from improper shifting. Once they get rounded off enough, they don't fit properly in the corresponding slots or holes in the gear and the transmitting of torque will force them apart. Hence the transmission pops out of gear. It may be acceleration or deceleration or both depending on which side the parts are worn or damaged.
Most transmissions have the engagement dogs undercut so that acceleration torque actually pulls them together helping complete the shift.
So, putting in the clutch every time means I won't damage my transmission, right?
No, not really. Sloppy shifting is still sloppy shifting and will cause extra parts wear whether you use the clutch or not. Obviously, disengaging the clutch will help lighten the load considerably, but it won't eliminate it entirely. Usual examples of sloppy or poorly executed shifts include shifting too fast, but believe it or not, shifting too slow can be just as bad or worse. Also, coming to a complete stop and then trying to get the vehicle in a lower gear is not good for the transmission as well as using heavy deceleration (engine braking) at every stop.
If you want a graphic demonstration of some bad shifting, simply put the clutch pedal in, shift to neutral and then coast for a couple of seconds with the throttle shut off before up shifting or downshifting. Notice how much stiffer the shift lever feels, how slow the transmission is to shift and how clunky it sounds. It might even make a grinding noise as the dogs fight to engage. One example here should be enough, OK? The reason is the two transmission shafts, main and counter, are now way out of synchronization with one another. The countershaft is still being driven by the rear wheel while the main shaft is being spun by the engine, but only at idle rpm. Slow, lazy shifts can have somewhat the same effect although obviously not as pronounced.
So have you figured out why your car clunks when going into first gear from neutral while stopped? Yep, the countershaft is stopped while the main shaft is being spun by the engine. Your clutch has some drag, especially when the engine is cold and doesn't disengage all the way.
Back to timing again. Ideally, we want our shifts to be timed, along with the proper change in engine speed, so that everything is spinning at approximately the same speed with the engagement dogs meshing smoothly and softly with the gears. No torque will be applied through the transmission until the next shift is completed and everything is fully engaged.
The true pro will also have the engine speed properly matched to road speed for the next gear. If it's an up shift, the engine rpm will be lower and for a downshift, it needs to come up higher. And this is true between shifts whether or not you actually disengage the clutch or not. Ever hear a road racer blipping the throttle as they brake into a turn. They're downshifting furiously, but they're not necessarily using engine braking. On a two-stroke there isn't much engine braking available to begin with, and most road racers have little to no weight on the rear tire under heavy braking. No, what they're doing as they come down through the gears is using a little clutch drag that's available even with the lever pulled in and matching speeds of the main shaft and countershaft for the next gear pair selected.
So, do you need the clutch to shift? How about some rules of thumb first. The lighter the vehicle, the less traction at the wheels ( i.e. dirt), the lighter the engine flywheel effect, then the less you need the clutch. Clutchless up shifts are normally much easier to perform than clutchless downshifts. At the other extreme, we have a big, heavy vehicle with a lot of weight and traction, a slow revving engine with lots of flywheel effect, and a big clunky transmission to handle all the extra torque placed through it. Yeah, you can shift it without the clutch, but you'd better be good and know what you're doing. I've seen transmissions damaged in a few miles and others that didn't start showing signs of abuse for several thousand miles. I can tell you this; anybody can tell how you shift by just looking at your transmission's internals. You're not fooling anyone when you tell them how you "baby" your car when the evidence points to the contrary.
So, you've got a big, torque-laden car and you want it to snick through the gears like your old 125cc dirt bike or your buddy's 600cc sport bike. Guess what, it isn't going to happen amigo. But you can make it as well as it is going to get if you'll try a few things. The first of these may seem obvious but I see a lot of people forgetting to do it on a regular basis. That is, use a firm, full motion on the shift lever. A lazy, half-hearted prod on the shift lever can lead to only a partial engagement of the dogs. This will prematurely wear the dogs, put all the torque through only a part of the load bearing portion of the engagement dogs and will lead to the transmission popping back out of gear.
To aid in the quest of full engagement, make sure your shift lever is adjusted so that you can easily get full travel for both up and down shifts.
Next, complete shifts quickly and deliberately. I'm not talking about "speed-shifting" here, but in addition to half-hearted stabs at the shift lever; the other trait of a lazy shifter is to delay shifting too long or to take too long in moving the lever. This isn't a double-clutching, 18-wheeler truck transmission where all shifts stop off at neutral between gears. With the exception of the real neutral, your vehicle's transmission wants to be in one gear or another. In other words, it doesn't want to spend a lot of time between gears. What happens is the speed of the main and counter shafts gets out of synch and this leads to a lot of unnecessary extra wear and grinding of the engagement dogs. Remember our example above of pulling in the clutch and delaying the shift for a time?
Conversely, excessive pressure on the shift lever and trying to shift the transmission too fast causes wear and tear of its own. Now the driver is pushing mightily on the lever trying to slam the next gear home. This puts excessive pressure against the shift selector mechanism and quickly wears or damages the shift forks. Taken to extremes, it bends the shift forks and we're back to the transmission popping out of gear again. It can also mean the transmission is made to start transmitting torque before it's fully engaged. Here, we'll see chipped fingers or blades on the engagement dogs and possibly damaged splines on the countershaft. The most brutal shift is the full-throttle, clutchless up shift. It may be worth the extra expense to a drag racer looking to cut a few hundredths of a second off their elapsed time, but for the rest of us, we should shut the throttle off and shift normally.
So, to use the clutch or not. The interesting thing here is this isn't a strict yes or no type question. You can use the clutch to varying degrees. First, make sure your clutch is working properly. Make sure it's adjusted with about ½" of free play at the pedal. Then make sure everything is operating normally and that the system is filled properly with good, fresh fluid. If the clutch seems to drag or not fully disengage once the car is fully warmed up, try bleeding the system. Most chassis builders don't put in a clutch pedal stop that means that it is possible over throw your clutch system as well.
Next, when coming to a stop or when engaging the gears from a stop, make sure the clutch lever is fully depressed. And don't ride the clutch. Keep it fully depressed or shift to neutral and let it out all the way. The later works well when entering camp. For those that don't have gear dash indicator.
Now, experiment with varying degrees of clutch disengagement as you shift up and down through the gears. If I'm coming up on an especially slow corner and will be quickly executing several downshifts while braking, I may simply push the lever all the way in and blip the throttle lightly as I work my way down through the gears. In this case I'm not using the engine braking but simply matching up my engine rpm, road speed and gearbox selection for when I reengage the clutch and hit the upcoming turn.
You can also experiment with shifting without the clutch. To up shift without the clutch, you shift pretty much as you normally would. As you back off the throttle, up shift and roll the throttle back on. If done properly, you should not feel any fore or aft jerking sensation. In fact, all your shifts up and down, clutch or no clutch, should be smooth. It's one of your best indications you've made a good shift.
Downshifts are a little trickier. As you start to decelerate, you need to blip the throttle gently to unload the force on the gearbox and get it to that coasting state. This is a good practice for downshifts whether you use the clutch or not as it also helps keep everything spinning in synch. Then, as you blip the throttle, pull the lever and complete your downshift while closing the throttle again if slowing or opening it back up if accelerating. Again, you shouldn't feel any fore and aft jerkiness.
What's a throttle blip? A very gentle and quick opening of the throttle that raises the engine speed 1-2 thousand rpm. You don't need to grab a handful of throttle to complete these maneuvers.
You should also hear a positive mechanical acknowledgement that the engagement dogs have fully seated. With a fairly loud metallic sound usually described as a "clank."
So, get out there and experiment a little. Start off by using full clutch disengagement during shifts. When you've gotten to the point where you're smooth and proficient, try using less clutch lever travel, up shifts first and then downshifts. Finally, if you want, you can try a few shifts without the clutch, again starting with up shifts and then trying downshifts. If you're doing it right, the vehicle should remain smooth, there should be no extra noise from the transmission or drive train, and the shift should be completed quickly. If you're holding pressure on the shift lever while the engagement dogs grind into place, you're not doing it right.
Now, some like full use of the clutch, some partial use as I've outlined, while others may not use the clutch at all for shifting. Lots of racers don't use the clutch for up shifts and only use it lightly for downshifting. Then again, they are normally prepared to examine and rebuild their transmissions a lot more often than your average sand/dirt hobiest.
Learn to shift smoothly at all times and then try using a little less clutch action. You just might like it. And don't forget to be firm and deliberate with the shift lever and use all of its available travel. Like all that's best in life, not too fast and not too slow, but just right!
http://auto.howstuffworks.com/torque-converter.htm
