To clutch or not to clutch?
Actually, in the case of shifting your motorcycle’s transmission, that
should be "de-clutch" or to disengage the clutch between gear changes.
As with such controversies as oil, tires, helmet use and other deeply religious
aspects of motorcycle ownership, I leave these decisions up to the reader.
Instead, I’ll try to give a little insight into how your motorcycle’s
gearbox operates. Then you, as the informed consumer, can decide what’s best
for your application.
The typical modern motorcycle 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. This differs from some
older designs where the gears slide back and forth on shafts, engaging one
another one pair at a time. 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 mainshaft and the driven gear on
the countershaft. In most cases, the mainshaft is driven directly by the clutch,
which in turn has one set of plates connected to the engine and the other set
connected to the mainshaft. Most clutches are driven off the engine’s
crankshaft by a gearset as well. They may use direct gears or a chain or belt
drive. This is called the primary drive.
The countershaft drives the transmission’s output device, typically a
U-joint in the case of shaft drive, or a countershaft sprocket if it’s chain
or belt drive. This is called the secondary drive.
One of the gears in a pair of gearsets, 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. The
first use multiple fingers and corresponding holes, typically in the gear
itself. Others have fingers built into the gear and the corresponding holes in
the engagement dog. The Valkyrie’s transmission is built this way. Another
type is a blade and slot design. There will be a pair of blades, looking much
like common screwdriver tips, on the engagement dog and a set of corresponding
slots in the gear. Usually there will be twice as many holes or slots as there
are fingers or blades. This is done to aid engagement speed as the dogs and
gearsets only have to turn half as far to engage. Older Gold Wing transmissions
use the blade and slot arrangement for example. They can be slower shifting than
the finger type engagement dogs, but provide a bit more torque handling
capability for a given size dog and gearset.
To move the engagement dogs back and forth along the countershaft, they have
a slot cut perpendicular to the shaft into which a shift fork fits. In turn, 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. Because of the different ratios, if two
or more gear pairs are selected at the same time, the transmission will be
locked and unable to turn.
Now here’s a hint for you troubleshooter types: If your engine runs OK but
stalls out when you start to engage the clutch, and the bike won’t roll
freely, you’ve just found your problem. Your transmission is locked and
probably engaging more than one gear pair at a time.
Most 5 and 6 speed transmissions use 3 shift forks. On a typical 5 speed,
there will be 1st and neutral, 2nd and 3rd, and then 4th and 5th. Because the
engagement dogs have to sit between gear pairs, you can also get false neutrals.
Notice that neutral itself is considered a valid gear range in the transmission.
Starting out in neutral, the rider disengages the clutch and presses down on the
shift lever. 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 or main shaft. Letting the clutch out (engaging it) couples the
engine’s output through the transmission and on to the rear wheel. As speed
picks up, the rider rolls off the throttle, disengages the clutch and lifts up
on the shift lever. The transmission selector slides the 1st gear engagement dog
back to a neutral state 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 basically how your transmission was designed to
operate.
A note here for historians and technoids: A typical modern motorcycle (and
some racing cars) transmission 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 can 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 motorcycle, as
it’s one at a time up and down. There is another type of transmission gear
selector not commonly seen anymore called a "preselector." This is
where you shift to the next desired ratio in advance, but don’t actually
engage it until a declutching action takes place. (Also see preloading towards
the end of the article)
Now, there are three states (four if you include being stopped) in your
drivetrain 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" for lack of a better term. During acceleration or
deceleration, torque is being applied through the transmission. In turn, this
applies a load against the shafts, engaged gearsets, engaged dogs, the clutch,
and the primary and final drives. Any effort to shift the transmission when the
motorcycle 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.
So how do dragracers 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 wheel. We can
then upshift or downshift with relative ease. If we pick too low a gear ratio
for the road speed we’re at, the transmission will start overspeeding and
apply some torque as well, but it’s next to nothing compared to what we’ll
experience when we let out the clutch!
Screech! Chirp! Skid! Hop, hop, hop!!! Ooooppss…
In other words, it’s best not to shift into low at 60 mph and let out the
clutch!
The next way to shift gears is to simply roll off the throttle so that the
motorcycle is neither accelerating nor decelerating momentarily; it’s
coasting! All of you dirtbike riders and others who have shifted a lot without
using the clutch know you momentarily roll the throttle off on an upshift,
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. It sure helps cut down on
those embarrassing oops.
So how does an electric shifter work? Simple really. As you start to push on
the shift lever, it engages a microswitch that momentarily kills the ignition.
Add an air ram, storage bottle and control switch and you now have an air
shifter where you just hit a button on the handlebars under full throttle and
it’s instant upshift. They’re real popular with the dragracers who may not
be able to get their foot to the shifter right away.
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 airshifter example is the most critical. This is where
everything has to be set up perfectly. In between, we have the rider 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. Weird,
huh. 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.
Another technical tidbit: Most dragracing only transmissions have the
engagement dogs undercut so that acceleration torque actually pulls them
together helping complete the shift. The problem with this is if it is more than
2 to 3 degrees, the transmission will pop back out of gear under deceleration
forces. So, a dragracer stages in 1st gear, hits their air shifter button on all
the upshifts never releasing the throttle and then pulls in the clutch and
coasts to a stop at the end of the run. Letting off the throttle and feeding
deceleration forces through this type of transmission will damage or destroy it.
So, pulling 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 bike 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 pull the
clutch in, shift to neutral and then coast for a couple of seconds with the
throttle shut off before upshifting 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 mainshaft 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 bike clunks when going into first gear from
neutral while stopped? Yep, the countershaft is stopped while the mainshaft is
being spun by the engine. Your oil-bath clutch has some drag, especially when
the engine is cold and doesn’t disengage all the way.
Back to our old friend 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 upshift, 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 roadracer 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 roadracers 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 mainshaft and
countershaft for the next gear pair selected. And all this time you thought they
did it just to sound cool!
So, do you need the clutch to shift? How about some rules of thumb first. The
lighter the bike, the less traction at the wheels (i.e. dirt), the lighter the
engine flywheel effect, then the less you need the clutch. Clutchless upshifts
are normally much easier to perform than clutchless downshifts. At the other
extreme, we have a big, heavy cruiser 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 hundred miles and others that didn’t start
showing signs of abuse for several thousand miles. I can tell you this, even
yours truly, let alone any competent shop mechanic, 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 bike when the evidence points
to the contrary. Taken to severe extremes, it also voids your warranty.
So, you’ve got a big, torque laden cruiser 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 ain’t gonna happen amigo. But you can make it as good 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. Although most shift selector mechanisms
use an over-center design where the spring-loaded ramp and pawls will try to
complete the shift on their own, they’re not always successful. 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.
Everyone has different foot sizes, wears different kinds of shoes or boots and
sits on the motorcycle differently. Adjust the lever so that it fits you. Also,
make sure it doesn’t hit any engine parts or bodywork that will limit its
travel as well. Have a friend check your lever adjustment and travel for you
while you sit on the bike in a normal manner. You may need to lower or raise it
some. And you want to make sure your foot isn’t resting against the lever
except during a shifting operation.
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, usually between 1st and 2nd
gears, your motorcycle’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 rider 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 upshift.
It may be worth the extra expense to a dragracer 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. If it’s a cable type, make
sure it’s adjusted per the manufacturer’s instructions. If it is
hydraulically operated, 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 bike is fully warmed up, try bleeding the system.
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 at stoplights
and the like. Keep it fully depressed or shift to neutral and let it out all the
way. Holding the bike on a hill with the clutch simply heats up the clutch
plates, usually making them grabby. Use the front brake to hold the bike until
you’re ready to roll again.
Now, experiment with varying degrees of clutch disengagement as you shift up
and down through the gears. Personally, I like to use two fingers on most bikes
and pull the clutch in about a third of the way for upshifts and about half way
for downshifts on a big cruiser like the Valkyrie. On a sportbike with a close
ratio transmission I find just a slight pressure release for upshifts and a
quarter to a third for downshifts if I’m using engine braking between the
gears. If I’m coming up on an especially slow corner and will be quickly
executing several downshifts while braking, I may simply pull 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 curve. To blip the throttle while braking, use your thumb to gently
roll the throttle on and off. It takes a bit of practice at first to be smooth
and not interfere with your control of the front brakes.
You can also experiment with shifting without the clutch. If nothing else, it
provides you a way to get home if your clutch cable breaks or your hydraulic
system fails and you can’t get the clutch to disengage. (To start off from a
dead stop with the clutch engaged requires starting the bike while it is in
first gear so you may have to overcome a starter interlock switch. And push off
with your legs as you hit the starter button to help the bike get going. As you
come to stop, shift to neutral and stop the engine. If you miss neutral, just
stall it out with the rear brake. Hitting the kill switch while the motorcycle
is still rolling in gear can have the effect of trying to toss you over the
handlebars.)
To upshift without the clutch, you shift pretty much as you normally would.
As you back off the throttle, upshift 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, push down on 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. On sportbike this might be a gentle click or
"snick" while a big cruiser with give off a fairly loud metallic sound
usually described as a "clank." If you don’t get this, you may not
have fully engaged the dogs. Here, it’s best to shift to another gear and back
again to make sure everything is fully engaged before applying much throttle.
Otherwise the transmission may start popping out of gear with greater and
greater frequency until repairs need to be made.
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, upshifts first and
then downshifts. Finally, if you want, you can try a few shifts without the
clutch, again starting with upshifts and then trying downshifts. If you’re
doing it right, the motorcycle should remain smooth, there should be no extra
noise from the transmission or drivetrain, 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 upshifts 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 street rider. I’ve also outlined my personal
preference of using partial clutch disengagement on most modern motorcycles. If
it’s an old bike I’m riding, then I use full clutch travel and take my time
with the shifts. Old Harleys, Triumphs, BSAs and BMWs are especially bad in this
regard. You just can’t hurry the shifts.
I’m also going to dispel another common bit of moto folklore, namely the
practice of preloading the shifter. Yes, this may hasten the shift process and
may even seem to make the shifts more positive in their engagement, but think
about what it’s doing to the transmission. You’re now applying pressure to
the shift selector mechanism and one of the shift forks. The transmission
doesn’t shift yet because it’s in an acceleration or deceleration state. In
fact, if you backed off the throttle momentarily, the transmission would likely
complete the gear change just like any other clutchless shift. A lot of old
timers will tell you this is the way to go. The problem is most of them don’t
know how the transmission operates. I also see a lot of them complaining about
how their transmission jumps out of gear if they don’t preload between shifts.
If you need to preload the shifter to get the transmission to successfully
complete shifts, chances are good it’s already damaged and needs repairs.
Don’t preload the shifter, OK?
Modern motorcycle transmissions are better now than they’ve ever been.
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!