Five years of hydraulic clutches on KTM's left me with a minor
addiction for the smooth feel when I bought my KX. Plus, the
pull of the KX cable-actuated clutch was making my hand
sore. So I ordered up a Hebo universal hydraulic clutch kit
from the good guys at eRider. The kit is designed to fit most
motorcycles and comes with a bag full of assorted parts that
will probably work for just about any application. Here's what
I got from eRider:
Master cylinder, lever,
and slave cylinder. The
master cylinder looks a
lot like what you'd see
in a brake system,
except the lever is on
the opposite side. It
even uses DOT4 brake
fluid.
Parts and accessories.
Note the two bags on the
left. These are pop rivets
that are used to adjust the
action of the slave cylinder.
Left: The system came set up with a
cable end that wasn't compatible with
the KX's actuator arm. No problem,
there was a clamp-on cable end in the
parts bag that fit perfectly in the
actuator arm. To get the incompatible
cable out of the slave cylinder, I
removed the circlip...
Instructions -
English or Spanish
(your choice).
...then pulled out the
cable end stopper
thingy...
...and then the cable could be
pulled out of the cylinder.
Above: I used a different
cable from the parts kit. It
had one of the same cable
ends for use in the cylinder,
but the other end of the cable
had nothing on its end. That
end was inserted into the
cable end clamp that fit on the
KX's clutch actuator arm.
Above: Here's the
incompatible cable assembly
removed from the cylinder.
The hook tool helped pull out
the cable end stoppie thingy.
Below: Now, the fun part.
The general idea is to mount
the slave cylinder somewhere
where the cable has a fairly
straight shot to the clutch
actuator arm. The picture
doesn't show it, but I found a
flat piece of metal with holes
drilled in it; one end of the
metal piece was attached to
the cylinder mounting hole
and the other end was
attached to one of the power
valve cover bolts. You can see
that I haven't yet attached the
cable end to the actuator arm.
Above: Here's another view. I
wrapped part of the cylinder
with an inner tube because
the slave cylinder was
touching the corner of the
engine. Hebo recommends
that the cylinder be kept away
from heat sources. Note that I
haven't installed the rubber
boots that come with the
parts kit. You can see the
cable end clamp that fits on
the clutch actuator arm. The
cable end goes through a hole
in the fitting and a screw
clamps everything in place.

See the rubber boot on the
left end of the slave cylinder?
Here's where the pop rivet
comes in. The end of the rivet
happens to be about 30mm
long, which is how deep Hebo
recommends the piston inside
the cylinder should be from
the outside end of the
cylinder. I used the pop rivet
to push in the piston 30mm,
then clamped down the cable
end clamp in the actuator so
there wasn't any slack in the
cable. After that, I cut off the
excess cable. It would be nice
if they included some cable
end caps like bicycles use (the
cable is too thick for bike
cable ends).
Does it Work?
Oh yeah, it works.
Beautifully. I tried it out at the
Lebanon opening round of the
Missouri Hare Scrambles
Championship. For the first
time since I've owned the KX,
I rode without a hint of arm
pump in my clutch hand. The
clutch action is typically
smooth, as with all hydraulic
clutches. To be honest, I was
just a bit skeptical that the
pull could be as light as
advertised. While it's not an
astronomical difference in
pull, it is just lighter enough
that my clutch hand was
never sore. In fact, I never
even noticed the lever at all.
The AJP lever is a different
shape than most, and it's a
shorty-style lever, which I
haven't used in many years.
The action is pretty much
two-finger, and it feels the
same throughout the whole
pull and never feels any
different no matter how much
you abuse the clutch.

The other concern I had with
the Hebo slave cylinder was
its size in comparison to the
Magura units. But as the
pictures show, it tucks out of
the way and is protected from
frontal impacts by the pipe
and side impacts by my boot.
The fittings on both ends of
the system are standard
banjo connections, just like
hydraulic brakes (it uses
DOT4 brake fluid; the
Magura's use oil).

All in all, the Hebo kit is a
great add-on. While not
exactly inexpensive, any mod
that makes me forget about
the bike (or a sore hand) and
concentrate on riding is a
good mod. I'd recommend it
for any bike.
Above: Here's the lever and
master cylinder. The lever is a
little funky, but adjustable like
most. The lever and master
cylinder are  made by AJP,
which is pretty well known in
the trials bike world. I had to
disconnect the line from the
master cylinder to get it routed
up to the handlebars, then
bleed the system. The bleeder
screw requires a 7mm wrench.
Update January 2005:
Had a little problem with the
Hebo's cable...it broke. Here's
the culprit:
Since the cable doesn't have a
perfectly straight line from this
housing to the clutch actuator
arm, it gradually rubbed a hole
in one side of the housing. The
hole itself wasn't necessarily a
bad thing, but the sharp metal
left behind was enough to cut
the cable. In the pictures
above you can see that the
cable end is a bit funky, so
finding a replacement was a
concern. But the good guys at
Donelson Cycles in St. Louis
were able to find me a $15
clutch cable with ends that
matched pretty well with the
original (eRider also sells the
replacement parts, but I didn't
need all the housings and
other parts that come with it).
I have no idea what kind of
motorcycle this cable came
from, but Donelson's had it
hanging amongst a bunch of
spares. And the best part is,
the replacement cable has
identical ends at each end of
the cable (does that make
sense?), so I have a spare in
case it ever breaks again.

On the KX, I'm not sure there's
a way to prevent the cable
from wearing a hole in the
housing. But the life of the
housing can be prolonged if it's
rotated every so often. That
way, the cable's not always
wearing in the same spot. In
the picture at right you can see
where the cable is going to
wear on the new housing. The
housing can be rotated without
taking anything apart.

Also, the stock cable housing
can be cut off and used in place
Left: original cable
Right: replacement from
Donelson Cycles
Master Cylinder: Check the banjo bolt washers
One other thing that happened was during a cold spell in
December '04 (the Hebo's first exposure to significantly
below-freezing weather), the banjo bolt leaked out the brake
fluid. Not sure exactly why, but I'd guess that maybe some
moisture got in there and froze, creating a small gap in the
sealing washers. I replaced the washers with new ones and it
seems to be O.K. Just another thing to watch out for.

Update October 2007
After the Upland, Indiana enduro, I noticed the slave cylinder
had developed some "incontinence". Brake fluid was leaking
out the cable housing, due to the age and abuse of the
internal seals. Naturally, the seals are odd-sized metric
o-rings, hard to find anywhere this side of McMaster-Carr. A
repair kit does exist (see photo below), but good luck finding
it. Your best bet is ordering up 14.5x1.5 Viton o-rings for the
piston and 14.1x1.6 for the cylinder. McMaster-Carr has both
- the part numbers are 9263K576 for the piston o-rings and
9263K625 for the internal cylinder o-rings. Unfortunately,
these come in packages of 25 (only two of each o-ring are
required).
of the supplied set of cable housings. It appears to be a bit
stronger, less prone to wearing from the cable, and the rubber
boot fits perfectly around the housing to seal out more dirt
and grit.

One final note: just about any clutch cable can be used as a
replacement, even if the end isn't exactly like the original. It
just needs an end that's bigger that the hole inside the slave
cylinder that the cable fits through. I would have used a
regular clutch cable if Donelson's hadn't found me such a
good match.
These things are remarkably simple.
This is the Hebo repair kit, part number HR8910961
Update April 2008
Those of you with more knowledge than me on the science of
o-rings (which is most of the human population) probably
raised an eyebrow or two when I used Viton o-rings in an
application involving DOT4 brake fluid. Turns out Viton and
DOT4 don't play well together. The o-rings tend to melt and
stretch when exposed to polyethylene glycol-based fluid
(Wikipedia, makin' me sound smart).

As always, there are options to solve this predicament. The
first is to locate a Hebo slave cylinder repair kit. Rising Sun
Imports (a/k/a
TrialsPartsUSA.com), located in a small
Indiana town remarkably close to the farm where I grew up,
carries all things Hebo, including the repair kit. As you can see
from
this photo, there's not a lot to it. In fact, all I really
needed was the 4 o-rings. Unfortunately, the retail price for
the kit is $32.95.

Instead of spending over $8 per o-ring, I did what any other
cheap bastard would do: I switched to DOT5 brake fluid. It's
silicone-based and compatible with Viton o-rings. Many auto
parts stores carry DOT5 - I found a 12-oz container for about
$7 at Murray's Discount Auto Store. It is a bit of a chore to
clean out the DOT4 brake fluid from the whole system. I took
apart everything - the AJP master cylinder (including the
plunger), the braided steel line, and of course the slave
cylinder. The two fluids are not compatible, so the DOT4 must
go. Now, the o-rings and the brake fluid live in harmony.
Click on
pictures for
larger image
HEBO HYDRAULIC CLUTCH CONVERSION
March 2004
Update January 2009
After nearly a full season using DOT5 fluid, I decided to suck it
up and spend $32.95 to buy the rebuild kit. One of the
downsides to DOT5 is that it doesn't have the lubricity of
DOT3/4. This probably doesn't matter as much in braking
applications, but for the moving parts inside the slave
cylinder, a more slippery fluid was needed around the seals.
The clutch action wasn't as smooth with DOT5. It felt like the
seals were sticking slightly at a couple points within the range
of cylinder movement. Upon inspection, the seals themselves
looked just fine. They just needed to slide more easily across
the metal surface of the cylinder.

Other notes from the 2008 season:

  • The AJP master cylinder cap is apparently very sensitive to
    the tightness of the cap screws. At the Rock Biter Enduro,
    I had problems with the clutch fading, which were solved
    when I only tightened the cap screws just past finger tight.
    The master cylinder wasn't able to vent properly with tight
    screws.
  • Parts Unlimited makes a clutch cable for the KX250 that is
    perfect for use as the Hebo cable actuator (mfg. part no.
    K282156; Dennis Kirk part no. 193475). Although this
    might be considered an "el cheapo" clutch cable for
    standard use, it has the correct ends to fit into the cable
    housing inside the slave cylinder. Also, you can hack off
    the cable guide that slides into the housing on the engine
    case, and you've basically got the same cable actuation as
    the standard clutch cable.
Here's the pieces I cut off from the Parts Unlimited clutch
cable. The metal cable guide (short piece in bottom of picture)
fits into a slot on the engine case, just like it does with a
standard clutch (refer to
this picture). The cable movement,
over time, will still wear a groove into the small end of the
cable guide (right side) because the angle isn't perfectly
aligned with the clutch actuator arm. Eventually this can cause
the cable to break. However, if you rotate the guide in the
engine case housing every so often, the cable won't always be
rubbing the same spot on the small end of the guide and the
cable will last longer.
The cheaper-type cables have ends like this (the higher quality
cables sold by Motion Pro and others have just one rounded
piece that's pressed into the cable). In this case, cheap is
A-ok. The larger rounded piece can be slid off the cable and
discarded. The other end of the cable is identical, so it's like
you're getting two clutch cables for the price of one.
The best I could do with the
supplied parts. See the January
2009 update (below) for a better
alternative.
This is how the cable end fits into the guide inside the slave
cylinder: