Muniac Manor - Building a MUni (Part II Disc Brake On)

For those interested in this type of stuff.

>From Muniac Manor - Building a MUni (Part II Disc Brake)

 As some may remember, I wrote an article (posted to NG on 11/24/99) about
 building a custom MUni. At the conclusion of that article I mentioned an
 upcoming (part II) write-up describing a disc brake enhancement. This
 article discusses how I added the hydraulic disc brake and presents other
 bits of information collected over the past month of MUni riding. I write
 this with the hope that the information contained herein will be useful to
 other MUni riders. Drawings are available for the fabricated parts. Anyone
 requiring additional information or wishing to comment, please feel free to
 e-mail me at the address shown at the end of this article. In general my
 custom MUni has performed well given the rough riding it has been subjected
 too. As mentioned in part I, a Schwinn 24" frame was cut and two aluminum
 risers added to increase the fork height to allow a 26" tire to be
 installed. Each riser was installed with 4 1/4-20 SS screws top and bottom.
 These have stayed tight over the past month without the use of red loctite.
 I'm not anticipating any problems with these risers. The 26" Mavic D321 rim
 and 36 SS spokes also held true. The Schwinn axle/hub assembly didn't do as
 well. The hopping and landing done on the 6-

1/2" crank arms and associated torsional stress caused premature failure. The
axle didn’t actually break it twisted and bent outboard of the bearing race
during a hopping maneuver. It shut my riding down for about a day or so.
Fortunately the new aluminum hub I’d been machining was ready for spokes.
Discarding the bent axle/hub and saving the rim, my friend at the bike shop
“spoked” in the new aluminum hub. Since the new hub didn’t have an axle yet, I
whipped together a 3/4" shaft with turned down ends to allow the new hub/rim
to be placed in the bike shop’s truing fixture. Dropped the job off at 2:00PM
and picked up the completed wheel that evening. Hats off to the mechanics for
a job well done. Having the rim and hub was still not enough though. My hub
design uses aluminum center bored to 3/4" to accept a separate axle. This
approach was chosen to isolate axle’s performance and fit. Given the stresses
involved, I chose 3/4" O-1 tool steel round bar stock (drill rod) to construct
my axle. The axle steps into the hub’s 3/4" bore with a full length 3/16" key
way and is held in place with 4 set screws at 90 degs pressing the shaft into
the key way. Hardening of the axle was done to Rockwell 58 followed by a drawn
down process to soften the steel to Rockwell 53 so as not to make it too
brittle. At the time I was drawing the steel I didn’t know it would fail so
quickly. Hours of time tossed into the garbage can. Work like this will test
your patients. More on the axle saga later. Next step was to install the axle
in the new hub. First the oxide was polished off the hardened axle to achieve
a light tap fit. Then, after installing the key stock, I drove the axle into
the aluminum hub with the application of some synthetic grease. Once the axle
was centered I buttoned up the 4 set screws to hold it tight. Next I fastened
the disc rotor to the left hub flange. With the rotor installed, I tapped on
the modified frame rails and fastened them together using the seat post and
through bolt arrangement typical of Schwinn unicycles. With the basic MUni
assembled, I could then take some measurements to establish the position of
the caliper mounting holes on the left frame rail (2 holes). Once the mounting
holes were located the left side frame rail was removed for drilling and
tapping. After reinstalling this frame rail I installed the caliper and
shimmed it for proper clearance to the rotor. The disc brake I chose was the
CODA Expert (front brake) because the caliper clearance and rotor diameter
provided the best overall fit. Hydraulic tubing was run up the back edge of
the frame rail to minimize damage from rocks/debris when the MUni goes down.
An “under the seat” mount was made to allow the brake hand lever to reside
there. I attached a small finger board to the lever so squeezing it against
the seat bottom activates the brake. The finger board was constructed of
polycarbonate with enough flex to allow the brake to be feathered easily. Also
when the seat cracks into a rock or log after a “pitch off” the polycarb won’t
break and provides a bumper for the aluminum brake lever. So the theory goes.
Last thing was to add the CODA blood and bleed the brakes. CODA provides a
nice little kit for performing the bleeding function. On a mountain bike it’s
pretty easy to
do. On a MUni, … well read on. Disc brakes, on a mountain bike are clear of
the crank arms. Not so on a MUni. The caliper sits on the frame rail right
within the swing radius of the crank on that side. The alloy crank arms I
used are not straight rather they project slightly outward giving a bit
more room between the frame rail and the wheel side of the crank. Good
thing too, because that extra room allowed the caliper to fit. Almost. The
caliper bleed valve (there are two) projects towards the crank arm and,
wouldn’t you know it, right in the way of the crank arm swing. No big deal,
the nipple on that valve was cut off freeing up the required 1/4" of space.
With the bleed valve nipple gone, you can’t bleed the brakes using CODA’s
procedure. What I did was force brake fluid in at the brake lever (opposite
to CODA’s approach) and push the entrapped air out of the caliper valve
(the one that was cut) into a cup. Once the air was forced out, I closed
both values and I had brakes up in the MUni. Now for the test ride. Having
a brake on a unicycle is definitely weird but useful in certain situations.
In my opinion, the brake must apply a smooth constant drag. The amount of
which must also be controlled easily. Quick application/release is also
desirable in rapidly changing terrain. No doubt about it the disc brake is
silky smooth. When applied it gives a constant drag with no high spots like
some times can happen with a rim/pad brake. It also doesn’t get wet as
easily as a rim/pad brake. A plus if you’re riding in wet terrain like
streams, mud, rain or snow followed by trail situations requiring the
application of a brake. Also, with light pressure, the wheel can be locked
if required. I’m not sure this has any value yet. Ramapo Mountain near me
offers some tough terrain like cliffs, ledges, downhill, streams, rocks the
whole bit. Although much of the terrain is beyond me, I ride what I can and
put the rest on a “to do” list.< grin> The disc brake was nice to have up
there. Last MUni ride at Ramapo I made a wrong turn and got onto a fire
road which dumped me out on Skyline Dr. (an access road that’s pretty
steep). Since daylight was running out I decided to MUni down that road
(steep hills) for a quick exit to the lower parking lot where my car was
parked. While riding down those hills (about a 1/2 mile or so) I reached
under the seat and pulled that brake lever. The constant drag, afforded by
the brake, was easy to lean against and reduced the effective grade of the
hill. Pressure comes off the crank arms and evens out the force of
pedaling. You can actually get down the hill faster through consistency. Go
figure! It really was an interesting experience. With cars whizzing by at
break neck speed, it was nice to do a controlled descent. You have to keep
a constant hold on the brake lever though which makes you look like a
stand-up comic grabbing his balls. No wonder horns were blowing. Hats off
to a brake here. South Mountain Reservation is another MUni paradise not
too far away. The terrain there can also get steep. One ride I take is
about a 3 mile down hill run through the woods starting from a top parking
area and ending in a bottom parking lot. A dual vehicle situation. Most of
that trail I can do except for one smart downhill that keeps beating me. I
figured the disc would help me hop down that steep sweep. No such luck.
While hopping down terrain, I seem to need the feel of the cranks to micro
adjust and stay up. When I locked the wheel and try it pogo style it didn’t
work too well. Since the sweep is smooth dirt, I think applying the disc to
soften the sweep and keep my speed in check would be a better approach.
Next time out I’m going to try that. Need to get better balance with one
hand inboard to complete this maneuver I think. By the way, my Gazzaloddi
3.0" tire arrived. Let me say that tire, at 1540 grams, is one big chunk of
rubber. Interestingly, the tire with all its grandeur really isn’t 3" wide
but measures only 2-3/4" wide at max pressure (29
PSI). I’m still wondering why it says (26"x3.0") on the sidewall. That’s
marketing I guess. The Intense 2.7" inner tube that fits it weighs in at 485
grams (less air). With the Gazzalodddi installed MUni curb weight rose to
about 18-1/2 Lbs. An increase of about 3-1/2" Lbs over the previous tire.
Remember the Mavic D321 rim mentioned earlier? Its extra width allows a fat
boy tire to mount and not shear off the rim as might happen on a narrower
standard rim. Anyhow, I quickly pried off my Michelin Wild Gripper Hot S and
installed Gazzo. When I climbed on the MUni and started to idle, it felt like
someone cut my cranks back 2" or so. Simply stated the increased mass of the
tire/tube at a 13" radius creates more rotational inertia requiring the rider
to apply more force during rapid acceleration and deceleration. Newton’s F=Ma
thing for those with a physics background. This takes some getting used to. I
was anxious to give this beast a spin in the woods to see what would happen.
Little did I know… Chimney Rock Park was to be the test basin. Out of
my car, on the MUni and off into the woods. Not more that 500’ out on the
trail, there’s a little 8" dipper created from perpendicular washout. I hit
that thing at max revs and when I hit the outbound edge, SNAP! My axle, I
worked so hard on, snapped like a toothpick between the bearing race and hub
on the left side. Fortunately no upward octave shift in the voice. I also bent
the frame on both sides under the impulse of crank pressure as I stumbled off
the MUni immediately after the snap. Had to scrub the test ride. Bummer! After
a closer look though, the damage wasn’t too bad. Just bend the frame back and
make another axle. What’s another six hours of repeat work when you’re having
so much fun. Since the axle snapped in two pieces like a glass rod, I tested
its interior for hardness hoping to discover the reason for failure. Glad I
did this. I found the axle’s inner core to be very brittle. This is why it
snapped so easily. Recalling the heat treating process after pulling the axle
from the furnace (1750 degs F), and quenching it in oil, I didn’t begin the
draw down soon enough which allowed the steel to get cold. Dumb mistake. If
anyone has made a smart mistake I’d like to have heard about it then. A second
axle took me half the time to make. Practice makes perfect so the story goes.
This time I was careful to heat treat the steel properly. It takes about 3- 4
hours to do it correctly. Bent the frame rails back into position, installed
the new axle and I was back up and running again. Second axle is okay so far.
I’ve been pounding the daylights out of it to the tune of about 12 rides.
We’ll see what happens after a couple of months go by. Knock on wood I think
this time I got it. Now back to the Gazzaloddi tire I’ll call Gazzo for short.
Hills I could climb on Mich I can still get up with big heavy Gazzo. Things
like small logs and berms cleaned with inertia seem to come off a bit easier
with Gazzo. Unless you MUni with a bag of cement in your lap, you can’t get a
pinch flat with Gazzo. He’s just too damn big and fat. Mud is sort of a wash
on traction because big knobby Gazzo tends to pack and hold mud a little more
than Mich does. Mich’s silica rubber is nice that way for shedding mud. If you
leak some air from Gazzo, he’ll break the shock of a landing better than Mich
when you go off things. That’s a plus I think. Gazzo rolls over log pile-ups
pretty nice too. I need to get better and ride Gazzo more to learn about him I
think. As time goes by I’ll see whether Gazzo becomes my friend. For now I’m
optimistic. I stabbed myself in the back with a Shimano BMX pedal last MUni
ride. For those who don’t know, the Shimano BMX pedal comes to a dull point on
the outboard side. Now I’m taking a day or two off to recover and catch up on
writing. When the pain stops I’ll be back at it again. It all happened whilst
coming down a sweep at South Mountain Reservation on wet mud. I did your basic
involuntary front dismount and, with MUni tumbling behind, planted my two feet
in slippery mud on the last third of the downhill sweep. As I stiffened my
knees to catch myself, my feet skated down the hill causing me to fall back on
the MUni whose only offering was a face-up pedal. OUCH right in the left
kidney! I did make a nice back-pad but left it home that day. Except for that
stretch of trail So Mt is pretty mellow which lulled me into a false sense of
security. Don’t let your guard down ever while MUni riding. Be safe. Hope
everyone had a great new year. That’s all for now.

“The Muniac”