American Classic hub design problem

Hello folks. Recently, my American Classic rear hub had a problem. Those of
you familiar with the design will know it's problematic. To differentiate
his design from shimano \ campy, Bill Shook decided to avoid using
traditional spring-loaded pawls. The idea here is to decrease coasting drag
friction, as the AC pawls do not drag across the freehub teeth when
coasting. This is great, in theory.

The problem is that the 6 pawls are engaged through a "pawl plate". The
pawl plate is engaged, amazingly, by a flimsy piece of wire that is wound
around the inside face of the freehub. A couple of millimeters of the wire
are bent in towards the pawl plate. This portion of the wire is angled
obliquely such that it drags against the pawl plate's engagement holes. When
coasting, the familiar machine gun sound is heard. However, this is not the
shimano \ campy spring-loaded pawl sound.

The problem is that it's ill-advised to rely on this flimsy piece of wire
for the critical task of engaging the pawl plate. The bent portion of wire
must be angled perfectly. If it hits the plate too squarely, then coasting
drag is huge; if it hits too shallowly, then there's a chance it won't
engage the pawl plate when pedalling. This happened to me on a ride,
luckily I stopped off at a friend's and switched out the wheel.

I have since serviced the hub. Getting that wire to hit the pawl plate
properly is a true nightmare. It's currently set up with the wire hitting
the plate somewhat squarely, in order to ensure engagement. Sadly, this
does result in much more coasting drag than either shimano or campy.
Ironically, I'm sure Bill Shook's goal was to eliminate coasting drag...

Bill, if this is forwarded to you, I would suggest that the next generation
of hub incorporate a much better solution for pawl plate engagement.
Something spring-loaded is a must. Relying on the modulus of elasticity of
a material (bent wire) really is a shortcoming in this otherwise-elegant
design.

Thanks.

--
--------------------------
Andre Charlebois
AGC-PC support
http://agc-pc.tripod.com
BPE, MCSE4.0, CNA, A+

Andre Charl writes:

Hello folks. Recently, my American Classic rear hub had a problem.
Those of you familiar with the design will know it's problematic.
To differentiate his design from Shimano \ Campy, Bill Shook decided
to avoid using traditional spring-loaded pawls. The idea here is to
decrease coasting drag friction, as the AC pawls do not drag across
the freehub teeth when coasting. This is great, in theory.

There is a picture of this mechanism on their web site:

http://www.amclassic.com/Road_Hubs.html

However, various escapements have been invented over many years and
the silent pawl used by Regina, SunTour and others has practically no
drag because the large "heel" has enough viscous friction in the body
to not snap back at rotational speeds of interest. That is also why
they cannot be heard.

The problem is that the 6 pawls are engaged through a "pawl plate".
The pawl plate is engaged, amazingly, by a flimsy piece of wire that
is wound around the inside face of the freehub. A couple of
millimeters of the wire are bent in towards the pawl plate. This
portion of the wire is angled obliquely such that it drags against
the pawl plate's engagement holes. When coasting, the familiar
machine gun sound is heard. However, this is not the Shimano \
Campy spring-loaded pawl sound.

Unfortunately there is no picture of this device assembled but it
seems to rely on the drag of the wire on the pawl plate. This being
an unreliable drag, the engagement is equally unreliable. Because it
cannot be heard, the assumption is that there is no drag... but there
is. Besides, the actuator wire slides over the pawl plate across the
series of holes visible in the picture of the parts.

The problem is that it's ill-advised to rely on this flimsy piece of
wire for the critical task of engaging the pawl plate. The bent
portion of wire must be angled perfectly. If it hits the plate too
squarely, then coasting drag is huge; if it hits too shallowly, then
there's a chance it won't engage the pawl plate when pedaling. This
happened to me on a ride, luckily I stopped off at a friend's and
switched out the wheel.

I find amazing how many people do not study history, in mechanics,
politics or warfare. We don' need no steenkin new escapements. See
Hugi, the loudest and most expensive ratchet on hubs with no redeeming
value. Besides these problems, the mechanism is not well protected
against water and dirt.

I have since serviced the hub. Getting that wire to hit the pawl
plate properly is a true nightmare. It's currently set up with the
wire hitting the plate somewhat squarely, in order to ensure
engagement. Sadly, this does result in much more coasting drag than
either Shimano or Campy. Ironically, I'm sure Bill Shook's goal was
to eliminate coasting drag...

Well, Sturmey Archer went through the spring-less pawls on their SW
hubs only to discover they had feet of clay. Riders stood up to pedal
and flew forward in neutral, the pawls not engaging at all because the
oil was more viscous than the inventor had imagined.

Bill, if this is forwarded to you, I would suggest that the next
generation of hub incorporate a much better solution for pawl plate
engagement. Something spring-loaded is a must. Relying on the
modulus of elasticity of a material (bent wire) really is a
shortcoming in this otherwise-elegant design.

Although the pawls do not make contact when coasting, the actuator
wire does and has more drag than typical good pawls.

Jobst Brandt

In article ,
wrote:

However, various escapements have been invented over many years and
the silent pawl used by Regina, SunTour and others has practically no
drag because the large "heel" has enough viscous friction in the body
to not snap back at rotational speeds of interest. That is also why
they cannot be heard.

Jobst,

Are any currently-available hubs equipped with the silent pawl you
describe? If so, which ones? Up to now, I've found Shimano to be quieter
than the other hubs with which I'm familiar, but if there's a hub even
quieter than that, I'd like to know about it. I am appalled by noisy
hubs like Chris King, which sounds to me something like a swarm of angry
bees.

David Newman

David Newman writes:

However, various escapements have been invented over many years and
the silent pawl used by Regina, SunTour and others has practically
no drag because the large "heel" has enough viscous friction in the
body to not snap back at rotational speeds of interest. That is
also why they cannot be heard.

Are any currently-available hubs equipped with the silent pawl you
describe? If so, which ones? Up to now, I've found Shimano to be
quieter than the other hubs with which I'm familiar, but if there's
a hub even quieter than that, I'd like to know about it. I am
appalled by noisy hubs like Chris King, which sounds to me something
like a swarm of angry bees.

I haven't disassembled a Shimano hub so I don't know what they use.
The problem with ratchets arose when freehubs reduced the operating
diameter of the ratchet and at the same time MTB's began using less
than 20t on chainrings with as much as a 1:2 ratio... four times any
gears that were encountered with previous freewheels. With Pawl
failure, most designs went to what they considered failsafe, using
double or triple engagement and unusual pawls.

In freewheels with ball bearings, that invariably are not perfectly
adjusted, eccentric rotation is probable and in that case only one
pawl carries the entire load. This is something engineers of the past
were aware of and therefopre never attempted multiple engagements.
Regina for instance had two pawls 180 degrees apart and 21 ratchet
teeth to give fine 42 engagements per rotation.

Campagnolo made an aluminum freewheel that didn't work even though
they thought they had triple engagement (of three pawls). Since they
were singly carrying the entire load at some point, they went into
yield under high pedaling torque. Hugi used the face spline that has
all teeth engaged at once but these also suffer from slightest
eccentricity that is inherent even elastically with the chain pull as
great as occurs at maximum torque.

As far as I could see, superficially, Shimano bit the bullet and made
their single pawls wide enough to hold the load one at a time. I
think their large size makes them noisier than classic freewheels.
Take one apart and see if there are an even or odd number of teeth in
the ratchet and the number of pawls.

Jobst Brandt

wrote:

Take one apart and see if there are an even or odd number of teeth in
the ratchet and the number of pawls.

2 pawls @ 90 degrees, 16 teeth

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

Marten Gerritsen writes:

Take one apart and see if there are an even or odd number of teeth
in the ratchet and the number of pawls.

2 pawls @ 90 degrees, 16 teeth

Oh how crude. 16 clicks per revolution isn't a low backlash device
when compared to old Regina and Atom freewheels with 42 clicks per
revolution. At least they gave it some thought. At 90 degrees, both
pawls (if perfectly spaced and identical in size and shape) can be
load bearing at the same time as they crowd the rotor against the ball
bearings on the opposite side. Still, the greatest load is held
primarily by one pawl that is at the top (where the chain pulls). At
other positions the load is divided between them variably.

www.m-gineering.nl

That's a nice collection of failures in the "Oops" site. Most of
those should not have occurred.

Jobst Brandt

m-gineering wrote:

wrote:

Take one apart and see if there are an even or odd number of teeth in
the ratchet and the number of pawls.

2 pawls @ 90 degrees, 16 teeth

Are all Shimano hubs like this? I've had many apart, but never counted the
teeth! I always assumed it was an odd number, with one pawl carrying the load
like previous freewheels.

Matt O.

Are any currently-available hubs equipped with the silent pawl you
describe? If so, which ones? Up to now, I've found Shimano to be quieter
than the other hubs with which I'm familiar, but if there's a hub even
quieter than that, I'd like to know about it. I am appalled by noisy
hubs like Chris King, which sounds to me something like a swarm of angry
bees.

Old LX silent clutch hubs are still available.

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

They are also available through J&B distributors.

--
Phil, Squid-in-Training

Phil Lee writes:

Are any currently-available hubs equipped with the silent pawl you
describe? If so, which ones? Up to now, I've found Shimano to be
quieter than the other hubs with which I'm familiar, but if there's
a hub even quieter than that, I'd like to know about it. I am
appalled by noisy hubs like Chris King, which sounds to me
something like a swarm of angry bees.

These guys are all scrambling to make a ratchet that can take the load
of overweight riders on 1:2 chain ratios and within the smaller
confines of current slide-on sprocket carriers. I'm not sure most of
them understand the problem with ratchets and which tooth is receiving
what loads.

Old LX silent clutch hubs are still available.

I'm not thrilled with roller ramp 'clutches', commonly used in
automatic car transmissions. They are silent and continuous but large
for their ability to transmit torque. They can be essentially
no-backlash devices.

Jobst Brandt

wrote:

I'm not thrilled with roller ramp 'clutches', commonly used in
automatic car transmissions. They are silent and continuous but large
for their ability to transmit torque. They can be essentially
no-backlash devices.

Large indeed. In fact the LX silent clutch weighs quite a bit more than the
standard one -- perhaps 5-6 ounces. To prevent literally exploding, it has to
be made of steel and fairly stout.

They're not my favorite design either, but I haven't heard anything bad about
them. They've been recommended for heavier riders, and are usually on sale
cheap because they're just *so* heavy, they're guaranteed to slow you down on
every climb. Cops use 'em, of course.

Matt O.