On 9/25/2018 6:58 PM, Mark J. wrote:
On 9/18/2018 7:18 PM, Frank Krygowski wrote:
On 9/18/2018 1:43 PM, AMuzi wrote:
On 9/18/2018 12:03 PM, Frank Krygowski wrote:
I'm finishing up the build of a sweet kids bike, including a
NOS Shimano 3CC coaster brake hub of unknown vintage.
(Thanks again to Andrew as the source of the appropriate but
rare shifter.) The bike is a very lightweight and pretty
little antique. It also has hand brakes.

The bike is in my workstand and ready to go, but I have one
worry. When turning the cranks, there seems to be excess
resistance. It's not the bottom bracket, because I
overhauled that, plus the cranks feel very free during the
forward or backward motion until the drive or the brake
engage. It doesn't affect coasting; the rear wheel seems to
spin very freely, so the coaster brake is not dragging. The
friction seems to be in the drive motion itself.

(About five and ten years ago, I resurrected two other bikes
with Shimano three speed hubs and don't remember feeling
this resistance. But that was long ago.)

I've added lubricating oil via the axle's pushrod hole, but
so far I perceive no difference. I'm (understandably?)
reluctant to disassemble the hub, not only because I'd like
to deliver the bike in three days. Is there a reasonable
chance it will "wear in" and loosen up? Should I consider a
solvent flush and adding oil? Or I wonder if there's a
bearing adjustment that applies to the drive mechanism,
separate from the main wheel bearings?

I've gazed at the Shimano hub manual available at Sheldon's
site
https://www.sheldonbrown.com/sutherl...-5-shimano.pdf
but at least so far, I don't recognize a solution there.

Any tips?


Unusual problem these are so simple and reliable generally

1. Unlikely to be the problem but check hub bearing. Mount the wheel
in a vise adjustment side up.Â* Hold the axle in one hand and move the
rim up and down in the other.Â* Adjust for a trace of play at the rim.

2. Maybe a tight spot in the chain adjustment? Easy to check for that.

3. Possible frame ends not parallel and axle is flexing. This would
have to be extreme for a symptom.

4. Perhaps dirt/crud/rust in gearbox.Â* Wouldn't hurt to undo the
adjustment enough to peek at the bearing. If rust shows, these are
simple assemblies don't be afraid of a rebuild/clean/lube.

Do write back I'm curious to know what you find.

Well:

1) I put the wheel in an axle vise in my bench vise and played with
the wheel bearing adjustment. I didn't see any improvement, but I'll
keep it adjusted a tad looser than before, just in case.

2) No, the chain is definitely not tight. If anything it's a bit loose.

3) Dropouts look fine. I had to do quite a lot of cold setting to get
the hub into the frame in the first place, and the two 5/16 bolts with
nuts and washers that I used to test the dropout alignment were still
in the top of the relevant bolt jar. The point precisely at each
other. Probably more important, the dropouts are stamped and only 1/8"
thick, so they seem unlikely to exert serious bending loads even if
they were out.

4) I pulled the left hand brake arm and the bits that came with it.
All looked greasy and black inside the hub. The grease was higher
viscosity than what I might choose, but it wasn't dried out

I noticed that with the axle in the vise, when I turn the sprocket
forward by hand, I could feel some reaction torque in the brake arm -
IOW, the arm wanted to rotate with the wheel. I put a spring scale on
a short length of chain. I measured about 3.5 inch-pounds of torque to
drive the wheel, and a reaction torque of about half that on the brake
arm. So half the drag was internal.

So I stripped the hub, following Sheldon's PDF, but I didn't bother to
pull the palls, planet gears, etc. out of the sub-assemblies. The hub
internals were entirely slathered in heavy grease. I cleaned most of
it out, washed all the components down reasonably well with WD-40 and
inspected everything. I saw no problems at all. In fact, I'm sure the
hub has never been used.

I reassembled using lighter grease on the ball bearings, heavier
moly-disulphide grease (used for CV joints) on the brake shoes, and
automatic transmission oil everywhere else. I squirted in additional
oil when it was all together.

It's all back together, and it may be slightly improved. (I didn't
bother putting the spring scale on it.) But it's still somewhat
draggy. I'm now assuming it's just the nature of the beast. Maybe it
will "run in" after some miles, although I didn't identify anything
that would make that happen.

BTW, this hub seems more picky about shifter cable adjustment than a
Sturmey-Archer. Gear #2 skips if the adjustment is even a tiny bit loose.

Anyway, I consider the project done, and it is what it is. Thanks for
the ideas.

One last minute idea, which may not apply to Shimano.Â* I just overhauled
a Sturmey-Archer AW three-speed hub from the 70's.Â* Re-reading Sheldon's
site (don't remember which page, of which there are many), I was
reminded that the "Ball ring," which screws into the drive-side
hubshell, has a double-track thread - i.e. two separate spirals cut in
it - so that you can initially engage the threads in two ways, which
result in final positions 180 degrees apart.

Sheldon says it matters which of the two ways you start it.Â* Dumb me
said "what difference can it make".Â* Now I know.Â* With the ball ring
spun 180 degrees, the bearings don't adjust well, the sprockets "wobble"
while coasting (no big deal there), and you get some of the friction you
describe in your Shimano.Â* Oh, and if you true the wheel that way, then
when you put the ball ring back where it belongs, the wheel has a small
but symmetric "wobble."

Now I've put everything back the right way, it's amazing the difference
(and yes, I did re-true the wheel).Â* What I can't understand is how the
manufacturing process causes one thread engagement (of the
"double-thread") to be nice and concentric, and the other one to be
off-axis - or what else is causing these differences.Â* If someone
understands what is really going on there, please enlighten!

Again, Shimano may not have copied the double thread, so this may not
apply to your hub.Â* But if so, I can give first-hand testimony that it
can really matter.

Interesting. I've rebuilt S-A hubs, but I don't remember thinking about
that double thread.

I doubt it matters with this Shimano hub, though. For one thing, I'm
convinced the hub was factory original, never used. And the instruction
PDF I got from Sheldon's site didn't mention that.

Anyway, it's kind of moot now. The kid's got the bike and he loves it.

--
- Frank Krygowski