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.
--
- Frank Krygowski