Stripped axle nut, Shimano 8 speed hub gear



A

Andre Jute

Guest
Does anyone have suggestions for replacement cap nuts on my Shimano 8
speed hub gear axle? The Shimano code is Y-314 14010 and the spec is
BC 3/8" 26TPI.

I stripped one on my Trek Cyber Nexus, where Trek replaced Shimano's
own supplied cap nut with a shorter generic item to make it fit inside
the chaincase. I was torqueing it up to 40Nm at the time, which is
well within the spec for the Shimano's OEM type of 30-45Nm. Clearly
the replacement part isn't of the same quality as Shimano's original.
(And anything I choose shouldn't be machanically better than Shimano's
original: it would be horrid to strip the axle instead of the nut...)

Trivia: in replacing the stripped nut on the Trek temporarily with one
from my Gazelle Toulouse, I noticed that a) Gazelle get their cap nuts
custom made by Shimano's supplier (possibly via Shmano) with their
antelope symbol enamalled on the top in red -- nice -- and b) Gazelle
got their chain cases custom made to fit the cap nut, whereas Trek
bought their chaincase off the shelf, and tried to make it fit the
custom Shimano cabling (with expensive results in the first few bikes)
and had to replace the cap nut for clearance. There's a lesson in the
economics of scale here.

Sheldon reminder: Sheldon advised that the axle on the Nexus hubs be
greased, and a spot of grease used between the nut locking face and
the anti-turn washer in order to obtain a good hold with less force.
This is conveniently achieved by rubbing the grease across the locking
face of the nut so that the excess is on the internal thread, from
where it will transfer to the axle threads. I use Vaseline petroleum
jelly as routine thread grease: it's clean and it works well in my
undemanding conditions.

How high should you torque the Nexus hub's axle nuts? My LBS didn't
even own a torque wrench, and didn't use the one I bought to give him,
so by over-tightening he made indentations in the ali dropouts (1) of
an earlier bike of mine, which ****** me off and persuaded me to learn
to do my own maintenance. I started at 30Nm and eventually developed
chain slap, which indicates that the hub shifted forward. 35Nm and the
chain slap took longer to arrive. So I tried 40Nm with the above
result...

Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE & CYCLING.html

(1) Technically, track racing frame end cutouts are not dropouts,
because the axle cannot drop out.
 
R

Ryan Cousineau

Guest
In article
<[email protected]>,
Andre Jute <[email protected]> wrote:

> Does anyone have suggestions for replacement cap nuts on my Shimano 8
> speed hub gear axle? The Shimano code is Y-314 14010 and the spec is
> BC 3/8" 26TPI.
>
> I stripped one on my Trek Cyber Nexus, where Trek replaced Shimano's
> own supplied cap nut with a shorter generic item to make it fit inside
> the chaincase. I was torqueing it up to 40Nm at the time, which is
> well within the spec for the Shimano's OEM type of 30-45Nm. Clearly
> the replacement part isn't of the same quality as Shimano's original.
> (And anything I choose shouldn't be machanically better than Shimano's
> original: it would be horrid to strip the axle instead of the nut...)


Something's very wrong. Those axles have pretty big diameters and pretty
big threads, and we're talking steel nuts on steel axles. Stripping at
axle tightening pressures seems pretty odd to me.

It shouldn't even be a case of a poor-quality part, barring some sort of
weird manufacturing flaw. Can you even get steel nuts in those sizes
that won't (by spec) deal with these torques?

--
Ryan Cousineau [email protected] http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."
 
T

Tom Ace

Guest
On May 5, 9:13 pm, Ryan Cousineau <[email protected]> wrote:

> Something's very wrong. Those axles have pretty big diameters and pretty
> big threads, and we're talking steel nuts on steel axles. Stripping at
> axle tightening pressures seems pretty odd to me.


Nut threads strip more readily on an axle with flats than on an axle
without flats.

Tom Ace
 
A

Andre Jute

Guest
On May 6, 11:32 am, Tom Ace <[email protected]> wrote:
> On May 5, 9:13 pm, Ryan Cousineau <[email protected]> wrote:
>
> > Something's very wrong. Those axles have pretty big diameters and pretty
> > big threads, and we're talking steel nuts on steel axles. Stripping at
> > axle tightening pressures seems pretty odd to me.

>
> Nut threads strip more readily on an axle with flats than on an axle
> without flats.
>
> Tom Ace


I don't think it is Ryan's weird material failure, though the flats on
the axle may have made what happened easier by providing a hook. Once
I sourced another domed nut and also an open-ended gripnut of the
right thread (not the sort of thread the hardware stores sell -- they
carry only UNC -- but my LBS had some spares), I could see what
happened. To fit the axle nut under the full chaincase, Trek replaced
the tall Shimano axle nut with a much shorter one. In fact a standard
item, which I assume the one from my LBS to be, is shorter still. The
axle is not shortened. I moved the wheel a fraction to the right,
exposing more axle beyond the dropout, the Trek-supplied dome nut
banged on the end of the axle, and the torque wrench kept driving, so
tensioning the thread from both sides. Perhaps the corner of the flat
on the axle then helped to rip off the weakened thread when I
repeatedly unscrewed the nut and tried to screw it back up. It wasn't
until I inspected my Gazelle and referred to Shimano's literature that
I understood that the tall cap nuts are tall for a purpose. The
shorter dome nut from my LBS will clearly not do the job. So I fitted
the gripnut, which with its ridge is thick enough to cover the entire
axle extension beyond the dropout, such a tidy job that it is a shame
to hide it behind the chaincase. The whole affair is just a freakish
set of happenstances, nothing fundamental to worry about once one has
sorted out a nut that will fit and do no damage.

Thanks to all who contributed.

Nice ride of about ten miles in the lanes of West Cork after I fixed
it. Saw only a couple of cars and their drivers waited until we pulled
over for them and then thanked us with a raised hand for letting them
pass.

Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE & CYCLING.html