I Bent My Rear Axle!

 Had the rear tire replaced at the dealership today.  Just because I'm anal
and because I went over one pothole in the middle of the night that just
about broke my back (the "hit" seemed to be the rear tire coming out of the
hole), I had ordered a new rear axle in advance and picked it up at the
parts department and gave it to the service department to swap in.

I looked at the old axle.  I cleaned it up with a paper towel.  It seemed to
be bent, but because of the marks on it, I couldn't be sure it wasn't an
optical illusion.  We got out a straightedge ... yep, bent.

The bend is very minor, maybe about 1/16 of an inch runout.

The bend itself isn't centered on the axle -- it is closer to one end than
the other.

It wasn't a safety issue.  The dealership told me stories about axles bent
so badly that they couldn't get them through the wheel to remove them.  The
things won't fracture.

All interesting.

It gives me a data point, to know that this can be done and how much force
it takes.  Seriously, that bump was really close to breaking my back.

DF

 wrote:


Well then, that side of your *swingarm* may be permanently bent/
twisted too.

In order to determine this, you need to check whether or not the rear
wheel is vertical at the same time as the front wheel (with the front
wheel pointed straight ahead) and check to see that the rear axle is
parallel with the swingarm pivot bolt

If the axle and swing arm pivot bolts aren't parallel, your swingarm
is twisted.

It might be easier to have a shop with a laser alignment tool to do
this for you...

 
There is a whole lot of complexity in evaluating that statement, and my only
response is "I'll check the swingarm when I have it off, probably over the
Winter".

Here is the complexity ...

My axle threads through from the left, and the nut is on the right.  The
chain is on the left.

The bend in the axle is further towards the right (closer to the nut, and
further from the chain).

Looking at the bike from the back, it appears that the tire is not centered
in the swingarm or along the axle because of the sprocket and cush drive.
So, any extreme forces on the wheel might tend to bend the axle at a point
further to the right (even if the forces were straight up).

Also, it has been a year or two since I had the wheel off and apart, but
(again because of the sprocket and cush drive), my recollection is that the
two bearings for the rear wheel might not be symmetrically placed with
respect to the left-right center of the wheel.  I don't remember if this is
true, but I remember there were two seals in there ...

Anyway, if the bearings aren't symmetrically placed, it might again mean
that a straight up force on the tire would tend to bend the axle at a point
to the right rather than at the center of the axle.

So, I don't know if the bend not being centered on the axle means there were
lateral forces on the wheel, or if this is an unavoidable consequence of the
mechanical design even without lateral forces.

Shorter answer:  I'll check the swingarm.  Good call.

DF

 wrote:


Have somebody follow you while you ride down a flat road to see if the
rear wheel seems to be running at a slight angle from the vertical and
the motorcycle is running down the road like a puppy dog.

Another way to tell if something's bent is that the motorcycle will do
a big dutch
roll around all three axes when it hits a bump.

 wrote:

Or you could buy a motorcycle with decent suspension.


Naaaaaaahhhhhhhhhhh.