Calvin Jones here, Park Tool Company, with Tech Tuesday.
This week we had this used bike come through our shop and it had an interesting symptom.
Let's have a look at it, and take notes, because you're gonna have an exam.
Let's have a look
I want us to watch the rear cogset
That's kinda fun, isn't it?
So, what is it?
A: It's a new dynamic pedaling system that changes our gear ratio every pedal stroke
B: it's a loose cassette lockring, that's all. The cassette cogs are not tight to the freehub body.
C: it's a cross threaded freewheel. It was put on crooked to the shell and it's cross threaded
D: it's a broken axle. That's all it is.
E: it's a bent axle.
Well, one way to find out and that's to drop that wheel
but let's back up and eliminate some of these things here.
Did you answer A: dynamic pedaling system?
Well, it actually is changing that moment arm, that distance that you're pulling,
but it's not every pedal stroke; couldn't be A.
B: loose cassette lockring. Sometimes you see that,
this case: it's a screw-on freewheel. Not B.
C: cross threaded freewheel. Well, it is a free wheel, it's not cross threaded.
This last cog would wobble greatly to the center of the bike and we're really not seeing that.
D: a broken axle.
Grab the rim, grab the frame, pull back and forth hard,
no clicking, no popping, no snapping. Probably not broken.
I'm holding out for E: bent axle.
Let's find out!
Drop it, pull it back, out it comes.
Let's give it a spin.
Oh man, that is bent.
Is it broken?
I pull outward - it is not broken.
Definitely a badly bent axle. The motion there is causing that to float around.
E: bent axle.
Well, what caused this and how can we fix it?
Let's start with the latter part first.
Replacement is definitely the best option of the axle, and possibly the bearing cones,
from being ridden with this really bad tight-and-then-looseness
possibly trashed the bearings inside.
Let's take it a step further and inspect the frame.
And now we'll talk about how that could have happened.
It takes, actually, a really bad smack of a curb, a pothole, to bend things.
These are called frame and fork alignment tools, Frame and Fork Gauges,
What this does, it lets us see if the dropouts are aligned.
I install one on one side, I install one on the other,
we bring them together symmetrically and they're actually good.
So the frame here is not the problem.
If they were crooked, then we would know that our frame is badly out of alignment
that causes the axle to bow in between
but here it's sitting pretty reasonably straight.
So possibly that impact that also bent this wheel
that maybe is what led to this bent axle.
See you next time.
Turns out the answer is actually F: none of the above.
- We took it apart...
- something surprised me...