I snapped my rear mech off 160km into the Dirty Reiver 200 yesterday. Just riding along a gravel path, no sticks or big rocks involved. Here's why I think it broke. Is there an alternative reason? I just want to be sure it doesn't happen again.
Bike is set up with a Superstar 38T chainring, XT cassette, Deore 9 speed (non shaddow) rear mech and an XT chain. The chain is neither too short or too long; the long cage mech takes up all the slack w/o being overly tight in the big-big combination.
Hub is a Superstar Switch Ultra Rear Hub with a steel freehub body. I've noticed a few times that the freehub drags a little when freewheeling, i.e. it is still going round slightly with the wheel rotation. Just enough that I've noticed the chain sagging a little above the chainstay.
So it would appear that it stuck badly yesterday, pulled a lot of chain above the chainstay, shortening the amount of chain between the chainring and mech, hence snapping the gear hanger.
Does that sound about right?
Not to me. I doubt there's anywhere near enough inertia in a slow freehub to do that. Unless you think it could've "held" the chain on and allowed it to wrap right around the cog, back down to the mech?
Looking at the snapped mech hanger it would appear that it was bent backwards, which is the opposite of what I thought could have happened. I'm confused 🙁
The only other thing I've noticed when examining the mech is that the bottom jockey wheel isn't running very smoothly, but not sure if that is a pre or post-damage issue.
If the FH jammed/stuck, I can see how it might reel the mech in, once it's pulled the cage far enough to yank it over and get caught in the spokes it's the leverage of the wheel acting on the mech that's going to finish the job, rotating clockwise (facing the driveside) that will pull the hanger back (further towards the rear)... Does this sound right?
Wouldn't the chain snap before the mech?
But did you manage to finish?
Nipper99 - Member
But did you manage to finish?
Sadly, I didn't finish. Taken off in the broom wagon of shame.
cookeaa - Member
If the FH jammed/stuck, I can see how it might reel the mech in, once it's pulled the cage far enough to yank it over and get caught in the spokes it's the leverage of the wheel acting on the mech that's going to finish the job, rotating clockwise (facing the driveside) that will pull the hanger back (further towards the rear)... Does this sound right?
Looking at the broken hanger it is definitely twisted in towards the spokes as well as backwards. What you've described does sound about right. Cheers. I'll have a look to see why the freehub is a bit "draggy"
if the freehub sticks and you're pedalling slower than your back wheel is now coasting your rear mech travels back wards and gets ripped off.
A little bit of drag is neither hear nor there, all my bikes drag, because I grease the crap out of the freehub mech to make them quiet. I've never snapped a rear mech / chain because of it though.
Slight hijack. I greased thee free hub body/lugs whatever you call them on my full susser and found it missed engaging straight after I did this. I just presumed grease is not good and haven't done it again. Is that not the case?
Mate of mine was complaining of a free hub sticking, on investigation it was actually a seized axle/wheel bearing. This could rip your mech off
Had this exact thing on my hardtail, chain picked up some mud off road then when I hit loose gravel track a stone jammed the chain up in the top jockey wheel and the (awesome)power of my weedy legs did the rest, rear mech and hanger ripped off in backwards direction!!