neeonbrowwn

so i ride a Swobo Otis to and from work rain or shine..

was on my way home the other day and heard a deafening crunch, briefly felt something akin to chain suck, and then found myself on the ground, staring at the sky

turns out the bolt attaching the action arm of the coaster to the frame had sheared. so when the brake was applied, the arm spun freely, and also on the other side of the hub, the cable attachment for the shifter spun as well, wrapping the cable around the hub, popping off all the attachments from the hub to the shifter and in turn shortening the length of the cable, forcibly turning the handlebars, throwing me from my Otis.

damn. so i removed the wheel, unspun the cable, and hobbled home in first gear.

i see now since i used an M5 instead of an m6 for the bolt at the swing arm attachment, that is the likely culprit..

so could i beef up the weak point by using a stronger bolt? ie the titanium M6 bolts on ebay. would these have more tensile strength?

also is my hub shot? the cable where it attaches the hub is frayed. see attached pic


thanks for any imput

AnkleWork

You think the bolt sheared but you are concerned about tensile strength? Oh well, it's your story.

To answer your question, a titanium M6 is not likely to have greater tensile strength than a steel M5, depending on actual alloys, heat treatment, and some other stuff (even though titanium is much more fashionable than steel) .

Dan Burkhart 

What hub is that? Looks like a Sachs/Sram cog, but the shifter mech doesn't look like anything I recognize.
Titanium bolts are generally not known for superior shear strength over good old steel.
Under normal circumstances, a loose reaction arm would not cause axle rotation which would be necessary to wrap the shift mech around like that. Were the anti rotation washers in place? (Might be only one on that hub) and if so, did it tear out of the dropout as well?
It could be an internal problem in the hub precipitated these events.

dsbrantjr

It is likely that your bolt sheared because it was moving and wearing in the reaction arm hole. This could have been caused by its being under-tightened, undersized or both. In addition a 6mm bolt has roughly 50% more area than a 5mm one (6 squared divided by 5 squared) so should be roughly 50% stronger. A larger bolt will also distribute the shear stress across a larger area for a given hole size. A bolt like this https://www.boltdepot.com/Metric_sock...m_x_1.0mm.aspx
should be plenty strong if kept tight.

Titanium fasteners need to be engineered as a system, with proper hole sizing and attention to so-called fretting corrosion and other issues. Just replacing steel with titanium is unlikely to give the desired increase in strength. I suspect the the Ti fasteners on Ebay are not of the best alloys or finest workmanship but are made more to cater to "weight weenies".

hueyhoolihan

i would buy the proper, probably steel, bolt and washer, if there is a washer. and check that any devices used the keep the axle from rotating are in order.

if you have the sheared bolt to atest to it being sheared. i agree that it was probably the cause, but if you don't have it, and it had a nut on it, i wouldn't be surprised if it just backed itself off, given the slop afforded it by using an undersized bolt. just a guess...

sounds like you had a "Perfect Storm". glad you weren't hurt.

i'm finding difficult to picture a cable wire that runs through a cable housing that can be shortened, unless a cable housing stop or two failed or the housing runs all the way from the handlebars to the rear hub. and it may for all i know.

Jax Rhapsody

it will if you're trying to stop. happened to me on a schwinn santa fe II. the bolt fell out and the torque arm after each unknown stop, spun. every time it spun it tightened the lugnuts.I didnt figure it out till the second time I stopped and it didnt want to.

Dan Burkhart 

The reaction plate, to which the reaction arm is attached usually also incorporates the left bearing cone. (again I say, the OP has not shared with us the make or model of hub), so theoretically, when the reaction arm spins free, it will rotate the cone, tending to loosen the bearing adjustment in the hub, but if the locknut is properly tightened on the cone/reaction plate, and the outer locknut on the outer side of the dropout is secured, there is a limit to how far it will rotate.
To spin the shift mech requires rotation of the axle, which can only occur if the anti rotation washer was A) not present in the first place, or B)failed in the course of the above calamity.

Jax Rhapsody

it is a geared hub and may act differently than a standard coaster. I'll give you that. Just comparing a similar sutuation.

neeonbrowwn

i hear you guys on the titanium. I think i should be covered with upsizing to a M6 and keeping it tightened.

Dan.. i think it is this hub: https://www.amazon.com/Sram-I-Motion-.../dp/B004YIDCHM
-dou you think it is likely self fixable, take it to the shop, or scrap it altogether?

also i didnt have an anti-rotation locknut.

Dan Burkhart 

Probably fixable if you have a nearby shop that has a gearhub guy. Not many do.
It's almost certain the bearing adjustments, which are critical to proper operation of a gearhub have been thrown out of whack. Can't see from the photo you posted if any damage was done to the shifting mechanism, but that may just be a matter of replacing the cable.

Dan Burkhart 

Another note about Sram 3 speed hubs. I admit limited knowledge here, I know more about their 7 speed hubs, but I did have a couple of bikes in my rental fleet a number of years ago with Sram Dual Drive hubs. Those bikes came from the factory without anti rotation washers. I remember thinking at the time that was strange and risky. What I can't remember for sure is whether the axle had flats to accommodate them.
I kept the lock nuts tight and never had an issue.

FBinNY 

Even steel bolts vary in strength. I'd take out extra insurance by using a heat-treated bolt, or at least a stainless steel one. Either is stronger than a standard commercial plated bolt. (see chart).

Also the proper bolt will have solid shank through the arm and only be threaded where the nut attaches. This ensures full strength in the shear zone vs. the reduced strength at the root of the thread.

fietsbob

Cables on coaster brakes?

MEversbergII

Cables on gear hubs that have coaster brakes.

M.

fietsbob

so you go to , what Shimano tech manuals , that are online .. much will be displayed ..

if you can read the lettering on the hub ,. that may help. to get which one you have..