Catastrophic drivetrain failure

[Psycolist]

I've suffered a series of chain breaks recently (all preceeded with that tell tale clicking) and have been lucky enough to escape without any damage, except to my pride, but about 5 years or so ago, on a particularly windy day, I had a plastic bag blown into my drive train. The resulting damage was exactly that seen by 'benb'. I've not heard of this happening without some off bike intervention by a piece of debris or animal (surley you have all had a squirrel bounce off y'spokes at one time or another) but from posts in this thread it seems to be a very common event. You live and y'learn. !

 

[Pale Rider]

It's not good. The mech mounted directly to the frame, and the part of the frame aft of the dropouts is badly bent - so much that it is touching the cogs on the cassette. The LBS doesn't have the facilities to deal with this, so I'm going to take it to a framebuilder in Croydon. The bike was £1,100 new, which was 18 months ago, so I'm thinking if it costs more than £400 to repair, it's not worth it.

I wonder if the twisting force against the base of the nut has bent the axle.

 

[mickle]

Reynolds 725 I think.

That'll be the tubing, not the lugs.

 

[mickle]

I wonder if the twisting force against the base of the nut has bent the axle.

No.

 

[mickle]

Well I have known it to happen: makeshift shortened chain, accidental shift into big-big resulting in derailleur rubbing against/scuffing spokes (but not enough to entangle - luckily). I see no particular difference between chain overtension due to short chain vs chainsuck. I am not saying chainsuck is definitely what happened to the OP, it's just a possibility.

http://sheldonbrown.com/derailer-adjustment.html
"If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination"

Sheldon shmeldon.

 

[GrumpyGregry]

GC, Once metal bends beyond a certain point it will not go back into place safely.

Now try this get a piece of metal and bend it once fine, now bend it back you have weakened it.

Your advice should carry a safety warning.

What metal?
What degree of bend?
Is that metal used to make drop outs on 725 tubed frames?
Is this particular drop out bent to that degree?

 

[Pale Rider]

No.

Mickle shmickle.

 

[GrumpyGregry]

Am I right in thinking the hanger thread (M10 x 1) is the same as Shimano rear axle? So a step up from using a shaved gorillla (© Greg Collins) with an adjustable spanner could be to screw a bit of axle into the hanger hole and then apply the same shaved gorilla.

Funny you should say that. I've got an old axle or two and was going to give it a try on a beater SS frame (which has a bent hanger) with a view to carrying the axle on next years night rides as I find the complexity of an adjustable spanner hard to master at 04:00 with no sleep. But then shaved gorilla's like yours truly are easily confused.

I shall report back if it ever stops raining (my workshop is the great outdoors).

 

[GrumpyGregry]

Reynolds 725 I think.

any chance of a shot of the drop out from behind and or below?

 

[mrandmrspoves]

Similar problem happened to me a few months ago when the Deore rear mech snapped at the hinge and collapsed into the wheel on my 631Dalesman. Also had a bent hanger....the problem with the big spanner approach is that even a small degree of inaccuracy will lead to major indexing issues. I purchased a hanger allignment tool (cyclo) for less than £30 and sorted it myself. Easy job with the right tool...

 

[mrandmrspoves]

Like Mickle's offer - happy to lend the tool, though postage wouldn't be cheap as it's a heavy bit of kit. You screw one end of the tool into the gear hanger and then line the sliding gauge up so it just touches the wheel rim at 12 o'clock, then rotate the tool to 6 o'clock, 3 o'clock and 9 o'clock. ... this then ensures that the hanger is correct in both vertical and horizontal plains.

 

[benb]

Well, picked it up today from Chas Roberts frame builders. They had to heat the frame to straighten it, drill out the ruined thread from the mech hanger, and put an insert in with a new thread.

Total price £70.

Now it's at Pearsons for some new spokes, new rear mech, new chain and general check. That might be another £70-£100

Can't wait to get her back.