Shi. 105 r. der. parts replacement question
 

I will ask here since my LBS does not know, and I am likely to get the most expensive answer from the other LBS and Shimano:

I sheared off both sides of my 10 speed 105 rear derailleur short-cage this morning (the arms holding the upper and lower pulleys). the pulley wheels and the main body of the derailleur seem to be fine. does anyone know if:
a) I can get this replaced under warranty (stock on new bike)
b) if shimano sells rear derailleur cages separately, or do I have to plunk down for a whole new rear d.
c) if the latter, can I retrofit older shimano cages onto the new 10 speed one?

a related question is:

the 10-speed chain is also busted open--is it possible to cut and replace the mangled link, or would this require two special shimano-pins, and therefore would I better just replace the chain?

BTW this is on a relatively new bike, so the whole new chain-old cog issue should not apply.

Not sure on the RD, but if you managed to bust your chain at a set of outer plates, you just won yourself a brand new power link.

Did the chain and/or rear derailleur faol due to an accident or was it really a JRA (just riding along) failure?

If there was no obvious cause then maybe you have a warranty claim. If you had an accident or picked up a stick or other obstruction, I'm afraid the burden is on you.

I recommend you get a new chain. You will need a section of new chain and two pins to repair the old one so you might as well go for new.

As to the rear derailleur, the only repair parts I know you can get are the two pulleys. Even if available, other parts would be so expensive they make repairs unattractive, particularly the damage you reported.

BTW, 9-speed 105 rear derailleurs are available at very attractive prices these days (~$35) since they are "obsolete". However, they will function perfectly with 10-speed components so consider that as a replacement.

it was a just riding along accident--I have a 52/36 compact front, 12-25 10-spd rear, was on the 12- or 13-cog, shifted to the 36 to pop up a grassy knoll, and kaboom. No twigs around. Managed to avoid hitting a parking block and then teetered over because I couldn't unclip one foot.

That sucks about the parts. I just noticed that the main pivot for the derailleur cage is flat and therefore not serviceable (grease had made it look like it had a screw head on quick view). A brand new derailleur it is, then.

The 9-speed derailleur would then give me 9 speeds on a 10-speed cassette, correct? Or does the shift range overlap and the indexing controlled by the brifter?

Just figured out where that word came from, BTW: brake +shifter="brifter". But why not "shake"?

That derailler is essentially "dumb" in terms of speeds, it is controlled by the shifter. The total range on 9 speeds (even 8) is the same as 10 speed so the RD will move throughout the total range fine.

Newer Shimano rear derailleurs (like yours) will not allow easy replacement of the cage because it is secured by a pin that is staked into place. Look at the underside of where the cage attaches to the der. body and you will see it; it will be a b1tch to get out.

In the "old days" cages could be removed (and their tension springs adjusted) by removing the pivot limiting screw, but that part is now pressed into place and cannot be removed.

Try to get your shop to warranty it. If they won't, your best bet is to find a new RD on e-bay or check on-line for a deal; as previously noted a 9-speed will work just fine and probably be fairly cheap.

I'd guess that the chain spilled to the inside when you shifted and that's what caused the damage to it and the derailleur. You should seriously consider adding a Third Eye Chain Watcher or an N-Gear Jump Stop to your bike. A 52/36 chainring combination is a BIG jump for any front derailleur and you need the protection of having a chain travel stop.

Yes, the "9-speed" rear derailleur will work with any rear cog number since the brifter controls the movement.

Shake? Naw, I don't think so. "Brifter" is awkward enough. :)

Yeah, did the bike come 52/36? that ain't no compact double I ever heard of

Truvativ compact double:

It's a 50/36, my mistake.

I will def. look into the third eye thing, as I def. don't want this happening again soon. this is my cross bike, I imagine it will come in handy when the drivetrain gets gunked in mud.

Basso road a 52/36 in some hilly stages of the TDF or Giro last year. But it's not stock gearing on anything.

Most modern deraillers aren't rebuildable. They're also not too expensive. Especially if you can get it covered under warranty.

Since the 105 ten speed group is new, Shimano might be interested in your "failure story". I would contact them. Even if it isn't a warranty replacement, sometimes companies like to take a look at parts that failed for quality control reasons. They might give you a good deal on a replacement. It is worth a try.