Bicycle Mechanics - My rear derailleur...kind of fell apart. With Pics!

Hi,
I have recently bought a used Gary Fisher Tassajara. The rear derailleur is a Shimano Deore.
While I was riding yesterday, I heard a noise and the next thing I know, the chain was no longer spinning the rear wheel.
I stopped and looked around, but the only thing I could find in the grass was a pulley - in the first picture.
Question - can this be repaired or do I need a new derailleur? From a search on the internet, it seems I would need a bushing and a bolt. Is this correct, where can this be bought? I'm pretty handy and have tools so I would like to fix this myself.
Thanks in advance.

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Can't tell from the picture if there's any collateral damage, but it looks like a simple case of the upper pulley bolt having loosened letting the inner cage plate slip and the pulley dropping off.

Assuming all is OK, and you have all of the pulley, you can simply screw it all back together and be on you way. The only likely issue may be that the cage plate is stripped, but you'll know soon enough. Also consider cleaning the screw and plate threads with acetone (not nail polish remover) or alcohol, and using some loctite to prevent a recurrence.

From the picture, you are missing at least one of the blushing covers see part #11 http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/RD/EV-RD-M510-1896_v1_m56577569830609142.pdf, it just fell apart, you need to work out why, did the upper screw strip out or just work loose over time (unusual for this to happen)?

Thanks for the responses. I didn't even realize that the bolt was still there until I looked at the diagram and the picture again. The hole wasn't stripped, I guess the bolt must have backed out somehow.
What is the best place to get the bushing covers? LBS or some place online?

What is the best place to get the bushing covers? LBS or some place online?

You can't buy those separately, Either buy a new pulley, or if you have a relationship with a local mechanic he might scavenge one off a used RD that died for another reason.

parts bin at the LBS likely has old parts, from crashed upon derailleurs.
while you are at it , check ALL the bolts on the bike,
and see if any others are loose and on the verge of falling out.

While you are reassembling and tightening things you might want to consider using some blue (removable grade) Loctite to help keep things from coming apart again. You might also take the opportunity to clean and lubricate your derailleur.

You might also take the opportunity to clean and lubricate your derailleur.


+1 may have precipitated the issue to begin with.

Your pulley hanger looks bent. Any chance that the derailure got caught in the spokes? Funny how some folks pooo poooo the old spoke guard "dork discs", but they did help keep misadjusted derailures from floating into the spokes.

IF your pulley hanger or even the derailure assembly hanger is bent then any time or materials you spend on fixing it will be wasted.

+1 may have precipitated the issue to begin with.

Actually, the #1 reason for this type of problem is probably installing the RD onto a bike that already has a chain. Most mechanics, including myself, find removing and replacing a pulley the fastest way to do this job.

The factories do a decent job tightening pulley bolts so they don't come off, but it's easy to get paranoid about stripping when replacing them, and so there's a tendency to under-tighten them. I'm not a big fan of Loctite for most bike work, but this is one place where it makes sense, especially with an aluminum inner cage plate.

Your pulley hanger looks bent. Any chance that the derailure got caught in the spokes? Funny how some folks pooo poooo the old spoke guard "dork discs", but they did help keep misadjusted derailures from floating into the spokes.



You're eyes must be much sharper than mine. Either that, or you have the new 3D graphics card and glasses.

In any case snagging the spokes wouldn't cause this problem, it would simply rip the cage or entire RD off. This is a simple case of a screw working loose.

BTW- to the OP, on taking a second look at the photo, I noticed your chain. If you're not using red chain-lube, it needs more frequent care. It didn't cause this problem, but running dry chains shortens their lif and can cost you dough. (of course you should consider the source when evaluating this comment).

"Actually, the #1 reason for this type of problem is probably installing the RD onto a bike that already has a chain. Most mechanics, including myself, find removing and replacing a pulley the fastest way to do this job."

This is exactly why I install a master link on all of my bike chains. It is then literally a snap to open or close a chain.

I have long believed that many times the cause of backed-out pulley cage bolts was that the "sandwich" of pieces being clamped together by the bolt had dirt stuck to and between the mating surfaces.
Thus, when the bolt is tightened/torqued, the layer(s) of dirt get compressed nicely, but does not maintain bolt tension over time.

For this and other reasons (like the prev-mentioned alloy cage plates that don't sustain quite so much tightening), LocTite is a very good idea on these bolt's threads, and is in fact pre-applied to the bolts of better derailers at the factory.
Certain off-road racing derailers have even come with supplementary circlips to further secure these bolts from falling out!

I don't always use LocTite here, but am somewhat cautious about tightening it together with all dirt removed from both sides of each pulley's dust shields and from the inside surfaces of both cage plates when reassembling pulley cages.

I once had an upper pulley bolt loosen while out training, which put the chain between the freewheel and spokes.
I actually pulled my shoulder joint out of it's socket trying desperately to yank the chain free, which cost me several early-season races that I had trained all winter long for. Lesson learned.