I think I bent my rear derailleur. Will new cage plates fix it?

[scotsbikester]

Long (ish) story. My RD is XT-M772 SGS (the long cage one). Front is, er, I can't remember, some sort of Shimano triple. Wrestling the rear wheel off last night I think I bent my rear derailleur. Sequence of events is this:

1. Needed to take rear wheel out. Difficult, as tyre catches chainstay bridge mudguard bolt. Lesson learnt - deflate tyre first. Also my rear wheel removal technique needs improving. Anyway, it was late, and dark, there was much huffing and puffing.

2. Got it out, did what I wanted to (new disc pads). As I'd broken the chain, took opportunity to take cassette off, clean etc. Wheel back in, new chain on. Rear derailleur untouched, except for cleaning crud off guide and jockey wheels.

3. All back on. No way could I get it to index properly. I hadn't changed the cable tension - the cable wasn't unclamped, the adjuster wasn't touched. Endless fiddling, still couldn't get it to index.

4. I happen to have several spare XT-M772s. I put another one on, used but good. With only the most basic set-up it indexed perfectly. Had to do a bit of fiddling with the B-screw to get the guide wheel out of the way in big-big (not that I'll ever use that).

My conclusion is that the hanger isn't bent, but the "duff" derailleur is. I actually have two NOS new in box derailleurs, so tried to compare it to one of those. But the shape of a derailleur makes it hard to judge - lots of things at different angles.

Is my conclusion correct? That it's the derailleur itself, rather than the hanger? My simple "test by substitution" would suggest yes.

And I assume that the only part of a derailleur that can really be bent is the cage. Is that correct? Given this is "old" kit, I'm tempted to buy a new pair of cage plates, if that's all it takes to get it back to good working condition.

Any suggestions gratefully received.

 

[All uphill]

These derailleurs are tough; I have one that has acquired loads of scrapes in its long life; still works perfectly.

I can't imagine how removing a rear wheel could bend the plates, unless you were using a crowbar.

So, sorry, I'm no help. All I can suggest is closely comparing your suspect rd with the known good one.

 

[scotsbikester]

These derailleurs are tough; I have one that has acquired loads of scrapes in its long life; still works perfectly.

I can't imagine how removing a rear wheel could bend the plates, unless you were using a crowbar.

So, sorry, I'm no help. All I can suggest is closely comparing your suspect rd with the known good one.

Yes, I'm aware of their reputation. Which is why I have so many of them. A pair of plates is ~£40, I can get a new M592 for not much more than that. Mainly I'm really annoyed at myself - if it was my clumsiness that has damaged it. This was a NOS a year ago.

On the subject of how I damaged it, if I did, I'm afraid it was a combination of working on the bike when tired, and the fact that my wheel is a bit tight, and that I think my basic technique is poor. Not a crowbar, but I'm sure I got hold of the cage at some point to try to get it out of the way.

Yes, compare to known good one. Just holding two side by side isn't very informative. I think I'll have to take the cage plates off this and a good one, put them on a flat surface to compare, or something like that.

 

[Punkawallah]

My conclusion is that the hanger isn't bent, but the "duff" derailleur is. I actually have two NOS new in box derailleurs, so tried to compare it to one of those. But the shape of a derailleur makes it hard to judge - lots of things at different angles.

Is my conclusion correct? That it's the derailleur itself, rather than the hanger? My simple "test by substitution" would suggest yes.

And I assume that the only part of a derailleur that can really be bent is the cage. Is that correct? Given this is "old" kit, I'm tempted to buy a new pair of cage plates, if that's all it takes to get it back to good working condition.

Any suggestions gratefully received.

You could be throwing good money away by buying new parts that might not make it work? I’d be tempted to put the money towards your next NOS part and save the ‘broken’ one for spares.

 

[scotsbikester]

You could be throwing good money away by buying new parts that might not make it work? I’d be tempted to put the money towards your next NOS part and save the ‘broken’ one for spares.

Thanks. Yes, you could be right, I might be throwing good money away. Though there aren't any more NOS M772s available, I think I might have bought the last one in the UK, possibly the world!

 

[fossyant]

If anything has 'bent' on the M772, it will be the steel inner plate on the cage. These aren't expensive. You can straighten them.

 

[Punkawallah]

Thanks. Yes, you could be right, I might be throwing good money away. Though there aren't any more NOS M772s available, I think I might have bought the last one in the UK, possibly the world!

Try picking up a Suntour Perfect 14-32t freewheel :-)

 

[mickle]

Bend it back.

 

[Big John]

Bend it back.

+1 👍