Bent RD? How to Fix?
 

Hi,

I have a hybrid with an Altus RD. I think the RD is bent slightly inwards (see pics) but it rides fine apparently. Is this a significant enough issue to fix? If so, do you just bend back the hanger?

Use the services of your favorite bike shop , it is likely the frame hanger for the RD that bent,

the alignment is Crucial if you expect the Indexing to work

and it gets fussier as you add more "speeds" the Shop Tool compares over 270 degrees
of the wheel to get the hanger right on .





./.

If it is shifting well enough I would suggest leaving it alone. Never Fix A Running Piece.
If you insist on fixing it the correct approach would be to use a gauge to measure/adjust the hanger alignment and then mount the derailleur and evaluate its straightness. As it stands you have no way to determine if it is the hanger or derailleur (or both) which is (are) bent.

So it is bent?
 

Thanks. From the pics is there an issue? I wasnt sure if MB RD were supposed to be inwards leaning

apply crescent wrench, carefully apply leverage, reassemble. it's totally easy, and the hangers are replaceable anyway, so you won't be any worse off if you try to fix it.

If it works, don't mess with it.
IF you decide to mess with it, you best locate and PRICE a replacement hanger first.
You may decide it's just fine after all.

http://derailleurhanger.com/
http://www.jensonusa.com/Derailleur-Hangers?by=Category
http://wheelsmfg.com/derailleur-hangers.html

+1 And if you decide to buy another hanger, buy a spare.

It is difficult for anyone to give you advice on if its bent from a photo unless it seems obvious. Typically the derailleur is straight up and down. Everyone's advice so far has been very good.

925 Engineering Replacement Derailleur Hangers

Cheap and beautifully CNC machined.

If you have a spare rear wheel you can use it in place of the proper tool as a gauge to check for a bent hanger. Remove the rear der. and thread the axle from the spare wheel into the hanger. If the wheels are parallel you are ok, if not you can use the spare wheel as a lever to bend the hanger until the wheels are parallel.

Very Clever.
 

Great tip. Thanks!

The problem not often mentioned about der alignment (note I don't say hanger alignment) is that it's the der cage and it's movement that counts. Not the mounting bolt several links above the cage. The angle of the parallelogram does effect, to a degree, the indexing. But I will say that from my shop experience the cage, how it pivots, how the guide pulley maintains it's in and out alignment WRT the plane perpendicular to it's pivot has a greater effect then if the mounting bolt is square with the wheel.

I see a lot of ders that when installed on a straight hanger have the cage/guide pulley rotate out of plane. So that when the cage is played out (like when the large ring and meddle to large cogs) the guide pulley is inward of the intended cog's center line YET when the same drivetrain is in the small ring and the middle to smaller cogs the guide pulley (having rotated about the cage pivot) is now running outward of the cog's centers. How does one reconcile this? How does this happen?

It happens when the cage is not flat/square to it's pivot bolt more the when the mounting bolt isn't square to the frame. Why migh the mounting bolt not be square to the frame when the hanger is straight? When the mounting bolt is bent, it's threads are not coaxial to the bolt's shaft or the bolt's B spring plate and retaining clip are not allowing the bolt to seat square when tight. I have seen MANY ders that go through a orbital wobble while threading the upper mounting bolt into the hanger. Happens far more then not. An interesting point is when a hanger is aligned and one der hangs not so straight yet another der does... with no further hanger work.

I have watched other mechanics who have much experience go to the der hanger alignment tool more then once during a repair to solve why the indexing isn't consistent across the full range of the cassette. As though the straight hanger is the end all and they must not have achieved that result even after the second or third time...

This is a long winded post about a topic I have given a lot of time and thought to. I know I am bucking the pedestal that hanger alignment is considered. But indexing is about how the guide pulley maintains it's location below each cog that counts. How that is achieved is the question. I welcome other's thoughts, especially those with years of experience and not just those who read a lot. If you reply please consider offering your years of experience as a reference. Andy.

An age old pitfall, "there's a tool for that" Lots of mechanics, not anywhere near as much experience. Me with almost 50 yrs, bicycles, motorcycles and cars = still learning.

I'm glad you brought this up. I have seen this too, the hanger alignment perfect and derailleur looking droopy... and changing planes WRT chain length and Big ring or small ring. Mostly I blame Shimano about this , with there "B" screw adjustment, which I don't think is really needed, but it adds another sleeve or bushing within the mounting bolt that has some play or droop built into it. Sometime I have resorted to "just grab the RD and bend it" method.

Thanks but I'll add that I've seen the same with "old guard" ders like Campy NR and SunTour V series (to name some) which have non spring loaded hanger mount pivots. In fact that is when I first begun to think about the geometry of der's many moving and rotating elements.

Then there's the ders that have suffered trauma and have their parallelogram twisted... Andy.