Why does a rear derailleur bend outwards?

[Deleted member 89023]

Hi All, my chain is sometimes hesitant dropping onto the smallest rear sprocket. It can shift instantly one minute, and then hesitate the next minute. I've indexed the gears and lubricated the shifter, but it's still temperamental. I now suspect the derailleur is bending outwards, I have included a pic for your good selves to correct me if needed. What's puzzling me is how does the RD bend outwards? Inwards yes, but outwards?

 

[Ajax Bay]

If you 'just' unclamp the cable, what sprocket does it settle on?

 

[fritz katzenjammer]

it’s really hard to tell from your photo but…

If your derailleur isn’t straight either it or the hanger bracket is bent. I would bet that one in five bikes I build have one or both of these problems straight out of the box. ( usually inward due to being banged about during shipping )

I’ve bent a lot of derailleur straight by hand, that’s no problem with a little care. These silly things can take an amazing amount of twisting and still work fine once straightened. The hanger bracket is a different matter, a slight bend in these can cause endless weird shifting issues and the only way to straighten one is with a proper alignment tool. If the hanger bracket is bent and you don’t own an alignment tool it may be cheaper to just buy a new bracket and fit it yourself as our shop would charge about $25 to straighten it using said tool whereas the bracket itself only costs about $15.

 

[Deleted member 89023]

If you 'just' unclamp the cable, what sprocket does it settle on?

The smallest.

 

[Deleted member 89023]

it’s really hard to tell from your photo but…

If your derailleur isn’t straight either it or the hanger bracket is bent. I would bet that one in five bikes I build have one or both of these problems straight out of the box. ( usually inward due to being banged about during shipping )

I’ve bent a lot of derailleur straight by hand, that’s no problem with a little care. These silly things can take an amazing amount of twisting and still work fine once straightened. The hanger bracket is a different matter, a slight bend in these can cause endless weird shifting issues and the only way to straighten one is with a proper alignment tool. If the hanger bracket is bent and you don’t own an alignment tool it may be cheaper to just buy a new bracket and fit it yourself as our shop would charge about $25 to straighten it using said tool whereas the bracket itself only costs about $15.

Looking from behind and lining it up with the wheel, the hanger seems dead straight.

 

[faster]

Looks straight enough to me.

Replace your gear cable, inner and outer (for the outer you'll probably get away with just replacing the short loop nearest the derailleur), and your problem will most likely be solved.

 

[presta]

Are the pivots on the parallelogram worn? Does the end stop need adjusting?

 

[Deleted member 89023]

Are the pivots on the parallelogram worn? Does the end stop need adjusting?

They all seem ok. I've just had it up on the stand and indexed the gears to almost perfection. I'll now wait and see how they are on a ride.

 

[raleighnut]

Hanger Alignment, it's no good just fitting a new one cos that will need aligning too.

 

[Ajax Bay]

If you 'just' unclamp the cable, what sprocket does it settle on?

The smallest.

Well make sure that there's no tension in the cable in that position.
Clamp the cable (with cable 'tight'), one click, and then use the adjuster to put a bit of tension into the cable enough to lift the chain onto sprocket 2. The H limit screw prevents the RD overshifting (not cable tension) outwards of the smallest sprocket.
Reverse the click and the chain will drop down.
The image shared does not suggest a hanger alignment issue (to me), nor does the OP 'symptom' description.

 

[screenman]

Hanger alignment, you cannot see it by eye, I have been writing about it since the forum begun, or nearly. I Have never once checked a bike that did not need it tweaking, unless it had been done recently.

 

[Gunk]

Pop into a bike shop and let them check it with a proper alignment tool. Most of the hangers I check are bent, however they need to pretty out of line to effect shifting.

 

[raleighnut]

Pop into a bike shop and let them check it with a proper alignment tool. Most of the hangers I check are bent, however they need to pretty out of line to effect shifting.

Ah but they never shift 'sweetly' without the hanger being set up properly and the more gears the more critical it becomes

 

[fritz katzenjammer]

Looking from behind and lining it up with the wheel, the hanger seems dead straight.

The issue described Sounds like a bent hanger. i Find that even a slightly bent hanger can screw up shifting. Often when I can’t get a bike to shift quite right I throw the alightment fixture on even though the hanger looks quite good, I’m often amazed at how bent or twisted they are. IEyeballing the hanger from the rear only gives you a part of the picture, if the hangar is twisted at all it can ruin shifting but still look straight.

 

[Witzend]

Hanger alignment, you cannot see it by eye, I have been writing about it since the forum begun, or nearly. I Have never once checked a bike that did not need it tweaking, unless it had been done recently.

I've just done mine with a newly-acquired hanger-alignment tool. I'd hung on buying one as it looked perfectly straight to the eye but it was actually out quite a bit on both the X- and Y-axis. Someone on here posted a link to a YT video where it said it often manifests itself with problems shifting into the highest or lowest gears, which matched mine (and this OP's) symptoms. Definitely worth getting/borrowing one if normal fettling fails to provide the desired results.