Rear derailleur , lower pulley problem

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Abhimanyu 244

New Member
Just bought a new cycle with front 3 and rear 7 gear combination. I have aligned and adjusted index several times but still whenever I shift to front third gear (i.e. outer most cassette) and rear 1st, 2nd and 3rd gear(i.e. inner cassettes) , chain doesn't sit on rear lower derailleur properly instead chain moves over it continuously, but when padels are rewinded chain perfectly sits over the lower pulley.
Please help me to solve the problem.
 

Ajax Bay

Guru
Location
East Devon
You describe cross chaining: large chainring (the larger toothed wheel at the front) combined with the edit: larger sprockets at the back. So the returning chain approaches the bottom jockey wheel ("lower pulley") at an angle. Try to avoid cross-chaining.
But having said that, you should be able to use these gears (7 speed triple) provided other matters are OK.
I offer 'rear mech alignment' and page @screenman
Check that the hanger (bolted to the right hand rear drop out - an aluminium bit) is 'absolutely' vertical. I'm going to guess that this a bicycle 'new to you' not new. If so quite likely it's been put on its side and the rear mech bent in (which could generate the symptoms described in the OP).
If the bicycle is 'new', get the seller to sort it out.
 
Last edited:
Location
Loch side.
Just bought a new cycle with front 3 and rear 7 gear combination. I have aligned and adjusted index several times but still whenever I shift to front third gear (i.e. outer most cassette) and rear 1st, 2nd and 3rd gear(i.e. inner cassettes) , chain doesn't sit on rear lower derailleur properly instead chain moves over it continuously, but when padels are rewinded chain perfectly sits over the lower pulley.
Please help me to solve the problem.

Allow me to translate and simplify. I hope I have this right. Your problem occurs when you are in the big chainring (front) and big sprockets (rear). In that position, the bottom pulley doesn't run perfectly with the chain when you pedal forwards. Is that the problem? I don't want to go down a wrong rabbit hole with an inappropriate answer.
 
The pulleys are designed to go in the mech in a particular order. One is the guide, the other one is the tension pulley. The way to tell, is that the ‘guide’pulley has ‘play’ built in, to allow it to move cleanly with the chain, as it traverses the cassette. The tension pulley is much more rigid. The guide pulley goes at the top of the mech ( nearest the cassette ) and the tension pulley is the one that goes at the bottom. The pulleys should be marked with which one they are, just in case. The pulleys need to be in the right positions and the writing needs to be facing outwards. It’s not uncommon to find them in the wrong positions, or fitted back to front ( writing facing inwards ).
 
OP
OP
A

Abhimanyu 244

New Member
Allow me to translate and simplify. I hope I have this right. Your problem occurs when you are in the big chainring (front) and big sprockets (rear). In that position, the bottom pulley doesn't run perfectly with the chain when you pedal forwards. Is that the problem? I don't want to go down a wrong rabbit hole with an inappropriate answer.
Yes sir you are right about it.
 
OP
OP
A

Abhimanyu 244

New Member
I
You describe cross chaining: large chainring (the larger toothed wheel at the front) combined with the edit: larger sprockets at the back. So the returning chain approaches the bottom jockey wheel ("lower pulley") at an angle. Try to avoid cross-chaining.
But having said that, you should be able to use these gears (7 speed triple) provided other matters are OK.
I offer 'rear mech alignment' and page @screenman
Check that the hanger (bolted to the right hand rear drop out - an aluminium bit) is 'absolutely' vertical. I'm going to guess that this a bicycle 'new to you' not new. If so quite likely it's been put on its side and the rear mech bent in (which could generate the symptoms described in the OP).
If the bicycle is 'new', get the seller to sort it out.
It is a fresh bike. The thing is that in India we don't have efficient mechanics for cycles, thus can't rely much on them.
The aluminum bracket is in its best condition.
 

Ajax Bay

Guru
Location
East Devon
I failed to say it in my first post but - :welcome::bicycle:
Don't think I can add much to my suggestions above - the hanger may still not be vertical - you need to check it. @Yellow Saddle will be along to give you more advice now that you've confirmed that his interpretation is accurate.
The reason why, when you pedal backwards, the chain sits perfectly on the lower (tension) jockey wheel, is because it's under more tension than normal and it's joining that jockey wheel inside the rear derailleur (RD) cage and 'leaving' it to move forwards to the chainring.
@Cycleops may be along too with his preferred RD adjustment video link.
 
Location
Loch side.
Yes sir you are right about it.
OK, in that case, lets start here:

Accept that the derailler cage never changes angle. It simply moves parallel to the cassette sprockets. It keeps that perfectly parallel position from gear one to gear whatever (9/10/10/11/12 or however many gears you have). Conform that for yourself if you don't see what I mean.

However, the bottom run of the changes angle significantly. Only in the middle gear (say gear 5 out of 10), will the chain's bottom run and the cassette sprocket be parallel and in line. In all the other gears, the chain line and sprocket plane are out of sync.

In the lowest gear (largest sprocket at the back), that line between pulley and chain is at its worse. The chain wants to pull across the pulley. The pulley points directly forward but the chain pulls to the right. In other words, as the pulley rotates and a tooth falls into the next available space in the chain, it hits the chain's sideplate and then slides down into the hole. That's why a chain in that position is noisier than one in the middle gear. There is mechanical interference.

To minimise this mechanical interference, the derailler manufacturer gives that pulley a special shape. The pulley's centre line is offset to the right. In other words, the chain doesn't run perfectly in the centre between the two end points on the pulley's axis. Now, if that pulley is installed the wrong way around, it accentuates the problem rather than solve it. That's why the pulley has a directional arrow on it. It is an indirect way of saying Left and Right. It has nothing to do with directionality of rotation but with positioning the offset in the right place.
I suspect your pulley is installed the wrong way round. Have a look and let us know.

The reason it works perfectly in the reverse pedal mode is because then the incoming chain is fed directly from the pulley above it, which is perfectly in line. The noisy problem is not at the top instead.

I hope this explains it somewhat.
 
OK, in that case, lets start here:

Accept that the derailler cage never changes angle. It simply moves parallel to the cassette sprockets. It keeps that perfectly parallel position from gear one to gear whatever (9/10/10/11/12 or however many gears you have). Conform that for yourself if you don't see what I mean.

However, the bottom run of the changes angle significantly. Only in the middle gear (say gear 5 out of 10), will the chain's bottom run and the cassette sprocket be parallel and in line. In all the other gears, the chain line and sprocket plane are out of sync.

In the lowest gear (largest sprocket at the back), that line between pulley and chain is at its worse. The chain wants to pull across the pulley. The pulley points directly forward but the chain pulls to the right. In other words, as the pulley rotates and a tooth falls into the next available space in the chain, it hits the chain's sideplate and then slides down into the hole. That's why a chain in that position is noisier than one in the middle gear. There is mechanical interference.

To minimise this mechanical interference, the derailler manufacturer gives that pulley a special shape. The pulley's centre line is offset to the right. In other words, the chain doesn't run perfectly in the centre between the two end points on the pulley's axis. Now, if that pulley is installed the wrong way around, it accentuates the problem rather than solve it. That's why the pulley has a directional arrow on it. It is an indirect way of saying Left and Right. It has nothing to do with directionality of rotation but with positioning the offset in the right place.
I suspect your pulley is installed the wrong way round. Have a look and let us know.

The reason it works perfectly in the reverse pedal mode is because then the incoming chain is fed directly from the pulley above it, which is perfectly in line. The noisy problem is not at the top instead.

I hope this explains it somewhat.
That’s what I reckon as well.
 
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