Excessive noise when in lowest gear

[Fifelad]

Just fitted new rear derailleur cables inner and outers, jockey wheels still in good conditon and the gears are indexing perfectly, it’s just when in the lowest gear there is excessive noise like the chain is not sitting exactly right on the jockey wheels. I’ve adjusted the B screw to the limit in both directions and the jockey wheels are in the correct way around and guide in the correct position ie tension and guide wheels. The only thing I can think of is the hangar could be a minuscule bit out of line ?

 

[Paulus]

As it's only the lowest gear, could the chain be slightly rubbing on the front mech if it is not going all the way over?
Was it running silently before you changed the cables?

 

[13 rider]

Is a double up front ? , I'd be checking front mec

 

[Dogtrousers]

Could be the B screw.

Recently I've had a problem with my rear mech in that the B screw somehow undoes itself and over time the derailleur cage sits closer and closer to the big sprocket and gets noisy. If I don't catch it in time it gets to the point where it won't change up out of first. Easily fixed by a few turns of the B screw to tighten it up. I don't know why it's just started happening.

Or it could be something else.

 

[Cycleops]

Road or mountain bike? Double or triple up front? What mech have you fitted? How many speeds?
A pic of the cassette and RD would help.

 

[notmyrealnamebutclose]

Road or mountain bike? Double or triple up front? What mech have you fitted? How many speeds?
A pic of the cassette and RD would help.

Don't stop there - get his bank details

 

[Fifelad]

Thanks for the input folks. After much head scratching, I took it to a LBS where after further head scratching, the conclusion was that a new rear mech is tried out. It appears that the spring on the rear mech is not quite doing enough to sit precisely in the right position when on the largest sprocket. The B screw was taken out and a larger one tried, to no avail.

 

[ColinJ]

Given the time of year (salty grit on roads) and a problem that I just had on my bike... Are you sure that there is not any gunk/corrosion in the pivots of the derailleur?

(I noticed that my rear brake had started sticking in the closed position. It turned out that it was gunked up/corroded. Cleaning and lubing the pivots sorted it out.)

 

[Cycleops]

Don't stop there - get his bank details

It's not me but the LBS that will be asking for those for the new mech.

 

[Gillstay]

Did the problem start after you fitted the new cables ?

 

[Ajax Bay]

Before forking out any cash (or bank details) for a new mech, just try a different mech (OP (still) gives no idea of the bike/RD/speed).
I'd also actually check the hanger's verticality.
As for "the spring on the rear mech is not quite doing enough to sit precisely in the right position when on the largest sprocket" Yeah: right. The lateral position of the guide pulley is determined by, inter alia, the cable pull and shift ratio (and the L limit screw will position the RD over the large sprocket). The spring makes sure the cage moves down the cassette and has minimal function when on the large sprocket.

 

[C R]

Before forking out any cash (or bank details) for a new mech, just try a different mech (OP (still) gives no idea of the bike/RD/speed).
I'd also actually check the hanger's verticality.
As for "the spring on the rear mech is not quite doing enough to sit precisely in the right position when on the largest sprocket" Yeah: right. The lateral position of the guide pulley is determined by, inter alia, the cable pull and shift ratio (and the L limit screw will position the RD over the large sprocket). The spring makes sure the cage moves down the cassette and has minimal function when on the large sprocket.

Maybe the OP has one of those exotic shimano thingies that worked the other way around 🤔

 

[Ajax Bay]

Rapid Rise - I came across one of those on a tip bike rescue. Worked quite well, and bike's in family use.

 

[Dogtrousers]

Rapid Rise - I came across one of those on a tip bike rescue. Worked quite well, and bike's in family use.

My first ever derailleur was a Suntour Skitter (which was already very old when I got it - manufactured in the 60s) which also sprung towards the big sprocket ("low normal"). This meant both gear levers worked the same way - push back to change up, forward to change down. When I got a "normal derailleur" and you pushed the right one forward to change up and the left one back to change up, it was a real shock. I've never been quite the same since.

 

[Fifelad]

Did the problem start after you fitted the new cables ?

No