avidone1

I have a Shimano Altus rear derailleur
It's 8 cogs with 3 chainrings up front.
I mostly ride the second chainring shifting up and down the cassette as needed.
My bike is nice and quiet, especially since I lubed the chain the other day. It shifts smoothly up and down the cassette.
I have been noticing recently (even before the chain lube) that in 8th gear there is a slight grinding noise.
It is quiet on the other cogs, except for an occasional slight grinding sound in 7th
I'm pretty sure this is a minor adjustment issue, but i'm not sure how to go about it.
The front derailleur is fine, shifting smoothly on those rare occasions when I use it.
Any suggestions on adjustment will be greatly appreciated.

ThermionicScott 

Is the chain rubbing on the front derailleur cage?

Phil_gretz

Avid,
If I understand your question correctly, you're in the middle chainring and the smallest, outermost cog of your 8-speed cassette. You hear what you think is a slight misalignment of your derailleur to that cog with your shifter in the released or most relaxed position. The cable should be just slightly slack leading to your derailleur. Misalignments can be due to:

- inwardly bent derailleur hanger (I don't know how your bike is set up)
- binding of inner shift cable release due to rust/grit fouling the inside of the cable housing (usually in the final loop before the derailleur), typically seen when upshifting or releasing cable tension
- grit/debris fouling the movement of the derailleur parallelogram back to its rest position
- change in the initial setting of the high travel adjustment screw (not suggesting that this happened, or should)

Easiest check is to back out the cable binder bolt and see if the derailleur comes to rest with better alignment to the cog, with shifter in the high gear (relaxed) position. If it does, time to clean/lubricate or replace your cables. If it doesn't, then you have a derailleur alignment/position problem.

Has the derailleur been bumped inward? Is the derailleur cage axis in the same plane as the cog that has been selected? Your local shop can check to see if the derailleur mount is properly aligned within the frame dropout. There's a tool for this.

Is the derailleur clean? Might be time to remove the derailleur (while the cable's free) and clean it thoroughly. There are many threads on how to do this, but you want to get the grit and road contaminants free from all of the pivots and moving parts. Partial disassembly (pulleys, cage) makes access a bit easier.

That's where I'd start. How long since you've changed the cables?

Phil_gretz

Can you put your bike up on a bike stand for service?

avidone1

A** If I understand your question correctly, you're in the middle chainring and the smallest, outermost cog of your 8-speed cassette. You hear what you think is a slight misalignment of your derailleur to that cog
B**with your shifter in the released or most relaxed position.

A - you understand correctly.
B - I don't understand the term "released or most relaxed position". I can tell you that my bike has twist grip shifters. They shift all my gears smoothly. when I shift it into 8 on ANY chain ring, I get the grinding noise

I thank you very much for the time you are taking to help me solve this annoying problem.

Oh, and yes, I have a park tool bike stand

79pmooney

I read the OPs post and thought the same thing. But my thought was this sounds like the chain hitting either the teeth of the big chainring or the inside of the front derailleur cage. If this is the case, typically you will not see it happen when the bike is on a stand, but only when you are riding. When you put pedalling pressure on your chain, it will run straight from the chainring to cog, but in a stand the chain with no tension on it from pedalling forces will assume enough of an "S" that it will clear the big chainring teeth and front derailleur.

Remedies? This can be vexing, especially if it the chainring teeth that are being touched. (But it is more important to stop that contact because it can lead to unintended upshifts if the teeth get too bid a bite on the chain.) First, check the chainline. Looking from in back, does the middle chainring appear to be exactly between the 4th and 5th cogs of the cassette? Or is it closer to or in line with the cog closer to the wheel? If this is the case, then you have a bottom bracket/crankset issue. If the middle ring is properly aligned with the gap between 4 and 5, then that is good. There are chainring combinations where avoiding that tooth contact is difficult, especially when the middle ring is small and the outer ring is large. Also this may happen or be exacerbated on bikes with very short chainstays, usually aggressive racing bikes.

Now, if we assume that that the chain is not hitting those teeth, then the issue may well be that chain rubbing on the front derailleur cage. This can be as simple to fix as just rotating the cage a small amount counterclockwise as you look down from the seat. But that does require adjusting both inner and outer limit screws and may well affect for the worse shifting onto the extreme chainrings. I find it is often simply better to just live with the rub and do my best to minimize use of that gear choice (which is also a rather abusive combination to chain, cog and chainring life).

And last: I have been known to intentionally adjust the front derailleur to get that rub so the chain did not hit the large chainring teeth. The chain engaging those teeth when I am not planning on it? Bad! Cage rub? Costs money over the long run IF I can get that derailleur to last that long. In my very high mileage racing days I used to kill front derailleurs that way but working in a shop and having easy access to replacements, it wasn't a big deal. The new derailleur have typically much more metal there (thank you Shimano) and I haven't worn one out yet.

Phil_Gretz may be right about this being a rear derailleur issue. What he talks about is important and needs to be right, but I'm guessing the problem is forward of there. Address his points and see if it still happens. (I'm betting it does but your time will not be wasted.)

Edit: I didn't see the OP's last post before I posted. It's happening on all chainrings? Phil wins.

Ben

alcjphil

On any cassette, the closer you get to the smallest cog, the less smooth and the more noisy your chain will feel. This is because the smaller the cog, the less close it is to being truly round. If you find this happening, you should be shifting to your large chainring and to a larger rear cog that gives you pretty much the same gear ratio as the middle/small combination. The larger the radius of the cog or chainring, the smoother the chain will run

FBinNY 

Here's an easy test, but you'll need to borrow a dollar.

Arrange so your bike can't roll by either tying one brake on at the lever, or putting it in a corner with the front wheel leaning on the other wall. (right side out, so you can work on it)

Shift to the problem gear combination, get the pedals fairly level, and slide the dollar bill between the chain and front derailleur cage on whichever side is closer. Now put pressure on the pedal to tension the chain, and see if it traps the bill between the chain and cage. If so, you're hearing the chain drag against the cage, and this may be resolved by a slight trim (cable) adjustment. (do not touch the FD itself, and especially do not adjust the limit screws which have nothing to do with your issue)

Hopefully you have an inline cable adjuster, so you can fine tune the trim, because otherwise you have to move the cable at the pinch bolt which is harder for fine tuning adjustments.

avidone1

I have done this and it works very well. There is really no need for me to run on the smallest cog with the middle chainring. I have done it because it's faster to up and down on the same chainring but it's not really necessary.

Is it fairly common to have this noise or would a perfectly positioned and adjusted RD be silent in all gearing configurations?

cobba

Watch the video: https://www.youtube.com/watch?v=yDPc1WqT2PE

alcjphil

The noise is not caused by the derailleur. The noise is a combination of using a smaller cog and the angle at which the top run of the chain leaves the cassette. If you put your bike up on a work stand and run through the gears you will be able to see what is happening. Watch how the chain is coming off the cassette cog in that middle/small combination. Even on the big/small combination if you listen closely you will probably hear that the chain isn't quite as smooth on that small cog as it is on one a couple of sizes bigger. This lack of smoothness is particularly bad if your smallest cog has only 11 teeth

avidone1

Thanks for the vid.....excellent explanation of which gear configuration is optimal.
I will heed this advice.
thanks to all for your input.

cobba

Here's a image from a old Shimano technical document showing which gears they don't recommend using with a 8 speed cassette.