lovro

Hello,

I cannot adjust my rear derailleur properly. When in high gear, the chain is oscillating a lot between the two guiding cogs on the rear derailleur. This makes the chain louder and the pedals start vibrating.

You can see a slow-motion video here (I cannot make a hyperlink, because my account is new): www.youtube.com/watch?v=IS9IRDb2Ek8


I have no idea what else to adjust. It shifts well, the chain does not skip but in gears 28-30 this is an issue. Especially in gear 30 where the vibrations under force get so strong, I cannot force myself to use it.
Type: Shimano Deore XT T8000





Thank you,
Lovrenc

Iride01 

Might be a different story if the bike tires were on the pavement and pulling a load.

You might find that it works perfectly on the pavement, or the fact you are now pulling a load will show that there is something amiss such as the chain trying to shift when it shouldn't.

Don't ride it over 40 mph till you get it figured out.

lovro

Thank you for advising caution.


I just rode 250km travelling in the past couple of days and have had this problem in a real-life situation (on the pavement). I cleaned the chain/drivetrain, lubed it and adjusted it to the best of my knowledge.

Did not go out again after this procedure yet but the vibrations are really strong on the stand. Seems like nothing has changed.

masi61

Reminds me of a freshly waxed chain where the wax solidified. Flexing the tight links frees things up. Really, just riding the bike frees up the waxy links (I think).

What brand of chain is that? Is it new? What lube are you using?

I have run across a few new chains that were so tight that they skipped like this when new (a Wippermann Inox 9 speed & Taya 9 speed). Switching to a SRAM or KMC chain took care of the issue.

dsbrantjr

Perhaps a slight adjustment to the B-screw would change things enough to suppress the oscillation. Is your small cog perhaps 11 teeth? 2.2.1 Chordal Action

lovro

The chain is KMC X10
The bike is new, I have done about 600 km on it
I used a wet lube: Chain-L

Checked the links by hand, you might be right, some seem to be a bit stiff.


Yes, it is 11T and the link you posted describes my problems exactly. I will try adjusting the B-screw.

dsbrantjr

If you watch your top run of chain (out of view in the video) you can see it move up and down as the links come off of the cog. As an RF/microwave engineer I have a lot of experience chasing down and eliminating oscillations and have found that it often does not take much change in the system to kill them. If the B-screw doesn't do it perhaps lengthening your chain with a leftover inner link and an additional quick link will be enough of a change and it is simple to do, and to reverse if it doesn't work.

Troul 

A tooth or the entire plate of that 28 & 30 might be out of spec. Swapping the cassette with a new one might be a solution to the problem.

Iride01 

The tension pulley wheel on the t8000 might be directional. Did you pull the cage apart at some point and maybe put it in backwards? It's the lower one.

New bike? Bought at an LBS? Then let them figure it out.

sprockett

lovro Hey mate did you manage to figure this out? Anything you did that made it better? I'm facing similar issue on my new bike.