KD5NRH

Couple weeks ago I finally ditched the 7sp cassette and spacer, and put a new Shimano 8sp cassette, SunRace RD, (had a SRAM 1:1, and no 8sp shifters for it were available locally) and SunRace triggers on. Had it all working great, until yesterday.

No impacts or anything to bend the hanger, nothing unusual at all except that I did ride through a couple patches of deep wet sand that morning. Started getting that "need to trim" vibration under load. Cleaned everything, including pulling the chain and cassette to make sure I had all the sand out, and clean/repack the back axle bearings. Got it all back together, and I've got the same vibration on the 3 highest cogs, plus the derailleur is now acting like a 7 speed; I can tweak the barrel adjuster to get either the highest 7 or the lowest 7, but not all 8, and I'm still getting a rattle on some cogs like the RD just isn't quite right on, but others are fine. Adjusting the barrel a full cog changes which ones are rough, too.

What am I missing here? Could there be some grit in the RD changing the way it lines up?

hhnngg1

You still should verify that the hangar isn't bent. A slightly bent hangar gives you good shifting on one side of the cassette, but it gets dodgy on the other side, which sounds suspiciously like what you're getting. I know you didn't bang it, but it can be slightly bent without your realizing it.

dabac

Don't understand. Is the rear shifter 7-or 8-speed?


7/8 mixes are quite known to kinda-sorta work. At some level of wear, tune and cleanliness they run OK. But rarely over the full range of expected Life.


If a matched system shifts OK when going to bigger sprockets, but poorly when going to smaller, it's very often caused by excessive Cable drag. Clean and lube the Cable guide under the BB Shell.

xenologer

It's a recent install
the cables and housings are just settling in.
readjust the shifting and it'll probably be fine

70sSanO

Typically the first thing is the remove the cable from the rear derailleur and make sure you can easily move it by hand to all gears. If it is smooth, then you probably have crud in the cable. You may have to pull cable and blow out the housings. Some people use WD-40 or Triflow in housings, some people say it only attracts dirt and makes things worse.

John

KD5NRH

8 speed. Had a 1:1 ratio RD before, but couldn't get 1:1 8sp shifters locally, so I swapped to the SunRace 2:1 ratio RD to be able to get 8sp shifters without having to order them in.

KD5NRH

It's a 7100; cable routes along the top tube and down the seat stay. I'll pull the cable and housings today, re-clean and lube everything from the TT to the RD itself and see what happens.

ThermionicScott 

If you were using a 7-speed cassette and spacer and are now trying to shift all the way across an 8-speed cassette, it's possible that the RD hanger was always slightly bent and the accumulated error didn't manifest as a problem until now.

KD5NRH

After some cleaning, laying the hanger on a flat surface and giving it a couple whacks just in case, and putting everything back on, it seems to hit everything consistently except the smallest cog, which it will shift to, but slowly. However it still sounds like it needs to be trimmed out a bit on the largest ones. It does hit the megarange one fine, though.

Darth_Firebolt

That's not how you align a rear derailleur hanger. Problem found.