Hi all,
I’m having a strange issue with my Shimano GRX 1×12 drivetrain and I’m a bit stuck – even my local bike shop was confused (but was too busy to check more in depth).
The problem is that the rear derailleur won’t reach both ends of the cassette.
What’s confusing is the following: if I increase cable tension (as I do by hand in the video), I can get it into the largest cog. If I decrease cable tension, I can get it into the smallest cog. But with “normal” indexing, it won’t cover the full range. At best, I can only ever get one end, not both at the same time.
I’ve checked the usual things: the limit screws are set correctly and the derailleur hanger is straight.
I took it to my LBS briefly. They initially suspected a cable issue, but after taking a closer look they were quite puzzled but didn’t have time to fully diagnose it.
Has anyone experienced something like this with GRX 12-speed (or in general)? I’m wondering if this could still be cable or housing friction that’s not obvious, an issue inside the shifter, or something else entirely that I’m overlooking.
Any ideas or similar experiences would be really appreciated!
by again-and-a-gain
8 Comments
First thing I would do is release the cable at the pinch bolt and pull the cable to inspect. Then reinstall and follow the shimano install guide(assuming the cable looks fine).
Has it ever been able to shift over the full cassette?
I know you said limit screws – just verifying the b limit is dialed in too? They’ve gotten quite touchy compared to even 10 and 11sp.
Check the hanger with an alignment tool. Even a small bend can cause over/undershift on 12 speed systems because the indexes are very short.
Release the cable and check if it travels smoothly through the housing.
When you shift up slowly, one gear at a time, does it shift at each click, or are there shifts where the shifter clicks but the chain doesn’t change cogs? What about for downshifting?
Things I’d do:
1. Loosen off your barrel adjustor all the way and re-index, just to be sure this isn’t something strange with the indexing.
2. Detach the cable and hold on to the end. Click up with your shifter and count the “tugs”. Make sure it’s making 12.
3. Pull the cable and check it for friction in the line. I’d also check it for kinks and what not.
4. Check the shifter for debris.
Possibly bend hanger
Make sure that your cable is attached properly to the derailleur. It looks like it is, but that’s often the problem when it’s shifting 2 times like that
Maybe check your chain, it could be stretched out. I just had a similar issue and replaced the chain and now all is good.
Check your hanger to. Make sure its not twisted any