You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
I finally got around to replacing my bent GX with and XT. Everything is dialled in nicely with one issue;
In the two lowest gears and mostly the 50th, the inside of the mech cage rubs on the sprockets as it moves across. I can’t adjust B gap any more as the screw is all the way in.
Any ideas to allow it to clear?
Chain too long?
Have you tried it without chain and cable? Worst case is getting hold of a longer b screw but expect there's a way around that.
Chain too long?
Well I followed the +2 links where is meets with suspension compressed with chain large to large , but I'm interested in how this affects it mechanically?
longer b screw
I'll rummage in the bin and rescue the GX B screw in case its longer...
12s shimano stuff requires quite a specific chain length setup compared to others. It’s probably a good place to start.
Have you lined up the guide mark on the back of the mech cage with the 50t?
Mine doesn’t have the makings. On the plus side, the GX b screw is half as long again, I’ll fettle with it in the morning.
Hang on - haven’t you followed the sram guide on chain length with the suspension compressed? With that you use the white tool and let the air out the shock.
On Shimano I don’t remember the instructions asking for compressed suspension - it’s just a set length once you’ve wrapped the chain round the big rear cog. So your chain might be the wrong length - too long if your chainstays grow under full compression.
I’d check your chain again following the specific Shimano instructions for chain sizing on 12 speed.
I can’t see why else your be getting what you’re getting unless the cassette sits too far outboard for the Shimano mech to handle.
Edit - I’ve not seen a Shimano mech without the ‘51t’ marking to line up with the teeth of the big cog. It’s just a stamped marking on the back of the top of the jockey cage.
Right, fixed. Two things:
A) the GX B screw is half as long again. Swapping to this has allowed me to move the mech further out and…
B) just admit you’re getting old and put your reading glasses on, that way instead of the white chain gap line you’d expect to see you can actually see the stamped and therefore black line.
Thanks for the tips.
No worries - it’s not the most obvious line once the mech is on the bike
Yeah, its hidden behind the cassette! Just had a lovely ride, everything working flawlessly. Its great to have crisp shifting again, it brings to light how bad my original setup was.