Weird indexing issue – Shimano GRX400 front mech

I’ve put 2000km on my bike so I’m assuming the gear cable is now as stretched as much as it’s going to. Therefore, I shouldn’t need to adjust the cable tension anymore…

However, periodically, the front mech will stop changing up and I have to wind on more cable tension. I seem to have to do this every four weeks or so.

Today, I had to put about six complete turns on the adjuster and now the mech seems ok. Is this typical?

When fiddling with the adjuster, it occurred to me that there’s a limit to how much extra tension can be applied before the adjuster unscrews completely. Then it occurred to me that maybe the adjuster is screwing itself back in when it rattles.

Anyone experience anything similar and, if so, what was your solution?

This is the offending (I think) adjuster, which came stock on the bike (FWIW: 2021 Specialized Diverge)

https://i.postimg.cc/kG2wPfGj/20220823-192358.jpg

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Haven’t had the same issue (barring a general moan about finicky new Shimano mechs) but the mechanic in my local shop did say that Shimano advised against inline barrel adjusters on their new style front mechs. There’s a wee grub screw on the mech which does the same job.

Rather than re-cabling everything you could just wind the inline adjuster all the way in so it is effectively bottomed out, then perform adjustment at the mech instead, see if that solves it?

Look at online how-to videos – the newer front mechs require significantly more tension and you need to remove the slack to get the trim function to work. Internal cable routing often makes it tricker.

the newer front mechs require significantly more tension and you need to remove the slack to get the trim function to work.

The extra tension means that all but the very poshest and most well put together adjusters just screw themselves back together. I’ve seen this a few times, even went to the trouble of scribbling down that i’d put x number of turns on a screw adjuster before it was used. Came back with “front indexing problems”, perhaps unsurprisingly the adjuster was bottomed out.

Don’t fit them any more.

If I ever have to do more than 3 complete turns of a barrel adjuster then i just screw it all the way in, undo the cable clamp on the mech and re-tension it there.

Also, from what i’ve read elsewhere, the cable itself doesn’t actually stretch, the tension in the set up causes the cable outer and the end caps to compress together essentially exposing more cable. You could perhaps try compressionless outers.

My Ribble does a similar thing but over a longer time period as it’s got a BSA bottom bracket adaptor fitted in to a press fit shell. The whole BB/crankset very gradually moves towards the drive side.

+1 on checking the mech isn’t moving slowly down/round/up .
Also, have you clamped the cable tight enough?

Hmmm…
I’m aware of the grub screw on the front mech and it was aligned with the index point. And the cable is (or was, I’ll double check) sufficiently tensioned at the clamp when I last checked

I’ll also check the mech mounting isn’t loose but I’m somewhat ham-fisted when adjusting front mechs so don’t really want to remove the in-line adjuster or re-clamp the cable as I usually make a right mess of everything!

So, I’ll just keep a closer eye on the adjuster. Maybe wrapping some electrical tape around the adjuster may stop it winding in…??

Yeah my GRX would do this. It requires far more cable tension than previous front mechs and ay reduction in tension means it just refuses to shift. I have found I need to redo the whole process with the cable, grub screw etc every so often to keep it working. Did the second half of last years dirty reiver 200 in the small ring although on reflection this may have been providential 🙂

Odd, glad it’s not just me!

A different Shimano mech (newer 105) on my Topstone does that. Every now and then I’ve had to wind the grub screw in to get it to shift up to the big ring, then a couple of months later the same thing, until I had to release the cable, wind the grub screw out and reset it all.

With new builds, I’d wind in the high stop screw with the cage in the outer position, clamp the cable etc. Wind out the stop screw and fine-tune the tension with the grub screw. The higher cable clamp force also means cables get chewed/need replacing more often. I can only imagine this was done to encourage people to switch to 1x transmissions.