[roadbikepilgrim]

Good afternoon,

One here for the home mechanics and any Shimano pro mechanics who are on the forum. About a  year ago I managed to get a Claris triple groupset at a bargain price, so I swapped out the Microshift R8 triple groupset that came with my Triban 500 SE bike.

Installation was fine and the Shimano groupset overall is better than the Microshift was. Only one problem. I could never remove front mech rub when in the large 50T chain ring and the smallest 11T sprocket on the cassette. Dialling out the limit stop (to the point where the chain should really have been falling off the large ring) and increasing the cable tension (beyond the point of overdoing it) would not help put space between the chain and the front mech outer plate. I was following Shimano’s instructions in their dealer manual to the letter and it was just no joy. Besides, the setup of the Claris triple front mech is really boilerplate for a front mech, with no special setup features that you need to be aware of. In the end I shrugged my shoulders, created a bit of mech rub in the small chain ring large rear cog combination (in order to throw the front mech cage fractionally further out and give more space between chain and front mech outer plate) and resigned myself to some noise at both ends of the gear range.

However, yesterday I was putting on a new cassette and chain and while I was checking that indexing was still okay, I had the idea to pull on the front mech cable (externally cabled frame) while the chain was in the small rear large front combination. Suddenly the rubbing was gone and the front mech did what you would expect: it went out as far as the limit screw setting. When just using the shifter it matters not where the limit screw is set: the cage will just not go out far enough to avoid rubbing. So, I realised that the problem was not the front mech (the spring, the limit screw setting or the cable tension), but it was actually the shifter that was limiting the movement to allow sufficient cage clearance in the small rear large front combination.

Does this sound like a manufacturing fault with the shifter (its range is just slightly too short for three chain rings)? Is there an adjustment that can be made to the shifter’s mechanism (saw nothing about this in Shimano’s manual)? Or is that just the way that the Claris triple shifter functions, and the front mech rub is a “feature” and not a bug for the lower end groupsets?

All views welcome. It’s only my commuter bike, so I can live with the mech rub. But my pride wants to solve it!

Thanks and regards,

roadbikepilgrim

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[roadbikepilgrim]

Hi Rendel,

Hi Rendel,

Thanks for your message. Yes you are missing something , but what I am describing does not match anything I have experienced with the Microshift R8 shifter that the bike originally came with, and no doubt anything you have experienced.

As I wrote in the original post, the shifter itself seems to be the limiting factor. I can tighten the barrel (top quality shimano inline cable adjusters used on the gear cables) all the way to its limit so that the cable is far too tight and the shifts down to the middle and small chain rings are adversely affected or even prevented. However, this tightening does not move the cage out one iota compared with pulling on the cable.

The Claris shifter for the front mech seems to have some limit that the Microshift shifter did not. When I set up the Microshift shifter for the front mech, I used to shift into the large chain ring and keep the pressure on the shifter. I then dialled in the limit screw (while keeping pressure on the shifter) until I could hear rubbing, then dialled back out an eighth of a turn. Then to finish off I increased the cable tension (to replicate my pressure on the shifter) until any rubbing was gone. This is the method demonstrated by Park Tool in their video (https://www.youtube.com/watch?v=ZNG7g83lI-s) and it gave perfect results with the Microshift shifter.

Somehow the Claris shifter limits how much the brake lever can swing inwards and therefore how much the cable can be pulled. If I wanted, I could remove the limit screw from the body of the front mech and madly over-tension the cable and the chain would still not fall off the big ring. It’s almost like a fixed distance is built into the shifter to match the distance from small ring to large ring on an 8-speed triple crank, but it is out by a few mm. So, even though the spring on the front mech will take the cage much further out, you can only achieve this by a pull on the cable and not via the shifter. It’s not how I expect a shifter to work, which is why I wondered if there was some manufacturing flaw in the shifter I have.

As it happens, since I posted I found today a solution. Standard practice for setting up a front mech is for the cage to be absolutely parallel with the chain rings, and this is so for Shimano. However, Microshift set up was slightly different and the cage was meant to be setup at a slight angle where the back outer edge of the cage is lined up with the big chain ring’s outer edge and front outer edge of the cage is lined up with the big chain ring’s inner edge (https://www.youtube.com/watch?v=eGE8xF2tguc).

Given that the rubbing on my Claris front mech happened towards the back of the cage (where there is a bulge that helps lift the chain), I tweaked the position of the mech, so that it was still more or less a standard parallel to the chain rings, but the back part of the mech was now angled out slightly, to reduce rub on the chain. I knew that this was not the method given in the dealer manual for Shimano Claris, but figured it was worth a try.

It worked, and there is barely any rub now at the front mech. I still have not worked out what is going on with the shifter, but I am not going to sweat it now!

Regards,

roadbikepilgrim

[Rendel Harris]

Feeling I’m missing something

Feeling I’m missing something here…if you can pull on the front mech cable and that pulls the mech out far enough to stop rubbing, why do you think it’s not the cable tension that’s the problem? Take up the slack in the cable so that it holds the mech where it should be and that would do it, surely? As I say, I must be missing something but can’t think what from your description.

[Author]

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