My road bike came with a cheapy sq taper double crankset, which I replaced with a Sora double that Merlin were selling cheap.

Since then the front mech shifting has always been a bit suspect, as if it’s always on the edge of not shifting.
But lately, it won’t drop into the small ring from the big ring.
The cable is slack when in the inner ring position and the stop screw has no more adjustment to allow the mech to swing in any further; the mech is on it’s design limit for movement inwards. But the mech just doesn’t move enough to drag the chain down. In a bike stand, I can prod the mech cage and the chain will drop, so I know it’s marginal.

There seems to be a ton of adjustment on the outward swing of the mech, so I am wondering if the axle length of the original BB meant that the rings were sitting further out by a small amount.
Unfortunately, I sold the crankset and BB that came off the bike and don’t have any details about what it was (in terms of axle length).

The Sora crankset is mounted using the supplied hollowtech BB with no spacers, which I think is ‘correct’ for a frame with a 68mm shell, but am wondering whether to stick a spacer in on the drive side and see what happens….just worried I’ll lose some axle/crank overlap on the non-drive crank.

Any ideas apart from give it a try?
Here are some pics of the mech from in front and behind in it’s most ‘inward’ position, as well as the non drive side crank showing the amount of axle engaged in the cranks.
The chain is on the inner ring, but I’d shoved the mech to get it there…

Looking forward:

Looking backwards:

Non drive side axle:

Yeah, it could probably do with a quick clean…..!

Wheres the crank bolt.?

first of all get a new cable fitted . it is damaged and might slip through the bolt .

neilsonwheels – Member
Wheres the crank bolt.?

The crank bolts are in the crank. The plastic pre-load bolt was removed for the pic so the amount of axle could be seen.

cchris2lou – Member
first of all get a new cable fitted . it is damaged and might slip through the bolt .

Nah, it doesn’t slip but I do intend to replace it soon.
When the mech is trying to drop the chain from the outer to the inner ring, cable tension is irrelevant anyway. It is the spring that does the work to pull the mech inwards. I am not sure how replacing the cable will help the front mech move further inwards…..?

Sometimes the mech hits the frame so can’t go in any further
Sometimes over time the cage spreads and get wider, so give them a squeeze to bring the together a little.
sometimes if you just slightly twist the mech, rear emch towards the tyre a little the will help shift down.
Sometimes the mech is to high not 1-2mm above the big ring, so chain is missing the ramps on the inside of the mech (if it has them)

Post a photo with the mech in the big ring and face on & one from directly above in that position

Might be worth checking the cage isn’t bent first?
Otherwise I would undo cable, remove fd, clean it and lubricate pivots.
Refit making sure the cage is lined up correctly to the chainrings, with the L stop screw all the way out. With no cable attached it should be in its lowest position, if this doesn’t allow the chain to sit in the granny ring or closer to the frame then I guess the mech is either fitted at an angle or bent. I wouldn’t have thought the chain line would be so different that it can’t be made to work.
Fit a new cable before riding though 🙂

Did you fit a new cable and reset the FD when you changed bb and crankset?

My guess would be that the effective axle is indeed different and simply needs the mech setting back up.

MTB Rob – Member
Sometimes the mech hits the frame so can’t go in any further
Sometimes over time the cage spreads and get wider, so give them a squeeze to bring the together a little.
sometimes if you just slightly twist the mech, rear emch towards the tyre a little the will help shift down.
Sometimes the mech is to high not 1-2mm above the big ring, so chain is missing the ramps on the inside of the mech (if it has them)

I don’t think the mech is hitting the frame. It’s just reaching its limit of travel.
I will check for any bow or bending of the cage, but think it’s ok.
I think the vertical position is ok and the cage angle in relation to the chain but I will check this.

neil_1979 – Member
Might be worth checking the cage isn’t bent first?
Otherwise I would undo cable, remove fd, clean it and lubricate pivots.
Refit making sure the cage is lined up correctly to the chainrings, with the L stop screw all the way out. With no cable attached it should be in its lowest position, if this doesn’t allow the chain to sit in the granny ring or closer to the frame then I guess the mech is either fitted at an angle or bent. I wouldn’t have thought the chain line would be so different that it can’t be made to work.
Fit a new cable before riding though

I don’t think the mech/cage is bent.
Yeah, I might take it off and give it a good clean, but although it’s covered in a bit of surface crud it’s not that dirty.
What you mention above is effectively what I was trying yesterday; no cable and screw wound out of the way, but it still wouldn’t drop down.
I don’t believe the cable is an issue. If it moved onto the inner ring with the cable removed I would change it, but it doesn’t; the cable movement seems smooth.

vincienup – Member
Did you fit a new cable and reset the FD when you changed bb and crankset?

My guess would be that the effective axle is indeed different and simply needs the mech setting back up.

No, I didn’t replace the cable when I replaced the BB and crank although I did reset the FD set up. It took ages to get right and even then, the operation seemed marginal.

I think the effective axle is different, but there it no way of doing “…simply needs the mech setting back up”. There is no adjustment left in an inward direction. It’s like someone trying to turn a corner with the steering wheel on full lock but the corner is too tight and someone suggesting just turning the wheel more.

I’ve never had this sort of problem with any of the mech on my other bikes, which is why I think it’s a problem with more than just set-up or dirt.

Something to consider then might be that maybe the throw is wrong?

I’m not a derailleur historian, maybe the FD you have is simply not suited to an HT2 type crank?

Step back and while replacing that cable when you get round to it, make sure the uncabled mech truly covers the rings. If it does, and there’s no stiff linkage that wants a clean and oil, then fresh cable and outer and setup again. If that doesn’t do it try a new mech.

When I replaced my Sora kit with 105 recently the FD wouldn’t shift properly for ages until I took another look and found I’d built a cable trap into the bar taping. Retaping the bars after repositioning the outer and retension in the mech sorted that easily. Quickly rereading your original post, I think the slack when it’s on the inside ring is probably evidence of the root problem though.

Cheers for that, definitely a few things to consider.

Think I’ll take the mech off When I find time, give it a clean, stick it back on and check all the alignment. If I can’t get it working then, it is a simple enough job to try a spacer on the BB to see if it works like that; cheaper than a new mech for starters…!