Front shifter problems

[KermitGKona88]

Built a bike up for my mates son, some modern bits some old Raleigh RSP250 frame, tried fitting 110 setup 36/46 no go inner ring caught frame, changed to a compact 44/32/22, XT FM, cheap Wake shifter, first shift really long nearly puts it in top gear but when released drops back down in to middle then a short hard shift to top, down shift loads of grinding, chainslap, jamming, but only under load not on the stand, changed to a more modern Suntour FM, same problem. Removed cheap shifters put on STX fine on stand, but once again under load miss shifting and loads of rattling, Curve rings on a powerpro crank and clarks chain... Anyone got any ideas what might be happening????

 

[ishaw]

First issue could be you've got too short a BB mated to your cranks, causing your small ring to catch the frame.

Front shifter issues could be incompatibility of shifters and mechs i.e. different cable pull ratios.

Then there's the jamming. Maybe your front mech isn't set up close enough to the rings, when on the top ring the clearance should not be much, 2-5 mm iirc. Could also be chain width and gaps between rings.

 

[KermitGKona88]

BB is right no catching now, it does seem like the pull is wrong, but it works when not under load, it only happens when there is a load on the cranks.

 

[Woz]

Double check the cable is properly set in the groove at the pinch bolt. It's easy to do, and will cause odd indexing if wrong.

If it's a bottom pull FD there may be too much cable friction at the under BB guide; put some teflon inner there. Again, this can cause some odd indexing behaviour and weirdness between up and down shifts.

If the down shift is just messy and not powerful enough to dislodge the chain when under load after all of that, sorry to say the FD may be *ucked with too much play in it's pivots or the spring is now too weak. Man handle the cage while it's still attached and compare it to something newer.

If the outer and middle chain rings are older and don't have any gates, get the file out and take off the tops off some teeth. Even with a FD on it's way out, it will be easier for the chain to derail.

They are the only things I can think of, plus you know your stuff so don't doubt the position of everything.

 

[ishaw]

Maybe a worn chain? No load on it, it's just dropping on the rings, with load, chain could be twisting and then not sitting right or catching on multiple rings at once?

 

[KermitGKona88]

Maybe a worn chain? No load on it, it's just dropping on the rings, with load, chain could be twisting and then not sitting right or catching on multiple rings at once?

Brand new cassette and chain