Happy weekend everyone!
So after my recent RTA the bike needed a rebuild, due to many broken components and some that were worn anyway and were due replacement. This is new territory for me and so far it’s gone pretty well; I have the correct tools so just needed to pace myself and use YouTube to double check anything I wasn’t entirely sure about.
Jobs done so far are:
- frame stripped down to bare bones and cleaned
- frame scanned and given clean bill of health by local specialist Carbon repair firm
- new press fit bottom bracket fitted
- new headset and crown race fitted
- new crank axle, front chainrings and spacer set fitted
- new carbon bars fitted
- gear cables and hydraulic lines internally routed
- new lever hoods and end caps fitted
- brake lines reconnected to callipers (all cleaned up)
- new front derailleur fitted and set up
- new rear derailleur hanger fitted
- new rear derailleur (straight swap for old unit) fitted
Jobs left to do in the order in which I intended to complete them:
- set up rear derailleur
- fill up and bleed hydraulic brake fluid
- adjust and set brake callipers
- wrap on new bar tape
- re-check all bolt torques / lube chain
- fit new pedals
- Go for a ride
I’ve hit a stumbling block with the rear derailleur set up and need some advice / guidance from the forum on solving the problem.
NB #01: the rear derailleur and rear hanger are identical units to those that came off the bike. I’m 100% certain of this and have even (due to exasperation) measured them all and triple checked.
NB #02: the bike is a 2017 Cannondale Synapse Carbon disc. Components are Shimano Ultegra 8000 mechanical.
Having set up the rear derailleur (set limit screws / set chain gap with B screw) and then tightening the gear cable when I run through the gears using the lever, (but with no chain or wheel on), it runs up and down crisply with no issues, and seemingly aligns nicely to all 11 cassette cogs, in particular it aligns perfectly with the 32 cog and the 11 cog.
However when I attach the wheel and chain then attempt to change up and down, the derailleur moves only as far as the second-but-last largest cog and fails to reach the 32 cog. The lever to move the chain up the cassette feels a bit like it is ‘double’ clicking on the first click when moving off of the 11 tooth cog (although this is inconsistent) and so the ‘10’ full clicks I would expect to feel (that work perfectly and crisply without the wheel and chain on) only takes the chain to the 10th cog - rather than the final biggest 32 tooth cog.
Process I followed is:
- Manually align top jockey wheel to small and large cog on cassette (11-32) with chain off
- Use H and L limit screws to micro adjust so it is perfect
- Use B screw to make sure chain gap is 6mm or so between 32 cog and top jockey wheel
- Double check nothing has moved on any of these three variables as a result of adjustment to another
- Click lever many times to make sure it is in smallest cog position (11 tooth) whilst pulling on the cable to ensure it is properly tight
- Nip-up the cable end using the 4mm screw
- Manually run up and and down the gears (10 clicks each way) to test the range of motion of the derailleur before refitting the wheel and chain.
- Re check that the limit positions of the jockey wheel still align to the 11 and 32 tooth cogs (they do)
- Re fit wheel and chain
- Attempt to run the chain up and down the cassette - this is where it fails (as described above) …
What I have checked, and triple checked:
- Nothing is fouling the levers (hoods / dirt / plastic etc)
- Gear cable end is properly seated in lever cup
- Cable is nice and tight when nipping-up the 4mm retaining screw
- Lever has been ‘clicked’ many times to move it to the lowest cog position at the point prior to the tightening the 4mm screw for the gear cable
- Components are correct and identical replacements (Ultegra medium cage for 32 tooth cog)
- Small cog limit is still visibly correct after chain and wheel is refitted
- Front derailleur isn’t fouling anywhere
- Wheel is on properly and cassette is OK
- Chain was newly new and is in v-good condition, no bent or twisted links
- Derailleur is correctly attached to the hanger and isn’t in the wrong position - IE - too far forward on the hanger which I have seen some people make as a mistake before
So my question is, am I just needing to un-thread the adjustment barrel on the rear derailleur to ‘solve’ this problem or is there something else amiss here?
On a previous bike I once unwound the barrel too far and it came undone and I couldn’t get it back on, so I am a bit concerned this may happen in this circumstance, given the chain isn’t even getting to the 32 tooth cog and there are no more ‘clicks’ in the lever left at that point.
My past (limited) experience was that the barrel adjuster was simply to micro-correct the chain movement so there was no side rubbing and the changes up and down the cassette were crisp, as opposed to solving what to me as a novice appears (at face value) to be a more fundamental issue.
Moving the barrel adjuster a few clicks doesn’t solve the problem.
Any advice gratefully received - this has currently got the best of me