Full bare-frame rebuild after crash - hit a stumbling block

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 :grin:

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 :confounded:

Cheers
Dave

Swapping like for like rear wheel?

Yep - same wheel and cassette :+1:t2:

So it’s the wheel that was in the RTA?

If so, could be out of dish?

1 Like

Just add more cable tension, either with the adjuster or wind the limit screw in until the chain is ‘ticking’ (trying to change up to 2nd cog), clamp cable and re-set limit screw. You haven’t got enough cable tension at rest if it takes 2 clicks to make the first change.

7 Likes

Yup this definitely sounds like cable tension to me too. After you attached it and ran through the gears you got some stretch and cable housing settling, and now there isn’t enough tension. When I worked as a mechanic I would always install, run the gears a few times and intentionally try and get up into the gears it couldn’t, then head back down to the 11t, undo the cable and re-install it before I even touched the barrel adjuster. A good place to start with the barrel adjuster is one that lets you turn either way right from the start, not just out. Good luck!

2 Likes

agreed with @alexgold123 and @alexvanneste.

What I always do, install the thing. To install the cable, I put the barrel adjuster in all the way, then dial it out 1/2 turn or 1 full turn. Same for the front. Run the cable through, and pull it very taught, using a third hand, or some pliers to pull the cable tight and then clamp down. Don’t adjust anything, shift into Big/Big, and leave it for a while (overnight for me works fine). Then shift the rear first and dial in with the barrel adjuster (or release the bolt, set the barrel adjuster in all the way, and pull taught again) and then use the barrel adjuster to adjust. Then do similar for the front, drop to small ring, barrel in all the way, pull taught, and reclamp, and then adjust.

2 Likes

@alexgold123 @alexvanneste @iamholland - excellent, thanks for the advice.

Cable tension it is then - I will give it my best shot and report back :ok_hand:

Many thanks
Dave

Checked this as well - all is good on the wheel - but good point so thank you :+1:

Agree with all others it’s the cable tension. When you pull the cable tight also make sure your shifter is in the 11th position. Then follow this vid…

Fairly easy one to follow.

Around 2.45 into the vid is indexing

1 Like

Thanks - it was the tension.

The position of the nipping screw was preventing me getting full tension on the cable with the pliers I am using - so I leveraged them against the back of the screw / plate housing and it did the trick.

Thanks everyone for the diagnosis - nearly done now - just the brake fluid and handlebar wrap to do.

:grin: :grin: :grin:

3 Likes

Do you have one of these? It really does makes cable tensioning a breeze.

2 Likes

Doh!

If only I had known this even existed - I have all sorts of bike tools but for some reason this one has escaped my radar. Thats a top recommendation - think I will order one anyway for future use :+1: