Slipping gears on the big chain wheel

[colinmc400]

Guys, been having some issues with my gear shifting for a few weeks. If it was a car with a clutch, i'd say the clutch was slipping. It only seems to happen on shifts on the big chain ring and mainly shows itself as, i move shifter, cranks seem to spin freely for a couple of revs and then a gear gets selected and sometimes that gear can be more than 1 cog on the back, so the cranks are still going at some rate. It always seems to happen when i am pushing on, so attacking the bottom of a rise etc. Just cruising and shifting normally, no bother.

The Spesh Roubaix road bike came as std with a mix of 105, Tiagra and Axis components and all seemed to work fine for the first few hundred kms. Then it went back to the LBS and had a set of Ultegra 6700 cranks, shifters and brakes fitted(same gearing) and thats maybe were the trouble started. Its been back to the LBS(Spesh dealer) a couple of times, for re-adjustment, cable replacement, housing replacement, lube replacement etc etc and still no joy. So a couple of questions:-

1. Anyone had this same issue and wanna comment?
2. Would using Wheels adaptors to convert the BB30 to Shimano cause any bother? Does that extra adaptor stand the crank off the frame a bit more and maybe change the angle the chain runs at, from front to back? Chain too tight maybe?
3. I now have Ultegra 6700 cranks and shifters, but 105 front and rear derailleur's. Is there any mismatch between the parts that might cause this? Theres an ultegra FD, RD, chain and cassette on its way from c r c, so it will be all 6700 ultegra before too long.

So much for upgrades eh(and before anyone asks why, because i could and am a bandit for ebay)!!

Cheers - Colin

[Baalzamon]

Sounds like a bit of tension is needed in the front derailleur wire. If you have a barrel adapter on the line somewhere. Give it a quarter turn then try again.

[colinmc400]

Sounds like a bit of tension is needed in the front derailleur wire. If you have a barrel adapter on the line somewhere. Give it a quarter turn then try again.

Ok noted and i'll add that to the list of things to try - cheers.

[Baalzamon]

New cables will stretch within a few hundred km's so they need to be tensioned up a tweak

[colinmc400]

New cables will stretch within a few hundred km's so they need to be tensioned up a tweak

In fariness to the LBS, that was one of the things i had seen them try and they did talk about different tension on the shifting cables, as well as eventually swaping the cable completely and cleaning out any old lube etc. Still no joy.

[Mulger bill]

Any noise when it's slipping?
Might be worth checking alignment and setup of the front mech.

[colinmc400]

Any noise when it's slipping?
Might be worth checking alignment and setup of the front mech.

No i think thats part of the problem when it has caught me out, no misalignment or horrid noises. You assume its shifted correctly, i stand up on the pedals and theres no resistance and all your weight is thrown forward. Has nearly had me off a couple times.

I took another look last night and this now has me wondering. The shift levers are new Ultegra 6700 STI levers fitted by the LBS and the front mech is the OEM Tiagra. Could that be a mismatch?

[DuncanS]

Issue is with rear shifts? On down-shifts to a larger cog? Sounds like the chain might be "standing up" on the edge of the cog but not fully shifting. I'd say try adjusting rear barrel adjust a few clicks anticlockwise. If that helps, (get the shop to) do a full RD tune to dial everything in properly.

[pacra]

This is not a solution to your problem, but may point to the cause.

I have/had a related problem. I ride in peak traffic all the time, stop/accelerate for 18km, so on the last chain change I put a 44 on the small ring. I found that frequently if I dropped to the small ring while on the 17 cog the chain went down ok but instead of meshing it smoothly ran over the top of the teeth on the big ring (53), almost noiselessly, without engaging. To re-engage I had to shift rear cogs up or down. At 17/44 the chain is in almost perfect straight alignment.

8000 km later the problem appears to have gone. Visually running it on a stand I could see no reason why but can only guess one or two reasons.
- 44/53 is too close to allow the chain to drop in cleanly.
- the lifters on the big ring somehow retarded the chain meshing.
- unlikely but an incompatibility between the chain and the small ring, Campag. C10 and a Stonglight 44.

Hope these observations help.