Slow rear gear changes (sometimes)

[maxfox44]

Guys

I need your advice, please.
My Giant Defy 0 (2015) is 11-speed Ultegra and the chain is about 800 miles old.

Recently, the gears have been misbehaving and changing (usually up, but not always) slowly. I can turn the pedals for quite a few seconds before the gear will settle in.

I've checked the chain and it's not got any stiff links and isn't showing 0.75 wear yet. It's the second chain on used on this cassette, which also still looks good. No point teeth, as with the chainrings. I've also looked at the mechanism and cable, both seem really free. The hanger isn't bent, had that checked and finally the gears index perfectly.

Have I missed anything? What else could I check?

 

[HarryTheDog]

I just had the same problem, the cable was snagging in the cable guide under the bottom bracket as the winter weather had started to corrode it. New inner cable and outers since I was taking things apart and all fixed. Slow cable release is usually the inner starting to snag on something, or another common thing is it can be fraying in the actual STI changer mechanism.

 

[Yellow Saddle]

Slow gear changes are NEVER due to chain issues. It is due to tardiness in the cable. There's friction somewhere. On road bikes, the problem is usually at the point where the cable slides under the bottom bracket. Road crud or sticky, leaked cooldrink from the bottles all form a sort of friction pad there that slowly releases the cable, especially on small shifts. If that section is clear, look for other cable issues, particularly little short runs like the noodle that serves the derailer.

 

[Tim Hall]

Adding to @Yellow Saddle 's point, the delay in up shifts is a pointer towards friction in the system somewhere. Down shifting is accomplished your the mighty power of your ham like hands moving the lever, whilst up shifts just rely on a relatively puny spring in the rear mech. Dirt in the fuel line cable outer works its way in and shifting gradually deteriorates.

 

[raleighnut]

The little section of outer from the last stop to the mech is a likely contender, as is muck around the last stop. The 2 often go hand in hand.

 

[jay clock]

^^^ what they said about cables

 

[DRHysted]

I had this issue with one of my bikes until I increased the length of cable to the rear derailleur, so there was a greater radius of the bend.

 

[confusedcyclist]

If this problem just surfaced after 800 miles with no prior problems, I doubt cable length is the issue. If you've ruled that out I think it's more likely your cable tension needs tweaking, or your hanger has taken a knock (but you say that's ruled out, are you 100% that's not the problem?)

See: http://www.parktool.com/blog/repair-help/rear-derailleur-adjustment#article-section-6

Try tiny adjustments, particularly if you have it indexed ok in the stand, but not working ok out on the road. No more than 1/8 turns. If it doesn't work, stop at the side of the road, turn again. Ride on. Rinse repeat until it's smooth. If that doesn't help, then I suggest your hanger is probably to blame, or the rear dérailleur pivots/spring are damaged (although, on a bike as new as yours, this is a bit of a stretch).

 

[raleighnut]

If this problem just surfaced after 800 smooth milles and hasn't been a long standing problem, I doubt cable length is the issue.

If think it's more likely your cable tension needs tweaking. See: http://www.parktool.com/blog/repair-help/rear-derailleur-adjustment#article-section-6

It isn't cable length he's on about,

I had this issue with one of my bikes until I increased the length of cable to the rear derailleur, so there was a greater radius of the bend.

It is that short length of outer causing problems, what happens is because of the acute bend the inner cable (and all the grit that it transports into the casing) wears the liner sleeve of that section leading to 'stickyness' and poor shifting and a mileage of about 800 is when I'd expect that wear to occur. the cure is to renew the cable and whilst you're doing that increasing the length (within reason) makes the bend less acute therefore slowing down the wear slightly.

 

[confusedcyclist]

Sorry I meant outer cable length, shorter cables = tighter bends. Pictures of the outer cables would be good.

I guess it does make sense that if the outer cable length is too short, it would wear faster, but 800 miles seems quite soon (disclaimer, I'm no expert, home mechanic with limited experience !)

 

[amasidlover]

I've just experienced this and almost cured it; in my case (105 5800) it was the rear derailleur spring/bearing that twists the cage to take slack out of the cage - it had got gunged up and was not putting any tension on the chain a good clean has improved it, but I think I'll be sending it back to Shimano as I've never had a derailleur do this before in 20 years of commuting and my cleaning / lubing regime has not really changed...

 

[maxfox44]

Thank you, everyone, much appreciated. I will look at the cable beneath the bottom bracket, as I use this bike as a commuter it is prone to getting muddy.
Can the cable be clean/oiled or something? Or should it be cleaned and left?

 

[confusedcyclist]

Yes you can clean it. They were reffering to one of these under the bottom bracket which can get bunged up.

 

[Lonestar]

I spray the cable runs with WD 40.

 

[maxfox44]

I'll give it a good clean and spray them. Thanks everyone!