Kotoa

Hi,

I'm having trouble diagnosing an issue I have where my chain skips under pressure in any gear combination, hope you guys could help. When under little pressure (rotating with hands) it shifts between each gear perfectly, but when I apply pressure (to accelerate or climb a hill) my pedal rotates, my chain makes a huge grinding noise and there's no acceleration - I've tried to identify where it's skipping, but it happens too fast.

I just received it back from my LBS who fitted a brand new ultegra cassette, ultegra chain and ultegra rear deraileur. (it didn't do this before, replaced because my previous ultegra derailleur somehow got caught in my spokes and sheared off, also breaking the chain >.<)
I would take it back to the LBS and ask them to take a look at it, but it's very difficult when I work almost the same hours as them.

I haven't changed the front rings or derailleur, they've gone through 5000 miles - could this be the issue?

digibud

from your comments it sounds like it's a front derailleur issue you are talking about, or at least a front shift issue. If your old chain was badly worn and it was replaced along with the rear cogs, it's not impossible that your front chain rings are worn and need replacement. your lbs should have seen that but maybe they didn't. a badly worn chainring is fairly obvious. The teeth would no longer be nicely formed and the "U" shape would be elongated. You can find pics of that kind of thing with some web searching. If the issue is in the rear it's a matter of adjusting the cable tension.

cny-bikeman

It does not seem that a front derailleur problem would cause the behavior in every gear combo. A more likely cause is the freehub pawls, as I assume only the cogs were changed. There is also one remote possibility, that you have a problem with integrity of the rear triangle. If there is a crack or separation it could allow the triangle to shift significantly under power.

Kotoa

I'll take another look in the morning, I remember it does look fairly worn but not too bad, but it has been through a lot of mileage.

Yes I'm using the same freehub, but I didn't have this issue before; could the freehub have been slightly damaged or too worn for the new cassette? I'll also look at the triangle tomorrow morning.

Thanks for both your comments

cny-bikeman

Well, actually I posted hastily - thought you took it to LBS to address the issue, not that it happened since. If it happened immediately after getting the bike back it would be a natural conlusion that the skipping has to do with the shop. Are you able to take it back to have them diagnose?

Bjforrestal

I'd tighten your rd cable tension to take up all slack if any while on the smallest cog. Maybe 1 or 2 full turns on barrel adjuster. If this doesn't fix your issue, check the rd hangar alignment. I've had this issue and cable tension fixed it immediately

Kotoa

I think you're right, I messed around with the barrel adjuster on the way to work this morning; I managed to totally remove the issue, but it was awful at shifting between gears... I've managed to adjust it the best I could without taking the cable off and messing with the L/H screws, it now shifts alright(ish) and doesn't skip unless I apply about 20% higher pressure than before. I'll set it up from scratch when I get a chance.

Didn't think it would be an issue with the rear derailleur considering my LBS only just fitted it! Thanks for your help guys.

Bjforrestal

I think you're right, I messed around with the barrel adjuster on the way to work this morning; I managed to totally remove the issue, but it was awful at shifting between gears... I've managed to adjust it the best I could without taking the cable off and messing with the L/H screws, it now shifts alright(ish) and doesn't skip unless I apply about 20% higher pressure than before. I'll set it up from scratch when I get a chance.

Didn't think it would be an issue with the rear derailleur considering my LBS only just fitted it! Thanks for your help guys. [/QUOTE]

If your rd shifts all the way through the gears both ways without falling off I wouldn't mess with the h and l settings. Take some time and keep tweaking the cable tension. I always use the barrel adjuster by the rd, never mess with the down tube adjuster much, but I think you'll get there. Oh one more thing, make double sure it's a 9 SPD chain. If they messed up on the cable tension, this is another easy screw up, I've done it myself on my own bike, caused me havoc for a week before I figured it out, exact same discrepancy as you are having.

Kotoa

Unless Chain Reaction Cycles messed my order up (again) or my LBS mixed up chains, I'm using an ultegra 6701 10 spd - is it easy to identify if it's actually a 9 SPD?

Bjforrestal

Unless Chain Reaction Cycles messed my order up (again) or my LBS mixed up chains, I'm using an ultegra 6701 10 spd - is it easy to identify if it's actually a 9 SPD?[/QUOTE]

Not sure about shimano chains, but I figured out my issue with googling pics of SRAM chains and comparing. Took 5 minutes. I had an 8 SPd on a 9 speed setup no fun. Just double check, and keep messing with cable tension if its the right chain. Oh, one more thing to double check is the rd cable routing to the rd connection, if its connected wrong
you will be chasing your tail.