Rear derailleur blues
April 12, 2012 5:08 PM   Subscribe

Adjusting my bike's rear derailleur on the workstand results in perfect shifting. Shifting while riding, on the other hand...

I have a relatively new cyclocross bike, and I'm having a bizarre issue that I've never really had to deal with. In short, as I've had to deal with cable stretch, I've had to make incremental adjustments to the bike's rear derailleur -- a 2012 Ultegra 6700.

Now, while it's on my workstand, I can get the shifting dialed. The minute I get on the bike, however, is a whole other issue. The crisp shifting is no longer crisp -- downshifts, i.e., towards the larger cogs, are sloppy, and the upshifts also seem slightly off. I have to go through the whole process of riding for a bit, getting off the bike, making slight barrel adjuster changes, and repeat. This might sound like fun, but its a major drag.

I though I might resolve the issue by having the entire cablework redone professionally, so I took it in to another bike shop (in order to determine if this was an issue with original bike shop's setup), and replaced the cables and housing with my preferred brand of choice. They also checked the derailleur alignment and cassette during this process and discovered no problems. Again, this bike is a couple of months old, and everything is still relatively new.

In short, I get it back from the shop, and it's working perfectly. A couple of weeks later, I'm dealing with stretch from the new cable, so I'm having to do adjustments again, and I'm having the same exact issues. I've never had a derailleur behave so differently on the stand than during a ride.

Here's what I know:

1) I'm only making adjustments via the barrel adjuster. The high and low limits, along with the b-tension appear to be set correctly, and furthermore, the derailleur appears aligned. I have not touched these settings.

Again, I want to reiterate that the setup has been done *twice* by two separate and well-regarded shops.

2) I can get it adjusted perfectly on the workstand.

3) There doesn't appear to be any cable issues, although this is hard to rule out without ripping out the cable and checking for kinks.

4) The crankset and derailleur are torqued to spec, with regards to all bolts.

I do quite a bit of work on my own bikes, but this bike is proving to be tricky. Ideally, I want to adjust this on the stand, but I'm out of ideas at this point. I can keep taking it back to the shop for adjustments, but something as simple as this should not be causing this many issues. Can you think of anything that I may have overlooked?
posted by aflores to Sports, Hobbies, & Recreation (17 answers total) 6 users marked this as a favorite
 
What's your frame made of? And are you a heavy guy?

Combine a steel frame with a heavy rider and you might get enough frame flex to screw up indexing in the rear.
posted by hollisimo at 5:13 PM on April 12, 2012 [2 favorites]


how old are your chain and cassette? have you checked the former for stretch and/or ruined the cassette by riding a stretched out chain on it in the past? I'm wondering if the extra friction of wheel-on-road is requiring a bit more effort and the chain/cog combo just isn't having it.

Yokozuna cables are great, though I know you said you've already replaced them - especially for a down and dirty cross build.
posted by kcm at 5:14 PM on April 12, 2012


I thought the same thing as hollisimo. I usually have to adjust the derailleurs on my steel touring bike a little when it's fully loaded for a trip because of frame flex.
posted by bradbane at 5:23 PM on April 12, 2012


Yeah, I'm thinking frame flex too. Is it worse while under heavy power versus on flats or downhills? Is your frame spindly, especially in the rear triangle?
posted by supercres at 5:30 PM on April 12, 2012


The way cables work should eliminate any frame flex issues. Is the cable tied down somewhere it shouldn't be?

Further, once the misadjustment sets in, does it remain misadjusted when you set it on the workstand? Then flex isn't the problem. (Unless the frame is actually bending and staying bent. But you'd probably notice that.) What I would do is put a dot of paint where the cable is clamped down and see if it is slipping.

Is your adjuster one of those ones that had detents for each gear? Maybe the spacing between the detents of the adjuster is just not compatible with the rear gearset spacing.
posted by gjc at 5:40 PM on April 12, 2012


Thanks for the help so far!

What's your frame made of? And are you a heavy guy?

The frameset is a 56-ish cm aluminum 2012 Giant TCX 0. I was thinking about frame flex, but I weigh about 175 pounds -- about 15 pounds over my typical weight.

how old are your chain and cassette?

The chain and casette are 6 months old. I can try checking to see if there is any chain stretch.

Further, once the misadjustment sets in, does it remain misadjusted when you set it on the workstand?

This is actually the strange part. It doesn't remain misadjusted when I put it back on the stand.
posted by aflores at 6:09 PM on April 12, 2012


Is your adjuster one of those ones that had detents for each gear? Maybe the spacing between the detents of the adjuster is just not compatible with the rear gearset spacing.

I'm using an Ultegra casette with an Ultegra derailleur, using the stock barrel adjuster.
posted by aflores at 6:16 PM on April 12, 2012


Please read my comment from this previous post...

http://ask.metafilter.com/162861/Are-my-bar-end-shifter-and-derailler-fighting-each-other#2340676

It includes an often overlooked adjustment described in detail and a manufacturer's service pdf to back it up.

Otherwise my intuition tells me a bent derailleur hanger could also be the problem.
posted by No Shmoobles at 6:35 PM on April 12, 2012


One cause of "cable stretch" in my experience is slippage of the cable screw-down at the end of the derailer (or brake). Tightening the clamp tighter may or may not make a difference. It can be quite difficult to set cable tensions and bolt down the clamp nut tightly enough. The shift will work on the bench, as you described, but slip and require retensioning as soon as weight is put on the bike.

The best solution I've found is a fourth-hand tool or cable stretcher. This tool allows one to set cable tensions easily, then tighten the cable nut without fuss. Not a cheap tool, but one I've never regretted buying.
posted by bonehead at 6:41 PM on April 12, 2012


Once you make those fiddly adjustments after riding does it stick?

Apart from initial stretching, I also find I have to make adjustments with major temperature changes. I weigh ~120 (on a steel frame) and have had to make on the fly adjustments to my cables once I'm on my bike after it worked fine on the stand. I also deal with the maintenance for my bf's bike (aluminum) and I think I've adjusted his cables, like, once in 4 years. He also rides his bike far less than I ride mine, but it seems like maybe some systems are more forgiving than others.
posted by mandymanwasregistered at 7:51 PM on April 12, 2012


I would find a bike shop or friend with a trainer you can put it on, especially if you can simulate heavy load. With the new information, frame flex isn't terribly likely, but that's an easy way to see what's happening.
posted by supercres at 8:18 PM on April 12, 2012


My campy-equiped road bike is like this. Dial it in perfectly on the stand and it won't be quite right when riding. I always put it down to the extra tension in the system through actually riding along rather than just turning the pedals by hand.

My shimano equiped mountain and road bikes are fine.

I've got extra barrel adjusters on the down tube, so I just reach down and give it the final quarter turn as I ride along, although I've noticed some new road bikes don't seem to have these, so um, yeah... If you can't get this figured out and you don't have adjusters you can reach while riding you could always install one, I think you can even get ones that just sit in-line with the cabling and don't need a mount. Something like this.
posted by markr at 9:16 PM on April 12, 2012


Thanks for all your help everyone! I just spent the past three hours working this issue out.

The good news is I figured out what was causing the derailleur issues. The bad news? The mechanic who threw the bike together has some explaining to do. And I literally mean "threw."

So, taking the flex suggestions into account, I was thinking that maybe it wasn't such a bad idea to go over all the bolts in the drivetrain, making sure they are all up to torque. Sure enough, the crankset bolts that I thought were at torque weren't. So I torque them near the higher end of the proper range, and continue with my bolt check. I then adjust the rear derailleur on the stand, where everything seems to be shifting smoothly.

I then take the bike out for a ride, and I hear the most horrendous creaking sound emanating from the bottom bracket.

So, I pull the crankset out. Or, I try to -- it was literally stuck. I apply a little more pressure, and I'm finally able to remove the left crank from the spline on the spindle.

And there is no grease.

Like, there is absolutely zero lubrication where the left crank arm spline connects with the spindle spline. And some of the anodization from where the crankarm meets the spine is worn away.

So, I then go about trying to remove the right crank along with the spindle, and the same problem occurs. It was stuck to the pressed bearings.

I finally manage to remove it, and again, there is no grease where the spindle meets the bearing cups. In fact, the area where the spindle meets the bearings is completely shiny, like its been worn through.

I put some grease all on all the relevant parts, have a nightmare of a time putting the spindle back in through the bearings, tighten all the bolts to spec, and wouldn't you know it, the bike shifts like a dream now -- on and off the stand.

I'm super pressed now, guys. I don't even know what I am going to say when I call the original shop back tomorrow. This is the first time the cranks have ever been taken off the bike since I special ordered it a few months ago, and I'm completely furious right now.

If you were in this situation, what would you ask of the shop? I mean, it's working fine now, but man, that spindle looked worn.
posted by aflores at 11:04 PM on April 12, 2012


My best guess for why this actually solved the problem? I'm guessing that without grease, the left crank was improperly seated on the spindle, even when properly torqued, which would cause lateral play only when I was on the bike.

I mean, I guess it seems reasonable.

Again, thanks for all of your suggestions!
posted by aflores at 11:17 PM on April 12, 2012


You should be furious, that's completely unacceptable. A greaseless BB would be toast very quickly---I'd want replace the bearings and spindle cups. I'd also want to examine the BB cups for wear or pitting. The worst wear on bearings happens when the balls micro-weld/adhere to the race surface when the bike is stationary. When the bearing starts to move, it cracks off, leaving a rough spot behind. These rough spots can rapidly develop into pits and wear spots. There's no way to repair this. Replacement is the only option. I'd consider this when talking to the shop.

For the crank-spindle connections, some mechanics don't grease the crank flats/splines, some do. The theory is that you don't want that connection to move, so putting grease there can only cause wear in the long term. That part being greaseless is more ok.
posted by bonehead at 6:09 AM on April 13, 2012


Some mechanics are simply wrong. Always grease metal interfaces. Here's Mr Brandt on the subject, for example. The only reason parts become loose is that they're not fastened tightly enough initially, grease or no grease.

It sounds like it's not the case in this instance, but another common cause of poor shifting or ghost shifting under load is cable friction through the bottom bracket cable-guide as the frame flexes. It get dirty down there. A drop of grease in the guide can make all the difference.
posted by normy at 10:11 AM on April 13, 2012


Indexed shifting needs to be adjusted from both directions. If you're aligning with your lowest gear and adjusting the barrels as you go up the cog, when you're done with that you have to do the same thing in the other direction (from the big side to the small), as well as from each of the chainrings.
posted by rhizome at 10:32 AM on April 13, 2012


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