SpikedLemon

I'm looking for advice on the rear derailleur adjustment (10spd Shimano Tiagra). I've now tossed the chain into the wheel twice (I got it jammed between the cartridge and the plastic disk to protect it from destroying my spokes). I can't see much damage beyond one of the tabs on the derailleur jockey wheel was a little bent.

My bike had a tune up earlier this year (perhaps two-three weeks ago?) and, as I was heading up hill and approaching a red light, I shifted all the way down while pedalling anticipating needing to stop (and re-start on the hill).

I noticed, after the first jam, that my adjustment was way out and I wasn't reaching my smallest gear. Figuring that was the issue: a few turns and I am running again.
After the second: I checked the lower stop and it was backed nearly all the way out (WTF?).
I can't imagine, that recently after a tune up, that I would be that far out on both.
Today's commute into work, once adjusted, was without incident.

What should I check on the derailleur for damage (e.g. how do I know it needs to be replaced) or am I on the right track and just keep an eye out for these kinds of shenanigans.

I really don't feel like getting stuck on the side of the road again.

techsensei

First thing you should check is the hanger and derailleur alignment. Sight down the derailleur from the rear and from above. The pulleys should hang perfectly vertical and run parallel with the cogs in both cases. If not take it to the shop to have that addressed. As for the limit screws, there is supposed to be a mechanism inside the derailleur to prevent the screws from vibrating loose. If the screws feels particularly easy to turn, that mechanism isn't working correctly. You can add a drop of thread locking fluid ("locktite") on the screws to secure them.

SkyDog75

Since you've had so much trouble with your rear derailleur's adjustment, I'd personally recommend going through the derailleur adjustment procedure yourself, top to bottom, to ensure it's set up right. (After following techsensei's excellent advice about the hanger and limit screws.) Once you've confirmed the hanger and adjustment are good, you should be able to have some confidence that shifting should be relatively problem-free going forward.

Park Tool has a good tutorial on their web site that'll walk you through the steps. If you've got just a little bit of mechanical aptitude and some attention to detail, it's not difficult to follow.
Rear Derailleur Adjustment | Park Tool

FBinNY 

The process must start with understanding the signs and their implications.

First of all, limit screw adjustments rarely change on their own, and the odd against both changing such that you overshift to low, and cannot shift to high are astronomical.

So before tinkering, you need to explain this amazing coincidence, and there is only one possibility. The RD itself is now more inboard than before, the result of the rear hanger being bent inward. This can happen in a single hard drop or crash or as the result of multiple insults moving it by degrees.

So, the process begins with straightening the hanger, then independently adjusting both limits based on the newly established correct position, and ends with fine tuning the trim.

Any repair not including the 4 steps is incomplete.

dsbrantjr

The derailleur may have gotten hit without you knowing it, like when the bike was parked. Aren't you glad you had the much-maligned spoke protector AKA "dork disc"?

SpikedLemon

Yep. And, on the side of the road, I was grateful for the kickstand on my road bike (apparently another faux pas)



Absolutely agree.
I can't think of anything that would have damaged it to the point of bending it unless it was damaged much earlier and I'd simply not noticed until just now.
I'll be completely honest, though, I hadn't paid any specific attention if I had or hadn't been reaching all 10 gears after the adjustment. For all I know: it could have been out of adjustment to start - with only the stop screw moving.

I'll be checking it out tonight to check that it's true and aligned and if it'd need to be replaced.

One item I do recall is that the low limit screw was VERY easy to turn and, as a mental note, I can see it moving again so it'll see some loctite/liquid teflon to keep it from moving on its own.

Bike tinker man

Other than all the good advise given above I would come back to the highest gear (smallest cog) then release / disconnect the cable before you try any alignment, there is no good trying adjustment screws if the cable is set wrong, another simple trick, when you move it back to the smallest gear, is the cable slack or still tight ?

SpikedLemon

Thanks for all the advice.

The quick sight-line of the deraileur is that it appears to be aligned. I used pliers to close the guide on the lower jockey wheel without any issue.
Tightening down the lower stop screw and re-adjusting the adjuster wheel has me moving again with little complaint from the rear end of the bike. Though I've only had opportunity to put in about 30-40km since I made the adjustments.

The rear deraileur does, however, have a little side-to-side play in it that isn't coming from the bolt holding it to the frame. I assume this is normal as I have some similar play on my MTB as well.

fietsbob

To Be right the alignment tool uses a reference of the wheel thru 200+ degrees Its a better way to get it right than Just Looking

overshifting and doing damage to 25% of the spokes in the rear wheel; 'dork discs' which are spoke Protectors are not so dorky after all .