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Old 09-21-10, 06:41 PM   #1
Ghostcode
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So I was following the Park Tools instructions on adjusting my rear derailleur...

Quote:
L-Limit Screw

The L-limit stops the derailleur from moving inward (toward the spokes). The limit screw does not make the derailleur move, pulling the inner wire makes the derailleur move. The L-screw allows the pulley wheels to shift the chain to the innermost sprocket and yet not shift off the sprocket into the spokes.

Shift bike to middle chainring (or smaller ring of double chainring bikes) and to second-to-innermost rear sprocket.
Pedal bike at a quick cadence, approximately 60 rpm or more.
Pull inner wire by hand to shift derailleur sprocket inward. When adjusting the L-screw, be concerned with two situations:
The inward shift from the second-to-innermost sprocket to the innermost sprocket.
How the chain rides on the innermost sprocket.
If shifting seems adequate, tighten L-screw 1/4 turn, and repeat shift. Continue to tighten L-screw until symptoms of too tight appear. These symptoms are that the chain will not complete shift even with pressure on inner wire, the chain hesitates before shifting inward even with constant pressure on inner wire, or the chain rattles excessively when riding on innermost sprocket


When symptoms of a too tight L-screw appear, loosen L-screw 1/4 turn and check shift again. Repeat process of shifting and correcting by 1/4 turns. When too tight symptoms disappear, L-screw is at tightest acceptable setting, and limit screw setting is done."
Everything was working great for the H screw, I adjust it correctly, and it feels like it's shifting crisp on to the lowest rear sprocket. But when it came to the L-screw, I am stumped. The whole reason I tried to adjust my rear derailleur, is because it was skipping when I shifted in the second highest sprocket. (Mind you, I'm on a 10 speed Dura Ace 7900 CAAD9-1). So I'm following the L-screw instructions. I simply CANNOT get the chain into the second cog without it skipping one lower or just hanging on the edge of the cassette. I put the front into the smallest, and I couldn't get the RD to stick to the largest back. I adjusted the L-screw until it was so loose it was coming out. It still wasn't far left enough. I'm not sure if there is something I'm missing, but I tried to follow the instructions to a "T" and I couldn't even get the initial chain onto the second largest sprocket smoothly.

I am new to the whole "mechanics" thing but I followed the instructions on the front derailleur and got it to work great. Any advice/tips could be appreciated before I take it into the shop to have them look at it. I'd rather do it myself if I can, trying to learn. Bottom line, I couldn't get the rear derailleur pulleys perfectly aligned with the largest sprocket or two/three.
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Old 09-21-10, 06:45 PM   #2
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check derailleur hanger alignment
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Old 09-21-10, 06:49 PM   #3
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Quote:
Originally Posted by reptilezs View Post
check derailleur hanger alignment
I tried to figure that out, I mean being new to this, the only instructions other than H/L Screw for the derailleurs on the Park Tools was the B Screws. I didn't see anything obvious on how to check/adjust hanger alignment.
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Old 09-21-10, 06:56 PM   #4
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Too many variables. 10's are finicky.

a. You might be losing some throw if your cable isn't sitting right under the pinch bolt.
b. The end of the L-screw which contacts the little stop inside might be damaged/chewed up.... also, the little stop inside might need some love (filing).
c. Cables/routing and/or wacky angles/not seating in the cable stops.

Best place to start is describe when/why it started doing this. Did it ever shift right to begin with?

Even the brifters can do strange things after high mileage.

Last edited by duckforcover; 09-21-10 at 07:10 PM. Reason: words
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Old 09-21-10, 06:57 PM   #5
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Well I didn't see it the first time so now I feel dumb, I see the hanger alignment link they offer. From the looks of it, you literally just bend it with physical force?
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Old 09-21-10, 07:05 PM   #6
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Yes,...but the secret is knowing exactly how far and in which direction. The right tool helps.
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Old 09-21-10, 07:11 PM   #7
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Quote:
Originally Posted by duckforcover View Post
Too many variables. 10's are finicky.

a. You might be losing some throw if your cable isn't sitting right under the pinch bolt.
b. The end of the screw which contacts the little stop inside might be damaged/chewed up.
c. Cables/routing and/or wacky angles/not seating in the cable stops.

Best place to start is describe when/why it started doing this. Did it ever shift right to begin with?

Even the brifters can do strange things after high mileage.
It shifted flawless for the longest time. I got the bike 1000+ miles ago. I never got the "initial" 300 mile checkup, from stretched cables and such. I did some manual cable adjusting, and barrel adjusting. Just last week or so, the front derailleur wasn't shifting to the big ring. I followed park tools instructions and got it to work great, it seems to be shifting great right now - the front that is. A few days ago, I just started to notice a little skipping in the larger sprockets of the rear cassette. Only possible thing I can think of that changed was I had a professional fit, and the guy put it on the trainer, so other then putting it on and off the trainer. I can't think of anything that changed/adjusted in the rear.
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Old 09-21-10, 07:25 PM   #8
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Just eliminate one thing at a time.

For the L-screw... shift it into the highest gear on the brifter/cassette temporarily. Then, see if you can push the derailer past that distance with thumb pressure. This wil tell you if the screw is being effective...make sense?

probably do this while turning pedals with other hand. DONT LET YOUR FINGERS GET CAUGHT IN THE RINGS.
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Old 09-21-10, 07:28 PM   #9
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My hunch on this one is a new chain, BTW.
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Old 09-21-10, 07:43 PM   #10
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Quote:
Originally Posted by duckforcover View Post
Just eliminate one thing at a time.

For the L-screw... shift it into the highest gear on the brifter/cassette temporarily. Then, see if you can push the derailer past that distance with thumb pressure. This wil tell you if the screw is being effective...make sense?

probably do this while turning pedals with other hand. DONT LET YOUR FINGERS GET CAUGHT IN THE RINGS.
I could very easily manually pull the cable towards me and it would shift just fine. I had to hold the cable there obviously, if I let go it would go back between the 1st/2nd, or 2nd/3rd. I also noticed if I held shift lever pushed in (as if I were shifting up) it would do the same thing - which appears to do the same thing as me pulling on the cable manually. Not sure what can be deducted from that if anything, I didn't physically try to push the hanger and see if I could move it past the distance with my thumb.
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Old 09-21-10, 07:50 PM   #11
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It sounds as if you simply need to add some tension to the cable. Turn the barrel adjuster counter-clockwise 1/2 turn at a time until the chain stays on the largest cog. If you turn it too far the chain will hesitate or refuse to go to the smallest cog.
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Old 09-21-10, 07:51 PM   #12
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no, no... not pushing on the hanger.

On the parallelogram part of the derailer body, where the name is printed.

That is the function of that screw, to stop the movement from going past that gear and into your spokes.

If you have the screwdriver on the screw and turn it, while putting some pressure on the derailer, you should be able to feel that.

Anyways, I gotta fly... good luck
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Old 09-21-10, 08:07 PM   #13
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Quote:
Originally Posted by Al1943 View Post
It sounds as if you simply need to add some tension to the cable. Turn the barrel adjuster counter-clockwise 1/2 turn at a time until the chain stays on the largest cog. If you turn it too far the chain will hesitate or refuse to go to the smallest cog.
I tried and had 2 others after my group ride mess with the tension. It would go to the largest if the tension was adequate, but when it came to shifting down from the largest, it would start skipping. Couldn't seem to get a happy medium.


Quote:
Originally Posted by duckforcover View Post
no, no... not pushing on the hanger.

On the parallelogram part of the derailer body, where the name is printed.

That is the function of that screw, to stop the movement from going past that gear and into your spokes.

If you have the screwdriver on the screw and turn it, while putting some pressure on the derailer, you should be able to feel that.

Anyways, I gotta fly... good luck
I'll have to check it out when I have daylight, thanks though for your insight.
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Old 09-21-10, 08:19 PM   #14
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Originally Posted by Ghostcode View Post
I tried and had 2 others after my group ride mess with the tension. It would go to the largest if the tension was adequate, but when it came to shifting down from the largest, it would start skipping. Couldn't seem to get a happy medium.
This may mean that you have excess friction friction along the shift cable. Check for any kinks in the cable housings or dirt in the cable guide under the bottom bracket. How old are the cables and cable housings. It may be time to replace them. Always replace the housings when replacing shift cables.
Also try hosing out the shifters with WD40. This will often restore shifting performance.
I do not believe adjusting the limit screws will help.
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Old 09-21-10, 09:38 PM   #15
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It seems that you have about hit the extent of what you can do yourself. The problem is that most of the time, it is a simple tension or such adjustment, but sometimes it can be the things that you dont think about or did know could happen that is causing the problem. If nothing from any other posts help, take it to a bike shop where they can look for the more complex reason that could be behind this
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Old 09-21-10, 11:28 PM   #16
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I was trying to guide him thru setting the L-screw back where it belongs, and then leave it alone... regardless, of how it shifts after that.

Realistically, the brifters control the shifting. Everything else is just in the path, unless cassette and chain have worn.

But, it has to be right.

Last edited by duckforcover; 09-21-10 at 11:38 PM. Reason: more woerds
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Old 09-22-10, 02:22 AM   #17
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Just take it in to the shop where you bought it. Better not to mess with it at this point. But if you must? I'd say just redo the whole rear derailleur setup from the shifter down.
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Old 09-22-10, 03:21 AM   #18
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I second the idea that you need to eliminate one thing at a time. Unfortunately with rear dérailleur issues, the first problem to eliminate should always be to check for a bent hanger if you can. Especially if you tried adjusting tension and limit screws and still have problems.

Deciding whether you want to buy the appropriate Park tool will depend on how many times you think you'd use it. I've already straightened 5 bent hangers in the last 18 months. But then again there are a lot of bikes in the family and I also do this for a few friends.
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Old 09-22-10, 05:53 PM   #19
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My cables needed adjusted, it was mostly all tension being the problem. Having messed with the limit screws, I had to readjust it all once I pulled the cables a little tighter. Learned quite a bit in the whole process. Probably would have taken a experienced mechanic 15 seconds, took me a day :-)
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Old 09-22-10, 07:29 PM   #20
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Since you had it in a trainer (and I assume that means the rear skewer was swapped for that duty), has anybody checked to make sure your wheel is all the way into the rear dropouts?
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