Slowtwitch Forums: Triathlon Forum: Front Derailleur Shifting/Chain Dropping Question

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Slowtwitch Forums: Triathlon Forum:
Front Derailleur Shifting/Chain Dropping Question

atasic

Jul 4, 08 12:50

Post #1 of 6 (169 views)

Front Derailleur Shifting/Chain Dropping Question	Can't Post

I am relatively new to this and don't know much about adjusting of derailleurs. I have a '07 Trek E9, all Ultegra group. Today, at the beginning of a climb, higher cadence 95-100, chain in front on large chainring, shifting to smaill chainring, I dropped the chain 3 times to the inside. It does not happen all the time. Occasionaly with a certain combination of cadence and torque on the pedals it dropps when shifting from large to smaill chainring. Now, is this a matter of low gear limit screw adjustment or my technique is wrong. If my technique is wrong, would someone please educate me about it. When I place the bike on the stand and shift, it never does that. If this is only adjustment issue, it is a matter of turning the L screw clockwise about 1/4 turn at a time, shift and check. Correct?
This worries me to death. This is on the race course for next week's race that I have coming up. There are several climbs where shift the front from large to small is required. I do have free adjustments from the bike shop, but it is a little drive away and I have been there way to often. I am affraid they will get tired of me.
Thanks for the advice.

Whitenose

Jul 4, 08 12:59

Post #2 of 6 (166 views)

Re: Front Derailleur Shifting/Chain Dropping Question [atasic] [In reply to]	Can't Post

Shift your rear derailleur down 3 cogs, then (or simultaneously) shift your front derailleur . What is happening is that you are cross chained across the cassette (I'm assuming that you are in your 25, 26, or 27 gear on the back, whichever is you easiest gear), so that when you go from your big ring to your small ring, the chain is pulled right over the top of the small ring without ever catching the teeth on the small ring.

atasic

Jul 4, 08 14:26

Post #3 of 6 (149 views)

Re: Front Derailleur Shifting/Chain Dropping Question [Whitenose] [In reply to]	Can't Post

Ok. That is a good start. So, 3 down from the lowest gear (from the largest rear cog), than shift the front. That should eliminate cross chain condition. I will give that a shot. Where I get myself in trouble with this is as I am on the flat, crancking 95 rpm, somewhere down toward the highest gear( few up from it), pretty hard effort, start the uphill, start shifting to lower gear, maintain cadence, there comes a point where I have to now go to small chainring in front, that is where I dropp it.But, not always. I don't think that I am far down the cog set. I think I get close to what you recomend, but I will pay attention to make sure.
Thanks.

sinkorswim

Jul 4, 08 14:45

Post #4 of 6 (146 views)

Re: Front Derailleur Shifting/Chain Dropping Question [atasic] [In reply to]	Can't Post

Front der. adjustments can be challenging. I'd recommend letting a shop handle it if you have an event coming up, but here is what I think you need to do:

The low (L) limit screw likely needs to screwed in, but be careful ... 1/4 turn at a time. What I'd recommend would be to put the chain in your smallest gear (largest cog) in back 25, 27, etc. and on the small chainring. Next take all of the tension off of the front der. cable(either loosen the bolt on the derail or loosen barrel adjuster). If you turn the low limit screw in without loosening the cable, the cable will actually loosen, which could cause big ring shifting problems.
Next, make sure that the front derail cage is correctly positioned - not twisted in or out - outer plate of der. cage should be parallel with large chainring. (I assume front der. height is correctly adjusted).
Next adjust low limit screw so inside plate of front der. is nearly touching chain when in small chainring and largest cog.
Now tighten front der. cable. Shift to large chain ring and smallest cog and adjust outer plate w/ high (H) limit screw so outer plate is just outside of chain. You might have to tighten cable a bit if the der. is not getting all the way over past the large chainring.

Hope that helps.

atasic

Jul 4, 08 14:59

Post #5 of 6 (136 views)

Re: Front Derailleur Shifting/Chain Dropping Question [sinkorswim] [In reply to]	Can't Post

Thanks for the advice. I ain't touching front adjustment. I will take it to the shop. I am affraid that I will screw more up than adjust. Doing what you said under qualified person supervision would be ok, but me alone would lead to a disaster. I thought that it was simply a matter of turning a screw in 1/4 turn. Thanks again. Man, I have a lot to learn.

Whitenose

Jul 4, 08 18:46

Post #6 of 6 (111 views)

Re: Front Derailleur Shifting/Chain Dropping Question [atasic] [In reply to]	Can't Post

If you drop the chain off of the big chain ring, you can often get it back on by shifting back to the big ring, and pedalling slowly so that the chain has time to catch the teeth on the chain ring. Of course, if this occurs on an up hill, your time to attempt this is rather limited. You may need to keep the rear derailleur in a harder gear to get this to work too, as you will attempt to cross chain the chain so that it catches on the chain rings again.

Probably the safest thing to do, is to anticipate the need to shift to the small chain ring ahead of time and shift while you are not in a cross chained situation. This may be easier said than done while in a race situation.

If you go into the bike shop and have them work on this problem, spend time with the mechanic watching what he is doing. It will help you in the future should you need to make the adjustment again.