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help with rear derailleur(9 posts)

help with rear derailleurPeterRider
Aug 10, 2001 9:40 AM
Hi,

I have something annoying with my 8spd rear derailleur: if I call 1 the smallest cog and 8 the largest one, the derailleur usually shifts fine 1-2-3-4-5-6-7-8, but on the other way, usually is doing 8-8-7-6-5-4-3-1. Actually, previously it was doing 8-8-7-6-5-4-3-2, and then after a while hopping from 2 to 1. Of course I suspected the 2 tuning screws to be the origin of my problems, I tried plenty of combinations yesterday evening, and the best I got to have the chain go out of 8, was 8-7-6-6-5-4-3-1. (if I put the L screw tighter, I won't be able to go to 8)

Do you have an idea about that ? I don't pretend being an expert with screw H and screw L, but I tried about everything I could think of. Do you think what is to incriminate is the derailleur, or the STI shifters ?

The system is a double/8speed 4 year old Ultegra, the cassette is 12-23. I had the classical problem with the "sticking Ultegra STI shifter", but with the help of my friend WD40 I got rid of that problem (just saying that to tell that my STI right shifter is not brand new and it could be the thing to incriminate)

Thanks for your ideas, suggestions, explanations.

Pierre
re: help with rear derailleurtommyb
Aug 10, 2001 9:46 AM
The problem is probably not going to be solved by adjusting the H and L screws. These are used to set the limits of motion. If you can get to the top and bottom gears, these screws should not affect shifting in the middle. You need to adjust the cable tension, using the barrel adjuster where the cable enters the derailleur. If you are having problems shifting from smaller to larger gears, then you likely need to tighten the cable by turning the barrel adjuster counter-clockwise. Usually a half turn will be enough to see if it's getting better or worse.

Good luck
i'll try, but the cable is already quite tight ??PeterRider
Aug 10, 2001 10:15 AM
With the right tension in the cable, is the cable still tight when you are on the little cog, or is there *almost* slack in it ?

And indeed I can get to top and bottom gear without problem. When the L screw is too lose, the derailleur touches the spokes as it has to.

What I thought is if I tighten the L screw, it will offset the shifting a little bit so that getting from 8 to 7 is easier. My current setting, which I was describing by 8-7-6-6-5-4-3-1, is with a L screw rather tight and a H screw rather lose. Is all this wrong ?

Pierre
i'll try, but the cable is already quite tight ??tommyb
Aug 10, 2001 10:23 AM
The barrel adjuster doesn't affect cable tension in a very noticeable way. It's a rather subtle, fine adjustment. Follow the link in the following reply, it gives a better description than what I can type in this box. But to answer your question, the L and H screws should not offset the shifting, only stop it from going to far. If you look inside the derailleur, you will notice that the mechanism is not touching the screws when you are in the middle of the range, only when you get to one end or the other.
re: help with rear derailleursearcher
Aug 10, 2001 10:11 AM
All your questions can be answered at this site:

http://www.sheldonbrown.com/derailer-adjustment.html
Out of Phasegrzy mnky
Aug 10, 2001 10:19 AM
Shift all the way down to the smalles cog while using some slight tension along the cable. Now shift it up one gear and let go of the cable. The bike should be in gear #2 according to your convention (really #7). If it's not all happy or even in the gear you need to adjust the cable length (not really the tension since the force doesn't vary). Once you get this dialed in run up and down through all of the gears - if you can't hit the extremes then adjust the limit screws. The thing to remember is that the limit screws just adjust the end stops while the cable length controls which gear you're in. Good luck.
just a detail....PeterRider
Aug 10, 2001 10:37 AM
(cause I'm french, my english is not perfect) - what you mean by "let go of the cable", is it giving slack in the cable (barrel adjuster) ? If I do that, won't the derailleur switch to #1 (real #8) ?

Thanks for your explanations, it's very nice !

Pierre
Clarificationgrzy mnky
Aug 10, 2001 1:10 PM
I meant that if you're way out (several gears) the cable may be slack when shifting into the smallest. This slack may show up anywhere along the cable run, but you want to make sure it makes it all the way back to the part that is supposed to move - the der. so that you get the natural response from the system. I could have left that little bit about letting go of the cable since it should be fairly obvious once you're messing with the bike. Hope this helps!
re: help with rear derailleurLC
Aug 10, 2001 11:21 AM
Sounds like the cable is sticking. Pull out the cable and put some light oil on it, or replace it with a new one. Don't use wax (i.e. White lightning) or heavy grease or you will get exactly the symtoms you described. If you already have something in the housing then replace that too if needed.