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Author Topic: Rear Derailleur not shifting down very well  (Read 1078 times)

tomc

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Rear Derailleur not shifting down very well
« on: January 03, 2016, 09:11:29 PM »
I have an XT rear derailleur that I've had forever. Never given me problems. It is straight, the pulleys seem fine, and it shifts up fine. But it has a tendency to not want to shift back down to smaller cogs(unless I shift twice in which case it will shift down one and maybe eventually all the way after many pedal strokes). The housing and cable fairly new and I have a new lx shifter. By eyeballing it the cage looks pretty lined up with the chainline and cogs.I've played with the cable tension enough that it never finds the sweet spot.


 I don't know that I've heard of this before but could it be the return spring that is giving me grief?  I'm just about to give up on it but thought I'd ask for some input. Is a spring something that can be replaced if that is the problem? Just guessing here as I can't seem to find the root of the problem.

chmaeet

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Re: Rear Derailleur not shifting down very well
« Reply #1 on: January 03, 2016, 09:25:53 PM »
Have you ever taken it off the bike and given it a good cleaning?  I only have experience with SRAM but every other year I pull all of the moving components off and clean the gunk out that I can't get with everything assembled.  Maybe with a good cleaning and re-lube you might get the original operation back.  Also, when I reassemble I go through the mfg setup guide and reset all of the adjustment points in the order they describe.  From what you have talked about it doesn't seem like you have anything bent and if your cables and housing are new and shifter is ok, then focus on the RD.  Do you or someone you ride with have a spare RD you could mount to try?


Chris

gmcttr

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Re: Rear Derailleur not shifting down very well
« Reply #2 on: January 03, 2016, 09:46:21 PM »
...The housing and cable fairly new....

The symptoms you describe point toward the cable not sliding freely in the housing. This could be due to dirt, a worn housing or a fraying cable.

Shift to the smallest gear and then move the derailleur, by hand, up to the larger gears, back off one gear at a time and see if the derailleur shifts properly. If it does, the problem is most likely with the cable and housing and not the shifter or derailleur.

mtbikernate

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Re: Rear Derailleur not shifting down very well
« Reply #3 on: January 04, 2016, 02:39:17 PM »
The symptoms you describe point toward the cable not sliding freely in the housing. This could be due to dirt, a worn housing or a fraying cable.

Shift to the smallest gear and then move the derailleur, by hand, up to the larger gears, back off one gear at a time and see if the derailleur shifts properly. If it does, the problem is most likely with the cable and housing and not the shifter or derailleur.


This is true. It's the cheapest and easiest to check, and would be first on my list. It is possible for derailleurs to wear out, though, and they get sloppy.

tomc

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Re: Rear Derailleur not shifting down very well
« Reply #4 on: January 07, 2016, 09:29:42 PM »
So, I appreciate the comments. I'll say that awhile back that same derailleur had problems shifting into the smallest cog. I took it off and cleaned the whole thing, lubed it up, and when i put it back on it did shift into that little cog. Guessing all the gunk in the spring and pivots didn't let it shift into that position. But problems shifting down to smaller cogs happened quickly after that. 


When I manually shift the derailleur by hand it does shift well. I notice that when I shift it with the shifter it just doesn't want to go far enough but if I give it a little push with my hand it will shift into the correct gear. So, this means that either the cable/housing is gunked up OR the spring is just not powerful enough to overcome the friction. Would that be correct in saying that? I'm not sure which it is though as the housing seems to slide well over the cable when I loosen everything up and slide the housing around.


So here's my next move. I have a bike I'm building up that, as far as I can tell, needs all full length housing. There are no cable stops except to the front derailler which there is one. I've never run full length housing before so don't know if it will give me more friction or less. I guess I'll just set it up and see what happens. I have all new housing I bought from Pricepoint and it is apparently their brand. No experience using this stuff but it was on sale so thought I'd give it a try. I'm sure I'll run into some snags on this build (no pun intended) but whatever, at least I learn as I go. Thanks for the input.   




David Kuehnen

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Re: Rear Derailleur not shifting down very well
« Reply #5 on: January 08, 2016, 08:52:11 AM »
Full length cable housings may have more friction but they also keep a lot of out since the cable is not exposed except at the derailleur. 
David Kuehnen, PE

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chmaeet

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Re: Rear Derailleur not shifting down very well
« Reply #6 on: January 08, 2016, 03:53:59 PM »
Quote
When I manually shift the derailleur by hand it does shift well. I notice that when I shift it with the shifter it just doesn't want to go far enough but if I give it a little push with my hand it will shift into the correct gear.


Have you tried adjusting your limit screw yet?  Local hand pressure might be enough to shift but leverage and force applied by the shifter/cable might not be enough if the limit screw is right on the edge of allowing a shift.  This of course would only apply to the smallest cog shift you mentioned.

 

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