Bicycle Mechanics - Rear derailleur shifts poorly
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09-20-12, 06:48 PM
Hey guys, I'm having difficulty adjusting my RD. I'd appreciate any help from you.
Recently, I've opened teh RD cage and struggled a bit to put it back. I'm not sure if I put it back correctly. I've lost the bolt on the lower pulley so I put another in, which is much longer.. I didn't touch the hanger, L and H and B-screw so I assume there is not problem with them. Here a photo of it.
1. First, I put the chain to smallest cog and largest chainring. The RD has trouble shifting up --> cable too loose (according to Parktool) --> adjust the cable, more tension. Shifting up is jerky (press lever once, chain doesn't shift up, press lever another time, chain jumps two cogs, shift down from the third smallest cog works properly from there) , doesn't always work. But that's quite acceptable compared to the next problems.
2. Now another issue with shifting up in RD. Middle chainring, fourth largest cog and third largest cog now. Chain rattles, making noise. Like the chain goes from the upper pulley to the third largest cog doesn't go smoothly and the transfer makes noise. Also, shifting down from the third largest cog to the fourth largest cog doesn't work, I press the lever another time and it jumps down two cogs, to the fifth largest cog..
3. In smallest chairing, Shifting up from third largest cog to second largest cog doesn't work, I press the lever once (6->7, 8 speeds) chain jumps straight from third to largest cog and the lever is super tight, very hard to press from 7->8.
Hope it makes sense. If it doesn't, I'll try to youtube the whole process.
There's so many issues with this bike now:mad:. and I hope with you guys' expertise, we may be able to work it out :).
Andrew R Stewart
09-20-12, 07:42 PM
I like to seperate out the various aspects of shifting from each other during adjusting or assessment. The main components of the system are the der, the cable, the shifter and the chain/cogs.
First is the rear der. Is it parallel (the cage) to the wheel through out the range of movement? Does it move the correct amount, is the upper pulley directly under the large and small cogs? Are the pulleys in good shape and in the right order (Shimano upper pullies have a touch of end play without hardly any rocking)? Is the upper pulley as close to the cogs as possible w/o knocking against the large cog? Does the parallegram have good movement, no slop, good return spring action?
Second is the cable. Does it move freely through the casing and past any guides (rust, grit and dry of lube)? Are the casings the proper SIS kind, are the end caps the right ones for the casing size and are the lengthwise casing strands in good shape (and not poking through the end caps)? Is the cable fraying, espicially in the shifter pod? Is the cable of the right diameter? Is the cable properly anchered at the rear der?
Next is the shifter. Does it click through all the positions freely? Both ways? Is it the right one for the der and cogs (count and road VS ATB)? Is there any interference with the bars, brake levers, hoods?
Last are the chain and cogs. Are they worn (chain wear lengthwise is easy to measure, side ways flex less so)? Do the match in gear count and family? Are the cogs properly spaced, over the full number of cogs? Is the lock ring the right diameter? Any bent or broken cog teeth? Any twisted or tight links? Any link pins sticking out of side plate bulges? Is the chain within the right range of lengths?
There are more factors but these are the main aspects that I look at when I take a bike in for service. If the customer mentions shifting issues we look a bit deeper.
The first thoughts about your issues are cable related. The frictionless movement. The condition of the casing and end caps. The cable's routing under the ancher bolt. Second is the pulley wheels, is the upper the SIS one? Is the upper so worn that it rocks cockeyed like? The noises and partial shifting is easily explaned by cable problems. If the cable is not freely moving it will hang up and only (maybe) 75% of the lever's command will communicate to the der's movement, a partial shift. Another shifter click and the cable moves the der 110%. When shifting down (up the cog) it's the strength of the hand and slight overshift that influences this. Shifting up (down the cogs) and it's the der's return spring that pulls the cable. They are different degrees of force. I would thing the chain condition might be the next concern, but it has less effect then cables.
I would suggest a new cable and casing. Care taken to have well shaped lenths of casing with proper end caps with good cable lube (Triflow). The cable should be well routed under the ancher bolt plate (this can be confusing, Shimano has a tab that is not meant to go over the cable). This is inexpensive and after a few years should be done reguardless. The after adjusting the limit screws and the SIS tension work the system a number of times to seat the cable/casing and retension the SIS as needed.
Really only looking at and working the system can any one say what is going on but these are my suggestions. Andy.
09-20-12, 09:29 PM
You simply cannot diagnose or correct mechanical problems by listing multiple symptoms, and really neither can we. There are simply too many variables, as Andrew indicates above. You have to first follow the correct procedures for lubrication, alignment, adjustment, checking wear, etc. on the derailleur and if necessary the entire drivetrain. Until you have done that there is no reference point for correcting any problems that are still present. I have no idea why you disassembled the cage - I assume there was something wrong, but what?
A bicycle may be fairly simple but it still involves a lot of interacting parts. You can't just wade in without thought. You either need to have gained knowledge of how the different parts interact or have the ability to observe and understand their operation. At this point I would advise you to find a knowledgeable friend or bike co-op so you can get some in-person guidance, and if that's not available take the bike to a shop. Also, that long bolt on the bottom of the cage is potentially dangerous, as it could go into the spokes.
One final request if you post again - please do not randomly scatter bold, colored and different size fonts in your post. It's very distracting and makes providing assistance more difficult.
09-20-12, 09:36 PM
and get rid of that long bolt before it ends up in your spokes and really causes a problem! find the right one in a bike shop junk bin or trim the long one.
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