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-   -   Can't get Rear Derailleur working properly (https://www.bikeforums.net/bicycle-mechanics/817969-cant-get-rear-derailleur-working-properly.html)

thnksfrtht 05-14-12 09:51 AM

Can't get Rear Derailleur working properly
 
Hello, apologies in advance if this is an easy answer.

I've been trying to get my rear derailleur working properly, but am just getting frustrated. The H, L and B screws are all in line. I have the tension as tight as I can get it on the cable, and the first couple of shifts work smoothly. Then, at about the 3rd (or 4th) cog, it hesitates. I'll then use the barrell adjuster to tighten until the chain jumps up a gear. After that, the cable is too tight, and if I shift down to the smallest cog, it won't shift past the second smallest.

My cassette is new, my rear D is fairly new (and straight), and my cable is brand new.

Any help is appreciated - I don't know what's causing the trouble.

DannoXYZ 05-14-12 09:56 AM

List all your components, there may be mismatch of some kind.

thnksfrtht 05-14-12 10:00 AM

Unsure of cassette (I bought at the tail end of last season), I just know it's nine-speed. Derailleur is XT Deore. Shimano Chain.

Homebrew01 05-14-12 10:00 AM

http://www.parktool.com/blog/repair-help

FBinNY 05-14-12 10:07 AM

You may have the cable adjustment off by one gear position. Slacken the cable slightly, shift so the chain is on the second smallest sprocket, set the lever for the 3rd to high gear (7 for a 9s), and adjust the barrel adjuster while pedaling until it shifts. Now find tune around the shifting between the 2 and 3rd smallest sprockets in both directions, and the rest should follow.

If not, check that the cable runs smoothly, the gear hanger adjustment, the "B" screw adjustment, and just in case use an improvised feeler gauge to check that the gap between the cassette sprockets is uniform.

thnksfrtht 05-14-12 10:23 AM

Thanks for the responses - I'll try these suggestions tonight.

Again, appreciated.

JonathanGennick 05-14-12 10:34 AM


Originally Posted by thnksfrtht (Post 14220769)
I'll then use the barrell adjuster to tighten until the chain jumps up a gear.

If I turn the barrell adjuster enough to spark the shift, it is often too much. My technique is to: 1) Turn barrell adjuster a click or two (or whatever), 2) reverse course a few cogs, 3) come at the shift again to see whether it works.

Have you put a hanger alignment gauge on the hanger to verify alignment? What you're experiencing seems pretty classic for a misaligned hanger.

Sixty Fiver 05-14-12 10:35 AM

FB always give great advice.

Sometimes it is easier to start from 0... release the cable and make sure the shifter is in the right position.

The cable adjustment screw on the derailleur should be turned out from it's stop 4-5 turns to give you some +/- adjustment when you are setting things up and you can usually make fine adjustments at the lever.

A really important aspect of indexed systems is ensuring that your derailleur and hangar are aligned... a bent hanger will defeat your best efforts at trying to dial things in every time.

If you are really still fubar after this send me a smoke signal as it looks like we hail from the same great city and would be happy to take a look at things for you... my shop is north central (Kingsway) and I also volunteer at the Bicycle Commuter's Society and since we opened the north location I am usually there.

The crew at the south side is pretty good and they have expanded hours there and would trust that they could remedy most issues.

thnksfrtht 05-14-12 02:48 PM

Hey, @Sixty - I cant PM you, but I wanted to say thanks for the descriptive reply - and I'd love to make visit your shop! Hit me with your details!

Regards!

Standard Issue 05-14-12 09:30 PM

I had similar shifting issues. The first time it was because I was using a suntour rear D with shimano shifters/cassette. The 2nd time switching out the chain solved the issue. You'll have to try every component to really solve the issue. It may take a while a cost a few bucks but eventually you'll figure it out.

FBinNY 05-14-12 09:36 PM


Originally Posted by Standard Issue (Post 14223961)
You'll have to try every component to really solve the issue. It may take a while a cost a few bucks but eventually you'll figure it out.

This kind of trial and error is the most expensive way to fix a mechanical problem.

Take the time to analyze the possibilities, and start by testing and ruling in or out those things that can be done for free, ie. adjustments or measurements. Only when have you narrowed the issue down to a short list or single proven culprit should you spend cash to replace it.

Most problems, especially things like erratic shifting don't call for new parts, just better adjustments of what you have.

Pepper Grinder 05-14-12 10:29 PM

Cable friction. Old housing? Lube inner cable with very thin coat of teflon-impregnated dry lube/wax lube. Also be sure to lube bottom bracket cable guide.

ruirui 05-14-12 11:39 PM

you might want yo check this video out: adjusting deraileur

Sixty Fiver 05-15-12 12:28 AM


Originally Posted by ruirui (Post 14224355)
you might want yo check this video out: adjusting deraileur

That is a good video but does not address troubleshooting things like bent hangars and differs from my method when it comes to setting the barrel adjuster... I can usually install a cable and by feel can usually have it at nearly perfect tension and only have to make small adjustments and like to set that barrel adjuster so there is room to go up or down +/- in case the cable is a little too tight and needs to be backed off a little.

I do this with all barrel adjusters so I can increase or decrease cable tension during set up.

I might be the odd duck in this but this has been working for me for years.

In re-reading the OP my thought is that since the OP's bike shifts well to the middle of the cassette and then goes off that there is an alignment issue with the hangar or that the derailleur has been bent but without seeing things closely or in person it can be hard to tell what is causing the issue.

Could even be a mismatch between the shifter and cassette... you can get 8 and 9 speed shifters to shift 9 and 8 reasonably well until you get to the middle and then things can go off just a little.

Kimmo 05-15-12 03:34 AM

Given your components are compatible, there's not much else it can be other than cable friction.

You first need to either confirm or eliminate this possibility.

With the bike upside down or in a stand, have someone turn the cranks so you can shift while pulling the derailleur outboard to maximise cable tension.

If this makes the bike shift fine, the signal isn't getting through to the derailleur properly - there's too much friction for the derailleur's return spring to overcome.

If it doesn't, you likely have a bent hanger, or just maybe something less obvious.

JonathanGennick 05-15-12 05:19 AM


Originally Posted by Sixty Fiver (Post 14224443)
...and like to set that barrel adjuster so there is room to go up or down +/- in case the cable is a little too tight and needs to be backed off a little.

Interesting you mention that, because I've taken to doing the same. I sometimes have wondered whether I'm the only one.

Amesja 05-15-12 05:33 AM

Make sure the cable housing at the RD isn't getting caught up and can move freely as the derailleur goes through its motions. I had a case the other day where the cable was getting just barely snagged by the hardware that had been used to mount the rear rack. It would get snagged just very slightly by the bolt head and it would cause the tension to be messed up in certain derailleur positions until it popped itself free. Sometimes a very small thing like this will cause enough of a drag or change in tension on the cable as to make it very hard to tune the shifting to work consistently across the the entire spectrum of gears and derailleur positions.


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