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Rear derailleur issues

Old 01-23-20, 04:20 PM
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OKCFF
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Rear derailleur issues

I for the life of me cannot get my new GRX 812 rear derailleur to index properly. And it takes an act of god or me physically putting the chain on the highest and lowest gear. I’ve done all the adjustments I can. Anyone have any advice or tips? I’m running a SLX 11-42 11 speed cassette. I honestly have no clue at this point. The hub is a 9 speed hub. Could that be the problem? My Grx 810 had no issues with the 11 speed 11-34t cassette I had on it. I’m just lost. I’ve adjusted upper and lower limit screws with no luck. Any help would be appreciated.
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Old 01-23-20, 04:45 PM
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berner
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Might the derailleur itself be defective? Specifically, the pivot may be loose. Try to jiggle the derailleur left to right. There should be almost no movement at the jockey wheel. I raise this point because I've had two rear derailleurs with poor shifting due to the bushing appearing to be worn out even with few miles on them. The second one was new so clearly defective.

Last edited by berner; 01-23-20 at 04:46 PM. Reason: spelling
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Old 01-25-20, 03:22 AM
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Originally Posted by OKCFF
I for the life of me cannot get my new GRX 812 rear derailleur to index properly. And it takes an act of god or me physically putting the chain on the highest and lowest gear. I’ve done all the adjustments I can. Anyone have any advice or tips? I’m running a SLX 11-42 11 speed cassette. I honestly have no clue at this point. The hub is a 9 speed hub. Could that be the problem? My Grx 810 had no issues with the 11 speed 11-34t cassette I had on it. I’m just lost. I’ve adjusted upper and lower limit screws with no luck. Any help would be appreciated.
I would recommend making sure the hanger is straight
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Old 01-25-20, 04:20 AM
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Yep, check RD condition and hanger alignment. Also check the cable.
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Old 01-25-20, 07:22 AM
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If the cassette fits on the hub and the lockring tightens, the hub is not a problem. Without knowing your level of experience with installing and setting up a rear derailleur, its hard to guess at the problem. I doubt it has anything to do with the derailleur itself. The most common mistake with that type derailleur is not hooking the tab on the derailleur hanger and the B screw adjustment won't do anything, because the derailleur is free to rotate around the mounting bolt.

You know the 812 is intended for 1x setups only, correct? I only mention this because you said you were changing it out from an 810, which is a 2x derailleur.and has more chain wrap capacity..
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Old 01-25-20, 10:57 AM
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Originally Posted by Kimmo
hanger alignment.
For rear shifting issues that defy normal cable adjustments, hanger alignment is ALWAYS the first thing that I check.
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