TheCommenterXVI

Hi,
I have a SRAM GX derailleur that's not working. It happened after I fell and the derailleur hanger bent, a bike mechanic straightened it back but could not fix the gears. the issue is that the derailleur does not have full reach of all my gears (I have a 1x12 gear system). I have screwed the H and L screw as far out as possible until they no longer limit the range of my derailleur, but that only gave me a range of 11 out of 12 gears. changing the tension of the cable of course only changes which 11 gears I can use (high tension gives me gears 1-11 and low tension gives me the gears 2-12). It's almost as if the gear shifter does not release enough cable ber click, but it would surprise me if it's the shifter that is the issue.
Does anyone know how these things work and what could cause this problem?
Thanks in advance for any help.

Iride01 

Did the bike mechanic suggest a fix? Or did he suspect you a cheap SOB and not worth their time messing with you? (not that that is any excuse for them)

If a hangar has been bent bad enough it might need to be replaced as the proper offset might have been messed up. Or perhaps the DR mechanism was bent or messed up also.

Might be a cable issue. Messing with the limits won't do anything for that. I will have thought the mechanic would have checked, but it you just made it sound like you wanted a quick fix or were in a hurry and couldn't leave the bike...

TheCommenterXVI

Hi Irde thanks for the reply,

the story of the bike mechanic goes as follows.
I left the bike at the shop for him to fix the shifting, when i came back a few days later to pick it up he said that it was all fixed (technically true on a bike stand). the mechanic said that the cable was too short and that he had to replace it. next time i was out biking i noticed that the higher gears were not actually working when applying pressure on the pedals (without any high pressure as you would have when pedaling the bike with your hands with the bike on a bike stand it worked fine). because the mechanic already had straighten the derailleur hanger I thought i could fix the gears by my own, so i started with the highest gear but then i noticed that i could not reach the lowest. i fiddled around for a while but could not find the problem.

my guess is that the mechanic somehow managed to squeeze the derailleur right in the sweet spot where, again, it worked on the bike stand but not when biking.

I hope this clears some thing up surrounding the mechanic, as for the hanger itself i don't think that it's an issue since i can reach both sides of the gears, just not without changing the tension in the cable

Iride01 

If it wouldn't go in the higher gears (the small rear cogs), then I'd have first lengthened the cable by screwing in the barrel adjuster. If I couldn't do that, then I'd change the position of the cable in the pinch bolt, making the widow end a little shorter.

It also needs to be determined what gear index your shifter is in when you try. If the shifter is in the position for your highest gear ratio, then is there some slack in the bare cable that runs along your downtube? Or does your bike have full length or internal routing?

Limit screws get set first when installing a DR. They should always be the last thing you try for any DR adjustments after that. And when you do, if the DR doesn't move as you turn the screw, then stop and turn the screw back to where you started.

Andrew R Stewart 

As gear systems have gained cog counts they have lost tolerance for slight misalignments, cable friction and such. This is one of the costs of increasing tech WRT cable controlled gear systems. As stuff gets bent/twisted the alignment relationships and the cable pull/der movement ones suffer.

Not unlike modern all wheel drive cars that when a tire gets damaged (easier with the trend to lower and lower aspect ratios) one finds out that all 4 tires will be needed to be replaced of the anti lock/traction control systems depend on tires with exactly the same tread wear.

I think you will come to the conclusion that replacing parts will be the final solution. Rear der, hanger, cable are the likely needs. Andy

TheCommenterXVI

Did that, but then it doesn't reach the lowest gear. That's my issue, all indexing (changing the cable tension) does is changing what group of gears I can use but I can never get the full range.

There is no slack in the cable, I have made sure of that, but it's not too tight either.
All the cables run alongside the frame, none go inside but they're all protected by tubes if that's what you're asking. the bike model I have is the Canyon Neuron 7 2019 or 2020 (the one with the vertical rear suspension).


Yes, I fully expect that I will have to replace, probably the derailleur, if not more. I came here because I would like to understand what the problem is since I cannot wrap my head around it. From my limited understanding of how the derailleur (or shifting) works (based on tinkering and theorising), such an issue should not be possible so I wish to understand why it is.


Thank you both for replying, I doubt that I will get the answers I seek but if you have a theory, I would be glad to hear it.

cxwrench

I would think this would be obvious...find a different mechanic. They should be able to adjust it easily OR determine if it's a warranty issue (which has happened w/ those derailleurs).

Andrew R Stewart 

OP stated he fell and bent the der so no warranty claim to be had.

I speculate that the mechanic didn't test ride the bike after doing the work. Which is not too surprising as many shops don't have this step as the REQUIRED one before the final writ up. Still a really good practice to do, even better when another (then the wrench) does the test ride. Given the crush of work many shops are seeing these days I. again, am not surprised if this wasn't done.

If there's a bend to the cage the guide pulley will have some in/out placement changes as the cage is played in/out with cog combo changes. This effectively changes the guide pulley's intended location from right below the cog to slightly either side of centered. Also why would a manufacturer make the cable pull amount of the lever any other then that which is correct for a new and in spec system. It's not like the preindexing days when there was extra lever spool room for loose cables or different ders. Andy