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Discussion Starter · #1 · (Edited)
I'm setting up a Shimano 12 speed drivetrain for first time and have some questions.

I'm using a SLX 10-51 cassette, *SLX m7100 rear derailleur, SLX 12 speed chain, XT Shifter, and SLX m7120 crank with 32t ring (using a thread together PF92 BB which is a little wider than normal so removed spacer on drive side and have only 1 on non drive side so chainline probably a little less than 55mm, for the sake of being thorough).

I measured the chain and the bottom side was in between cassette teeth so I allowed a little slack to drop into teeth and added 5 links plus quick link. After installing chain I tried to adjust B screw and when the tip of teeth is level with the line on der, the line isn't perpendicular with the tooth and slopes down towards *back of bike. The manual and couple pics I found show it being more perpendicular or tangent to the teeth but isn't mentioned so I'm not sure if this is important?

At first I assumed it was important, and making the chain longer seemed like it would correct it. So I broke off an extra inner link and added a second quick link which essentially added 2 links, an inner and outer. This allowed me to adjust B screw so perpendicular when line level with teeth tips, but when in 10T there was obviously too much slack in chain so I removed the extra.

I haven't messed with shifting too much but with a quick adjustment it seems to skip a little and feels like there is resistance(?) when spinning cranks. Not sure that's the best description, but it's not smooth.

Anyone know if the line is supposed to be perpendicular with teeth when lined up with tips? Or have any comments or suggestions?

Sorry so long, always try to describe everything as much as possible and go overboard...

*Edit - a picture probably would make things easier:
Edit 2: forgot to mention I checked the hanger before installing anything and it's straight

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Discussion Starter · #3 ·
Literally saw your post and this video about the same time... Hope it helps:

Thanks for the reply.

In that video the line is much more perpendicular with the teeth which is what I'm concerned about. I can adjust it so the line is above or below and it never becomes perpendicular and always drops down at the rear of the line. Everything I've found so far shows the line much more perpendicular. So if a tooth is at the beginning of line and the next at the end, the line basically goes straight from tip to tip. My setup is impossible to get like that and makes it seem like the derailleur is at the wrong angle. It seems like chain length would determine this, which is why I tried adding some length which let me set it up perpendicular, but was then too long in the smallest cog.

Really not sure how important this is or what to do to correct it. But it's definitely not spinning or shifting all that smooth. Not terrible, but not great either.
 

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Discussion Starter · #4 ·
Just in case anyone has this issue in the future and finds this thread, I found that my derailleur hanger is out of spec. I found those specs here:


As well as www.UniversalDerailleurHanger.com which is a push to have one common hanger and lies at one end of the Sram specs range.

Basically my derailleur is 2mm higher and 5mm further back than the outer limits of the specs. Not a lot, but enough that it causes the above, which doesn't allow proper derailleur placement/ angles or crisp shifting. Especially with 12 speed where a few mm of B screw adjustment can throw shifting off.

Now to figure out what I'm going to do...
 

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Discussion Starter · #6 ·
I'm using the hanger the bike came with which like most frames has a fairly unique interface with the hanger. Unfortunately, it's just a poorly designed hanger that doesn't fall within current specs for a 12 speed drivetrain der hanger as provided by Sram (and since they were the 1st w/ 12 sp, I assume Shimano adopted the same). I wish it was a UDH hanger as it would put the derailleur in the correct spot.
 
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