Orientation of rear derailleur
 

I was having trouble with my rear derailleur and took it to a LBS. The mechanic found a couple of issues, first of which was that the RD was installed on the hanger incorrectly. He pointed out that the RD has a tab which he said must be lined up over a matching tab on the hanger, so that the orientation of the RD on the axis parallel to the hub axle can only be at one place. In other words, before you tighten the hanger bolt, the RD can be turned like the hand on a clock, but according to the mechanic, it can only be installed at one specific place on the "dial", by lining up those two tabs.

Between that and a couple other issues, problem solved.

Now I'm re-installing the RD - Shimano XT 772 - on my other bike. If I follow his rule, the short run of cable housing cannot be installed in the conventional loop, because the point where it inserts into the RD (which would normally be the barrel adjuster, but the 772 does not use a barrel adjuster) won't allow it. I can only install with a straight run of housing, no loop. But if I break the mechanic's "rule" and install the RD about 45 degrees later (earlier?) on the dial, I can make the loop?

Is the mechanic correct that those tabs must be aligned, or am I doing something wrong?

I think the best thing is to direct you to Sheldon Browns derailleur adjustment page.

Derailer Adjustment there's also some good you tube vids on the subject when you google "detailer adjustment"

What I believe your LBS mechanic was talking about is when a derailleur or the hanger gets "bent". it should be straight up and down inline with the gear.

http://gearmechhanger.com/WebRoot/Na...ect_size_3.jpg

Orientation of rear derailleur
 

CBRSTAR, your reply concerns the the position of the derailleur in respect to the plane parallel to the rear wheel. My issue concerns the position of the derailleur in respect to the plane parallel to the rear axle wheel. In other words, looking at the derailleur from the side of the bike (as opposed to the diagram in your reply which looks at the derailleur from the back of the bike). The position you address would be affected by a bent derailleur, the position I am concerned allows the whole derailleur to be rotated until the mounting bolt is tightened down.

Bent derailer hangers do that, the shop should have straightened the hanger

Orientation of rear derailleur
 

Again, the position of the RD as would be affected by a bent hanger is not the issue. I'm asking where to position the RD on the hanger before I tighten the mounting bolt.

Once again, people have not read the original post very well. That particular derailleur, if properly installed does not require a large loop of cable housing. The proper housing will have a bit of a curve, but will not form a semi circular loop. This question has nothing to do with derailleur hangers, bent or not

Thank you, alcjphil, for closely reading the post.

So, I should follow the mechanic's rule, line up the tabs, and use an approximately straight run of short housing (as opposed to the loop)?

Rotate the rear derailleur as far rearward as it will go. AKA, clockwise around the mounting bolt. Then tighten the mounting bolt. That will ensure that the tab on the RD is properly behind the tab on the hanger.

As for the M772 and its cable loop, by the design of the RD (which Shimano calls "Shadow") the cable run will be straighter than a conventionally-designed RD.
You can see on my bike, the cable comes out horizontal from the cable stop on the chain stay, bends up a bit and then back down into the RD. If your cable stop is on the seat stay (common on 'cross bikes and MTBs), then the Shadow routing is even straighter.
http://i1060.photobucket.com/albums/...psle7ydsyt.jpg

As you noticed, the Shadow RD doesn't have a cable adjustment barrel. So, you'll probably want to install and inline cable adjuster somewhere. On mine, the downtube cable stops have an adjuster. On another bike, I use a Jagwire inline adjuster.

After looking at the derailleur and a video of one mounted on a bike, it looks as if the housing should have a gentle curve from the last cable stop into the derailleur itself. Actually, Tim Iowa's picture is about how it should look

Orientation of rear derailleur
 

alcjphil and Tim Iowa, many thanks. And that's a sweet looking bike, Tim.

Agree

Thanks, guys. It is retro fantastic, for sure, and a super comfortable ride.

It's a '97 Rivendell Road Standard. Newvex lugs by Richard Sachs, Reynolds 753 tubes (531 fork), silver brazed by Waterford. It's much sportier than most of Rivendell's current offerings (Roadeo notwithstanding); it has pretty classic sport/touring geometry.
I found it on my local CL for a great price, with vintage 90s Campy bits and Phil Wood hubs (freewheel rear). But it barely cleared a 700 x 28 tire, no fenders, minimal clearance.
I built some 650b wheels, and now it fits 38 mm tires under fenders, using Paul Racer brakes.
I'm running a 3 x 10 drivetrain. It has dynamo lights and USB charging.
I've since swapped the saddle for a Brooks B17 Special (hammered copper rivets) and the bar tape for Brooks leather.
I use it for touring, commuting, and gravel riding. I can add front panniers with a Tubus Tara, but the front rando bag is perfect for most everyday uses. It's not that light (~30 lbs as shown), but it rides incredibly smooth.

When I want to ride faster/lighter, I take my CF Foundry Auger disc. But when I want to ride for miles and miles, this is the bike I take. I've done one full RAGBRAI and several shorter tours on it. Based on the condition of the original drivetrain, the previous owner put a lot of miles on it as well.

It's a lifetime bike that I will never sell.

If you Google images of that rear derailleur you will see that the cable and housing do not require a loop like road derailleurs. Depending on the bike your rear cable run may have a curve but no loop - and may run straight in.

http://i.imgur.com/Xf1CAL5.jpg

My guess is that you are doing something terribly, terribly wrong, Toledo Tom. Both in setting up the derailleur and in life more generally.

The derailleur hanger has a tab(at the bottom) that the B-tension screw of a normal derailleur would rest against. The Shadow derailleurs have a tab that sticks out, where the b-tension screw would be on a normal derailleur. The derailleur tab must be behind and rest against the hanger tab, so the derailleur can't rotate counter clockwise past the hanger tab.