I purchased the Parktool Derailleur Hanger Alignment Gauge. The reason was when I adjusted my rear derailleur last Friday I had to move the lower limit screw way too much and I figured the hanger was out of whack. Sure enough, it did appear so. Now it appears, according to the tool, to be aligned. But now there is absolutely no way to get into the lowest gear. Anyone have any thoughts?

One issue I did run into was screwing on the Derailleur Hanger Alignment Gauge the first time it was VERY tight, I am wondering if I mucked up the threads on the hanger. But I figured if that was the case, now that the gauge goes on smoothly, the derailleur would simply use the same threads.

I am clueless as what to do now, other then get a wider range cassette and treat the 11 speed like a 10 speed.

So you checked cable tension, the L limit and the B screw?

Sticky RD cable?
The lower loop of cable housing, because of it's location, is always subject to water/sand/road goop.

What's preventing the derailleur from moving? If you've got external cable routing, grab the length of exposed cable along the downtube, try to pull the derailleur by hand, and observe it. Is the derailleur's travel limited by the low limit screw? If so, adjust it. Is the upper pulley getting too close to the cassette's big cog? If so, adjust the B screw.

Should this "Parktool Derailleur Hanger Alignment Gauge" be in everyone tool box that has bicycles?

Absolutely!

Only if you have a use for it.
If you have to ask......

Folks, I forgot to mention, it is a Di2 bike. No cable to adjust. Here is a link to two pictures of the issue, don't know if they help or not:

Zenfolio | Sam Carleton | The Bike

So even if you back out the L limit all the way and trim all the way it won't shift?

I forgot to mention, the bike is Di2, here are some pictures: Zenfolio | Sam Carleton | The Bike

My eyes hurt looking at the wire scrunched under the QR.
Did it go into the low gear in the past ? What changed ?

It did. As I stated in the OP, I was having some trouble shifting into the lowest gear so I figured the derailleur hanger was out of alignment again. So I took the opportunity to order the Parktool Derailleur Hanger Alignment Gauge. It came in today and I tried it out. Sure enough it was badly out of alignment. I used the tool to get it back into alignment (or so I thought) and now it won't event get close to the lowest gear.

Again, for others: The bike is Di2, not mechanical.

There are no mechanical cables to adjust for a Di2 system, but there is an adjustment/calibration procedure. Now that your hanger's aligned, have you readjusted your derailleur to compensate for your derailleur's new position?

A link to the Ultegra 6870 Dealer's Manual is below. Adjustment instructions are on page 52.

https://si.shimano.com/php/download.p...001-00-ENG.pdf

Di2 still has trim and limit screws.

I played with that this morning. What I discovered (which I sort of suspected) is that it did NOT move the derailleur one whole cog. All the screws are designed to move things just a touch one way or another, not whole cogs. Guess I need to find a real shop.

Does it shift well between all of the other cogs?

yes and no, generally it shifts fine, but there is one gear you have to press the button twice to get it to shift, I think it is on the lowest cog.

There you go. That's your problem.

Get the first shift right (smallest cog to second to smallest cog) and the rest will work fine. I'm not familiar with DI2, but if it were a mechanical derailleur bike you'd need to tighten the cable until that first shift worked correctly.

What is probably going on is that the shifter is running out of "gears" to shift to. When it's in the 2nd gear (second to biggest cog) it thinks it's in the 1st gear, so it won't shift anymore.

Fix the first thing above and the other side of the range will work fine. You may have to tighten the L limit up again to prevent the chain from going into the spokes since you unscrewed it most of the way.

EDIT: After sifting through the manual, it seems like my advice isn't very useful. I'd bet that perhaps you set adjustment mode on the wrong cog, therefore the derailleur thinks it's in one "lower" gear than it actually is. The premise is the same, the adjustment is different.

I had trouble with my 7 speed, eventually it was the low limit screw needed more adjusting.

Yes...

I don't understand what you said. What screws?

This is Di2, it has lower and upper limit screws, called "top-side stopper bolt" and "low-side stopper bolt" in the manual. See page 55 of the dealer manual. These are set after centering the shifts via "adjustment mode". And the small cog stopper works differently than on a mechanical derailleur--it needs room for the temporary overshift that happens when going to a smaller cog!


From the manual:Read the manual
You must read the manual. It's a "dealer" manual, but it's easy to follow, and all the steps are spelled out.

Setting up a Di2 derailleur is simple, but not obvious at first. Follow the steps, starting at page 52, and it'll work the first time. See Skydog75's link to the manual pdf above.

(If you are still off, I'd get into adjustment mode again, then press the large paddle repeatedly until the adjustment is all the way to one end. Then click the other paddle 16 times to get back to the middle of the 33 step adjustment range, and then follow the manual.)

That is very good advice, something I am embarrassed to admit I was not doing. I am at work now, and have a few minutes of downtime, I started reading the manual. The first paragraph of the first step on P52 read this way:
When I do exactly that, the guild pulley lines up with the second to largest sprocket. No mater how I moved the B-tension adjustment bold or the low-side stopper bolt this morning, the derailleur would NEVER get close to the largest sprocket. I would see it move a little, but never a whole sprocket worth of movement.

When I get home tonight I will recenter the adjustment range to 16 and try again.

I honestly don't know what happened. Nothing was lining up and it simply wasn't working then I move the low-side stopper bolt out just a touch more. It looked like it was still lining up with the second largest sprocket, but then when I shifted it snapped into the lowest gear. So very strange! It still doesn't look like it should be in the lowest gear, but it shifts there! Guess there something to reading the manual!!!!

See page 55 of the dealer manual.

My goodness, I've just been convinced that Di2 is not for me!

I read page 55, I am not 'getting it', care to expand on things a bit?