The crankset will work, and I guess technically the calipers, but you'll need derailleurs, wires/battery/etc, and shifters. The shifters come with calipers usually.
I haven't gone electronic yet so I don't know exactly what wires, batteries, and junction boxes you'll need. It might be cheaper and easier just to replace the entire groupset so you can sell your old groupset as a complete group.
If you're lucky, you can find just the shifters. A set put me back $520 recently and I've seen them as high as $1200 on eBay. But like @Volsung stated, you're going to need a new RD/FD, junction box with a charge port up front (there's a couple different styles), junction box near the BB and cables to connect everything (it's better to have a little too much cable, then a little too little 😉 ). BTW... you can use Ultegra mechs with GRX if it works for you (i.e. you can actually find one but not the other)... I'm running a 46/30 in front with 11-46 in the back using GRX Di2 shifters and Ultegra RD/FD. I used the Wolftooth Roadlink DM and changed out the bottom pulley with a KCNC 15t. Another factor is if your frame allows you to get the Ultegra FD down far enough to properly engage the 46/30 on the 600 Crank. YMMV
Are you going to be external or internal? Here is the minimum list you need to run at least the rear derailleur.
Right Shift lever RD Junction A Battery Wire from RD to Junction A Wire from Battery to Junction A Wire from Right lever to Junction A
I'm actually running just the RD on two bikes using the right lever on one bike and the left lever as a right lever on the other (they can be programmed to do the same job). Unless a shop sets it up for you, you are going to need whatever connector is necessary to hook it up to your computer and access the Shimano etube project.
If you want the front derailleur as well (I've never bothered because Shimano front cable shifting is really good and not an issue for me) then you will need the FD and will probably want to get a Junction B to simplify your cable routing. You will need two more wires as well.
BTW it is totally worth it. I did it so I could have shifting from multiple locations (I can shift from the end of my aerobars, the regular lever and while on the tops) but I would do it again even if I was just shifting from the one lever. It is quick, requires almost zero maintenance, cables don't have to be replaced, and it never has to be adjusted unless you switch components. I can't think of one single improvement to my cycling experience since I began 40 years ago that has been more enjoyable.
Beware, once you have it on one bike, then you won't like your old cable shfting. I'm sure there are people who say its no big deal, but I would guess those people fall into one of the following categories: 1. They use top end XTR/Dura Ace mechanical. 2. They are meticulous in their maintenance and either pay a shop or enjoy doing their own work. 3. Like me for the first 30 odd years of their cycling, they put up with mediocre to bad shifting. 4. Both A and B
If you want the front derailleur as well (I've never bothered because Shimano front cable shifting is really good and not an issue for me) then you will need the FD and will probably want to get a Junction B to simplify your cable routing. You will need two more wires as well.
Lol.... I got Di2 ONLY for the front shifting as the arthritis in my left thumb got so bad I couldn't shift from small to big without excruciating pain. Now I would never go back for all the other reasons you point out.
Lol.... I got Di2 ONLY for the front shifting as the arthritis in my left thumb got so bad I couldn't shift from small to big without excruciating pain. Now I would never go back for all the other reasons you point out.
That's funny. My issue with the front is clearance on my bike. It's a dual-suspension drop bar bike and the rear suspension interferes with the function of the di2 FD. Plus, I really want the bigger 16 tooth jump and I use a rear XT for my 42 so the road FD won't work with the mtb RD.
