Electronic & Hydraulic Shifting (Di2, Ui2, customisations)

I have recently bought a 931 Equilibrium Disc (frame is Di2 compatible) and suddenly found used ST-R785 shifters for about 70 GBP here. Now contemplating whether to go Di2 and swap the current RS505/5800 drivetrain for Ultegra Di2. What parts exactly would I need apart from derailleurs, and is it good to buy everything used or something particular is better bought new with warranty? Also how much do you estimate would I need to spend to get all the needed parts?

I wouldn't buy 785 shifters. They're first gen, big, rattly, etc. There's a reason they're cheap.

Once you’ve factored in the price of the individual wires, the battery, the junction boxes and a charger, it’s soon not very cheap after all

What's the best way to clean rotors? I can't figure out if the pads are contaminated, the rotors or both so I've got new pads and want a foolproof way to clean the rotors.

Douse in isopropyl alcohol, or brake cleaner. Wipe clean with a paper towel. If you're really worried, run some medium grit sandpaper over them before all of the above.

Can I use the same process on the pads or are they straight to the bin

In my experience, no. The pad material is slightly porous and the fluid/grease/whatever soaks into it. You could try burning the contaminants out by putting them on a thick pan on a hob, which is the old garage bodge trick. I wouldn't though.

One pair is brand new so assuming I can get the rotors and new pads working properly, I might mess around and see if I can rescue them enough to have them as a spare set for emergencies.

I use Muc-off brake cleaner but I'd use IPA when that can runs out. Failing that I'd just brake really aggressively until the pads worked or wore out.

Looks like cleaning the rotors (bought a can of muc-off from the least awful LBS) helped a lot but the front pads are still howling. Going to throw on fresh pads and see if it helps. If not I'll just ride up and down the big hill near my place a bit.

Did you bed them in properly?

I'd done about 1000km with them before they started to howl hence the belief its contamination. I've got a 2km climb/descent right by me so I'll mince to the top of it a couple of times over the weekend.

I chuck muddy puddle water on my rotors as an emergency contamination fix. Normally grinds off the top layer of the pads after a few hard brakes.

Are they metal or resin? My metal pads are always loud. It's really useful for scaring peds about to walk in front of you.

Or just ride in UK for more than 20min and it'll sort itself out.

Resin. Had a few sets no problem. Happened when the LBS "fixed" my brakes for me. Went in silent, came out howling like a cow with its udders trapped in a gate.

Resin are a lot quieter so yeah sounds like contamination of some sort (maybe they dripped oil when repairing brakes). I'd clean it and if that didn't fix it I'd ride with the brakes locked on to try and bake off the shit. But really, I'm so used to squealing brakes I don't even care now.

I got an 8spd Alfine Di2 groupset on eBay and it seems to have everything I need. I set it up like this:

ST-S705 shifter → SC-S705 display/junction box → SM-JC41 (I think) internal junction box → SM-BTR2 seat post battery & Alfine Di2 hub (not sure what part number exactly)

But when everything is connected (and I've ensured there's a solid click when I push these cables into each component) it's completely unresponsive, nothing lights up in the SC-S705 display and it doesn't shift. It could just be a dead battery and I asked to borrow one of these to try out this theory but I'm worried if the problem is elsewhere it'll have been a waste of everyone's time.

Any suggestions as to next steps before I just take it to a shop with all the right equipment so I can pay them to point the finger at the culprit? Also suggestions for a Di2-enabled shop? Thanks!

It could be a firmware issue. You can download the Shimano software on to a PC, if you have one, and it will do the update for you. I had the same problem once, on a non-Alfine di2 setup, and once all the firmware was updated everything worked.

Start by plugging the battery directly into the display and disconnecting everything. It should at least light up even with nothing else on the system. If it doesn't work, try a different cable.

Sorry I didn't make it clear that the set I bought didn't actually come with a charger. I guess I should get one anyway as I'll need one sooner or later... I guess I just wanted to know if this thing was hosed or not before spending even more money on it!

Yeah, not buying a charger feels like a rookie mistake. Maybe you can convince an LBS to charge it for you for some beer or biscuits

Whereabouts are you? Your welcome to borrow my charger for a couple of days.

Thanks. I tried this with every cable I had and in both connectors on the display but nothing appeared. Guess this points to the battery being dead (low on juice or literally just dead), or I guess the display being broken, right? I suppose I'd put my money on the former.

West, near Paddington. It would be ace if nearby. Otherwise I'll just buy one.