I have recently installed and bled a set of R785 road shifters/calipers. The back one is spot on but the front...when I undo the bolts, grab the brake and tighten the bolts there is a lot of rotor rub. I am fairly sure the rotor is straight, visually it is and it runs fine on my other disc bike that I have used the wheelset on.
The front does have a lot less lever travel than the back, I presume I can't change this without letting out some of the fluid? Is it just the bleed over-filled the system? I used the same bleed block front and back though.
I find that riding around a bit (especially downhill with brakes dragging) sorts this sort of thing out.
Is it flat mount? If so then they are pretty sensitive to the mounts being well aligned / faced. I had this issue with my forks and ended up filing the adapter to align the caliper. The best solution is to get the mounts faced at a shop with the right tool though. If they are post mount then it could be a similar issue but they tend to be less finicky
You need to do the alignment fully, the grab-and-tighten one doesn't always work.
Take the pads out and push both pistons back into the caliper.
Loosen the caliper and adjust it so that it sits centrally over the disc.
Insert pads then pull the brake lever a few times to push them against the disc, first few pulls will be soft but it will firm up when done.
Spin wheel and see if there's any rubbing.
If not, you're done.
If there is then you need to balance the pistons.
Look down at the caliper as you press the lever, note which pad is closer to the disc or moves the most.
Release lever then use something like a flat screwdriver to hold that pad away from the disc as you press the lever gently to encourage the other one to move more.
Check the movement after each small adjustment.
Continue until both pads touch the disc at the same time and there is no or little rubbing.
Ride round the block using the brakes on and off then check again.
Make further small adjustments if needed.
Hope have a good video showing how it all works, same technique for road or MTB brakes. Never failed to have a good brake on any bike using this method.
^ what reluctantjumper said for the aligning.
I wouldn't have expected an overfill if you used the provided shimano bleed blocks. Do the aligning first and you might find it is sorted and both feel fine. Maybe the rear needs a quick mini-bleed?
The back is spot on so don't fancy playing with it. I'll try pushing the pistons back in and refitting the pads before centering it and hopefully that sorts it. Thanks for the help!
Hayes make a disc alignment tool that I use and it makes getting disc aligned much easier.
The best way (if you haven't got a special tool) to align a brake caliper is by eye. You need to do this in a well lit room. Simply centre the caliper over the rotor so there's an equal gap between each pad and the rotor, hold the caliper firmly, then tighten down the bolts.
The old "loosen the bolts, squeeze the lever then tighten the bolts" doesn't work as the caliper usually gets pulled out of alignment by the hose (especially on the front) because it's under duress from having to pass through awkward bends in the frame/fork. This then flexes the rotor so it's not straight.
I've never been able to do it by eye, it boggles my mind that anyone can do it this way. Anyway, stripping the pads out and resetting the pistons, then reassembling while depressing the brakes has done the job. Now spot on.