I’m fitting a new ultegra lever and caliper. I have a decent bleed kit. Followed the park tool youtube video and all appeared to be going well. Final step is to attach oil cup on shifter and receptacle onto caliper bleed port. When i get to the step that says to squeeze the brake lever a number of times to purge air bubbles, i continusly get bubbles through the caliper bleed port no matter how many times. Is the shifter introducing air at some point? Any advice welcome.
Thanks for your help
are you making sure that you’re applying pressure to the lever, then opening the bleed screw to let bubbles out, and closing the bleed screw before letting go of the lever?
If you leave the bleed screw open, the bubbles will just go back into the caliper.
yes perhaps my technique was not as you suggest. I’ll have a go using your method.
Thanks for the response.
Actually i did this - open bleed screw then press lever then close bleed screw, then release lever. Slightly different to your advice. But maybe the issue.
I did initially connect syringes with oil to shifter and caliper to push fluid back and forth before checking YouTube. Could this have damaged a seal in shifter?
I doubt you’ve damaged anything. I’d only recommend pushing from the cailper next time though.
Have you burped the levers too?
Pushing through the calipers is usually the last thing I do.
I push fresh oil from the caliper, burp the levers, and then do small pushes to the caliper by:
Make sure you have a good amount of clean oil in the funnel while doing this as your lever will pull in oil! 
When in doubt, ask Calvin Jones! 
Thanks for the tips Eddie. Burping the levers - can you clarify how to do this?
I followed Calvin but was getting bubbles at the caliper bleed port 
It’s shown at 9:20 in the video
I’m trying this now. Step by step -new calliper, shifter, hose olives etc. when I push the lever and open the bleed screw bubbles continuously. Pull lever extremely slowly almost no bubbles. Pull quickly (following Calvin )and bubbles. Bleed screw is closed before releasing lever.
I’ve refilled the cup several times. Not letting it go low.
It’s like the shifter / brake lever is introducing air. It must be something I’m doing wrong.
Did you torque the hose bolts to spec? I’m assuming that your levers came with the barbs and olives, so those must be the right ones, correct?
Does the lever feel firm when the bleed screw is closed after a few squeezes?
Shimano does say that you can open that bleed screw and the bubbles will come out on their own after a while… I find this strange since air usually rises and doesn’t fall, but it could be worth a try. Again, make sure that you’ve got plenty of clean oil in the funnel first.
Also, when you filled the system with oil did you ensure that your syringe and hose were air-free from the beginning? I like to fill the syringe and then give it time to settle before pushing out any air inside and then proceeding with the bleed.
If this issue persists, I’d recommend pushing more oil from the caliper to the lever. Give the brake hose a few flicks which sometimes helps to get any stuck bubbles moving. If you have your bike in a work stand, you could also flip the bike over a few times. Sometimes air gets stuck in weird spots because it’s trying to rise up in places where there’s nowhere to go. Flipping the whole bike over might get it past whatever it’s stuck on.
If you’re not seeing oil leak out of anywhere in the caliper or lever when pulling the brakes/bleeding, things should be set up just fine. Take a close look at the caliper and pull the lever nice and firmly though. They are manufactured in two halves and I have seen oil leak out of the seam in faulty calipers before.
One last trick worth trying before you give up is to strap the lever down nice and firmly (so the brake is on) and leave it to sit overnight. There is supposedly a little valve in the lever that can let air out when the brake is depressed. I’ve had brakes that feel ~90% feel like 99% the next morning after doing this in a pinch.
Good luck!
Possibly daft question - is it one of the newer Shimano calipers with a one way bleed system or an older one with the two way bleed? As my understanding of the one way system is you don’t need to be opening the bleed port while pumping the levers. I see the Parktool video posted above is 4 years old, not sure which generations of Shimano upgraded when but certainly the 105 bike I bought in 2020 was still a 2 way bleed.
Hmm, is there the o-ring on the bleed cup thread? Or if it’s the type of cup with the adapter, is that tightened to the cup well?
Thanks for all your responses. I got the system pretty well purged at v slow lever pull. Thought id try and see what the system feels like with pads and wheel in .seems ok Will get properly tomorrow.
Incidentally - I’ve got the new R8170 calipers fitted to the older ST-R8020 shifters. I fancied that extra rotor clearance ( I realise its a tiny amount) but now fitted seems good.
Ah this could be the issue. I’ll do some more investigating. I’ve upgraded to the new R8170 calipers, need to find a video of how to bleed the one-way system. Thanks for the suggestion.
Pretty much followed all this. Thanks for the repsonses.
The link @stevepetts372 provided is for the newer levers.
As long as your lever feels firm and not squishy, I’d give 'em a go!
Yep thanks. Found a video for the R8170 it seems that bleeding with the R8070 method was misleading me (Calvin needs to get on it!) Seems a lot easier and might have saved me 5 hours every day a school day.
Thanks again Eddie et al - i think we got there.
One wrench at a LBS said to gravity bleed them. shrug