Disconnecting hydraulic levers and hose compatibility

I plan to upgrade the 105 groupset on my Cube Agree C:62 to Di2 and I am hoping to be able to do most of it myself (so probably more questions to come).
First thing is to take remove the existing groupset including the break levers.
Couple of questions:
- Do I need to drain the system before disconnecting the hoses from the levers? And if so, does anybody know of a good guide on how to do so?
- Secondly, I am hoping I could leave the hoses and I am considering leaving the 105 callipers in place so I just have to swap the leavers. Does anybody know if the hoses and connectors are compatible? And does anybody know if there is a big difference between the 105 and Ultegra callipers? If not, I might sell on the Ultegra callipers on.


  • redvee
    redvee Posts: 11,922
    Can't help on wether you'll need to drain the system or not but a bleed/top-up might be advisable after the swap. No doubt others will agree or correct me here.
    I suspect R9020/R8020/R7020 all use the BH90 flange connecting bolt so it should be simply a question of undoing the hose from one lever and connecting it to the next.
    Differences between 105/Ultegra callipers will obviously be the branding and I suspect the piston material, one could be resin and Ultegra ceramic.
    I've added a signature to prove it is still possible.
  • kofsw4
    kofsw4 Posts: 39
    I remember seeing a GCN video where they showed how to switch hoses and therefore which brake lever operated which brake (converting continental style brakes to UK for example) where they took a few precautions and suggested that in most cases a full bleed wouldn't be required. Might be worth digging out.
  • pilot_pete
    pilot_pete Posts: 2,120
    If the hoses fit (as mentioned I think they are all BH90 connectors) then simply remove one lever, keep the hose end upright to prevent any more fluid loss, fit the new lever, connect up and then attach a syringe of fluid at the caliper end and with the lever bleed port screw removed and either the cup or second syringe from your bleed kit attached at the lever, force the fluid slowly up from the caliper end. This should force the air out at the top of the system (the lever).

    It depends how long the fluid has been in - I would make sure it runs clear - so in effect changing the fluid by flushing the old out of the top, especially if it comes out dark to start with.

  • Thanks for the help. This was useful!
  • I believe it might help to pump the brakes a bit with the wheels not in before disconnecting the hoses. However, you should be able to keep most of the fluid but i'd rebled the system after anyway.

    You'll need a new olive for when you swap the cables over as this gets against the cable by the bolt in order to keep the cable in this shifter unit. They're pretty cheap though.