Let's offroad / mountain bike / mtb / ride dirt

Well, in my case I think there were two problems that reinforced one another:

1. The hose run to my rear brake was too short for the design of the calliper and would tug on the banjo connector during big hits when the suspension was at full compression, letting in air/letting out oil.
   
2. Not a single one of the guides available, either official or not, on bleeding Magura brakes is accurate/fully describes the process.
   
   

I addressed problem 1 by lengthening the protective sheath that the hose runs in under the bottom bracket, which means that there is enough slack in the line to cope when the suspension is fully compressed without exerting any force on the connection to the calliper.

With regards to 2, the issue is that if you try to bleed the system with the lever on the bar you are never going to get the air out.

An example: I changed the lever for the rear brake recently as the master cylinder started leaking. I have a theory as to why that is which I'll share off-forum.

Anyway, it meant that I had to fully bleed the system, so I did a traditional full bleed with a syringe at the calliper and the Magura professional bleed bottle at the lever end.

I pushed and pulled fluid from the syringe until no bubbles emerged from the lever bleed port.

Closing the system up at this point and testing it - it's appalling. Back in the stand with the bike.

Now, put a syringe in the lever bleed port with 20ml of fluid, and a hole at the 30ml line. Pull the plunger back to just before the 30ml line so there's a slight pressure drop in the system.

Next, and this is crucial, take the lever off the bar and continually move it around (taking care not to let air from the syringe travel back into the lever) whilst pumping and flicking the brake lever.

Large, then medium, and finally streams of small bubbles will come out - for around half an hour.

Remember - no bubbles came out during the traditional bleed we did before.

Anyway, keep going until your forearm muscles pump up irrevocably or the bubbles stop, whichever comes first.

Put the lever back on the bar, pull the plunger out past the hole, allow the fluid lever to settle, then pull the syringe out and close it up, dripping some fluid into the bleed port before fitting the screw in order to ensure that no air gets in.

Put everything back together - lever will now have a very firm, defined bite point. Success! Make a cup of tea.