I recently did the rear brakes on my Valk trike (Ford rear end) and was refreshing my memory about bleeding and also looking at the best order to do it in, and one guy said he _always_ bled, then drove for a while, like a few miles, then bled again. I did that and although I was very thorough the first time, I did get some tiny bubbles on the second bleed. I guess trapped in a corner somewhere.
Maybe try that?
If it is air, be very careful. If the air migrates from a wider section of pipe, or in the actual caliper, to a narrow section, it suddenly becomes a major player and you could have no brakes. DAMHIKT, from my bike years eons ago.
BTW, to make bleeding easier and safer, my way is to get a plastic tube that is a good tight fit on the nipple, then take the tube _upwards_ above the nipple, then syringe some brake fluid down into it (alternatively you can stick the tube into the brake fluid to get some fluid in there then keep the upper end blocked until you get it onto the bleeder). Make sure the fluid is in the way of any air getting to the bleeder. Put the tube, still going upward, into your receiver pot or jar: so the jar is higher than the bleeder. Then undo the bleeder and you can operate the brake without having to worry about air getting into the bleeder, or having to close the bleeder at every pump. And of course you can see any bubbles rising up the tube.
Just don't let the master reservoir empty!
Nick
