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I am trying to refill a Shimano Alfine BR-S500 disk brake system with oil. I have filled the reservoir with mineral oil...

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And am repeatedly squeezing the lever, but it feels like no oil is getting pushed into the hose line.

(Note that it is hard to see the clear oil in this photo, but the reservoir is full and the intake hole is submerged).

I have the bleeder at the bottom open 1/8 turn. I have also tried cracking the caliper apart just to see if any oil is coming down the line when I squeeze the lever, but none does.

The brakes were working fine before I drained it.

What am I doing wrong? How can I get the oil into the lines and into the caliper and pistons?

NOTES:

According to the manual, this system is not filled from the bottom like most oil-based bike brakes. Instead it says to open the bleeder at the caliper and then fill the reservoir up at the lever and pump the oil down.

(BTW: It is empty because I had opened the calipers to replace the o-ring in between the two halves.)

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It turns out I just needed more patience. To fill the brake line, you need to:

  1. Make sure reservoir is full of oil.
  2. Open the bleeder port
  3. Squeeze the lever in
  4. Close the bleeder port
  5. Release the lever
  6. Wait about 10 mins for the oil to s.l.o.w.l.y. get sucked down into the line.
  7. Repeat until oil is coming out of the port.

There must be a very small bypass port inside the lever assembly to let the pressure equalize over minutes.

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    You are right that the manual says you can fill the brakes this way, I'm very surprised by that though. I think I'd follow the general Shimano bleed procedure pushing fluid in from the caliper myself.
    – Argenti Apparatus
    Commented Apr 18, 2020 at 12:46

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