Filling the Brake Fluid
(June 15, 2025) Something I had on my mind for a while, I didn’t like having the brake line pass through the firewall through a simple grommet per the KAI. After a bit of searching, I found the perfect 90° bulkhead fitting, this Fitok stainless steel compression tube fitting, part # SS-BBLU-FL4. I already had a hole cut in the firewall for when I was going to use an AN flare fitting, so this was pretty easy to install. This bulkhead fitting wasn’t cheap (nearly $100) but it’s very well-made & feels substantial.
With this fitting now installed, I was ready to fill the brake system with fluid. I opted to use the vacuum method, where I attached a vacuum pump to the top of the remote reservoir on the firewall, and drew brake fluid up from each of the brakes calipers via the service (bleed) valve.
The vacuum pump I used was from a previous project (installing a mini split air conditioner). I used MIL-H-5606A Hydraulic Fluid per the Matco general instructions. I bought two pints from Aircraft Spruce, which wound up being way more brake fluid than needed; but it was convenient to have the two pints so that I could draw fluid up into each brake caliper simultaneously. One pint would be plenty for the whole system.
Although this method works pretty well, I did have an air bubble in the system, which I think was because of how the master cylinder is oriented. Being at a slight angle, I think there was a small air pocket left at the top of the chamber inside the cylinder. I was able to liberate the air bubble after pumping the brakes a few times (therefore filling the reservoir inside the master cylinder), and then pulling a vacuum again from the remote reservoir on the firewall.