My Wooden Airplane
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7/2/2016 - 7/4/2016

Brake Lines

After filling the brake reservoirs with fluid, I noticed I had some small leaks in two of the fittings, so I decided to take care of those now. The problem was, after replacing and/or resealing the fittings, I needed to bleed the brakes.

When I first attached the brake lines to the calipers, I attached them to the top of the calipers, and left the bleed valves at the bottom. This works fine if you are going to fill the brake lines from the bottom, but this is extremely messy, since you can't tell when the reservoirs are full until they overflow. Instead, I removed the tops of the reservoirs and filled them from the top, which prevented the mess (mostly), but I was unable to remove all the air from the lines. The reason was because I was unable to push enough brake fluid through the calipers before they fully clamped on the discs, and an air bubble remained within the calipers (behind the piston).

The solution was to reverse the attach points so that the brake line entered the caliper at the bottom, and the bleed valve was positioned at the top. This allowed the air bubble to rise and be pushed out the top of the bleed valve. I never realized such an arrangement could make such a difference, but I witnessed it first-hand! Now the pedals are nice and firm, and we'll see if there are any more leaks when I come back next week!

Total Time: 8.5 hrs.