One of my more advanced students started to complain about weak brakes as we taxied back in after a flight. I took the airplane, checked brake pressure and found nothing abnormal. Later, another student lodged the same complaint. We had practiced simulated aborted takeoffs and I attributed the problem to hot brakes. Again, when I took the airplane there seemed to be nothing wrong. When another student complained I knew I was missing something. I took the LEFT seat to taxi back to the hangar after the debrief and found out the right brake was spongy.
I learned that the two independent brake systems have their master cylinders behind the rudder pedals on the pilot side (#1 & #2). This means the reservoir can get low on the pilot's side before I notice a problem in the right seat. There isn't a common brake reservoir to simply add fluid. Fluid must be pumped in from the low spot in the system.
I needed to assemble some parts to make a kit to add fluid to the right brake system. The first step was to get some kind of a "pressure pot" to push the fluid into the system from the lowest point. Certus lent me theirs, a sophisticated version of a garden pump sprayer. ACE Hardware had everything else.
Problem: As I tried to loosen the valve it wouldn't budge. More pressure started to loosen the entire fitting so I held that in place with another wrench. I applied more pressure and it gave. Unfortunately, it sheared the valve off.
Fortunately, it was broken in the shut position but I now had to get another valve. Ace Hardware doesn't carry them. Certus does. FedEx delivered it this morning.
The replacement was easy. The original fitting replaced, I tested the valve to insure it worked properly and was relieved to see a drop of fluid when I loosened the valve.
The trick is to get the fluid started into the system then check the brake reservoir to see it get filled. I lined the cockpit floor with rags, opened the valve and stood by the cockpit watching bubbles come out of the vent hole on top of the cylinder. In a few moments, I had a steady stream of fluid spilling over on my rags so shut the valve.
I sat in the left seat and pushed on the toe brake. Good.
I cleaned everything up and did a thorough preflight. I pulled Sally out and checked the right brake for any drips. The taxi test went well. I did a full runup without issue. Then taxied back to the hangar and checked again. No runs, no leaks, no errors.
I put Sally back on the flight schedule.
