Leaking master cylinder

[JDH]

I had the same kind of leaks, mainly on one side (left). I kept adding, bleeding, etc, I'd have brakes for a couple of landings, then they'd go mushy, no more pedal, and I was getting fluid spitting out around the cylinder rod. At last year's annual, I paid to get master cylinders pulled, lines blown clean, seals changed and new 5606, new linings, etc... I had bought 2 seal kits from Spruce. Turns out they were not the right ones. So, had to buyt that from the shop doing the annual. Brakes were OK for a while, in fact lasted from July to September, needing bleeding only once (big improvement).
Then came ski season. Remove the wheels, install the spacer blocks for the calipers, fly for a few months on skis and back to wheels. Well, the left master cylinder was leaking at the top again...
The problem is now completely resolved. I pulled the master cylinders off the plane (it had not been done), thouroughly cleaned the bowls and other parts, replaced all seals with FAA approved replacement seals found at NAPA! flushed the lines with fresh, clean Dextron II; new linings and re-installed the masters, filled and bled the system and its been 135 hours of no more problems or leaks or needing to bleed or add fluid. Any little bit of abrasive (dust, sand dirt) in the fluid will end up on the seals and cause a scuff and a leak; thus, even if the bowl isn't full, the fluid will by-pass the leaky seal out the piston rod; "path of less resistance". Flush and clean your system, install new seals, make sure the vent hoes are not obstructed and bleed the system and you too will have good brakes and no more mess. JD

[JJH55]

Since the topic of bleeding brakes has come up, I thought I would pass on a painless way to accomplish this task that I have found very simple and almost fun to do. What’s better is that you can do it by yourself, no contorting around the master cylinders with 5606 and there’s virtually no mess.
If the master cylinder is full when you start, this procedure will cause it to overflow so plan accordingly by wrapping it with a rag, pump some fluid out through the bleed screw or draw some fluid off before starting.
Obtain a large volume syringe. I get mine through our local veterinarian but they can be purchased at many places. I’m not sure of the size in cc’s but get one about 5” long and 1” in diameter. You will also need a piece of plastic tubing that will fit securely to the bleed fitting on the caliper. About 12” of 1/8” tubing is what I use. Attach the tubing onto the syringe by pushing it on as far as it will go. Fill the syringe and tube with 5606. Loosen the bleed screw until fluid starts to drip and then back just enough to stop the flow. I do this to flush any debris from the bleed screw and to make sure the screw is relatively loose.
Don’t worry if there is air in the lines, it will soon be pushed up into the master cylinder.
Attach the tubing to the bleed screw and open the screw all the way. You will have to turn the tubing and syringe at the same time you’re turning the screw to avoid breaking the seal on the tubing. While holding the tubing with your fingers, to keep it from coming off from the pressure, inject the 5606 from the syringe through bleed screw up the brake line into the master cylinder. If there is any air in the syringe allow it to flow into the brake line first by holding the syringe (pointy end up) so that the air goes through first. Once you have injected all of the fluid, tighten the bleed screw and check the level in the master cylinder. If there is no fluid visible in the master, repeat process. On second applications make sure there is no air in the syringe or tubing to be pushed into the lines. That’s it.
Try it, you’ll never do it any other way again!
JJH55

[zero.one.victor]

Instead of a syringe,I use an oil-pump can,available at an auto parts store for a couple bucks. I also use the oil-pumper & hose for servicing the hard-to get-to master cylinders.

Eric