K1 – A Warning About Silicone Brake Fluid

by Jim Morrison

I am a firm believer in silicone brake and clutch fluid in Sunbeams. Unlike the Girling fluid, it is not hygroscopic (thereby keeping the inside of the master and slave cylinders from collecting water and corroding), and won’t take the paint off your car even if you area bit careless. But I discovered one drawback that could prove serious as it almost did in my case. When installing new stainless braided brake lines, I also switched over to silicone fluid. The brand I bought was purple in color (all silicone fluid seems to be colored. I have been told that this is so you can tell when it is the silicone fluid coming out when you are initially bleeding the system, at the cost of silicone fluid, this may be the real reason).

After installation, I discovered a slow fluid leak from the left brake line at the new hose. Even though I tried a number of times to fix the leak, it continued to slowly drip. To make sure that I did not run out of fluid in the master cylinder reservoir, I checked its level frequently. This was easily done without removing the cap from the reservoir because the reservoir is translucent and the silicone fluid was purple. So all I had to do was glance at the level of the purple fluid.

This technique proved potentially very dangerous. The silicone fluid had stained the reservoir purple and although the reservoir was almost empty, it appeared full from the outside. Fortunately, I found this out before I lost all my fluid and with it, my brakes. So the message is: always open up that reservoir to check the fluid level if you are using a colored fluid that can cause false readings from outside the reservoir.

By the way, I finally was able to discover the source of my fluid leak. The seat on one of the new stainless hoses had cracked (probably from my over tightening it trying to make sure I would not have any leaks). It required a very close inspection to discover this crack, as it was only barely visible to the naked eye. The hose with the cracked seat had a brass seat. I had a local hydraulic shop make up one to replace it, that has a stainless seat and have not had any problems since.