The Austin-Healey Hydraulic Brake System
By Norman Nock
Originally published in the Austin-Healey Magazine, July 1984
Inspection of your brake fluid in the reservoir will give you a good indication of the condition of its seals. If the fluid is turning black, this is a signal that the seals are deteriorating. There is only one way to solve this problem. You must replace all the seals in the system. An incorrect type of brake fluid usually causes the seal deterioration. All Austin-Healeys should use Girling type brake fluid. The brake fluid should be changed every two years. This removes most of the moisture from the system, helping to prevent corrosion of the cylinders.
Moisture in your Austin-Healeys brake fluid is unavoidable. Every time the cap is removed, small amounts of moisture enters the system. The water will sink in the fluid to the lowest point, i.e., the master cylinder; thus begins corrosion of the metal cylinder. Moisture can be drawn from the atmosphere through the flexible rubber hoses and seals. The rate at which this happens is dependent on your local humidity and the little use your car gets in the wintertime.
Silicone Brake Fluid "SBF"
Many reports have been written on "SBF." It is chemically inert, cannot harm paint, has a high boiling point, will not absorb moisture (therefore, it cannot cause corrosion), and is a natural rubber preservative.
There are three methods of incorporating "SBF" into your brake’s hydraulic system:
Remove brake fluid from the reservoir, replace with ‘SBF’ and maintain about three-quarters full. This will prevent absorption of atmospheric moisture into the master cylinder.
Bleed to empty the complete system until no brake fluid comes out of the bleed screws.
The system at this point is not empty as there remains some residual brake fluid in the wheel cylinders, master cylinder, and other places. Fill the reservoir with "SBF" and bleed the system via a hose into a glass jar. The old-type brake fluid that comes out will stay at the bottom of the jar, and the new "SBF" will float above it. Continue bleeding the brakes until all the old fluid has been expelled from the system. It is possible that you will have to bleed the system three or four times to remove as mush of the old fluid as possible. When your bleed jar has a quantity of "SBF," it is possible to siphon off only the "SBF." Close off the bleed screw, pinch the hose close to the screw, remove hose and hold below level of "SBF," siphoning the fluid into another clean jar. The "SBF" can be reused.
Complete removal and replacement of all seals and flexible hoses in the system. Blow out with 100-125 psi compressed air until all fluid has been removed from the system. Bleed system in the regular way.
Thirty ounces of "SBF" are required to operations 2 and 3.
Your brake system is now ready for the scenic drive around the Olympic Peninsula, Washington, with its high humidity, on the way to the West Coast Meet, Vancouver 1986.