VCCA Home Forums GENERAL DISCUSSION New User Forum Hydraulic brake leaks

Fellow Hobbyists:
At my age being called a "newbie" is cool.
After ignoring my project for five years (1936 Master Coupe) I`ve returned to find all wheel cylinders and master cylinder corroded and leaking. All of these were NOS and installed about eight years ago. Any ideas about what caused this and how to correct?

Thank you, Tom

I know this is controversial but I use DOT 5 (silicone) in my '48 and '55. I put a NOS master cylinder and 4 NOS wheel cylinders in my '48 back in '85, flushed the system with silicone and installed silicone fluid. Several years ago while I was packing the front wheel bearings I popped open the right front cylinder to see how it was doing and it was shiny clean and the only way I could tell it from another NOS cylinder was the horizontal marks on both pistons. I put new cups in but the old ones looked fine. Didn't have to hone - no need to. At that time the car had been driven 20,000 miles.

Why is it controversial?

Whether to use DOT 5 Silicone based brake fluid and is non-hydgroscopis, or to use DOT 3 or DOT 4.

DOT 3 or DOT 4 and also DOT 5.1 which are polyethylene glycol based fluids. Fluids such as DOT 3 & 4 and 5.1 are hygroscopic and will absorb water from the atmosphere. This has positive characteristics and bad characteristics.

DOT 5 was designed to be used in military sealed systems that prevent water condensation in the system and water will not dissolve in DOT 5, but remains as water drops. The older Auto and truck brake systens are vented to the atmosphere and allow water to condense in the DOT 3 and DOT 5 brake fluid. This prevents the water being in drops and turning into steam in a very hot wheel cylinder, or from freezeing abd causeing a solid blockage in the brake lines.
However disolved water in a brake system that isn't used will cause corrosion in the wheel cylinders.

Boiling Point Ranges
Dry Boiling Point Wet Boiling Point
DOT 3 205°C (401°F) 140°C (284°F)
DOT 4 230°C (446°F) 155°C (311°F)
DOT 5 260°C (500°F) 180°C (356°F)
DOT 5.1 270°C (518°F) 191°C (375°F)

DOT 5.1 -- Long-Life Non-Silicone Synthetic brake fluid is a
EXTRA LONG LIFE 100% synthetic fluid for hydraulically actuated-brake and clutch systems. (Based on Polyglycol chemistry). DOT 5.1 has an expected operating life of up to 10 years

DOT 5.1 NON-SILICONE BASE suitable for up-grade from DOT 3 or DOT 4.

Fluidity specially designed for anti-locking brake systems (ABS).

Fully compatible and miscible with Conventional Brake Fluids.

This version has extra anti corrosion additives that protect ferrous, white and yellow metal brake system components.

This fluid is clear and golden yellow in color.

No special procedures are required when bleeding and replacing conventional system fluids with DOT 5.1

Does this help?

Thank you MrMack. That is a real eye opener.I beleive I will have the wheel cylinders sleeved, master also, then use the 5.1 fluid.
Thanks again