Brake Fluid Question

[lake_harley]

As I close in on the last few items on finishing my FED, I'm ready to fill and bleed the brakes. I have a Strange Engineering master cylinder P.N. B3362 like this:    https://www.strangeengineering.net/product/dragster-master-cylinder-reservoir-777-primary.html/

On their website it states that silicone brake fluid is not recommended. I'll live with using DOT3 if I have to but I wonder why no DOT5 silicone fluid? I use DOT5 on my 2 hot rods and have no complaints.

When I was looking into DOT5 fluid for my hot rods (T roadster and Model A Coupe) I did find mentions of a "soft" pedal and difficulty bleeding the system since bubbles of air are very slow to rise out of the fluid. I've never had those issues on my cars.

I'd prefer to use DOT5 since it doesn't destroy paint and my brake bleeders are not real easy to get to once the body side panels are on. If I must use DOT3 (or whatever) I will, but I wonder what the reason might be for Strange's recommendation. I've tried to reach their tech service through messages and an e-mail but never received any reply. So.....does anyone have any experience with that master cylinder or know what the reason might be to not use silicone fluid in it?

Thanks. You gentlemen always come through with answers to my silly questions, and I appreciate it!

Lynn.

[denverflatheader]

From Strange dated August 26, 2021 - Master Cylinder page 1 of 3

Due to temperatures experienced during drag racing, DOT 4, DOT 5.1 or a high performance glycol based brake fluid is recommended. Brake systems are prone to moisture from humidity and regular use, therefore, moisture must be absorbed by the brake fluid instead of collected so the fluid does not easily boil.

DOT 5 (silicone based) is not recommended. It does not mix with other fluids. It is slightly compressible giving soft pedal/handle. It also does not absorb water. When moisture enters the system, it settles at the lowest point in which most cases is the caliper. At braking temperatures moisture can boil causing a loss or lack of pedal/handle.

Always perform a complete flush to the brake system when changing to a different brake fluid to avoid contamination. Do not use brake fluid from open bottles or bottles stored for long periods as moisture may have been absorbed. The dry boiling point is the temperature at which brake fluid will boil with no water (moisture) present in the system. The wet boiling point is the temperature at which brake fluid will boil when 3% is water by volume of the system.

In race applications it's assumed brake fluid is changed often therefore moisture is not present and the dry boiling point can be a better reference when deciding on which fluid to use.

DOT 3 Inexpensive, readily available, mixes with DOT 4 and DOT 5.1 Lowest boiling point, absorbs water, eats paint

DOT 4 Higher boiling point than DOT 3, absorbs water less readily than DOT 3 Absorbs water, eats paint

DOT 5 Does not eat paint, high boiling point Does not mix with water, difficult to bleed

DOT 5.1 High boiling point, mixes with DOT 3 & 4 Absorbs water, eats paint

[wideopen231]

Dot5 in every system I do from start. Now on street stuff, I run whatever came in it or manufacture recommendations. All of my Harleys and race cars have always been dot5.

[lake_harley]

Thanks for the info. It sounds like potential moisture is the reason rather than any incompatabilty with the seals they use.

When I put DOT 5 in my hot rods I was very careful to pour it in the MC in a way as to not introduce bubbles which can aggravate the potential soft pedal issue. Since the concern is moisture I can periodically drain the line going from my MC to the brakes to remove any "puddles" of moisture that might ever get into the system. Part of the brake line would be the lowest point in the system.

I appreciate the input and experience.

Lynn