Strange...
After installation of the master cylinder, the brake system must be bled. Use only DOT 4 or DOT 5.1 brake fluid.

Mark Williams...
Use of DOT 4 or 5.1 fluid with a high boiling point and lubrication for seals and pistons is recommended. Do not use (DOT 5) silicone fluids .

TBM brakes...
Seal compatibility is critical to caliper performance. Very simply put, silicone brake fluid has a very undesirable effect on ethylene propylene rubber found in most brake systems. This tendency to swell the seals, combined with the fact that silicone is compressible when heated or in high altitudes creates unwanted changes to the pedal travel. Seal swelling can also cause brake lockup when used hard. Either of these changes in travel can be so extreme as to cause complete pedal loss or the vehicle dragging to a stop. Therefore, we highly suggest our DOT 5.1 Xtreme 6 fluid, or a comparable DOT 3 or 4 compatible fluid.

Wilwood...
Wilwood does not recommend using DOT 5 fluid in any racing applications. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200 degrees F, and at 212 degrees F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel.


I use DOT 5 in Harleys, which specify it and have systems designed for it.

Everything else for my use (drag race, street) gets DOT 4.

Not sure where everyone gets the idea that the silicone stuff is the hot lick.