Re: D.O.T. 3-4 vs. D.O.T. 5 for a '56 Patrician

Posted by RogerDetroit On 2015/9/15 13:46:14

Why did you move to DOT5 in the first place? I am not aware of any OEM brake supplier for cars or motorcycles that specs DOT 5 and for good reasons.

DOT5 was developed by the military as a fluid for vehicles that are seldom used and stored most of the time. It has a somewhat higher boiling point and is less aggressive to paint. However, DOT5 will expand in high heat and at altitude causing the brakes to lock up. You would have to bleed the brakes in order to release.

There is some degree of air and moisture in ANY brake system. The problem with DOT5 is, the air and moisture remains separate from the fluid and it causes the brakes to exhibit a "spongy" feel.

BTW, are you certain that your entire brake system has components that are compatible with DOT 5? You do not just replace DOT3/4 with DOT5. You either have to have a new, clean system or thoroughly flush your system of any remnants of DOT3/4. The fluids will react when mixed and coagulate.

Therefore, you will not find DOT5 in my garage.